Upload
fightingentropy
View
16
Download
0
Embed Size (px)
Citation preview
All About Fittings
John W. Batts, IV
A practical guide to using and understanding fittings
in a laboratory environment
IDEX Health & Science619 Oak Street, Oak Harbor, WA 98277 USATel: +1 800 426 0191 · Fax: +1 800 359 3460 · Fax: +1 360 679 3830E-mail: [email protected]
© 2011 IDEX Health & Science LLC
About The Author
John Batts, a long-time employee with IDEX Health & Science, has extensive experience with HPLC and related techniques – as a lab technician, as an HPLC field service representative, and as a technical specialist. Driven by a passion for teaching and making difficult-to-understand concepts and material more fun and inviting, he embarked on the journey of writing — and updating — this booklet.
He currently resides with his family in the Pacific Northwest.
Copyright © 2011 IDEX Health & Science LLC
All rights reserved.
Reproduction or translation of any part of this book without the written permission of the copyright owner is unlawful. Contact IDEX Health & Science for permission www.idex-hs.com
Printed in the United States of America
First printing, July 2003 Second printing, August 2004 Third printing, March 2011
The following Trademarks and Registered Trademarks are found in this book:
Upchurch Scientific® is a Registered Trademark of IDEX Health & Science LLC
Delrin® is Registered Trademarks of E.I. du Pont de Nemours and Company
PEEK™ polymer is a Trademark of Victrex, plc.
NanoPort™ is a Trademark of IDEX Health & Science LLC
Halar® is a Registered Trademark of Solvay Solexis S.p.A.
Radel® is a Registered Trademark of BP Amoco Polymers
Ultem® is a Registered Trademark of General Electric Corporation
All About Fittings
2 Preface
3 Foreword
4 Introduction
6 JustWhatAREFittings?
thevitalrolefittingsplayinlaboratoryinstruments
16 HowDoFittingsWork?
basicsaboutfittingsmostclasseswon’tteach
24 WhatFittingDoIHave?
thequickwaytoidentifywhatfittingsyou’reusing
28 PlasticorMetallic—WhichDoIChoose?
what’sthebestfittingchoice?we’lltalkaboutit…
32 WhatIsHPLC?
sincewe’retalkingaboutitsomuch…
40 OtherPopular“Apps”...
tipsformakinggreatconnectionsin
microscaleliquidchromatographyandUHPLC
49 AFewExtraTips
otherusefulhintsformakinggreatconnections
54 Appendix
useful“extras”youmightneedtoknow
Table of Contents
PrefaceI’mveryexcitedaboutthisneweditionoftheAll About Fittingsbooklet!FrommyfirstdealingswithPaulUpchurchinthe1980’stomyinteractionswiththepresent-daystaffatIDEXHealth&Science,I’vealwaysbeenimpressedwiththeleveloftechnicalknow-howthatiscontainedwithinthiscompany.Althoughmanycompanieshavetechnicalexpertise,fewshareitaseffectivelyasisdoneinthislittlepublication.Notonlyisthetechnicalcontenthigh,butitalsoisfuntoread–asomewhatrarecombinationintoday’sHPLCliterature.
HPLCfittings,tubing,andrelatedproductsoftengetoverlookedindiscussionsofHPLCequipment.However,thesepartsarecriticalifyouwanttoobtaintheoptimumperformanceofyoursystem.Problemsaremagnifiedasweprogressto
columnswithsmallerparticlesthatgeneratenarrowerpeaks–apoorlyassembledfittingcancompromiseanotherwiseexcellentseparation.Theexplanationsanddirectionscontainedherewillhelpyouunderstandwhatis–andisn’t–importantwhenyouconnectdifferentpiecesofyourHPLCsystem.Thingslikethreadpitchandferrulegeometryseemabitesoteric,butyou’dbetterpicktherightparts…oryou’llbesorry!
Sotakeafewminutesrightnowandfamiliarizeyourselfwiththecontentsofthebook–10minutesofleafingthroughthepageswillmakeyoufamiliarwiththehighlights.Thenyou’llknowwheretolookwhenyouhaveaquestionaboutfittings.Evenifyou’reanoldpro,you’lllearnsomethingusefulifyoureadthisbookletfromcovertocover–Icertainlydid.
JohnW.Dolan,Ph.D.LCTroubleshootingEditor,LC/GCMagazine
2
All About Fittings
Despitethelargeinvestmentoftimeandmoneyspentonlabequipment—andtheeducationtoknowwhattodowithit—verylittleattentionisgiventounderstandinghowtomakegreatconnectionswithfittings.
Severalyearsago,inanefforttoaddresssomeofthemorecommonemergingtrendsinanalyticalinstrumentation,theoriginalAllAboutFittingsguidewasproduced.Sincethattime,techniquesinanalyticalchemistryhavecontinuedtoevolve,withsystempressuresinUHPLCbecomingthenewstandardthataccessoriesmustwithstandandwithmicro-andnano-flowapplicationshelpingtosetanewstandardforflowrates.Additionally,therehasbeenincreasedemphasisonIVDandotherlife-sciencetechniques.
Thisbookletprovidesessentialinformationoftenrequiredtoidentifythecorrectstyleandtypeoffittingneededformostlaboratoryapplications.Itincludesmorein-depthinformationonmakinggreatconnectionsinUHPLCandmicro-andnanoscaleapplications,aswellasofferinghelpfulhintsforlowerpressureapplications,too.
Ifyouhaveanysuggestionsforfutureeditions,orneedsomeadditionalhelpinidentifyingthefittingyouneed,pleasefeelfreetocontactusatanytime.
HappyConnecting!
JohnW.Batts,IVIDEXHealth&Science
AllAboutFittings4
Introduction
Introduction
WelcometoAll About Fittings!Youareabouttoembarkonanexcitingjourneydesignedtohelpyougraspthefundamentalsofequipmentfittingsandaccessories,aswellassomebasicsaboutliquidchromatographyasananalyticaltechnique.
Youhavemostlikelybeenintroducedtosomeofthetopicscoveredinthismanual.We’vefound,though,thatalotofthefundamentalinformationaboutfittingsandmakinggood
connectionsisn’tgenerallyknown...oftenbecausetheinformationisn’tcoveredinmostcollege-levelclasses.
Tomakemattersworse,mostfittingsandaccessories-manufacturingcompanieshaveavocabularyand“lingo”alltheirown—oftenconsistingofengineeringterms,mathematicalmeasurements,andalargearrayofmaterialnames...andtheyexpectyoutounderstandtheirterminology.
That’s what this book will help you do!
We’vebuiltintothishandbookinformationonfittingsbasics:howtodescribeafitting,howtodeterminewhereinyoursystemcertainstylesoffittingsareused,theinterchangeabilityofdifferenttypesoffittings—amongmanyothertopics.We’veevenbuiltinadiscussiononthespecialterminologyandskillsetneededto
workwithhyphenatedchromatographysystems,suchasLC-MSandevenUHPLCsystems.
Throughthisbooklet,youwillgaintheconfidenceyouneedtoknowexactlywhatfittingyouneedinalmostanylaboratoryapplication!
All About Fittings
www.idex-hs.com 5
IconsTheIconsbelowarefoundinthepagemarginsthroughoutthisbooklettohighlightextra-importantinformationyou’llneedtoknow:
KeyConceptPayextracloseattention...theconceptcoveredisimportanttounderstand!
HelpMe!Highlightsinformationthathelpsexplainatopicormakesomethingeasiertounderstand.
ThisorThat?Drawsyourattentiontoextradetailsyoumayneedwhendecidingwhatproducttouseorwheretouseaproduct.
PointofInterestIndicatesthere’ssomethingsointerestingthatitneedsasecondlook.
SecretRevealedUsedwhenevera“secret”isrevealed—somethingtohelpmakeyourlifeeasierorhelpmakesomethingmoreunderstandable.
HowIt’sMadeOffersdetailsabouthowcurrentequipmentisconfigured,tohelpmakeproductselectionalittleeasier.
PardonMoi?Denotesthosefrequently-askedquestionsthatpuzzlescientistsaroundtheworld!
KEY CONCEPT
SECRET REVEALED
PARDON MOI?
HELP ME!
POINT OF INTEREST
HOW IT’S MADE
THIS OR THAT?
AllAboutFittings6
Just What ARE Fittings?That’soneofthemostpopularquestionsneverasked!Infact,it’snotusuallyuntilyoursystembreaksdownthatyoueven
realizealltheplaceswherefittingsareused!
So...justwhatarefittingsanyway?Accordingtothedictionary,afittingis…
Inotherwords,anywhereyouneedtoattach,adapt,oradjustpiping—ortubing,inthiscase—there’stypicallyafittinginvolved!
Infact,allkindsoffittingsareusedinastandardlaboratorysystem:flangedandflangeless;metallicandnon-metallic;high-pressureandlow-pressure;flat-bottomedandconed;internalandexternal;wrench-tightenedandfinger-tightened.
...a small part used to join, adjust, or adapt other parts, as in a system of pipes
JustWhatAREFittings?
PARDON MOI?
KEY CONCEPT
As Paul Upchurch stated in his book entitled HPLC Fittings:
...everychromatographer
knows,inordertouseany
HPLCsystem,youspend
alotoftimeworkingwith
fittings.Youmustbecome
knowledgeablewiththe
plumbingofanHPLC
systeminordertodo
anypracticalHPLCwork.
Because fittings impact almost everything you do with your equipment, one of the best investments you can make with your time is to better understand fittings and how to use them properly.
All About Fittings
www.idex-hs.com 7
Threads of the receiving port
Geometry of the receiving port
Size and type of tubing used
Material from which the port is made
Amount of pressure expected
So, let’s talk about some basics...Actually,whatwecommonlycalla“fitting”intheanalyticalinstrumentworldreallyreferstoasystemcomprisedofanutandaferrule(pronounced“FAIR-ruhl”).
Ultimately,thechoiceofwhichnutandwhichferruletouseinyoursystemwillbedependentuponanumberofparameters:
Aww, nuts!Thefirstofthetwomajorcomponentsinafittingsystemiscalledanut.Thenutisresponsibleforprovidingthedrivingforcethatcausestheferruletoseal.
Thereareseveralcharacteristicsthatareusedtodistinguishdifferentnutsfromeachother.Oneofthemostobviousistheheadgeometry(e.g.,knurled,hexagonal,square,winged).Butperhapsthemostimportantfeatureofnutsisthethreadedportion,whichallowsnutstomatewiththeirreceivingports.Let’sdiscusseachoftheseinfurtherdetailtohelpdistinguishwhatproductsyoumightbeusing,aswellaswhatotherproductsareavailable.
Threads
Mostnutshave“externalthreads,”meaningthatthethreadsareontheoutsideofthenut.Somenuts,however,have“internalthreads,”wherethethreadsareontheinsideofthenut–commonlyreferredtoasa“capnut”or“femalenut.”(SeeFigure1onpage8)
...andseveralothers.Giventhenumberoffactorsinfluencingthefittingchoiceforagivenapplication,let’sseeifwecanshedsomelightonthesubjectofmakinggoodconnections.
KEY CONCEPT
THIS OR THAT?
AllAboutFittings8
Becausemostnutshaveexternalthreads,let’sfocusonthisnutgeometry…
Inordertodescribeathreadonafitting,somethingcalleda“threadcall-out”isused,consistingoftwomainnumbers..Thefirstnumbertellsyouaboutthediameterofthethread,andthesecondnumberdescribeshowclosetogetherthethreadsare.Here’saneasyexample:
Oneofthemostwidelyusedthreadsinlow-pressurefluidtransferis1/4-28.Noticethetwonumbershere,separatedbyahyphen.Now,let’sapplythedescriptionaboveandseeifwecandeterminesomebasicinformationaboutthistypeofthread.
Thefirstnumberinthethreadcall-outis“1/4.”Sinceweknowthisnumbertellsusaboutthediameterofthethreads,wehaveourfirstclue.Inthiscase,thecall-outunitofmeasurementisinches,sothisdenotesathreaddiameterofone-quarterofaninch!Thediameterofthethreadismeasuredfromthecrestofathreadallthewayacrosstotheoppositecrest.Inotherwords,we’reidentifyingthemaximumdiameterofthethread.
Theothernumberinthethreadnotationisnotsoobvious.Whatdoyouthinkitmeans?Remember,thenumbertellshowclosetogetherthethreadsare.
Anyideas?Well,ifyouthoughtthatitmeansthereare28threadsonthefitting,youwouldbeingoodcompany...butunfortunatelythat’snottherightanswer.Whatthenumbertellsyou,inthiscase,ishowmanythreadsperinchthereareonthenut.(Formoreinformationonhowtomeasurethesecriticaldimensionsonanyfittingyouhave,seepage24ofthisguideforanin-depthdiscussionondeterminingthethreadcall-outofyourfitting.)Internally-ThreadedNut
Externally-ThreadedNut
FIGURE1ThreadedNuts
JustWhatAREFittings?
HELP ME!
All About Fittings
www.idex-hs.com 9
Let’slookatanotherthreadoption—the“workhorse”ofhigherpressurechromatographyapplications:the10-32thread.Whatdoesthisthreadcall-outtellus?
Again,weknowthefirstnumbertellsussomethingaboutthediameterofthethread.Yet,inthiscase,itdoesn’tmeanyouhavea10inchdiameterthread!
Inthe“fittingsworld,”whenanEnglishthreadgoesbelow1/4”indiameter,thengaugenumbersaretypicallyusedwhenreferringtothethreaddiameter.Therefore,the“10”inthecall-outreferstoagauge10—whichtranslatestoalmostexactly3/16”(4.7625mm).Inmicroscaleandnanoscaleapplications,agauge6threadiscommonlyused.Thisthreadgaugeisalmostexactly3.5mmorapproximately9/64”indiameter.
Whynotjusttellyouhowmanythreadsareonthenut?
Simply because it’s not nearly as universal. Every time the length of the nut changed, the thread specification would also have to change, and that would make it very difficult to standardize. However, if the thread is measured in something like “threads per inch,” then it doesn’t matter if the nut is 1/2” long or 5 feet long...it still has the same “name!”
Formoreinformationonvariousthreaddiametersandpitches,seethechartonpage25,andformoreinformationonmakinggoodcapillaryconnections,seepage41.
Butwhataboutthe“32”?Aswiththe1/4-28example,thisnumbermeansthirty-two threads per inch.
So,ifyoucomparea10-32threadedfittingwitha1/4-28threadedfitting,whichwouldyouexpecttohavethreadsclosertogether?Itwouldbethe10-32thread,sinceithasmore“threadsperinch”orafinerthreadpitch.
FOODFORTHOUGHT…Why are 10-32 threaded nuts used in most high pressure applications instead of 1/4-28 threaded nuts? One reason is that denser threads means that there’s more threads to “share the load” and resist the pressure generated inside the receiving port.
...NOWYOUKNOW!
HOW IT’S MADE
SECRET REVEALED
PARDON MOI?
Youmayhavenoticedthattheterm“Englishthread”wasmentionedalittleearlier.That’stohelpidentifythatthethreadcall-outfollowsthetraditionalEnglishsystem,using“inch”asthecommonunitofmeasurement.Italsohelpsdistinguishnutsusingthissystemfromthoseusingthemetricsystem,whichisalsousedinchromatographyequipmentconnectionsbutuses“millimeter”astheunitofmeasurement.
ThemostcommonmetricthreadusedinlaboratoryequipmentisM6x1(althoughyouwilloftenonlyseeM6listed).Let’strytoapplythesameprincipleswelearnedwiththeEnglish-threadedfittingstothesemetricfittings.
First,rememberthatthefirstnumberreferstothediameterofthethreads,andsincethisisametricfitting,thediameteris6millimeters!
The“1”portionofthethreadnamedesignatesthedistancebetweenadjacentthreads!Therefore,thisthreadhas1 millimeter between each thread —theinverseofhowanEnglishthreadismeasured.WhileanEnglishthread(suchasthe10-32and1/4-28we’vealreadydiscussed)measuresthenumberofthreadsperinch,ametricthreadmeasuresthenumberofmillimetersperthread.
Evenwiththedifferencesbetweenthetwosystems,tremendoussimilaritiesexist,andbystudyingthisinformation,youshouldbetterunderstandhowandwhythreadsarenamedthewaytheyare!
Let’s Test Your Knowledge…Now that you’ve learned what the names of threads mean, let’s apply that to another thread.
Thethreadis...5/16-24.
What is the diameter of this thread? What is the thread pitch? Based upon this thread pitch, how many threads exist in 1/4” (6.35 mm)?
To see if you’re right, check the answer at the bottom of this page!
Thediameterofthethreadis5/16”,andthethreadpitchis24threadsperinch.In1/4”thereare6threads(24threads/inchx1/4”=6threads).
JustWhatAREFittings?
SECRET REVEALED
All About Fittings
www.idex-hs.com 11
HeadGeometry
Fittingsaredescribedbymorethanjusttheirthreads,aswe’vediscussed.Anothermajorfactorthathelpsdeterminewhatnuttouseisthegeometryofthehead.
Manynutscanonlybeproperlytightenedwithawrench.So,forthosenuts,it’simportanttonoteiftheyhavea“hex-head”or“wrench-flat”geometry,andthentospecifywhatthediameterisfromflatsidetoflatside.Thistellsyouwhatwrenchyouneedtouse.
Othernuts,however,canbetightenedwithoutawrench;allyoutypicallyneedareyourfingerstotightenthemproperly!Ratherthanusinga“hexhead”or“wrenchflat”geometrythatisdifficulttotightenbyhand,these“fingertight”fittingsoftenfeaturea“knurled”head...andsometimesareevenenhancedwith“wings”—tooffermoregrippingsurfaceandextrafrictionagainstyourfingers.Note:Inmicroscaleapplications,wherethefittingsareoftensmallerthanstandardfittings,itiscommontofindtheheadsofthesefittingsdesignedwitha“micro-knurl”pattern.However,becauseoftheiroveralldiameter,thesefittingsstilltypicallyrequiretheuseofcustom-designedtoolstoensuretheyaretightenedsufficientlytoholdtubing
totheirstatedpressurelimits.Besuretoconsultwiththefittingssupplierformoreinformationonpropertighteningofthesesmallerfittings.
OtherItems
Besidesthethreadsizeandheadgeometry,thereareotherfactorsthatinfluencewhatnutyouneedtouse.
Onethingtoconsideristheoveralllengthofthenut.Longnutsaregreatforuseinangledports,toincreasethegapbetweenadjacentfittings.Butlongnutsmaybedifficulttouseinsome“space-challenged”ports.So,forthoseports,shorternutsareinorder.
Youshouldalsoconsiderthedimensionsofthetubingyouareusing,asmostnutshaveaspecific-
KEY CONCEPT
FIGURE2
WrenchFlatHex-Head
Knurl WingedHead
THIS OR THAT?
AllAboutFittings12
sizedholepassingthroughthem(calleda“thru-hole”)whichfrequentlycorrespondstoatubing’souterdiameter.Therefore,whenchoosingthenutforyourfittingsystem,youwilloftenneedtoreferenceyourtubing’souterdiameter.
Anothermajordistinguishingfactorbetweenfittingsisthematerialthathasbeenusedtomanufacturethenut.Originally,thiswasn’timportant,asmostnutsweremadefromstainlesssteel.However,asfittingstechnologyhasadvanced,polymer-basednutshavebeendeveloped..MaterialslikeDelrin®,PFA,ETFE,polypropylene,PCTFE,PEEK™,andPPSarealloptions,andwitheachnewmaterialcomesnewadvantagesanddisadvantagestoconsider(e.g.chemicalcompatibility,threadstrength...evencolor!).RefertothePolymerReferenceChartandotherresourcesintheAppendix,orcheckwithyourfavoritefittingssupplierforassistanceinchoosingthebestfittingforyourapplication.
Ferrules
Nowthatyou’veabsorbedallthis“nutknowledge,”don’tforgetthisisonlyhalfofthefittingsstory.
Infact,thenutisn’treallythe“businessend”ofafittingsystem...it’stheferrulethat’sdoingmostofthework!
Moststandardlaboratoryfittingsystemsworkthroughexternalcompression(or“gripping”)ontothetubing’souterwall.And,whilethenutprovidesthedrivingforceforcompression,it’stheferrulethatcompressesagainstthetubingandthusholdsthetubinginplace.
Ferrulesaren’tnearlyascomplicatedastheirnutcounterparts,buttheydohavesomedistinguishingfeaturestohelpyoudeterminewhichonestouse.
WhatTheyLookLike
Whileferrulescomeinallshapesandsizes(seeFigure3),onethingtheyhaveincommonistheirtaperednoses...andit’sattheendofthisnosewhereferrulesdowhattheyweredesignedtodo—gripthetubingwall!
JustWhatAREFittings?
FIGURE3VariousFerrules
KEY CONCEPT
SECRET REVEALED
All About Fittings
www.idex-hs.com 13
However,thatdoesn’tmeanferrulesareallinterchangeable!Thingsliketubingsize,pressurerequirements,matingnuts,and—mostimportantly—thegeometryofthereceivingportmustallbeconsideredwhenchoosingtherightferruleforanygivenapplication.
WhereTheyAreUsed
Fromourdiscussionearlier,threadedportscanbeclassifiedas“highpressure”and“lowpressure.”Whilethedefinitionof“high”and“low”isoftendifferentdependingonwhomyouask,onedistinguishingfeatureisthegeometryofthereceivingport(seeFigure4).
Generally,lowpressurereceivingportsendinaflat-bottomconfiguration.Inotherwords,asthethreadsrunout,thebottomoftheportbecomesflatacrosstheentireportdiameter,withasmall“thru-hole”inthecenteroftheflatbottom.Theferrulesusedwiththistypeofportwilltypicallyhavetheirtaperednosesfacingtowardthenutandawayfromtheflatbottomofthereceivingport.Inthesefittingsystems,thethreadedbarrelofthenutwill
oftenfeatureaninternallytaperedsurface,designedtointerfacewiththetaperednoseoftheferruleandhelpcreateasealagainstthetubingwall.(Formoreinformationonlowpressurefittings,pleaseseethediscussiononpage22.)
Highpressurereceivingports,ontheotherhand,haveaninternaltaperjustpastthethreadedportionoftheport.Then,justbeyondtheinternaltaperisasmallpocket—oftencalledthe“tubingpocket” —whichisnearlythesamediameterasthetubingthatextendsintoit.Inthesetypesofports,thetaperednoseoftheferrulefacesawayfromthenutandtowardtheport.ALittleFerruleDitty
Tapered noses face the port When pressures are high But they face the nut When low pressures apply!
FIGURE4
Flat-BottomPort&Fitting
ConedPort&Fitting
AllAboutFittings14
ManufacturingMaterial
Oneveryimportantcharacteristicofanyferruleisthematerialfromwhichitismade.
Ferrulesareoftenmanufacturedfrommaterialssuchasstainlesssteel,PEEK™,ETFE,polypropyleneandPCTFE.MaterialssuchasPEEKpolymer(abeige-coloredplastic),PCTFE,andstainlesssteelareoftenusedtomanufactureferrulesforhighpressureapplications.Softerpolymers,includingETFEandpolypropylene,areusedprimarily(althoughnotsolely)inlower-pressureapplications.
OtherFactors
Makinggreatconnectionsisimpactedbymorethanjustthefittingitself.Otherthingstoconsiderincludethefollowing:
Tubing:Therearetwoprimaryfeaturesofyourtubingthatcanhaveadramaticimpactonthequalityoftheconnectionyouaremaking.First,it’simportanttoknowwhatthematerialisfromwhichthetubinghasbeenmanufactured.Somematerials—likeFEPandPFA—offeroptimalresistanceacrossabroadspectrumofchemicalsolutions;however,the“trade-off”isofteninpressureresistance.OthermaterialslikePEEKandstainlesssteelofferexcellentpressureresistancebutarenotaschemicallyinertassomeofthesofterfluoropolymeroptions.Knowing
thematerialwillhelpyoudetermineifthetubingyouhavechosenwillworkintheconnectionyouaretryingtomake.
Becausemostfittingssystemsgriptheoutsidewallofthetubing,knowingtheouterdiameterofyourtubingisimportant.Thisinformationbothhelpsyouselecttherightfittingstouseaswellashelpsensurethetubingwillfitproperlyintothereceivingport.
ReceivingPort:Especiallyinhigherpressureareasofyoursystemwhereconedportsaremosttypicallyfound,knowingwhatthematerialisfromwhichthereceivingporthasbeendesignedwillhelpyoudetermineifyoucanusethefittingyouhavechoseninthatreceivingport.Agreatruleofthumbisthatthereceivingportshouldbemanufacturedfromamaterialthatisatleastashardasthematerialfromwhichthefittinghasbeenmanufactured.Additionally,conedportsfeaturea“tubingpocket”withadiameterthatisdesignedtobepairedwithaspecifictubingouterdiameter.Thisisparticularlyimportanttonotewhenmakingcapillarytubingconnections,asthetubingisoftenofadifferentsizethanthereceivingportisdesignedtoaccept,requiringspecialaccommodationstoensureagoodconnectionismade.(Formoreinformationonmakingcapillarytubingconnections,seethesectiontitled“MakingCapillaryTubingConnections”onpage41.)
JustWhatAREFittings?
All About Fittings
www.idex-hs.com 15
Together at last!Asyoumight’veguessed,boththenutandtheferruleareimportantcomponentsofafittingssystem,amatchedsetdesignedtoworktogether!
Inanyconnectionsystem,youcannotexpecttousejustthenutalone,asnothingwouldbepresenttogripthetubing,andtheferrulecannotgripthetubingwallwithoutthedrivingforceofthenut.Theentiresystemmustworktogethertoprovideyouwithaconsistentholdandsealontheoutsideofthetubingwall.
...WhichLeadsUsToOurNextChapter
Insomepolymerfittings
systems,thenutandferrule
aretogetherasasingle
piece.Theseone-piece
fittingssystemsstillhaveall
thesamefeaturesasother
multi-componentsystems;
however,bycombiningthe
components,aone-piece
fittingssystemisusuallymore
convenientandeasiertouse.
KEY CONCEPT
AllAboutFittings16
How Do Fittings Work?We’vetakensometimetolearnsomebasicsaboutfittings,andwe’veevengoneoversomenewvocabulary.Now,let’sseeifwecanfigureouthowtheyactuallywork.
Butfirst,weneedtolaysomegroundwork.Wheneverwetalkabout“fittings”fromnowon,we’llmostoftenbereferringtothecombinednutandferrulesystem.(Beawarethatsomefittingshaveboththenutandtheferruletogetherasonepiece,asmentionedonthepreviouspage.)
Now, let’s dig in!Tounderstandhowfittingswork,it’simportanttoknowwhatfittingshavetoDO.
Specifically,fittingshavetwoprimaryfunctions:
Thesejobsmaysoundsomewhatmundane;however,whenyouconsiderthenatureofthechemicalsthatoftentravelalongagivenflowpath,coupledwiththehighpressuresthatoftenexistinline,youmaybegintorealizejustwhatadifficultjobfittingshave!
So, how do fittings do what they have to do?Mostlaboratoryequipmentfittingsgenerallyworkthroughaprocesscalledexternal compression.Inotherwords,asafittingholdsapieceoftubinginplace,itcompressestheoutside(orexternal)wallofthetubing.Dependingonthematerialusedtomakethefitting,thisexternalcompressioneitherbecomespermanent,throughaprocesscalledswaging,orremainstemporary,holdingthetubingusingsimplefrictionagainstthetubingwall.
HowDoFittingsWork?
KEY CONCEPT
HELP ME!
Preventing liquid (or gas) from leaking out of the flow path
Holding tubing in place against opposing pressure
All About Fittings
www.idex-hs.com 17
So,whatdrivesthiscompression?Ithastodowithaconceptcalled“interferingangles.”Thisgetsabitmoretechnical,solet’sdelvedeepertogainabetterunderstanding.
Wealreadydiscussedhowferrulesaremostoftentaperedonatleastoneend,andhowtheorientationoftheferruleusuallydependsonthepressureyouexpectthefittingtowithstand(andtheinternalgeometryofthereceivingport,ofcourse!).Generally,theprimarytaperedportionofanyferrule(orfitting,ifitisaone-piecestyle)willfacetheportionoftheportthatisalsotapered,resultinginaconnectionthathastwoangledsurfacescomingtogether(seeFigure5).
Let’slookatthethreepossibleoutcomeswhenthesetwoangledsurfacescometogether:
1.Ferrulehasawideranglethanthereceivingport
Inthisscenario,asthefittingtightensintoplace,thetipoftheferrule’staperednosedoesn’tactuallymakecontactwiththereceivingtaperatall;rather,contactoccurspartiallyuptheferrule’swall.Thisscenariocreatesineffectivecompressionoftheferrule’staperednoseonthetubingwallandmayresultinaleakingconnectionoralackofferrule“holdingpower.”
2.Ferruleandreceivingporthaveidenticalangles
Inthisexample,becausetheanglesmatch,theferrule’sentiretaperednosemakescontactwiththereceivingportatthesametime.And,no
FIGURE5FerruleOrientation
FerruleTaper(orangle)
PortTaper(orangle)
PARDON MOI?
AllAboutFittings18
POINT OF INTEREST
matterhowmuchyoutightentheaccompanyingnut,thetwomatingsurfacesaresimplywedgedmoretightlyintoplace,resultinginvirtuallynocompressiononthetubingwall.Again,thiswouldtypicallyproducealeakingconnection.
3.Ferrulehasanarroweranglethanthereceivingport
Here,thetipoftheferrulemakescontactwiththereceivingportfirst,andasthefittingistightenedintoplace,theferrulebeginstoconformtotheport’sangle,andcompressesagainstthetubingwall.Justwhatyouwant!
(Figure6illustrateseachofthesescenarios.)
Besidesthesealandgripcreatedaroundtheoutsidetubingwall,youalsoneedasealbetweentheoutsidesurfaceoftheferruleandtheinternalsurfaceofthereceivingport.Thequalityofthesealreallydependsonthesurfacequalityofboththereceivingportandtheferrule.Anyimperfectionsoneithersurfacemaycausealeak.
FIGURE6ThreeFerruleInterfaces
FerruleWiderThanThePort
FerruleSameAsThePort
FerruleMoreNarrowThanThePort
HowDoFittingsWork?
SECRET REVEALED
All About Fittings
www.idex-hs.com 19
Themostdemandingfluidconnectionsaretypicallyfoundinthehighpressureareasofasystem—infact,it’snotunusualforpressuresinHPLCtoreachandexceed4,000psi(276bar)andinUHPLCtoreachpressuresof15,000psi(1,034bar)andhigher!Becausetheseconnectionsexperiencethelargestamountofstress,let’sfocusfirstonhowtomakegoodhighpressureconnections.
OneofthemostpopularstylesofconnectionsusedforHPLCandUHPLChighpressurefluidpathwaysisa“swaged”connection.
Webrieflymentionedtheconceptofswagingearlier.Now,let’slookattheprocessofswagingalittlemoreclosely—whatitis,howitworks,andwhyitremainssopopulartoday.
First,asarecap,swagingmeans“permanently”attachingaferruletoapieceoftubing,typicallyinahighpressureapplication.Often,boththefittingandthetubingaremanufacturedfromsomeformofstainlesssteel,althoughthatdoesn’talwayshavetobethecase.However,swagingtypicallywillnotinvolveanall-polymerferrule.Mostpeoplewhoareswagingareusingstainlesssteelferrulesaspartofthefittingsystem.
High pressure connections
Inordertoswageaferruleontoapieceoftubing,slipthenutoverthetubingbeingconnected.Followthatbyslippingtheferruleoverthetubing,justbelowthenut,ensuringthetaperednoseoftheferruleisfacingawayfromthenut(rememberthelittlepoemfrompage13?).
Oncethenutandferruleareinplace,insertthetubingintothereceivingportuntilthetubingbuttsupagainstthebottomoftheport.PleaseNote:Thisprocessworksformostports;however,someportsdonothaveasolidstopagainstwhichthetubingcanrest.Forthese,extracareisnecessarytoensurethetubingremainsextendedpasttheferrule’snose...butnottoofar!
Withthetubingheldinplace,finger-tightenthenutcompletely,andthenwrench-tightenitanother3/4turn.Thisoftenwillcompletetheswage,crimpingtheferruleontothesurfaceofthetubing.Tomakesurethishasbeendonecorrectly,loosentheassemblyandremoveitfromthereceivingport.Inspecttheferruletoensureitwillnotcomeoff;ifit’sstillloose,reinsertthefittingandtubingassemblyintothereceivingportand
HELP ME!
AllAboutFittings20
tightenin1/4-turnincrements,checkingtoseeiftheferrulehasbeenfixedontothetubingaftereach1/4-turn.
PleaseNote:ThetighteningrecommendationslistedaboveareintendedforusewithtraditionalHPLCandrelatedequipment.IfyouareusingUHPLCsystemsorworkingatultra-highpressures,additionaltighteningmayberequiredtoachievethepressureholdingabilityyouneed.
FOODFORTHOUGHT...Swaged fittings offer some significant advantages. One is that they permanently attach to the wall of the tubing. This allows swaged fittings to hold to high pressures — almost always well above the pressure rating of the equipment into which the fitting is attached.
...NOWYOUKNOW!
Thefactthatswagedfittingsarepermanentlyattachedalsohelpstokeepthefittingswithapieceoftubing.Sincethey’reattached,theywon’tcomeoffaccidentally.(Thisisabighelpifyoutendtobe“challenged”withsmallthings!)
Unfortunately,thispermanentattachmentalsobecomesamajordisadvantage!Why?Becauseyoucanonlyusethefittinginoneport—theoneintowhichitwasswaged.
Yousee,whenafittingisswaged,thereisalwaysalengthoftubingextendingpasttheferrule.Ithastobethisway,ortheferrulewouldhavenoplaceto“bite”downduringthecompressionprocess.Thecomplicationisthateverymajormanufacturerrequiresthelengthtobealittlebitdifferent(seeFigure7).Thismeansthatonceswagedintoareceivingport,forthebestanalysisresults,afittingshouldonlybeusedwiththatoriginalport!Attemptingtouseaswagedfittingwithanyotherportmayresultineitherdeadvolume(seepages51–53foradiscussionon“deadvolume”)orachemicalleak–particularlywhenequipmentfrommultiplemanufacturersisbeingused!
HowDoFittingsWork?
FIGURE7“DimensionX”fromVariousManufacturers
DimensionXcanrangefrom0.080”(2.0mm)to0.170”(4.3mm)amongvariousmanufacturers
X
X=0.080”
(2.0mm)
X
X=0.090”
(2.3mm)
X
X=0.130”
(3.3mm)
X
X=0.170”
(4.3mm)
PARDON MOI?
All About Fittings
www.idex-hs.com 21
POINT OF INTEREST
permanentlyadheretothesurfaceofyourflowpathtubing,whichallowsthemtoberepositionedasneededtohelpavoidleakingconnectionsanddeadvolume.
Inadditiontotheobviousbenefits,otheradvantageshavehelpedthefingertightfittingbecomealaboratoryessential:
Biocompatible
Manybiologicalsamplesareknowntointeractwithiron,achiefcomponentofstainlesssteel...butnotacomponentofmostpolymers.
Universal
Whilemanycustomersareforcedtousesystem-specificmetalfittings,inmostcasesjustonestyleoffingertightfittingcanbeusedtomakeconnectionsthroughoutasystem.
Interchangeable
Becausefingertightfittingsdonotpermanentlyattachtothetubingwall,theycanoftenbemovedfromporttoportwhilestillallowingyoutomakeagoodconnectionbyensuringthetubingisfullyinsertedintothereceivingport.
The problem fixerOneofthemostcommonlyencounteredproblemswithfittingsisachemicalleak(e.g.,whenswitchingbetweendifferentbrandsofHPLCcolumns).Initially,whenaleakoccurs,it’softenbesttomakesurethefittinghasbeentightenedproperly.Often,though,aleakingconnectionisduetoaproblemwiththepositionalplacementoftheferruleonthetubingwall.Unfortunately,withaswagedfitting,theferruleispermanentlyattachedtothetubing,soitcannotberepositionedorchanged(atleastnotwithoutdamagingthetubingand/ortheferrule).Thisusuallyresultsinthrowingawaytheentirepieceoftubing—withtwoferrulesandnutsattached—makingthisoptionveryexpensive.
ThereISanotheroption...thefingertightfitting.
Fingertightfittingsaretypicallypolymerfittingsthatworkinthesamereceivingportsastheirall-metalcounterparts.Becausetheyaremanufacturedfromhigh-endpolymersratherthanfrommaterialslikestainlesssteel,youcanachievegoodperformancefromafingertightfittingwithoutusinganytoolsotherthanyourhand.Also,becausetheyaremanufacturedfrompolymermaterials,theydonot
THIS OR THAT?
AllAboutFittings22
comparableswagedfittings.Otherlimitationscanbelinkedtotheirperformanceinelevatedtemperatureapplicationsandevenlinkedtochemicalinteractioninasomerarecases.Nonetheless,fingertightfittingstypicallyoffersubstantialbenefitsthatfarsurpasstheirlimitations...whichiswhytheyhavebeensowidelyadoptedaroundtheworld!
WhatAboutLowPressureConnections?
Ofcourse,notallfluidconnectionsinyoursystemarehigh-pressureconnections—infact,mostoftheconnectionsarelikelyonesthatcanbeconsidered“low-pressure”connections.Typically,thefittingsusedtomake“low-pressure”connectionsaredifferentfromtraditional“high-pressure”fittings.
First,mostlow-pressurereceivingportsdonothaveaconed(or“tapered”)internalsurface.Instead,theyoftentransitionfromtheinternalthreadsoftheconnectiondirectlytoaflat-bottom.Ofcourse,asyoumightexpect,thesetypesofportsrequiredifferentfittings—fittingsthatarefocusedonmakingasealontheflat-bottomfeature.
Theoriginalstyleoflow-pressure,flat-bottomfittingswastheflangedfitting—astylestillinusetoday!Whenaflangedfittingconnectionis
HowDoFittingsWork?
FIGURE8FlangedFittingConnection
Theuseoffingertightfittingsispopularinbothanalytical-scaleapplicationsaswellasinapplicationsinvolvingcapillarytubing.However,whenfingertightfittingsareusedwithcapillarytubing,thefittingsoftenemployspecialfeatures—likecustomferrulesortubingsleeves—tohelpmakegoodconnections.Formoreinformation,seethediscussiononcapillarytubingconnectionsbeginningonpage41.
Ofcourse,fingertightfittingsarenotwithoutlimitations.Onelimitationisdirectlylinkedtooneoftheirprimaryadvantages--thattheydonotpermanentlyattachtotubingwalls.Whilethisisadvantageousforrepositioningconnectionsandoverallinterchangeability,itdoesmeanthatfingertightfittingsoftenhavealower-pressureholdingabilitythan
All About Fittings
www.idex-hs.com 23
made,theflowpathtubingisflaredoutattheend,andthesupportingfittingpressesthetubingflareagainstthebottomofthereceivingport.
Flangedfittingsarestillusedbecauseoftheirrelativelowcostandeaseofuse.However,ifanythinggoeswrongwithaflangedconnection,itcanbedifficulttorepair.Therefore,manypeoplehavemigratedawayfromflangedtubingconnectionsandswitchedto“flangeless”connections.
Inaflangelessconnection,ratherthanflareoutthetubingtomakeasealinthebottomofthereceivingport,thissystem(andotherssimilartoit)typicallyusesaseparatefittingandanexternalcompressionferrule.Butinsteadofhavingtheconedtipoftheferrulefacingawayfromthefitting,thisfittingstylehastheconedtipoftheferrulefacingtowardthefitting.(seeFigure5,page17,foranexampleofatypicalflangelessfittingsystem,shownontheright-handsideofthatfigure.)
Mostofthetime,lowpressureconnectionsdonotrequireanytoolstomakegoodconnections—simplyhand-tighteningissufficient.Also,whenaflangelessfittingsystem(orsomethingsimilar)isused,low-pressurecomponentsoftensharemanyofthebenefitsoffingertightfittings,includingbiocompatibility,interchangeabilityandevenuniversaluseinmostreceivingports!
BarbsAway!
Whilemanylow-pressureconnectionsuserigidorsemi-rigidtubing—andcanthusutilizetraditionalexternalcompressionfittings—therearesomeconnectionsforwhichexternalcompressionfittingswillnotwork.Specifically,whensoftertubingisused—forexample,withperistalticpumps—externalcompressionfittingsarenotusuallythebestoption.Fortheseapplications,themostcommonformofconnectoristhe“barbed”connector.
Abarbedconnectorworksbyforcingsoftertubingtoexpandoverabarbednose.Thiscausesthetubingto“grip”theconnectorandremaininplace.However,thisconnectionistypicallyonlygoodforlowpressureapplications,becauseasthepressureincreasesinsidesoftertubing,itcausesthetubingtoexpand.Eventually,withenoughinternalpressure,thetubingwillexpandsufficientlytoslipoffthebarbedconnectorbeingused.
FIGURE9BarbedConnectors
AllAboutFittings24
What Fitting Do I Have?Onceyouunderstandhowfittingswork,oneofthebiggestfrustrationscanbefiguringoutwhatfittingyouhave,soyoucanreplaceitwithausablealternativewhenneeded.
We’vealreadydiscussedsomedefiningcharacteristicsforfittings,allofwhichwillhelpyoudeterminewhatfittingyoualreadyhave...andthenhelpyoudecidewhichfitting(s)wouldbestsuityourneeds:
AThreadByAnyOtherName…
Wetalkedearlieraboutthethreadonafitting,andwhatthatthreadcall-outtellsyouspecifically.Reviewing,eachthreadcall-outusuallyconsistsoftwomainnumbers—bothtellingyousomethingaboutthethread.Forinstance,lookingatathreadcall-outsuchas1/4-28,the“1/4”referenceindicatesthethreadhasamaximumdiameterof1/4”,andthe“28”tellsushowmanythreadsperinchexistalongtheshaftofthefitting.
But,howdoyoutellwhattypeoffittingyouhave?Ifyoudon’thaveanyinformationaboutthefitting,thendeterminingitsthreaddescriptionisoneofthemostcriticalpiecesofinformationyoucanobtain.
Fortunately,youcanusuallydeterminewhatthreadyouhavewithacommonrulerandagoodeye.First,lineupthethreadedsectionofyourfittingagainstyourruler’sedge,asshowninFigure10aonthenextpage.It’smosthelpfulifyouuseatleasta1/4”sectionofthreadsforperformingthismeasurement.
Threads on the fitting
Geometry of the fitting (coned or flat-bottom)
Size and type of tubing being connected
Material from which the fitting is manufactured
Amount of pressure expected
WhatFittingDoIHave?
PARDON MOI?
All About Fittings
www.idex-hs.com 25
Next,countthenumberofthreadsalongthebarrelofthefitting,untilyougettothe1/4”markonyourruler.
REMEMBER:THEFIRSTTHREADISYOURZEROMARK...DON’TINCLUDEITINYOURTHREADCOUNT!
IfyouhaveanEnglishthread,oneofthethreadsonyourfittingshouldlineupwiththe1/4”mark(InFigure10a,thereare7threadsin1/4”).Then,allyouhavetodoismultiplyyourresultbyfourtogetthenumberofthreadsperinch—otherwiseknownasthethreadpitch!(Ifyouhaveametricthread,thenthiswon’twork!We’llgothroughthatinamoment...).
Onceyoudeterminethenumberofthreadsperinchonyourfitting,thediameterofthethreadedportionismucheasier.Simplyplacethethreadedbarrelofyourfittingontopofarulerandmeasurethewidestdistance,fromthethreadcrestsononesideofthenuttothethreadcrestsontheothersideofthenut,asillustratedinFigure10b,right,wherethisdistanceis1/4”.
FIGURE10ACountingYourThreads
0 1/8 1/4
FIGURE10BThreadDiameter
0 1/21/4 3/4 1POINT OF INTEREST
AllAboutFittings26
(the“x1”part).NoticethisisinversefromEnglishthreads,whichtellyouhowmanythreadsperinch.(Seepage10formoreinformation.)
Tomeasurethethreadpitchofametric-threadedfitting,holdthethreadedbarrelofyourfittingagainstarulerwithmillimeterincrements.Lineupthecrestofathreadneartheheadofthefittingwithoneofthemillimetermarkingsontheruler.Then,examinewheretherestofthethreadcrestsfall.ThemostcommonlyusedmetricthreadswillhaveeachthreadcrestlineupEXACTLYwitheachmillimetermarkonyourruler.Othermetric-threadedfittingsmaynothavetheirthreadsspacedonemillimeterapart;however,theywillfollowapattern(liketenthreadsinsevenmillimeters,forinstance—usedforaM4x0.7thread).
Tomeasurethediameterofyourmetric-threadedfitting,usethesamemethoddescribedforEnglishthreadedfittings,onlyusingthemetricsideofyourrulerasareferencepoint.
FormostEnglishthreadedfittingsusedinchromatography,thediameteroftencorrespondswiththethreadpitchaccordingtothischart:
ThreadsPerInch Diameter
20 1/2”(12.7mm)
24 5/16”(7.9mm)
28 1/4”(6.4mm)
32
3/16”(4.8mm)Gauge10,&9/64”(3.6mm)Gauge6
40 9/64”(3.6mm)Gauge6
Ofcourse,therearevariationswhichexist,butthischartcanserveasagoodstartingplace.
Whenworkingwithmetric-threadedfittings,manualmeasurementissomewhatdifferentbutusesthesameconcepts.
Rememberthatthemostcommonmetric-threadedfittingusedinchromatographyandrelatedapplicationshasthedesignation“M6.”Technically,thisisincomplete;therealdesignationforthethreadisM6x1.Ifyou’llrecall,thismeansthatthethreadhasasixmillimeterdiameter(the“M6”part),andhasathreadpitchofonemillimeterperthread
WhatFittingDoIHave?
HELP ME!
All About Fittings
www.idex-hs.com 27
In case you want it easy…
Nowthatyou’vegonethroughthethread-measuringexercise,youcanusethediagramsinthechartbelowtohelpyoumoreeasilydeterminethethreadingofyourfitting.
Tousethisresource,simplyholdyourfittingovereachofthesilhouettes
toseeifyourfittingmatchesanyofthem.Eachshadowdrawingisanexactreplicaofthethreadgiven;therefore,thediagramscanbeusedeithertoquicklyverifyathreadorasacheckagainstyourmeasurements.
Holdyourfittingoverthethreadsilhouettesbelowtoidentifythethreads.
U.S.CustomaryThreads
6-40
6-32
10-32
1/4-28
5/16-24
1/2-20
MetricThreads
M4x0.7
M6x1
WhatthreadsdoIhave?
HELP ME!
AllAboutFittings28
Plastic or Metallic — Which Do I Choose?Oneofthemostcommondilemmasafittingsuserfacesisdecidingbetweenplasticandmetallicfittings.Theseandmanyotherquestionsareoftenasked:
Mysystemalreadyusesstainlesssteelfittings,soIhavetokeepusingthem...right?
Willmychemicalsormysampleinteractwiththefitting?
IfI’musingmetaltubing,Ican’tuseplasticnutsandferrules...canI?
WhichtypeoffittingwillactuallyholduptothepressureIneed?
It’scommontothinkthatyouneedtousethesametypeoffittingoriginallyincludedwithyourinstruments.Infact,thisisoneofthemainreasonsstainlesssteelfittingshaveremainedaspopularastheyare!
Fortunately,instrumentperformanceisrarelylinkedtoonespecificfitting,whichoffersyouthefreedomtochangeyourfittingstobestsuityourapplicationandneeds.Tohelpchoosethebestfittingforyourapplication,firstconsiderwhatthefittingissupposedtodo.Doesitholdhighpressureorlowpressure?Whatisthechemicalenvironment?Whatis
theoperatingtemperature?
Oneotherfactortoconsiderwhendecidingwhatfittingtouseishowthefittingwillbeused.Ifyouplantoconnectapieceoftubingtoareceivingportandrarelytakeitout,thenastainlesssteelfittingisoftenagoodoption.However,ifyouexpecttomakefrequentconnectionswiththefitting,orifyouplantousethetubinginmultiplelocations(forinstance,withmultiplecolumnsinyourHPLCsystem),apolymerfittingisreallythebestoption.
Afteransweringthesequestions,look
Here, we’ll address the most common questions and concerns.
CanIReallyChangeMyFittings?
PlasticorMetallic–WhichDoIChoose?
All About Fittings
www.idex-hs.com 29
POINT OF INTEREST
forthefittingsystemthatoffersthecombinationofgoodperformanceandoveralldesignfeaturesthatmakeiteasytouse,reliable,andthebest“fit”foryourapplication.
Keepinmindthatwhiletherearesomeapplicationswheremetallicfittingsmakeusefulconnections,polymerfittingsareoftenanexcellentchoiceinmostapplications,regardless
ofwhatkindoftubingisbeingused.Ironically,theoppositedoesnotholdtrue—stainlesssteelfittingscannotbeusedinmanyplaceswherepolymerfittingsarebeingemployed...specificallyinthoseapplicationswhereapolymerfittingisattachingtubingtoaplasticport.Inthoseapplications,usingastainlesssteelfittingwilllikelycausedamagetothereceivingport!
WhatAboutTheChemicalEnvironment?
Thisisaveryvalidquestion,andonethatmustbeconsideredregardlessofwhattypeoffittingyouchoose.Ifincompatiblechemicalscontactafitting,itsabilitytosealanditsthreadintegritymaybecompromised.
applicationwherealowconcentrationofTFA(trifluoroaceticacid)isbeingused.Inthistypeofapplication,thePEEKferrulewillperformadequately.However,ifthesolutioncomesinprolongedcontactwiththenut(e.g.,ifsomeofthechemicalsolutiongotontheport’sthreadswhenthefittingwaspreviouslyloosened),eventuallythepolymerwoulderodeawayatthepointofcontact.Thefitting’sintegritywouldthenbecompromised—resultinginaleak!
Therearemanysourcesforup-to-dateinformationregardingchemicalcompatibility(asummaryofchemicalcompatibilityinformationisprovidedintheAppendixofthisbookletonpage61),includingthemanufacturerofthefittingsyouhavechosentouse.Othersourcesarealsoavailableontheinternet.Wehighlyrecommendyourefertooneofthesesourcesbeforefinalizingyourfittingsselection.
AGoodRuletoFollow:ALWAYS CONSIDER THE CHEMICAL ENVIRONMENT!
Additionally,sincemostfittingscomprisetwopieces—thenutandtheferrule—youshouldconsiderchemicalcompatibility
withboththenutandtheferrulematerial.Forexample,youmayhaveafingertightfittingwithaPEEK™polymerferruleandaDelrin®nut,andyouneedtomakeatubingconnectioninaLC-MS
AllAboutFittings30
WhatMaterialWithWhatTubing?
Bynowyouprobablyrealizethatyoucannearlyalwaysuseaplasticfittingonanytypeoftubing—polymerormetallic.Aslongasthefittingwillholdmorethanthepressureyouexpectwithyourapplicationandaslongasyourtubingissuitedforthestyleofconnectionyouaretryingtomake(e.g.,externalcompression,internalexpansion,etc.),thenyoushouldnothaveanyproblemswiththeconnection.
Ontheotherhand,itcanbedangerous—orevenimpossible—touseametallicfittingonplastictubing.Whenametallicfittingcrimpsdownonplastictubing,becausethemetalissomuchstrongerthanthetubingmaterial,itveryfirmlysqueezesthetubingwall.Infact,itmightsqueezethetubingwallsohardthatit
damagesthetubingorcollapsestheinnerdiameter,thusrenderingyourtubingunusableinyourapplication.Tohelpdeterminethepossiblefittingoptionsthatcanbeused—assumingtheflowpathtubingyouareusingisfairlyrigid—youcanreferencethepoemaboveandthefollowingtableasguidelines:
Fitting Tubing Port Recommended?
Plastic Plastic Plastic Yes
Plastic Steel Plastic Yes
Plastic Steel Steel Yes
Plastic Plastic Steel Yes
Steel Steel Steel Yes
Steel Plastic Steel No
Steel Plastic Plastic No
Steel Steel Plastic No
Table1—FittingsApplications
Which to Choose – a poem
SteelonplasticWaytoodrastic!PlasticonsteelWhatadeal!
PlasticorMetallic–WhichDoIChoose?
All About Fittings
www.idex-hs.com 31
WhatAboutThePressure?
Oneofthestigmasassociatedwithusingapolymerfittinginsteadofametalliconehastodowiththesystempressure.Infact,mostmetallicfittingswillholdtohigherpressuresthantheirpolymerfittingcounterparts.Yet,theREALquestiontoaskisjusthowmuchpressuremustthefittingwithstand?Ifyourapplicationonlycallsfor1,000poundspersquareinch(psi)(69bar),andyouhaveachoicebetweenastainlesssteelfittingthatholdsto10,000psi(689bar)andapolymerfittingthatworksto6,000psi(414bar),itdoesn’tmatterwhichfittingyouchoosebecausebothwillworkforthatapplication.
Forsuperhighpressureapplications,suchasUHPLCwheresystempressurescanexceed15,000psi(1,034bar),mostanalystsprefertostickwithmetalnutsandferrulesorotherspecializedfittingsdesignedforusewiththosepressures.Butforlow,moderateandstandardhighpressureapplications,apolymerfittingoptionusuallyexists.Besuretoconsultthemanufacturer’sdataonafitting’sabilitytoholdtothepressureyourapplicationdemands.
Summing upOverall,plasticfittingscanserveastheconnectionofchoiceforavastmajorityoftubingconnections.Thefollowingreasonsshowwhy:
A wide variety of polymer fittings is available
Polymer fittings frequently offer superior chemical compatibility
Polymer fittings can hold to most required pressures
Nearly universal functionality is possible with polymer fittings
Polymer fittings are reusable over and over again
Polymerfittingsareoftensuperiortosimilaronesmadeofstainlesssteelorothermetals.
The bottom line
THIS OR THAT?
AllAboutFittings32
What is HPLC?Oneofthemainliquidtransferapplicationsusingthefittingswe’vediscussedisHPLC.Becauseitissuchapopularanalysistechnique,itseemsappropriatetoinvestsometimediscussingit.
HPLCisanacronymthatstandsforHighPerformanceLiquidChromatography.(Manypeoplethinkthe“P”standsfor“Pressure,”astheoperatingpressuresformanyHPLCapplicationsisquitehigh;however,the“P”reallydoesstandfor“Performance.”)
HPLCbegantobeusedinthe1960’s.Thetechniqueallowsanalyststoseparateasampleofknownorunknowncompositionintoitscomponents,andthentoquantifyhowmuchofeachcomponentispresentinthesample.And,becausethistechniqueisgenerallynon-destructive,HPLCisaveryusefultoolinthelaboratory,asitallowsthescientisttocontinueperformingothertestsonhisorhersampleafterithasbeenanalyzedusinganHPLCsystem.
Separationoccursbyintroducingasampleintoaliquidchemicalstreamknownasthemobilephase,whichinturncarriesthesampletoaspecializedtubecalledthecolumnpackedwithsmall,chemically-activeparticlesknownasthestationaryphase.Insidethecolumn,thesampleinteractswithboththemobilephaseandthestationaryphaseandbeginstochemicallyseparateintoitscomponents.Otherequipmentinthesystemcreateandcollectdatafromtheanalysisofthoseseparatedsamplecomponents.Thosedataarethensummarizedinaprintedgraphicalplotcalledachromatogram.(WHEW!)
WhatisHPLC?
POINT OF INTEREST
KEY CONCEPT
All About Fittings
www.idex-hs.com 33
What makes up an HPLC system?
Beforewecangoanyfurther,itisimportanttounderstandwhatcomponentsarepartofastandardHPLCsystem.
AnHPLCsystemincludessevenbasiccomponents,eachwithavitalfunction:
Solventreservoir:Thesolventreservoirholdsthechemicalsolutionthatmovesthroughthesystem.Becausethissolutionismovingthroughouttheanalysis,itiscalledthemobilephase.
Pump:Thepumppullsthemobilephaseoutofthereservoirandpushesitoutthroughtherestofthesystem.Themostcommonpumpinusetodayisthedual-pistonpump—capableofdeliveringstableflowratesathighpressures.
Injectionvalve:Theinjectionvalveintroducesthesampleintothemobilephase.Themostcommoninjectionvalveisasix-port,two-positionvalve(seeFigure11).Thistypeofvalveallowsacontrolledamountofsampletobereproduciblyintroducedintothemobilephasepathwaywithlittleornodisturbancetotherestofthesystem.
FIGURE11TypicalInjectionValvePlumbingViewpoint From Rotary Knob
SampleIn(NeedlePort)
SampleIn(NeedlePort)
SampleWaste
SampleWaste
Pump
Pump
Column
Column
LOAD
INJECT
1
1
4
4
2
2
6
6
3
3
5
5
AllAboutFittings34
POINT OF INTEREST
Theinventionoftheinjectionvalvetrulyrevolutionizedchromatography,asitautomatedthewayforsamplestobeintroducedandanalyzed.Whatoriginallybeganasananalysistechniquewiththecapacityofworkingwith20-40samplesperday,HPLCsystems(whencoupledwiththeproperequipment)canhandlehundredsofsamplesperday,allowingforrapiddrugdiscoveryaswellashighthroughputgenomicsandproteomicswork.
Column:OftencalledtheheartoftheHPLCsystem,thinkofthecolumnasachemical“filter,”ofsorts.Thecolumnisatubeofsomespecifiedlengthandinnerdiameterandusuallyfilledwithsmallbeads.Typically,thebeadsarecoatedwithachemicalsubstancedesignedtointeractwiththesamplecomponentsandenhanceseparation.Mostfrequently,thebeads—describedearlierasthestationaryphase,becausetheydon’tmoveinthesystem–areverysmalldiametersilicaparticlesandtypicallyhaveoctadecylsilane(C18)chemicallybondedtotheirsurfaces.Other,morespecializedmaterialsaresometimes
usedinsteadofsilica.Also,inadditiontotheC18bondedtothesurfacesofthebeads,other,morespecializedmoleculescanbebondedtothebasematerialtofurtherenhancetheseparationachievedinthecolumn.
Detector:Thedetectorisresponsiblefor“seeing”thesamplecomponentsthatareseparatedinthecolumnastheyarebeingcarriedalongbythemobilephase.Themostcommonly-useddetectorpassesabeamofultra-violetlightthroughaspecialwindow(knownasthe“flowcell”).Asthesamplecomponentspassthroughtheflowcell,theamountoflighttransmittingthroughtheflowcellchanges.Theelectronicsofthedetectorthenconvertthechangeintransmittedlightintensityintoasignal.
Otherdetectoroptionsarebeingusedmorefrequentlyasthecostoftechnologycontinuestodrop.Detectorssuchasmassspectrometers(MS)andnuclearmagneticresonance(NMR)detectorsarefindingincreaseduseinmanylaboratories.Withimproveddetectionoptionsnowavailabletothechromatographer,HPLC—alreadyamainstayinmanylaboratories—isfindingincreasinguseasananalyticaltechnique.
WhatisHPLC?
All About Fittings
www.idex-hs.com 35
POINT OF INTEREST
Recorder:Therecordertranslatesthesignalgeneratedbythedetectorintoaplot,creatingachromatogram(seethediagramofsignalversustimeabove.)
Intheearlydays,thisdevicewasnothingmorethanastripchartrecorderwithapenthatmovedinresponsetothesignalcreatedbythedetector,writingonapieceofgraphpapermovingatacontrolledspeed.Then,thepeakswouldbecarefullycutoutandthepaperweighed(yes...weighed)on
ascaletoobtainsemi-quantitativedata.Nowadays,therecordingdeviceisusuallyacomputer,equippedwithsoftwaredesignedtonotonlytranslatethesignalfromthedetector,buttoalsoprocessthedatadigitally.Thisallowsmuchmorereproducibleinformationtobegeneratedandhasfacilitatedtheuseofsmallerandsmallersamples.
Wastereservoir:ThelastcomponentinabasicHPLCsystem,thewastereservoirsafelycollectsallthemobilephaseandsamplecomponentsaftertheypassthroughthesystem.
FIGURE12ExampleChromatogram
0 10 20
SIG
NA
LIN
TEN
SITY
Peak Baseline
TIME(MIN.)
AllAboutFittings36
LookingAtTheComponentsAsASystem
NowthatyouunderstandthebasicsofthekeyHPLCsystemcomponents,let’srunthroughthewholeprocessagain.Onceamobilephaseisprepared,thepumpthenmovesitthroughthesystem,whereitencountersthesampleandcarriesitthroughthecolumn.Insidethecolumn,thesamplecomponentsselectivelyinteractwiththemobilephaseandthestationaryphase,separatingintogroupsoflikemoleculesastheymovethroughthecolumn.Leavingthecolumn,thesamplecomponentgroupsthenpassthroughthedetector,which“sees”thecomponentsandsendsasignaltotherecordingdevice,whichinturncollectsandprocessesthedata.Thewastereservoirthencollectsthefluidfordisposal.
FIGURE13TypicalHPLCSystem
WhatisHPLC?
WasteReservoir
Column
SolventReservoir
Pump
SampleInjection
Valve
Recorder Detector
All About Fittings
www.idex-hs.com 37
Other system “stuff”WhileanHPLCsystemcannotfunctionwithoutthebasicsevencomponents,itmostcertainlycanfunctionwithmorethanthoseseven.Infact,therearemanycommonly-usedaccessoriesandcomponentswhichhelpenhancetheperformanceofastandardHPLCsystem,includingthefollowing:
Filters:Foundinthesolventreservoirandalongtheflowpathinnumerouslocations,filtersplayavitalroleinmaintainingsystemperformance.Filterspreventsolidparticlesfrompassingthroughthesystem;failuretousefilterscanresultindamagedsystemcomponents,increaseddowntime,andpoorchromatographicresults.(Formoreinformationonfilters,checkouttheAppendix,beginningonpage54.)
Guardcolumns:Guardcolumnsdoexactlywhattheirnameimplies...theyguardthemainanalyticalcolumn.Theyaretypicallysmallversionsoftheanalyticalcolumn,usedtotrapsamplecomponentsthatwouldotherwiseirreversiblybindtotheinsideoftheanalyticalcolumn.Theguardcolumnactslikeaninsurancepolicyfortheprimaryanalyticalcolumn,helpingtodelaytheoften-costlyreplacementoftheprimarycolumn.
Backpressureregulators:Abackpressureregulator(BPR)ismostoftenplacedinlinebetweenthedetectorandthewastereservoir.Itcreates
additionalupstreampressure,topreventanygaseswhichmightbedissolvedinsolutionfromoutgassingandcreatingbubblesalongthemobilephaseflowpath.(Ifanybubblespassthroughthedetector’sflowcell,aphenomenonknownas“noise”canshowuponthechromatogram’sbaselineandlimitthesensitivityofanalysis.)(FormoreinformationonBPRs,seetheAppendix,page57.)
Vacuumdegassers:Avacuumdegasserisapieceofequipmentthatiscommonlyplacedinlinebetweenthesolventreservoir(s)andthepump.Thisdeviceisengineeredtoextractthedissolvedgasfromthemobilephasebeforeitreachesthepump.Bydoingso,ithelpskeepthegasconcentrationinsolutionsufficientlylowsuchthatbubblescannotformoncethemobilephasetransitionsfromthehighpressureofthecolumntothelowpressurezonepost-column.Aswithbackpressureregulators,preventingbubblesfromforminghelpspreventbaselinenoiseandthusimproveschromatographicresultsaswellasreproducibility.
KEY CONCEPT
AllAboutFittings38
What goes where?
Ofcourse,fittingsarestandarditemsusedtoconnectthecomponentstogether,usingtubingastheflowpathbridgebetweencomponents.Yet,oneofthemostcommonly-askedquestionsregardingfittingsis,“Wheredoallthesefittingsgoinmysystem?”Inotherwords,howdoIknowwhattousewhere?
Onecommonwaytodistinguishbetweenfittingsisbyclassifyingthembasedonthepressuretheycanhold.Thisnarrowsthefittingschoicebasedonwhereinthesystemtheywillbeused.
Generally,fittingsareclassifiedaseither“lowpressure”or“highpressure”fittings.Correspondingly,“lowpressure”mostoftenreferstoapplicationsorareasinyoursystemwheretheflowpathpressuresdonotexceed1,000psi(69bar).“Highpressure”areascanhaveflowpathpressuresthatexceed6,000psi(400bar)!(Someofthedifferencesbetweenhighpressureandlowpressurefittingshavealreadybeendiscussedearlierinthismanual.)
InanHPLCsystem,therearegenerallythreepressurizedzones,eachwithitsfamilyoffittings.Thefirstzoneexists
betweenthereservoirandtheinletofthepump.Thisistypicallyalowpressurezone,asthepumpispullingthemobilephasefromthereservoirinthisarea,usuallycreatingsomenegativepressure.Thefittingsusedinthiszonearegenerallylowpressure,low-costfittings,mostoftenhavinga1/4-28flat-bottomgeometry,andaregenerallyfor1/8”(3.2mm)outerdiameter(OD)tubing.
ThesecondzoneinthesystemexistsfromtheoutletofthepumpthroughtheinjectionvalveandthroughtheHPLCcolumn.Inthiszone,thefluidflowisbeingresistedbythestationaryphaseinsidethecolumn,andassuch,thepumpexperienceshigherbackpressures...asdothefittings.
Inthissecondzone,fittingsaregenerallyclassifiedashighpressurefittingsandmostfrequentlyhavea10-32conedgeometryforusewith1/16”(1.6mm)OD(orsmaller)tubing.Becauseperformancedemandsofthefittingsaregreaterinthisareaofthesystem,themanufacturingcostsandpurchasepriceofthefittingsaregenerallyhigher.
Lastly,inthethirdzone—fromthetubingexitingthecolumnthroughthedetectorandontothewastereservoir—thesystempressuresaregenerallynearambientpressures,withslightlyelevatedpressuresbeingexperiencedwhenextracomponents
WhatisHPLC?
PARDON MOI?
All About Fittings
www.idex-hs.com 39
areused(likebackpressureregulators,forinstance).Becausethesystempressureinthisthirdzoneistypicallylow,thefittingsonceagainoftenassumeastandard,1/4-28flat-bottomgeometry,andtheyaretypicallyforusewith1/16”(1.6mm)ODtubing.
Itisimportanttonotethateventhoughthisthirdzoneisalowerpressurezone,manyOEM(“OriginalEquipmentManufacturer”)companiesrealizethatmostlaboratorieshavemorefittings
withthe10-32conedgeometryfor1/16”(1.6mm)ODtubingthananyothertypeoffitting.Therefore,thereceivingportsavailableonequipmentinthiszonemayrequiretheuseof“highpressure”fittings,eventhoughtheinlinepressuresarelow.
Thediagrambelowshowsan“accessorized”HPLCsystem,tohelpyouunderstandhowasystemisputtogether —includingwhatfittingstoputwhere.
FIGURE14TypicalHPLCSystem
39
HighPressureFittings
LowPressureFittings
SolventReservoir
InletSolventFilter Inline
SolventFilter
PrecolumnFilter
GuardColumn
Column
BackPressure
Regulator
WasteReservoir
RecorderDetector
SampleInjectionValve
Pump
AllAboutFittings40
Other Popular “Apps”
Big things come in little packages
InadditiontotraditionalHPLC,overthepastseveralyears,therehavebeenadvancesintechnologythathaveexpandedtheworldofchromatographyinseveraldirections.Twoofthesehavebecomethemostprominent—microscalechromatographyandUHPLC,orUltra-HighPerformanceLiquidChromatography.
Oneofthemostpopularadvancesinchromatographictechnologyhasbeenthedevelopmentofmicroscaleandevennanoscalechromatographicmethods.WhereHPLCusesthingslike1/16”(1.6mm)ODtubing,flowratesof1mL/min,andsamplesizesof20µL,thissmaller-scalechromatographyisknownformuchdifferent“standards”:360µmODtubing,flowratesinthelowmicrolitersperminuteorless,andsamplesizesinthenanoliterrange.
Somewhatintuitively,thissmallerscalerequiresanincreasedattention
tothequalityoftheconnectionsthataremade,asevensmalldeadvolumechamberscanhaveatremendousimpactonyourresultswhenoperatingundertheseconditions.Workingtoensureyourtubingiscutandpreparedwell(seepage44foradiscussiononhowtoproperlypreparetubing)andmakingsurethatyouareusingthebestfittingsfortheapplication(seepage41foradiscussionon“pitfalls”toavoidwhenconnectingcapillarytubingandtipsformakinggoodconnectionswithcapillarytubing)willpaybackhugedividendsintheformofhighqualitychromatographicresults.
OtherPopular“Apps”
All About Fittings
www.idex-hs.com 41
Making capillary tubing connections
Anotherimportanttopicistherapidlygrowingfieldofcapillarytubingconnections.
Asanalyticaltechniquesandapplicationsforcefluidvolumeslowerandlower,thesizeofthetubingusedfortheflowpathmustalsoshrinktoaccommodatethemethodology.Specialguidelinesareusefulinselectingandusingthebestconnectorsforcapillarytubingapplications.
First,capillarytubingcanbedefinedasanytubingwithanouterdiametersmallerthan1/16”(1.6mm)OD(chosenbecauseitistheprimarysizeoftubingusedhistoricallywithmostHPLCsystems).Asflowratesdecrease,oftenthetubing
ODandIDwillalsodecreaseinordertomaintainaconsistentlinearvelocity.Tubingsizeslike1/32”(0.8mm)ODand360micrometer(µm)ODarebeingusedwithincreasingfrequencyinchromatographyandrelateddisciplines,andusingthesetubingsizesrequiressomespecialconsiderationsnormallyunnecessarywith1/16”(1.6mm)ODtubing.Thisisespeciallyevidentwhenusingthesmallertubinginreceivingportsnormallydesignedforthelarger,1/16”(1.6mm)ODtubing.
Frequently,analystswillattempttoadaptexistinghardware(e.g.pumps,injectionvalves,evencolumns)toaccommodatecapillarytubing.Issuesabound,however,becauseofthegeometryandoverallsizeofthereceivingports.
POINT OF INTEREST
AllAboutFittings42
FIGURE15PotentialDeadVolumeinCapillary-BasedApplications
FIGURE16ExampleofaCustomizedFerrule
Aswe’vementioned,thehighpressurereceivingportsinmostanalytical-scaleequipmentonthemarkethaveaninternalgeometrysupporting1/16”(1.6mm)ODtubing.Thismeansthattheporthasaninternalpocketintowhichthe1/16”(1.6mm)ODtubingextends.Aslongastubingwiththissamediameterisused,thenpotentialdeadvolumeresultingfromtheconnectioniskepttoaminimum.However,whenthetubingyou’reusingissmallerthanwhatthereceivingportisexpecting,it’seasyfordeadvolumetobeintroducedintheconnection...which,withcapillary-basedapplications,canbeextremelydetrimental(seeFigure15).
Numerouswayshavebeendevelopedtoadaptsmaller,capillarytubingintothereceivingportsmeantforlargerODtubing.Oftheoptionsavailable,twostandoutasthemostpopular.
Thefirstoptioninvolvescustomizedferruleswhichlooksimilartothoseusedforthelargertubing,butwhichfeaturesmallerholesdrilledthroughthemtobetteraccommodatethecapillarytubing.Additionally,mostferrulesusedforthispurposealsoofferafixed-lengthnoseextendingbeyondthetaperedportionoftheferruletoreducedeadvolumeintheconnection.Ferrulesystemssuchasthesegenerallyholdthetubingwellandhavealongusablelifetime.However,therearedrawbackstoconsider.
OtherPopular“Apps”
DeadVolume
All About Fittings
www.idex-hs.com 43
First,custom-drilledferrulesare“economically-challenged.”(Inotherwords,theycanbeprettypricey.)Theseitemsaregenerallymanufacturedfromexpensivematerialsandaretypicallymachinedversusinjectionmolded...bothofwhichdriveupthecost.
Second,andmoreimportantly,theirfixedgeometrieslimitwheretheycanbeused.Asmostportshaveinternalgeometriesthatvaryfromonetoanother,usingferruleswithfixedgeometriescaneitherpreventtheferrulefromsealingproperlyorleaveemptypocketsinthereceivingportwheremobilephaseand/orsamplemaycollect.Thesedeadvolumepocketscanleadtopoorchromatography,includingissueswithcarryover,splitpeaks,andbandbroadening.Andwithsuchsmallsamplesizesandflowratesbeingusedincapillary-basedapplications,deadvolumepocketsplayamuchlargerroleinthequalityoftheresults.
Fortunately,thesecondoption—theuseofaspecialtubingsleeve—overcomesbothoftheprimarydisadvantagesexhibitedbythecustomizedferrules.
Tubingsleevesgenerallyhaveacontrolledouterdiameter(usually1/16”(1.6mm))whichallowsthemtofitintostandardthreadedports.And,sincethesleevewillslide
FIGURE17
IfDimensionXistoolong,leakswilloccur
Ferrulecannotseatproperly
IfDimensionXistooshort,adead-volume,ormixingchamber,willoccur
Mixingchamber
throughaferruleuntilitbottomsoutinareceivingport,thetubingpocketbeyondtheferrulewillbecompletelyfilledtohelpavoiddeadvolumeintheconnection.
Tubingsleevesalsoofferseveralsidebenefits.Oneisthestructuralsupportsleevesprovidetotheoutsideofthecapillarytubing,helpingpreventdamagetothetubingasitleavesthefitting.Also,becausethetubingsleevescomefromextruded
KEY CONCEPT
AllAboutFittings44
material,thesleevescanbeofferedinavarietyofmaterials.Furthermore,theextrusionprocessgenerallyallowsamoreconcentricconnectionthanprecisiondrillingandmachiningcanprovide,offeringamoreaccuratetubing-to-thru-holealignmentanddecreasinginlineturbulenceandmixing,allatareducedcost.
Forallthesereasons,usingatubingsleevetoconnectcapillarytubingintoareceivingportisthemethodofpreference—unlessthereceivingportisspecificallydesignedforusewiththesizeoftubingyouareusing!
Butwhataboutinstanceswherethereisn’tevenenoughroomforathreadedporttoexist,suchas
Lab-on-a-Chipmethods?Manypeopleusingtechniqueslikethisareforcedtogluetheirtubinginplaceinlieuofusingafittingfortheconnection.Thiscausesanumberofproblems,includingaweakholdonthetubingandinteractionbetweenthesamplebeinganalyzedandtheglue(oftenepoxy)securingthetubinginplace.
Oneavailablesolutiontothisprobleminvolvesbondingathreadedportdirectlytothesubstrate’ssurface.Bydoingthis,andbyisolatingtheadhesiveawayfromthemobilephaseorthesample,youcanmakeareliableconnectionwithyourtubingusingatraditionalfittingratherthanepoxy.Products,suchasIDEXHealth&Science’sNanoPorts™,weredevelopedspecificallyforthistask.
OtherPopular“Apps”
Besidesconnectingthetubingwiththeproperfittings,otherissuesshouldbeconsideredtoensuregoodconnectionsandgoodchromatographywhenyouusecapillarytubing.
Oneofthemajorissuescentersonhowwellyoucutthetubing.Dependingonthetypeofcapillarytubingandthecuttingtoolused,theeffectcanbedramatic.
Cutting fused silica and polymer capillary tubing
SECRET REVEALED
Let’stakefusedsilicacapillarytubingasafirstexample.Oneofthemostpopularmethodsforcuttingthistubingemploysaceramicscoringstone.This“tool”isreallyjustapieceofsharp-edgedceramicthatscoresthesurfaceofthefusedsilicatubing.Thisallowsthetubingtobepulledaparteasilyatthescoremark.
Intheory,thiswillallowforreasonablecutquality.However,inpractice,the
All About Fittings
www.idex-hs.com 45
resultsareusuallydifferent.Often,astheceramicstoneispulledacrossthetubing,thepolymercoatingisshreddedandthefusedsilicaunderneaththepolymercoatingisshatteredundertheforceoftheblade.Initially,youmaythinkthetubinglooksacceptable;however,onceinuse,thecoatingmaterialorpiecesofthefusedsilicatubingcanbreakoffandclogimportantinternalpassageways.Also,withdamagedendsonthetubing,usingstandardcompressionfittingstoholdthattubinginplacecancausethetubingtocompletelyshatterandresultinaleak,acloggedsystemcomponent,oracombinationofthetwo.
Itisalmostalwaysabetterideatocircumscribethetubingyouarecutting,goingallthewayaroundthecircumferenceofthetubing,ifyouwanttoachieveagood,reproducible,qualitycutonfusedsilicatubing.Whilethetoolsavailableformakingthistypeofcutarefairlyexpensive,theresults(andlackofadailyheadache!)usuallyfaroutweighthecostofthecutter.And,thesetoolsarefairlyeasytouse.
Interestingly,theconceptofcircumscribingthetubingappliestopolymercapillarytubingaswell...butfordifferentreasons.Often,whenpolymercapillarytubingisused,theinnerdiametersareverysmall—aslowas0.001”(25µm)insomecases!With
KEY CONCEPT
innerdiametersthissmall,itisvitaltokeepthethru-holeinthetubingopenandcenteredwiththepassagewayinthereceivingporttoavoidoverpressurizingtheconnection.That’swhereaccuratecuttingcomesintoplay.
Ifyoucutthetubingbysimplyslicingitwithablade,theforceofthebladepushingthroughtheplasticwillfrequentlycausetheinnerdiametertoshiftoffcenterorcollapse.Whilecuttingthiswaywon’ttechnicallycausedamagetopolymertubinglikeitwouldtofusedsilicatubing,itcanrenderitnear-useless,dependingonthedegreeofinnerdiametershift.Toavoidthisrisk,itisbesttocutthepolymercapillarytubingallthewayarounditscircumferenceaswell.
Again,thetoolstodothisareavailable,andtheyareabitexpensive;however,aswiththetoolsforproperlycuttingfusedsilicatubing,benefitsfaroutweighthecosts.
HELP ME!
FIGURE19CutPolymerTubing
ImproperlyCutTubingProperlyCutTubing
AllAboutFittings46
Putting the big squeeze on
AnotherpopularchromatographicdevelopmenthasbeentheintroductionofUHPLC.Inatrendthatstartedin2004,numerousmanufacturershaveintroducedequipmentandvarioushardwareandaccessoriesthataresuitableforuseinUHPLCapplications.
OneofthekeyfeaturesofUHPLCisthattheequipmentrunsatveryhighpressures.Themostcommonsystemsrunatpressuresatornear
15,000psi(1,034bar)—andsomeequipmentevensurpassesthatlimit!Ofcourse,withsystempressuresthishigh,thatputsevenmorestrainontheconnectionsinthesystem--especiallyinthe“highpressure”zone,wherethesystempressuresarethegreatest.BecauseofthepressureinvolvedinUHPLC,therearecertainproblemsthatcanoccurinUHPLCifthefittingandtubingconnectionsarenotasgoodastheyshouldbe:
Ifapoorconnectionhasbeenmadethatallowstheflowpathtubingtomove,therearepartsoftheUHPLCfluidpathwaythatundergoatremendousamountofstress—forexample,thefittingsthatconnectthesamplelooptotheinjectionvalve.It’softeninthesehigh-stressareasthattubingconnectionswillfailiftheconnectionsarepoorlymade.Withtubingslippage,theproblem
doesn’tappearintheformofanimmediateleak—it’sa“slowriser,”aproblemthatgraduallyappears.Whilealeakwon’tnecessarilyresultrightaway,youwilllikelynoticeyourchromatographicresultsdeterioratingduetothelargedeadvolumechamberbeingcreatedattheendoftheflowpathtubingasthetubingslowlyslipspastthegripofthefitting.
1)TubingSlippage
OtherPopular“Apps”
All About Fittings
www.idex-hs.com 47
WiththehighpressuresinvolvedinUHPLCapplications,it’sbecomecommonplaceforstainlesssteelfittingstobeusedonceagain.However,withtheuseofthesetypesoffittingscomestheproblemsassociatedwiththesetypesoffittings.
Oneofthoseproblemsistheamountofcompressiononthewallofthetubingthatoccurswhenametallicfittingisused.Dependinguponthetighteningtorqueappliedtotheconnection,it’sverypossiblefortheferruletocompressthetubingwallsomuchthattheinnerdiameteriscompressedaswell.Thisinnercompressioncreatesafluidpathwayrestrictionthatcanresultinathrottlingeffectofthemobilephaseandincreasedmixing.
Asecondproblemcanresultfromtheover-tighteningofametallicferruleintoametallicreceivingport.Becauseoftheforcesinvolved,itispossiblefortheferruletobeginshearingsomemetalfromtheinternalreceivingportsurface.Thisresultsinadamagedportthatcanleakandcanbedifficulttorepair.
Anotherproblemthatcanresultfromtheover-tighteningandimproperuseofstainlesssteelfittingsistheimpacttheycanmakeonthequalityofthesurfaceofthereceivingport.Notonlycangallingresult,butthereceivingportcanbedeformedduetotheforcesappliedbytheferrule.Thiscancreatea“ridge”alongtheinnersurfacethatcanpreventsubsequentferrulesfromsealingcorrectly.
2)Ferrule-RelatedStruggles
Asstrangeasitmayseem,itispossibletobeinjuredduetoimproperly-madeconnections.Specifically,ifatubingconnectionsuddenlyfailsandthefluidpressureswereuptoUHPLCpressures
andbeyond,thatsuddenreleaseofenergizedfluidcandamageskinandsofttissues.Wearingprotectivegearandexercisingcautionwillhelpavoidunnecessaryinjury.
3)PersonalInjury
BecauseofthesesourcesofproblemsinUHPLCapplications,itisvitalthatyouinvestthetime,effort,andresourcestoensureyouhavemadegoodconnectionsthroughoutyoursystem.Workingwiththerightfittingsandtighteningusingthepropermethodologywillproveinvaluableasyouseektomakegoodconnectionsinyourequipment.
AllAboutFittings48
IlikeusingFingertightfittingsformyHPLCconnections–canIstillusethemforUHPLCconnections?
Generallyspeaking,becauseoftheveryhighsystempressurespresentinmostUHPLCapplications,standardFingertightfittingswillnottypicallywork.MakinggoodconnectionsinUHPLCapplicationswillusuallyrequireeithertraditionalstainlesssteelfittingsorspecializedfittingsthathavebeenengineeredtoworkintheveryhighpressureenvironmentofUHPLC.
CanIusepolymertubing(e.g.,tubingmanufacturedfromPEEK™polymer)inUHPLCapplications?
MostsizesofPEEKtubing(andtubingfromotherpolymermaterials)havepressurelimitsthatarewellbelowthetypicaloperatingpressuresofUHPLC.Assuch,themostpopularlyusedtubinginUHPLCismanufacturedfromstainlesssteel.Otherspecializedtubingmayalsowork;thekeyistodouble-checkwiththetubingmanufacturer/suppliertoensureitisratedforuseatthepressuresyouwillencounterinyourUHPLCsystem.
OtherPopular“Apps”
But I still have some questions!
BecauseoftherelativeyoungageofUHPLCasacommercializedtechnique,therearesomefairlycommonquestionspertainingtomakinggoodconnectionsthatareasked.We’llpausetoaddresssomeofthemostpopularones:
DoIneedspecialfittingsthroughoutmyUHPLCsystem?
Thisismoretricky,becausemostUHPLCsystemsareonlydifferentinthehighpressurezone(seeearlierdiscussiononpage46formoreinformationaboutthedifferentconnectionzones).Thatmeans,whileyouwilllikelyneedtousedifferentfittingsinthehighpressurezonewhentransitioningtoUHPLC,inthelowerpressurezonestheconnectionswilllikelybeverysimilartothoseusedintraditionalHPLC.
All About Fittings
www.idex-hs.com 49
Hereareafewadditionaluseful“hints”formakinggreatconnections.
How do I adapt?Withthelonglistofmanufacturerscreatingequipment,andwithallthedifferentvariationsontubingsizeandthreadedportconfiguration,scientistswillfrequentlyneedtofindadapterstomakeaspecialtubingconnection.
Orwillthey?
Ironically,whilemanypeoplemightapproachmakingaconnectionwithanadapter,frequentlyadaptersareunnecessary.Tobetterunderstandthis,let’sdistinguishbetweenadaptersandtheircounterparts–unions.
Basically,adapters“adapt”betweentwodifferenttypesofthread/portconfigurations,whileunionshavethesamethread/portconfigurationonbothsides.
Toillustratethispoint,Figure18showsvariousconnectorsandclassifiesthemaseitheradaptersorunions.
Beforecontinuing,it’simportanttoestablishonegeneral“ruleofthumb”:Unionsaretypicallylessexpensivethanadapterswhileoftenperformingequallyaswell.Therefore,wouldn’titmakesensetouseaunionwhereverpossible?
KEY CONCEPT
SECRET REVEALED
A Few Extra Tips
FIGURE18Adaptersvs.Unions
Unions
Adapters
49
AllAboutFittings50
Therealquestiontoconsideristhis:
Howdoyouknowwhenyoucanuseaunion?
First,examinetheconnectionanddetermineifitwillbelowpressureorhighpressure.Sometimesthismaynotbesoobvious,butyoucanoftenmakesomeassumptions.
Forinstance,ifyouwanttoconnect1/16”(1.6mm)ODPEEK™tubingtoapieceof1/8”(3.2mm)ODFEPorPFAtubing,thenitwouldbesafetosayyouaremakingalowpressureconnection.Infact,itdoesn’treallymatterwhatpressurethePEEKtubingwillhold—theconnectionislimitedbytheamountofpressurethesoftertubingcanhandle.
Onceyouknowthepressureclassificationfortheconnectionyouneed,findoutwhat’savailableinthatclassificationfromyourfittingssupplier.(Forexample,forlowpressureconnections,anumberoflowpressureunionswith1/4-28internalflat-bottomgeometryonbothsidesareavailable.You’llalsofindavailableotheroptionswithmatchingM6and5/16-24internalthreads.)
Withthisinformationinhand,allyouneedtodoisfindfittingsthatworkwithyourtubingsizesthatalsomatewithoppositesidesofanavailableunion.Ifsuchfittingsexist,youcanuseauniontoconnect
them—evenifyourtubingouterdiametersaredifferent!
Let’scontinuewiththepreviousexample:alowpressureconnectionbetween1/16”(1.6mm)and1/8”(3.2mm)ODtubing.
Mostpeopletryingtomakethisconnectionwouldinstinctivelylookforanadapter.Ofcourse,manysuppliersmanufactureadaptersthatcanbeusedforthatpurpose.However,therearesupplierswhoalsocarry1/4-28flat-bottomfittingsforboth1/16”(1.6mm)ODand1/8”(3.2mm)ODtubing.
Thismeansaninexpensiveunioncanbeused,evenwithdifferenttubingsizes,withoutompromisingperformance.
Ofcourse,therearestillanumberofcaseswhereonlyanadapterwilldo.However,itisoftenworththeeffortoflookingthroughavailableproductstodetermineifaunionwillworkforyourneeds.
AFewExtraTips
SECRET REVEALED
All About Fittings
www.idex-hs.com 51
What’s the big ID?
Anotherproblemyoumightfaceischoosingtherightinnerdiameterforyourapplications.Becauseapplicationsinvolvingcapillarytubingtypicallyfeaturelowflowratesandincrediblysmallamountsofsample,thereisageneralpushtoreducetheinnerdiametertothesmallestpossiblesize.WhiletheseminisculepathwaysallowthefluidtotravelasfastaspossiblefrompointAtopointB,onethingoftenoverlookedisthebackpressurealongthetubingpathway.Thisisimportantbecauseifsystempressuresbecometoohigh
wherepolymerfittingsareused,thetubingmaypopfreefromthefitting’sfrictionhold,causingaleakandotherundesirableconsequences(e.g.,systemshut-down,sampleloss).Whilemanyfactorscancontributetosystempressure,theIDofthetubingoftenhasthegreatestimpact.
Pleaserefertothe“SpeakingofPressure”sectiononpage58intheAppendixforausefulformulathatallowsyoutocalculateexpectedbackpressureinyourfluidpathway.
Void, dead and swept...an interesting concept
Often,whenmakingconnections,peoplewantmoreinformationontheamountof“deadvolume”intheconnection.However,mostpeoplewhoinquireaboutthedeadvolumearereallywantingtoknowjusthowmuchinternalvolumeexistswithinaconnection,nothowmuchofthatinternalvolumeisconsidered“dead.”
Butwhatdothesetermsmean?
Specifically,threetermsdescribetheinternalvolumeofaproduct:deadvolume,sweptvolumeandvoidvolume.
Deadvolumeisthatportionofthevoidvolumethatisoutoftheflowpath.(SeeFigure20,page52.)
Sweptvolumeisthatportionofthevoidvolumeinaconnectiondirectlyinthefluidpathway.(Again,seeFigure20.)
Voidvolumeissimplyanotherwayofdescribingthetotalinternalvolume.Itisdefinedasanyspacewithinaconnectionintowhichfluidcanflow.
AllAboutFittings52
FIGURE20InternalVolumeDefined
AFewExtraTips
FluidIn FluidOut
Plugged
DeadVolumeSweptVolume
Mathematicallyspeaking,whendeadvolumeandsweptvolumeareaddedtogether,thetotalequalstheoverallvoidvolume.
VoidVolume=DeadVolume+SweptVolume
Deadvolume,however—particularlyincapillaryconnections—cancausesomeveryundesirablechromatographiceffects,including:
Analysis delays
Broadened peaks
Poor resolution
Sample carry-over
Split peaks
Gas collection
KEY CONCEPT
All About Fittings
www.idex-hs.com 53
Sample-to-sample contamination
Dispensing inaccuracies
Precipitation zones
Ifyourapplicationisnotchromatography-related,deadvolumecanstillleadtoproblems,including:
Inotherwords,nomatterwhatyouranalysistechniqueis,deadvolumewilllikelyhaveanegativeimpact.
Therefore,inadditiontokeepingthevolumeinsidetheconnectiontoaminimum,alldeadvolumeshouldberemovedfromtheconnection
The end of the storyWhileit’shardtocaptureallyouneedtoknowaboutfittingsinonecompactreference,it’sourhopethatthisresourcehasproventobehelpfulalready...andwillcontinuetobesomethingyoureturntooverandoveragaininthefuture.
PleasefeelfreetocontacttheCustomerServicestaffatIDEXHealth&Scienceifyouhaveanyfurtherquestionsorifyouhavesuggestionsforfutureeditionsofthisguide.Manyoftheimprovementsinthiscurrenteditionareduetosuggestionsfrominterestedpeoplejustlikeyou!
ifpossible.Ultimately,incapillaryconnections,thepreferredrelationshipcouldbeexpressedasfollows:
VoidVolume=SweptVolume(andshouldbeREALLYsmall!)
AHelpfulNote:AgreatwaytokeepmostofthevoidvolumetrulysweptvolumeistomatchthetubingIDascloselyaspossiblewiththediameterofthethru-holesinyourequipment.Thishelpsensurethatthefluid,onceitleavesthetubing,runscompletelythroughtheentireinternalpassageway.Thisdiametermatchingalsohelpsreducetheamountofturbulencethefluidexperiencesasitpassesthroughtheconnection.
AllAboutFittings54
AppendixI know it’s not a fitting, but…Whilethisresourceisfocusedonfittingsandmakinggreatconnections,thereareotherusefulaccessoriesthatcanbeusedinchromatography(andrelated)applications.Twoofthemorecommonaccessoriesarefiltersandbackpressureregulators(orBPRs).
Filters,FiltersEverywhere!
“WhywouldIeverreallyneedafilter?”youmightask...andyouwouldn’tbealone.Manypeopleassumetheirfluidpathwayiscleanwhenitoftenreallyisn’t,andthereareareaswhereusingfiltersisveryimportant.
Particlesofallsortscanbesuspendedinafluidstream.(Justbecauseyoucan’tseethemdoesn’tmeantheyaren’tthere!)Thingslikedust,solidsoriginatingwithasample,andsealwearparticlesareallreasonswhyfiltersareimportant!
Tohelpunderstandwhereyoucanconsiderusingfiltersinyoursystem,let’slookatcommonplaceswherefiltersareusedinHPLCsystems:
SolventInletFilters:Oneofthefirstplaceswherecontaminantscanenterafluidstreamisinthesolventreservoiritself.Whetherit’sbiologicalmaterialflourishinginsolutionoroutsidedustparticlescollectinginthereservoir,therearenumerouswayslargeparticlescanbecomepresentinthesolventreservoir.Placingasolventinletfilterinsidethereservoirattheendoftheinlettubingwillhelpensurethefluidstreamremainsfreeofphysicalcontaminantsandwillhelpprotectupstreamequipment.
Anotherusefulplaceforaninletsolventfilterisontheendofaheliumspargingdeliverytube.(Spargingisatechniqueusedtoremovedissolvedgasfromamobilephase.)Whenaninletfilterisusedforspargingpurposes,itdoestwothings:itdispersestheheliummoreeffectivelywhilealsopreventingparticles,stemmingfromthegassource,fromenteringthemobilephase.
Foramoredetaileddescriptionofthespargingprocess,pleasesee“MobilePhaseDegassing—Why,When,andHow”byDr.JohnW.Dolan,LC-GCVolume17Number10,October1999.
Appendix
PARDON MOI?
All About Fittings
www.idex-hs.com 55
InlineFilters:Particlesoftenoriginatefromsealwearinpumpandvalvemechanisms,andtheseparticlescancauseblockagesandequipmentmalfunctionsifallowedtoremain.Inlinefiltersareeffective“insurancepolicies”againstsuchproblems.Justastheirnamewouldsuggest,inlinefiltersareplaced“inline”,alongafluidpathwaywheretheycancaptureanyparticulatematterthatmaybetravelinginthesolventstreamandthusprotectagainstblockagesandequipmentdamage.
Inadditiontosealwear,inHPLC,flowpathcontaminationcanoriginatewiththesample.Tohelpprotectagainstphysicalparticulatesthatmaybeinthesamplematrix,aspecialformofinlinefilterisoftenused,calleda“precolumnfilter”.Placedimmediatelybeforethecolumn,aprecolumnfiltercombineseffectivefiltrationprotectionwhileminimizingthepossiblebandbroadeningthatcansometimesoccurinchromatographicapplications.
Anothertypeofcontaminationoriginatingfromthesampleischemicalcontamination,whichneedstoberemovedusingaspecialchemicalfiltercalledaguardcolumn.(Formoreinformationaboutguardcolumns,seepage37.)
Fortunately,bothinlineandprecolumnfilterstypicallyusereplaceablefiltrationdiscsreferredtoas“frits”.Availableinavarietyofporositiesandmanufacturedfromseveraldifferentmaterials,therearenumerouswaystocustomizethefilterforyourspecificapplication.
One important factor to consider when choosing the appropriate precolumn or inline filter for your application — especially if you are working with microscale or nanoscale applications — is the impact that the volume of the filter will have on the results obtained. Frits, by design, are very porous; as such, they typically contain quite a bit of volume — ranging from 18% –30%, depending upon the frits’ porosity. Because frits both increase turbulence as well as the time the sample is in contact with the mobile phase, choosing the right frit — and the right filter assembly — can be critical to obtaining good peak shape and peak resolution.
AllAboutFittings56
How long will filters last?
To test this quickly, temporarily remove the solvent inlet filter from the inlet tube and re-run a few standard samples. If the analysis results return to normal, then it’s likely that the pump was not getting enough fluid with the filter in place. Replace the filter with a new one, and begin your analyses again. Do not operate for long periods without a solvent inlet filter, as damage to your system may occur. (Remember this saying: “If in doubt, throw it out.” Solvent filters are generally inexpensive, making it easier to be safe than sorry!)
Ifyounoticethesystempressureincreasing,that’sagoodindicatorthatthefritinsideeitheryourinlinefilteroryourpre-columnfiltermayneedtobechanged. As your inline filter and pre-column filter do their jobs, the frits inside will collect particles from the fluid pathway. As more particles are collected, less room is available for fluid to move through. Eventually, the pump has to “push harder” to get the same amount of fluid through, causing the system pressure to increase.
To best determine if an inline filter needs maintenance, start at the end of your system and, moving backwards toward the pump, disconnect the fluid pathway fittings one-by-one, monitoring the system pressure. Watch to see if the pressure drops suddenly; if it does, look for the restriction to be in the portion of the flow path last removed from the fluid pathway. If this happens just before a filter, replace the frit inside the filter housing. (Remember to be careful and not create a chemical spill when performing this test.)
Appendix
POINT OF INTEREST
Thisisoneofthemostfrequentlyaskedquestionsregardingtheuseoffilters.
Unfortunately,thereisnostandardfilterlifetime.Youmaygoformonthswithverycleansamplesandmobilephaseandnothavetochangeyourfilters,ortheymayonlymakeitafewdays.Italldependsonhowcleanyourfluidsareandontheconditionofthesealsusedinyoursystem.
Agoodlabpracticetipistomakethereplacementofyourfiltersorfritspartofyoursystem’spreventative
maintenanceroutine,whichtypicallyoccurseverysixmonthstooneyear.
Therewillbetimeswhenyouwillneedtochangeyourfilterorfritinadditiontotheregularly-scheduledchanges.Buthowdoyouknowwhenit’stimetochangethem?Herearesomehintsthatmayhelp:
Ifyounoticeyourchromatogrampeakscomingoutlaterthannormal,itmayindicatethatyourpumpisn’tdispensingtherightvolume. If everything on the pump appears to be functioning properly, and if there is no evidence of a leak, then the solvent inlet filter may be clogged, restricting the solvent flow to the pump.
All About Fittings
www.idex-hs.com 57
Regulate me!Whenitcomestosystempressure,inlinepressureregulationisoftenanecessity.Andthat’swhereBackPressureRegulators(BPRs)comeintoplay.
ABPRisadevicethatcreatesastaticinlinepressure,relativelyindependentofthefluidflowrateorviscosity.
ButwhyuseaBPR?
TherearetwomainapplicationsthatcallforBPRstobeusedinHPLCsystems.
Thefirstapplicationistohelppreventnoiseonachromatogram’sbaseline.(Noiseisthetermappliedtotheerraticfluctuationsonthebaseline.)Asfluidpassesthroughyoursystem,itwillgothroughsometerrificpressurechangesinashortperiodoftime.Ifgasisdissolvedintosolution,bubblescanforminthefluidpathwayasthemobilephasedecompresses.Asthesebubblespassintothedetector’sflowcell,theycancausethedetector’ssignaltochangeirregularly,resultingin“noise”onthebaseline.
This“noise”makesitverytoughtoanalyzesmallpeaksonthechromatogram.
Ifthenoiseyouareexperiencingcomesfrombubblesintheflowcell,
therearetwosolutions:removethegasfromthemobilephase,orpreventbubblesfromforming.UsingBPRswon’tremovethegas,buttheycanhelppreventthebubblesfromforming.
TouseaBPRforthispurpose,simplyplaceitbetweenthedetector’sflowcellandthewastereservoir.Whenthefluidleavesthecolumn,theBPRwillhelpensurethemobilephaseremainsunderpressureasitflowsthroughthedetector,helpingtoinhibitbubblesfromforming.Keepinmindyourdetectorflowcell’spressurelimitasyouareselectingthecorrectBPRforyourapplication.
ABPRcanalsohelpyourpump’scheckvalvesoperatemoreefficiently.Manystandardcheckvalvesaregravity-fedandrelyonsystembackpressuretoworkwell.Ifyourapplicationdoesn’tcausesufficientbackpressuretobedeveloped,yourpump’scheckvalvesmaynotworkcorrectly.However,aBPRplacedimmediatelyafterthepump(butbeforetheinjectionvalve)oftencausesthepump’scheckvalvestooperatemorequicklyandthereforemoreefficiently.(Note:FormostHPLCapplications,itisunlikelyaBPRwouldbeneededinthislocation,asthetypicalHPLCcolumnwillcreatesufficientbackpressuretoensureefficientcheckvalveoperation.)
KEY CONCEPT
SECRET REVEALED
AllAboutFittings58
Conversion factorsHerearesomeotherusefulformulas:
InchestoMillimeters: Inchesx25.4mm/inch
InchestoCentimeters: Inchesx2.54cm/inch
InchestoMicrons: Inchesx25.4mm/inchx1000µm/mm
Diameterininchestolinear((Inches/2)x2.54cm/in)2xvolume(µL/inch)
x2.54cm/inchx1000µL/cm3
Diameterininchestolinear((Inches/2)x2.54cm/in)2xvolume(µL/cm)
x1cm/cmx1000µL/cm3
CelsiustoFahrenheit (Celsiusx9/5)+32
FahrenheittoCelsius (Fahrenheit-32)x5/9
psitobar psix0.06894757
psitoatmospheres psix0.06804596
psitoMPa psix0.00689476
psitotorr psix51.7150733
Speaking of pressure…Sometimesitmaybenecessarytopredicthowmuchpressuremightbecreatedinlinebyyourtubing.Here’saformulawehavefoundtobeveryaccurate(answerinpsi):
P=(9.86x10-8)( FLV
) d4
Where: P=pressuredropinpsi V=viscoscityincentipoise(cp) F=flowrateinmL/min d=tubinginsidediameterincm L=tubinglengthincm
Appendix
All About Fittings
www.idex-hs.com 59
Polymer informationPolymerfittings,tubingandaccessorieshaveproventobesuperiortostainlesssteelinmanyanalyticalapplications.Thefollowingperformanceinformationhasbeencompiledformanyofthepolymerscommonlyusedinanalyticalanalyses.
Please Note: For more information regarding the properties of the polymers listed below, please refer to www.idex-hs.com/materials.
Delrin®(acetal).Delrinexhibitsexcellentchemicalresistancetomostorganicsolventsaswellastomostneutral-pHaqueoussolvents.However,itisnotsuitableforusewithacids,basesoroxidizingagents.Thispolymer’shightensilestrengthyieldssuperior,highlywear-resistantthreadsandexcellentthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings60;TubingN/A
FEP(fluorinatedethylene-propylene)andPFA(perfluoroalkoxyalkane).BothofthesepolymersareinthesamefamilyasPTFE,andassuchareinerttovirtuallyallchemicalsusedinHPLC.However,becauseoftheirrelativesoftnessandlowdurability,thesepolymersaregenerallyusedforlowpressureapplications.ChoosePFAforhighpurityapplications,orchooseFEPasageneral,all-purposematerial.BothFEPandPFAhavegoodthreadstrength.
Maximumoperatingtemperatures(ºC):FittingsFEP-N/AandPFA-80;TubingFEP-50andPFA-80
Halar®ECTFE(ethylene-chlorotrifluoroethylene).Halarisamemberofthefluoropolymerfamily.Itoffersexcellentchemicalresistancecoupledwithamechanicalstrengthsuperiortomanyotherfluoropolymers.HalaralsooutperformsPTFEandsimilarfluoropolymersinabilitytowithstandradiation,makingitanattractivealternativeformedicalapplications.Itsexceptionallysmoothsurfaceenhancesopticalclaritywhilealsohelpingpreventthesheddingofmicroparticlesintothefluidstream.
Maximumoperatingtemperatures(ºC):FittingsN/A;Tubing50
PCTFE(polychloro-trifluoroethylene).PCTFEhasexcellentchemicalresistance.Ingeneral,onlyTHFandafewhalogenatedsolventswillreactwithit.Thisresilientfluoropolymerisidealforfittingsandsealingsurfacesandalsohasgoodthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings80;TubingN/A
PEEK™(polyetheretherketone).PEEKpolymeristheflagshipmemberofthepoly(aryl)etherketonefamilyofpolymers.Ithasexcellentchemicalresistancetovirtuallyallcommonlyusedsolvents.However,thefollowingsolventsareusuallynotrecommendedforusewithPEEK:nitricacid;sulfuricacid;halogenatedacids,suchashydrofluoricacidandhydrobromicacid(hydrochloricacidisapprovedforuseinmostapplications);andpurehalogenatedgases.Additionally,duetoaswellingeffect,becautiousinusingthefollowingsolventswithPEEKtubing:methylenechloride,THF,andDMSOinanyconcentrationandacetonitrileinhigherconcentrations.Excellentthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings125;Tubing100
PolypropylenePolypropyleneisarelativelysoftpolymercommonlyusedinlowpressureapplications,andisespeciallyprevalentinIVDandsimilarequipment.Polypropyleneisexcellentforaqueoussolutions;however,itshouldnotbeusedwithchlorinated,aromatic,andsomeorganicsolvents.Fairthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings40;Tubing40
AllAboutFittings60
PPS(polyphenylenesulfide).PPSisaresilientpolymerknownforitshightensilestrengthandexcellentchemicalresistance.PPSmaybesafelyusedatroomtemperaturewithmostorganicsolventsandneutral-to-highpHaqueoussolvents.However,itisnotrecommendedforusewithchlorinatedsolvents,inorganicacids,oranysolventatelevatedtemperatures.
Maximumoperatingtemperatures(ºC):Fittings50;TubingN/A
Radel®(polyphenylsulphone).Radelisanamorphousthermopolymerthatismechanicallystrongandoffersgoodchemicalresistance.Thispolymerwithstandsrepeatedautoclavesterilizationcycleswithoutsufferingthermalbreakdown.Thisproperty,coupledwithitsopticalclarity,makesRadeltubinganexcellentchoiceformedicalandotherapplicationswherevisualmonitoringisessential.Radelisalsoareadilywettedmaterial,minimizingairbubbleaccumulationontheinnerwallsoftubingmanufacturedwiththispolymer.
Maximumoperatingtemperatures(ºC):FittingsN/A;Tubing100
ETFE(ethylene-tetrafluoroethylene).Asamemberofthefluoropolymerfamily,ETFEhasexcellentsolventresistance.Itsphysicalpropertiesmakeitidealfordemandingsealingapplications.WhilemostcommonlyusedsolventsdonotinteractwithETFE,takecautionwhenusingsomechlorinatedchemicals.ETFEhasgoodthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings80;Tubing80
UHMWPE(ultra-highmolecularweightpolyethylene).UHMWPEisawell-knownanddurablemanufacturingpolymer.Itsphysicalpropertiesmakeitidealforgeneral,aqueous-basedenvironments.Takecautionwhenusingthispolymerinheavilyorganic-basedapplications.Goodthreadstrength.
Maximumoperatingtemperatures(ºC):Fittings50;TubingN/A
Ultem®PEI(polyetherimide).Anamorphousthermoplasticofferinghighheatresistance,highstrengthandbroadchemicalresistance.TubingmadefromUltemoffersahighdegreeoftransparency.Thispolymerwithstandsvarioussterilizationmethods,suchasrepeatedautoclavingaswellasgammaradiation,ethyleneoxidegasanddryheat.UltemmeetsthecriteriaforISO10993,FDAandUSPClassVIcertification.
Maximumoperatingtemperatures(ºC):FittingsN/A;Tubing125
Vespel®(polyimide).Vespelthermoplasticoffershighheatresistance,highmechanicalstrengthandbroadchemicalresistanceinmostcommonliquidchromatographyapplications.However,itisparticularlysusceptibletoattackbyhighpHchemicalenvironments.Vespelcanbeautoclavedandsterilizedusinggammaradiation.Vespeloffersinherentlubricity,makingitidealasachemicallyresistantbearingsurface.
Maximumoperatingtemperatures(ºC):SealingComponents200;TubingN/A
Appendix
For more Polymer information, see the Chemical Compatibility chart on the next page, or download our free app at the iTunes store for instant information.
All About Fittings
www.idex-hs.com 61
Che
mic
al C
omp
atib
ility
Cha
rt
DE
LRIN
®H
ALA
R®
PC
TFE
PE
EK
™‡
PERF
LUO
ROEL
ASTO
MER
POLY
PRO
PYLE
NE
PP
S1R
AD
EL®
R
FEP
/
PFA
2TE
FZE
L®U
HM
WPE
ULT
EM
®
Che
mic
alF
amily
Aro
mat
ics
RR
1R
RR
NR
RM
RR
NR
R
Chl
orin
ated
MR
MM
MN
RM
MR
RM
M
Ket
ones
RR
1R
RR
MR
MR
RM
M
Ald
ehyd
esR
R1
RR
RR
RM
RR
RM
Ethe
rsR
MM
MR
NR
RM
RR
MM
Am
ines
MM
RR
RR
RM
RM
MN
/A
Alip
hatic
Sol
utio
nsR
RR
RR
MR
RR
RM
M
Org
anic
Aci
ds
NR
RR
MR
MR
RR
RM
M
Inor
gan
icA
cid
sN
RR
RM
RM
MM
RM
MM
Bas
esN
RR
RR
RR
RR
RR
RM
Sulfo
nate
dC
omp
ound
sR
RR
MR
MR
MR
RM
M
Thre
adS
tren
gth
*Ex
celle
ntN
/AG
ood
Exce
llent
N/A
Fair
Exce
llent
N/A
Goo
dG
ood
Goo
dN
/A
Max
.Rec
om
men
ded
Op
erat
ing
Tem
p.(
°C)
FEP
PFA
Fitt
ing
s60
N/A
8012
5**
200*
**40
50N
/AN
/A80
8050
N/A
Tub
ing
N/A
50N
/A10
0**
N/A
N/A
100*
**50
8080
N/A
125
1Ch
emica
lres
istan
cea
ssum
esro
omte
mpe
ratu
reu
se.E
leva
ted
tem
pera
ture
smay
resu
ltin
asi
gnifi
cant
redu
ctio
nin
chem
icalr
esist
ance
.2
Whi
leth
ech
emica
lcom
patib
ilityo
fFEP
&P
FAis
virtu
ally
iden
tical
,ple
ase
note
the
tem
pera
ture
limit
diffe
renc
es.
RRe
com
men
ded
M
Som
eso
lvent
sin
this
cate
gory
are
satis
fact
ory,
othe
rsa
ren
ot.I
nad
ditio
n,m
axim
umco
ncen
tratio
nca
nva
ryw
ithth
esp
ecifi
cpro
duct
type
and
chem
ical.
Plea
seco
ntac
tUpc
hurc
hSc
ient
ificf
orfu
rther
info
rmat
ion.
N
RCh
emica
lsin
this
cate
gory
are
gen
eral
lyno
trec
omm
ende
dfo
ruse
with
this
polym
er.
N/A
In
form
atio
nno
tava
ilabl
e.
*Sh
earS
treng
th
**
Inso
me
case
s,PE
EKfi
tting
scan
be
used
toh
ighe
rtem
pera
ture
s.Pl
ease
cont
actI
DEX
Heal
th&
Scie
nce
fors
pecifi
cinf
orm
atio
n.
***
Rade
lisa
nam
orph
ousp
olym
er,a
nda
ssuc
h,it
supp
erlim
itse
rvice
tem
pera
ture
isa
pplic
atio
nan
dch
emica
ldep
ende
nt,a
ndm
ayb
ehi
gher
than
100
˚Cin
som
eca
ses.
***
Perfl
uoro
elas
tom
erm
ater
ialc
anb
eus
edin
app
licat
ions
ate
ven
high
erte
mpe
ratu
res;
howe
ver,
itssu
cces
sfulu
seis
typi
cally
limite
dto
the
perfo
rman
celim
itatio
nso
fthe
tubi
nga
ndth
eco
mpo
nent
suse
dwi
thit
.‡
Inso
me
circu
mst
ance
s,ac
eton
itrile
has
bee
nre
porte
dto
swel
land
occ
asio
nally
bur
stP
EEK
tubi
ng.E
xerc
iseca
utio
nwh
enu
sing
high
conc
entra
tions
ofa
ceto
nitri
lea
torn
eart
hem
axim
ump
ress
ure
ofth
istu
bing
.
AllAboutFittings62
If your fittings leak
TelltaleSignsofSystemLeaksBefore you see the first drip of mobile phase, your system can warn you that a problem exists. The most common signs of system leaks are:
1. No flow or pressure 2. Pump pressures up, but there is no flow 3. Noisy baseline 4. Baseline drift
While all of these symptoms could also indicate problems unrelated to leaking connections, it is always easiest to start there. Not only are leaking connections usually easy to repair, they are also typically the least expensive repair option.
Appendix
ofyoursystem.Toavoidthisproblemandensurecompatibility,useIDEXHealth&ScienceuniversalFingertightfittings.Becausetheferruledoesnotpermanentlyswageontoyourtubing,aFingertightcanbeusedrepeatedlyforseveralcyclesinmostsystems.
4.Checktheconditionofthesealingarea.Afterrepeateduse,afitting’s“sealingarea”(atthetipofthefittingorferrule),willgraduallybecomedeformedtothepointofbeingincapableofcreatingaseal.Assuch,itisagoodideatokeepanextrasupplyofthefittingsyouareusingsoyoucanreplacethemquicklyandavoidunnecessarydowntime.
5.Checkthereceivingportfordamage.Sometimesaleakingconnectionhasnothingatalltodowiththenutandferrule,butwiththereceivingport.Portsthathavehadstainlesssteelfittingsswagedintothemareespeciallysusceptibletodamage.Checkthereceivingportforvisibleburrsorscratchesandreplaceifnecessary.
6.Evaluatechemicalcompatibility.Usingfittingsmadeofmaterialincompatiblewithyourmobilephaseisasurewayofcreatingleaks.PleasevisittheIDEXHealth&Sciencewebsite,www.idex-hs.com,formoreinformationaboutchemicalcompatibility.
1.Checktomakesureyourtubingisseatedproperly.WhenusinguniversalFingertightfittings,thetubingmustbottomoutinthereceivingportbeforethenutandferrulearetightened.Ifagentletugdisengagesyourtubingafterthefittingshavebeentightened,loosenthenutandferruleandtryagain.
2.Thefittingmaynotbetightenedenough.Stainlesssteelnutsandferrulesrequireawrenchtotightenthem,evenafterrepeateduse.Fingertightfittingsalsorequireagoodtighteningtorque;however,usingtoolsincorrectlymayleadtoover-tighteninganddamagetothefitting.Assuch,toolsshouldbeusedwithcautiononFingertightfittings.
3.Youmaybeusingincompatiblefittings.Makesureyouareusinganutandferrulethatarecompatiblewitheachotherandwiththecomponents
All About Fittings
www.idex-hs.com 63
AdapterAunionwithdifferentthreadsoradifferentgeometryoneachend;generallyusedtoconnecttwodifferenttypesoftubingtogether.
BackPressureRegulator(BPR)Adevicetypicallyusedafterthedetectortomaintainapositivepressureontheflowcell,thusminimizingsolventoutgassingproblemsinthedetector.
BiocompatibleReferstothatspecialqualityofsomematerialsallowingthemtocomeintocontactwithbiologicalmaterialswithoutchangingthematerials’bioactivity.
CapillaryTubingOftenreferstotubingsmallerthan1/16”OD;frequentlyusedinhyphenatedanalyticalsystems,suchasLC-MS.
CheckValveAdeviceinsertedintoamovingliquidstreamthatallowsflowofthestreaminonlyonedirection.
ChromatogramAgraphicalplotrepresentingthechangeinsignalintensityfromadetectorandoftenusedinthenumericalanalysisofasample’scomponents.
ColumnAspecializedtube,packedwithsmall,chemically-activeparticlescalledthestationaryphase,inwhichtheseparationofasampletakesplace.
CrossAnx-shapedunionusedtoconnectfourpiecesoftubing.
DeadVolumeThatportionofthevolumewithinaconnectionthatisnotpartoftheflowpath;oppositeofsweptvolume.
DetectorAprimaryanalyticalsystemcomponentthat“sees”samplecomponentsastheyarebeingcarriedawayfromthecolumnbythemobilephase.
EndFittingUsedwithmoststandardcolumnsinthemarkettoday,itisthefittingattheendofthecolumnthatallowscommonlyusedtubingtointerfacewiththecolumntube.Additionally,theendfittingoftenholdsthefritinplaceoneitherendofthecolumntube,thusretainingthepackingmaterialwithinthecolumntube.
ExternalCompressionConnectionmethodutilizedbymostfittingssystemsinamajorityofanalyticalinstrumentation.Itisthenearlyuniversalconnectionmethodwhenrigidorsemi-rigidtubingisused.
FerruleAtaperedconicalringusedtomakethesealbetweenapieceoftubingandareceivingport.Ferrulesalmostinvariablymustbeusedinconjunctionwithanutofsomesort.
FingertightAspecialfittinginventedbyUpchurchScientificthatcanbetightenedtonormalworkingHPLCpressureswithouttheuseofawrench.
FilterAsystemaccessorywhichhelpsmaintainoverallsystemperformancebypreventingsolidparticlesfrompassingalongtheflowpathandpotentiallydamagingsensitivecomponents.
FittingsReferstotheconnectorsthatjointubingtovariouscomponentsinananalysissystem.
FlangedFittingAfittingusedinlowtomoderatepressureapplications.Thefittingrequiresflanging-orspreadingtheendofthetubing-beforeuse.Oftenusedwith1/4-28orM6threadedflat-bottomfittings.
FlangelessFittingAspecializedfittingdesignedtoreplaceflangedfittings,wherethroughtheuseofanutanduniqueferrule,asealcanbemadeontubinginareaswhereflangedfittingsweretraditionallynecessary.
GuardColumnAsystemaccessorydesignedtoprotectthemainanalyticalcolumnfrombeingdamagedbysamplecomponentsthatmightirreversiblybindtothestationaryphaseinside.
Glossary
AllAboutFittings64
HPLCAnacronymforananalyticaltechniqueknownasHighPerformanceLiquidChromatography,usedinmanylaboratoriesaroundtheglobe.
InjectionValveAspecializedvalveusedtointroduceacontrolledamountofsampleintothemobilephaseforanalysis,whilecausinglittletonosystemdisturbance.
MobilePhaseChemicalsolutionpumpedthroughoutananalyticalsystemforthepurposeofanalyzingsamples.
NoiseErraticsignalfluctuationsonachromatogram’sbaseline.
NutAcommontermusedtodescribethethreadedportionofafittingsystem.
OEMAnacronymthatstandsforOriginalEquipmentManufacturer.
PumpAprimarypieceofananalyticalsystemthatpullsmobilephaseoutofthereservoirandpushesitoutthroughtherestofthesystem.
ReceivingPortTypicallyathreadedholeintowhichafittingisattachedforthepurposeofholdingflowpathtubinginplace.Lowpressureportstypicallyhaveaflat-bottomgeometry,andhighpressureportsmostoftenhaveaconedgeometry.
RecorderAprimaryanalyticalsystemdevicethattranslatesthesignalgeneratedbythedetectorintoaplotofsignalversustime;mostoften,thisisusuallyacomputer.
Reservoir(orSolventReservoir)Oftenaglassorplasticbottlethatholdsthemobilephase.
StainlessSteelAnyvarietyofsteelalloysdesignedforcorrosionresistance.Thedifferentvarieties-primarily316grade-areusedtomanufacturehigh-pressure,chemicallyresistantHPLCfittingsandtubing.
StationaryPhaseThesmall,chemically-activeparticlesdenselypackedintoaspecializedtubeknownasacolumnandoftenofferinganoppositechemicalenvironmenttothatwhichisofferedbythemobilephase.
SwagingTheprocessofpermanentlyattachingaferrule(usuallymanufacturedfromstainlesssteel)toapieceoftubing.
SweptVolumeThatportionofthevolumewithinaconnectionthatispartoftheflowpath;oppositeof“deadvolume.”
TeeAT-shapedunionusedtoconnectthreepiecesoftubing.
ThreadPitchStandardizednumericalvaluedescribinghowclosetogetherthreadsareonafitting;Englishthreadshaveathreadpitchthatdescribesthenumberofthreadsperinch,whereasmetricthreadsaredescribedbythedistanceinmillimetersbetweenthreads.
TubingSleeveAshortlengthoftubingdesignedtoslipovercapillarytubing,allowingthecapillarytubingtobesuccessfullyconnectedtoaportdesignedforlargertubing.
UHPLCAnacronymthatstandsforUltraHighPerformanceLiquidChromatographyandgenerallyreferstochromatographicseparationtechniqueswhereintheinlinepressureapproachesorexceeds15,000psi(1,034bar).
VoidVolume(orInternalVolume)Thesumtotalofthedeadvolumeandthesweptvolumeinaconnection.
WasteReservoirThelastcomponentofastandardanalyticalsystemthatsafelycollectsthemobilephaseandsamplecomponentsaftertheyhavebeenanalyzed.
Glossary
Appendix
About The Author
John Batts, a long-time employee with IDEX Health & Science, has extensive experience with HPLC and related techniques – as a lab technician, as an HPLC field service representative, and as a technical specialist. Driven by a passion for teaching and making difficult-to-understand concepts and material more fun and inviting, he embarked on the journey of writing — and updating — this booklet.
He currently resides with his family in the Pacific Northwest.
Copyright © 2011 IDEX Health & Science LLC
All rights reserved.
Reproduction or translation of any part of this book without the written permission of the copyright owner is unlawful. Contact IDEX Health & Science for permission www.idex-hs.com
Printed in the United States of America
First printing, July 2003 Second printing, August 2004 Third printing, March 2011
The following Trademarks and Registered Trademarks are found in this book:
Upchurch Scientific® is a Registered Trademark of IDEX Health & Science LLC
Delrin® is Registered Trademarks of E.I. du Pont de Nemours and Company
PEEK™ polymer is a Trademark of Victrex, plc.
NanoPort™ is a Trademark of IDEX Health & Science LLC
Halar® is a Registered Trademark of Solvay Solexis S.p.A.
Radel® is a Registered Trademark of BP Amoco Polymers
Ultem® is a Registered Trademark of General Electric Corporation
All About Fittings
John W. Batts, IV
A practical guide to using and understanding fittings
in a laboratory environment
IDEX Health & Science619 Oak Street, Oak Harbor, WA 98277 USATel: +1 800 426 0191 · Fax: +1 800 359 3460 · Fax: +1 360 679 3830E-mail: [email protected]
© 2011 IDEX Health & Science LLC