pTHE ANALYSIS OF SYNTHETIC DETERGENTS - W. B. SMITH

8/20/2019 pTHE ANALYSIS OF SYNTHETIC DETERGENTS - W. B. SMITH

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THE ANALYSIS OF SYNTHETIC DETERGENTS 513

THE ANALYSIS OF SYNTHETIC DETERGENTS

W. B. SMITH*

A lecturedelivered efore he Societyon 15th May 1963.

The subject is introduced with a classification o• surface active agents

that are used in all types o• detergents. This is •ollowed by a review o• the

older qualitative tests and then an outline o• a new l•aper chromatographic

l•rocedure. Quantitative analysis, confined to the determination o• the active

constituents, is described under headings o• solvent extraction, colorimetric

determination, anionic-cationic titration, and miscellaneous methods.

THE WORDdetergentnowadayssuggestshe packet of spray-driedpowder

used for domesticwash'rag urposes, ut liquid productsused n the same

field may alsocome o mind. For the purposes f this paperother cleansing

materials,namely shampoos nd toothpastes,will be regardedas detergents;

soap s excludedas not failing within the definition of synthetic. However,

onlythe organicsurface ctive ngredientsof the detergentswill be considered.

Most surfaceactive agentswhich are used as detergentshave molecules

which are essentiallyinear and containat one end groupshaving an affinity

for water (hydrophilicgroups),and at the other end groupswhich are anti-

pathic to water (hydrophobicgroups). Surface active agents are classed

according o whether the active speciess an anton, a cation, a non-ionizing

groupor an ampholyticgroup. An ampholyticgroup s one which may act

as either anionicor cationicdepending n the circumstances,rincipallyoa

the pH value of the solution. Hydrophobicgroupsmay be classed nder

the headingsof carboxylicacids (mainly naturally occurringacids),alcohols,

hydrocarbons mainly synthetichydrocarbons erived from petroleum),and

others polyoxy propylene hains). Between he hydrophilicand the hydro-

phobicgroup, the moleculemay conta'ma linking group which may be an

ether, ester, or amide. The listing and classification f possiblestructural

groups s an essentialprerequisite o the construction f a schemeof quali-

tative analysis,and we still find the classificationdrawn up five years ago

to be a usefulstarting po'mt. The best systematicprocedure s to identify

first the hydrophilicgroup, hen the linking group, f any, and lastly the

hydrophobicgroup.

QUALITATIVEANALYSIS

Hydrophilicgroups

One of the best tests for anionic and cationic active compoundss tc•

*Marchon Products, Ltd., Whitehaven, Cumberland.


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514 JOURNAL OF THE SOCIETY OF COSMETICCHEMISTS

treat the substancewith a coloured eagent of the opposite onogenic ype

and shake he aqueousmixture with a non-polar iquid such as chloroform.

The reagentshouldbe such hat its saltswith inorganic onsare not extracted

by the solvent,but its salts with surfaceactive agents,containinga hydro-

phobicgroup n eachmolecule,will be readily extracted; the appearance f

the colouredmolecule n the organic ayer will show he presence f a surface

active agent.

The usualreagent for anionicsurfactants s methyleneblue, but this can

be used only in acid solution and cannot therefore detect the carboxylate

group. Dimidium bromide can be usedover a wide rangeof pH valuesand

can therefore be used for carboxylate groups as well as sulphate and sul-

phonate. For cationic surfactants,a wide range of dyes and indicators

containing he su phonategroup is available and bromophenolblue seems

to be most commonlyused.

An alternative procedure or detectinganionicor cationicsurfactants s

to test whether the substancewill discharge he colour producedwith a

known surfactant of opposite ype and an appropriate reagent. To test

for an anionic surfactant, an aqueousalkaline solution of bromophenolblue

plus a trace of a cationicsurfactant s shakenwith chloroform,and then the

sample is added and the mixture again shaken. To test for a cationic

surfactant, the material is added to acid methyleneblue plus a trace of

dodecylbenzeneulphonate lus chloroform. A compoundwhich discharges

the colour of the chloroform ayers in both anionic and cationic tests is an

ampho yticsurfactant.

Most non-ionicdetergentsare of the polyethanoxy ype and these will

combine with large anions, such as ferrocyanide, cobaltothiocyanate,

molybdophosphate,giving precipitates with the cations present, barium

being needed n the case of the last. Another test for ethanoxy groups s

due to Rosen and consistsof heating with phosphoricacid and testing for

acetaldehyde. The polyhydric alcohol type of non-ionic surfactant also

reacts with large anions; complex odidesare often used, but hexanitrato-

cerate is a simpler though lessspecific eagent.

Linking groups

The linking group is best investigatedby studying the stability of the

molecule owards acid and alkaline hydrolysis. In the caseof an anionic

surfactant, aliquot parts of a solution are assayed by a colorimetric or

titrimetric method (a) without hydrolysis, b) after refluxing n N alkali for

30 minutes, and (c) after refluxing n 2N sulphuricor hydrochloricacid for

2 hours. The sulphate group itself is essentially stable to alkali and is

hydrolyzed in acid solution, esters are completelyhydrolyzed in both acid

and alkaline solutions,while amidesare partly hydrolyzed n both media,


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the extent being characteristic f the particular am/de. If the sample s a

sulphate,or is a non-ioniccompound, hen more specific ests for the ester

and amide inks are needed. The hydroxamic est for esters s very useful ,

while amides can be detected through the primary or secondaryamine

producedon hydrolysis.

Hydrophobic roups

The hydrophobicgroupsare examinedafter hydrolysisof the surfactant:

mild alkaline hydrolysis is sufficient for carboxylic esters, moderate acid

hydrolysis or sulphateswithout a linking group, prolongedacid hydrolysis

for amides, hydrolysiswith hydriodic or hydrobromic acid for ethers, and

hydrolysiswith concentratedphosphoricacid for sulphonateswithout a

linking group. The liberated acid or alcoholmay be analyzed or acid value

or hydroxylvalue,but a muchmoreuseful echniques gaschromatography,

which is applicable to hydrocarbonsalso. Aromatic rings and ethylene

bondsmay be detectedwithout hydrolysis;ultra-violet spectroscopys most

useful or the formerwhilst otherphysicalmethods uchas nfra-redspectro-

photometryand massspectraanalysismay also be used.

PAPER CHROMATOGRAPHY

This technique s one of qualitative analysis,but it is usefu ]ydiscussed

under a separateheading. Over the past few years we have developeda

comprehensivecheme f identificationof detergentcomponents singpaper

chromatography. Tolueneand xy enesulphonates, rea, and alkano arnines

or metals used for neutralization are tested for in addition to the main

surfactants hichareexamined n respect f their hydrophilicgroups,inking

groupsand hydrophobic roups. Full detailshave recentlybeen given by

Drewry5 and, therefore, he presentpaperwill be restricted o a brief outline

of the schemeand an account of the developments hat have been made

since he former paper was written.

Paper chromatographys essentiallya separationby partition between

the stationarywater and movingorganicsolvents, nd the first requirement

is an optimum rdtia water contentof the paper. In our laboratory it has

been found that washing he paper (Whatman No. 1) in 50% ethanol, and

allowing t to dry in the air is sufficient. In other laboratories t may be

necessary o experiment with different drying conditions.

Initially, a large number of solventswas tried, but a mixture based on

tertiary butanol was the only one that gave a uniform development n the

presence f surfaceactive components. Later it was found that an ethyl

acetate mixture as describedby Gaspari• et al6 gave equivalent results o

the butanol solvent, hough n a development ime of only 2-3 hours nstead

of 15-20 hours. The solvent also contains a little ammonia and methanol.


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made from the publishedprocedure s the rather obvioussimplificationof

using one marker solutioncontainingall the referencecompounds.

Another method of identifying amides, applicableboth to the nonionic

alkanolamidesusedas additives and to amide sulphonates nd carboxylates

used as the main anionic surfactants, s to apply paper chromatography

after acid hydrolysis. The aidehydenitroprussidespray is the most useful

as it distinguishes rimary amines such as monoethanolamine nd taurine

(khaki spots) rom secondary minessuchas diethanolamine,N-methyltaur-

ine and sarcosinebluespots), ll liberatedby hydrolysis f the corresponding

fatty acid amide.

•)UANTITATIVEANALYSISBY SOLVENT XTRACTIONS

The most reliable technique of analysing mixtures of surfactants s a

seriesof extractions,with solventsand ion-exchange esins,before and after

hydrolysis, o separate the individual fractions which are then weighed.

Each fractioncan, f desired, e characterized y further analysisncluding

physicalmethodssuchas gas chromatography. A seriesof separations an

be assembledn a variety of ways and therefore t seemsbest here to discuss

the subject under sub-headings f the solvents. The general method for

liquid-liquid extractions is to use stopperedseparating funnels, and for

liquid-solid extractions s simple stirring in a beaker or centrifuge tube,

followed by filtration or centrifuging.

Light petroleum

Typical procedures or petroleum extraction are described n the B.P.

and U.S.P. monographsor sodium auryl sulphate. The sample s dissolved

in 50% ethanol, for the unsulphated alcohol is less soluble n this than in

an aqueous olutionof the sample (owing o reducedmiceilar effects)and

emulsification ifficultiesare fewer. Three extractionswith petroleum are

made. The combined extracts are dried, the solvent is distilled off and the

residue s weighed. A certain proportion of free lauryl alcohol remains

solubilized n the surfactant solution, as is shown by tests on synthetic

mixtures, even after 5 or 10 extractions. The loss dependson the con-

centrationof surfactants nd, for reproducibleesults, he latter is arbitrarily

fixed at about 5% w/v. Besides he questionof completenessf extraction

there are severalother difficulties n arriving at a standard method of high

reproducibility. Washing the petroleumextracts is always liable to cause

losses, nd thesemust be balancedagainst he errorsdue to contaminants.

Drying the extracts with sodium sulphate or another desiccantmay lead

to a loss,but omission f the drying step may cause osses y volatilisation

in steam. Removal of the solvent without loss of volatile alcohol is also a

problemand, finally, errorsassociatedwith weighing he residue n a large


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518 JOURNALOF THE SOCIETY OF COSMETICCHEMISTS

glass lask,namely,adsorption f moistureon the glass, lectrostatic harges,

and buoyancy errors, can all be significant.

Other uses of light petroleum as an extractant are to separate unsul-

phonatedoil from alky ar¾1sulphonates,nd to extract fatty acids iberated

by acidificationof soapsolutions. The solvent s alsoused o extract acids

and alcohols iberated by the hydrolysis of amides and esters .

Ethyl ether

Ethyl ether extracts he samecompounds s ight petroleum,and several

others too, particularly alkanolamides. Being a singlecompoundof low

boilingpoint it can be distilled rom the extract with lessuncertainty han

attends the removal of light petroleum, a•d for this reason t is preferred

in such determinationsas the total fatty alcohol n alkyl sulphates. Dis-

advantagesof ethyl ether are its higher solubility for water and for hydro-

chloric acid. It can only be used with dilute aqueousethanolicsolutions

and is thereforenot very satisfactory or extractingalcohols nd acids from

solutionsof sulphonates s a moderate ethanol content s needed o reduce

miceliar effects. Ethyl ether will extract hydroxy-acids which light

petroleum will not.

Ethyl ether will also extract alkylarylsulphonic cids from 2N hydro-

chloric acid, and this is useful for separating hese acids rom toluene- and

xylene sulphonates.

Accurate quantitative determinationsare limited by the same actors as

describedor light petroleum,and thesealsoapply in varying degree o the

other solvents below.

Chloroform

This solventwill extract most ethylene oxide derivatives, ncluding hose

with chains of six or more units which are not extracted with ethyl ether.

It will also extract alkylarylsulphonates, nd many other surfactants, rom

neutral solutions. One disadvantageof chloroform s that any ethanol in

the aqueoussolution must first be expelled, and even in the absenceof

ethanol, emulsification is often troublesome.

Alcohol

Extraction with ethanol is used to determine the total organic content

of built detergents, nd by separatelydeterminingunsulphonatedmatter,

additive, chloride, etc. the surfactant content can be found. To ensure ex-

traction of small quantitiesof active material containedwithin the beadsof

spray-driedpowders, t is necessaryo take the residueafter a few extrac-

tions, dissolvet in a smallquantity of water, and reprecipitatewith alcohol.

As ethanol is miscible with water it is clear that extraction from a solid


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is the only suitable technique. However, butanol and higher molecular

weight alcoholsare immisciblewith water, while isopropanols immiscible

with a concentrated aqueoussolution of sodium carbonate, and these can

be used in liquid-liquid extractions.

Ion-exchange esins

The use of ion-exchangeresins differs from the solvent extraction

techniques, ut it is usefullyconsideredwith them as, alongwith extractions,

it can be built into a compositeanalytical schemeof separations. Ion-

exchangeesinsprovide he only simplemeansof separating nionic,cationic,

and non-ionicsurfactants. Though simple n principle, he practical use of

ion-exchange esinswith surface-active olutions nvolvesseveralcomplicat-

ing factors such as the polarity of the solvent, usually an aqueousalcoholic

medium, the swellingand shrinkingof the resin, and hydrolysisof the sur-

factant on the resin or during elution. A great deal of work on the subject

has been done by P. Voogt, amongothers,but only a little of this has yet

been published '•ø.

Comprehensivecheme f analysis

The number of combinations f different surfactants hat may be present

in a commercial detergent is infinite, and no efficient general scheme of

separationcan be drawn up; the method of analysismust be chosen o deal

with the particular types of ingredientknown or expected o be present.

One decision o be made in dealing with several componentss whether to

extract them one at a time by the successivepplicationof specificechniques

or whether o proceed y divisionand sub-division, .g.with six components,

first separate wo or three from the others, hen proceedseparatelywith each

group. The latter technique is more complicated, but errors are smaller.

Another decision s whether to separate each component n a reasonably

pure form, or whether to extract two more more ingredients together and

deduce he contents y difference. The caseof a simpledetergentcontaining

free oil, ethanolamide,and alkylarylsulphonate,ogetherwith inorganicsalts

and water may be taken as au example. Scheme is to extract the free

oil with light petroleum from a 50% aqueousethanolic solution of the

sample,then the alkanolamidewith ethyl ether after dilution to 20-30%

ethanol, and finally the alkylarylsulphonatewith chloroform from the

residual aqueous solution, or with ethanol from a dried residue. Scheme

2 is to extract the first two components ogether, using ethyl ether, then

separate hese ater and to extract the alkylarylsulphonate rom the aqueous

layer. Scheme$ involves extraction of free oil with light petroleum,

free oil plus a kanolamidewith ethyl ether, and the total of the organic

compounds with ethanol, all on separate samples and the individual


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522 JOURNALOF THE SOCIETYOF COSMETIC HEMISTS

is importantand showshe reasons hy end-pointsb) and (d), at which

most of the indicator s in the aqueous haseand nearly all the surfactant

in the organicphase,are unsatisfactory ith commercialmatehals. End-

point (a) is rarely usedbecauset givesno warningof its approach. It also

has the disadvantagehat trace mpurities n the indicator,particularlyof

the oxidationproducts n methyleneblue, may impart a bluishcolour o

the aqueous ayer well before the end-point. The same impurities also

interfere n end-point e) and from our experiencewe recommendhe use

of this end-pointonly with the artionic ndicatorswhich are purer and more

stable han the cationic nes. This eaves nd-pointsc) and (f) as the best

for cationic indicatorssuch as methylene blue.

It might be mentionedat this point that methyleneblue seems o be

practically the only cationic indicator that is used for the titration and

despite he limitations t seems o be preferred o anionic ndicators n most

commercialanalytical laboratories n the U.K. and abroad. A wide choice

of artionicndicators f the sulphonphthalein,ulphonic cid,and fluorescein

classess available,but the vast majority of workersappear o follow closely

the techniqueof the early workers,Barr, Oliver, and Stubbins,and to use

bromophenolblue.

Standardisation

At the end of the titration in cases a) and (e) the wholeof the indicator

is in combination with surfactant, and a blank correction,which is constant,

calcu ab e, eproducible nd readily determined,must be applied. In cases

(c) and (f) only part of the indicator remains combinedwith surfactant and

the necessary orrectiondependsupon the proportion nvolved, and this

dependsn turn upon he relative volumesof aqueous nd chloroformayers.

Experimental determinations of the blank or of a correction factor have

been describedby severalwriters, but for routine analysis t is sufficient

to standardise he titrant under similar conditions o thoseof a determination,

thus eliminating the correction. The standard substancen this approach

must be of a similar composition o that being determined,which means n

many cases hat it must contain a mixture of isomersor of homologues s

do the commercialmaterials, and its composition an therefore only be

established y other analyticalmethods,principallyby extractionor ion-

exchangemethods. For na kyl sulphates,t is possibleo prepare he pure

matehals, and these can be used as standards in this field.

Miscellaneous Factors

After the choiceof indicator, of end-point and of standard,that of the

titrant is the most mportant. Cetyltrimethylammonium hloride nd cety -

pyridiniumbromideseem o be most frequentlyused or anionicdetergents.


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THE ANALYSIS OF SYNTHETIC DETERGENTS

The stearylcompoundsave the disadvantage f lowersolubility,while the

myristylandshorter hainhomologuesay react ncompletely. owever,we

have found hat N-alkyl-N-benzyldimethylammoniumhlorides ive much

sharper nd-pointshan the other wo groups f titrant. The stearylcom-

poundagain s of low solubility,but the lauryl, myristyl and cetyl com-

pounds ll havesimilarperformancesnd there s little to choose mong

themexcept hat the cetylcompound,f owest olubility,s the most eadily

purified by crystallisation.

Regardinghe concentrationf the titrant, many workers ollowEpton

in using itrationsof about 10 ml with .004 or .0053{ itrant, but larger

titrations with more dilute solutions,e.g. around 20 ml or .0013{ as used

by Barr et al normally give more precise esults,and are at least as accurate

if due regard is paid to the blank.

All titration proceduresre equallysuitable or determining nionicor

cationic urfactants,he concentrationf the otherbeingknown,and it is

also mmaterialwhether he solution f unknown oncentrations placed n

the titration vesselor in the burette, although he former is usually he

most convenient.

The singlephase itration

The earliestworkby Hartley and Runnicles seda single-phaseitration

of aniordc nd cationic urfactants,ut the end-pointwith bromophenol

bluewasnot soclearas when he two-phaseechnique asapplied. How-

ever, with fluorescent indicators such as eosin 5 and dichlorotetraiodo-

fluorescein6 the end-pointmay be as sharpas with the two-phasemethod,

and such ndicatorsmay repay urtherstudy. Their main disadvantage

is that large amounts of inorganic salts, and moderate amounts of inactive

organiccompounds,end to obscure he end-point.

OTHER •/[ETHODS OF ASSAY

Methods asedon the formationof an aminesalt with artionic urfactants,

usingan ordinaryprimary amine,have beenused or a long time. One

procedure* uses oluidine as the amine, extracts the salt with carbon tetra-

chloride,and determineshe amine n the extract by additionof ethanol

and itrationwithalkali. A similar rocedureauses enzidinendseparates

the salt by filtration. The salt may be weighed efore itration o givean

indication f the equivalent eight,whichcannotbe determinedy any

volumetric method.

For determiningationic urfactants,everalprecipitantsontaining

large artionsmay be used, and in a review by Chinnickand Lincoln 9,

phosphotungsticcid s recommended. on-ionic urface ctiveagentswith

an ethanoxy hainof suitableength or detergencyanalsobe precipitated


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524 JOURNALOF THE SOCIETY OF COSMETICCHEMISTS

with the heteropoly-acids; hosphomolybdiccid is preferred,as the pre-

cipitate can readily be analysed o determine he surfactant contentwhich

varies with different compounds. Ampholyticsurfactantsof the amino-

carboxylategroup are usually analyzed by the methods employed or

catiordcs,with specialattention to reactions n acid solution. Thoseof the

aminosulphonate roup are analyzed by the methodsused for anionics.

Ampholytics ontaining sulphategroupare subjected o acid hydrolysis

to yield an aminewhich is analyzedas a true cationiccompound.

CONCLUSION

A great deal of work on new methodsof detergentanalysis s being

undertaken n this country and abroad, but most of this falls into two

classes.The first is a thoroughexaminationof the traditional methods n

endearours o draw up national and international standards,and the second

is concernedwith new types of detergents,mainly biodegradable nionic

surfactants, nd a wide range of ampholytics.

Mostof thispaperhasbeenconfinedo a discussionf analyticalmethods

that have stoodup to the recent scrutinyand that are likely to be issued

as standards in the near future.

Among these procedures are two that have hitherto survived severe

criticism,but which have such nherent defects hat they are liable to be

supersededn the secondgenerationof standards. The first is the large

group of analysesby solvent extraction. Each operation s limited by an

equilibrium artition coefficient nd, thoughseries ontaining p to a dozen

extractionand washingstepshave beenrecommended,he overall accuracy

and precision f many is barely acceptable. With chromatographicro-

cedures n the other hand, usingcolumnsof ion-exchange esins,of alumina,

cellulose, nd silica, separationsmay involve hundredsof theoreticalequi-

librium stageswith no more than a few minutes'attention of the analyst.

Such methodswill becomewidely used n the future, but a great deal of

tedious study is needed before results can be accepted as reliable and

reproducible, speciallyamong different aboratories.

The secondprocedure s the two-phasecationic-anionicitration using

methylene blue and this suffers rom the same limitations of equilibrium

partition as the first method. The best hope for improvement ies in the

synthesis f a cationic ndicator designed pecially or this application. The

ideal indicator will probably contain only one basic group, this being a

quaternary nitrogen, and will have an intense colour, preferably blue.

Nevertheless, n ideal indicator may not overcome he inherent defectsof

the competing quilibria, or many investigators eem o ignore he extracta-

bility of both anionic and cationic surfactants, n the absenceof indicator,

in solventssuch as chloroform. The factors appear to be more serious n


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alkaline solutions, which underlines the need for a better indicator that is

usableat low pH values.

The other ieldof muchcurrentendearours the developmentf analytical

methodso dealwith newer ypesof surfactants. The searchor a detergent

that is readily decomposedn sewage reatment plants s to a large extent

concernedwith derivativesof natural fats, particularly of tallow which is

available n larger quantities han coconutand palm kernel oils; derivatives

are being made and tested at a faster rate than the necessarymethodsof

analysiscan be devised. The field of ampholyticsurfactantss another n

which new compounds re frequently appearing. When commercialcon-

siderations ave led to a more stablepattern of supplyand demandof both

typesof surfactant, hen the analystcan developprocedureshat are worthy

of publication. This situation is not likely to be reachedwithin the next

year or two.

(Received:7thMay 1963)

REFERENCES

Many references given in the first paper below have not been listed again. The

books referred to under 4 and 7 below are useful general works, and the former contains

a good guide to the literature, excluding the anionic-cationic titration.

• Smith. W. B. Analyst 84 77 (1959)

2 Holness, H., and Stone, W.R. Analyst 82 166 (1957)

a Rosen, M.J. Anal. Chem. 27 787 (1955)

4 Rosen, M. J., and Goldsmith, H.A. SystematicAnalysis of Surface-ActiveAgents

(1960) (Interscience, London)

5 Drewry, J. Analyst 88 225 (1963)

6 Gaspari6, J., Borecky, J., Obruba, K., and Hanzlik, J. CollectionCzechoslovak hem.

Commun. 20 2950 (1961)

* Longman, G. F., and Hilton, J. Methods or the Analysis of Non-soapy Detergent

(NSD) Products (1961) (The Society for Analytical Chemistry, London)

8 House, R., and Darragh, J.L. Anal. Chem. 20 1492 (1954)

9 Voogt, P. Rec. tray. chim. 78 899 (1959)

•0 Voogt, P. Proceedings, rd World Congress n Surface Active Agents II 78 (1960)

(University Press, Mainz)

• Jones, J. H. J. Assoc. O.l•c. Agr. Chemists28 398 (1945)

•a Abbott, D.C. Analyst 87 286 (1962)

•a Silverstein, R.M. Anal. Chem. 35 154 (1963)

•4 Cullum, D.C. Proceeding,$rd World Congress n Surface Active Agents II 42 (1960)

(University Press, Mainz)

•5 Dolezil, M., and Bulandr, J. ChemickeListy 51 255 (1957)

•6 Schwerdtner, H., Teztil u. Faserstofftechnik 569 (1955)

•? Marron, T. V., and Schifferli, J. Ind. Eng. Chem. Anal. Ed. 18 49 (1946)

•8 Blank, E. W. Soap Chem. Specialties $4 41 (January 1958)

•9 Chinnick, C. C. T., and Lincoln, P. A. Proceedings,1st World Conferenceon Surface

Active Agents I 209 (1954) (Chambre Syndical Tramagas, Paris)


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52•3 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

I)ISCUSSION

)/IR. G. A. C. PITT: What indicatorshave you tried other than methylene

blue and bromophenol lue ?

THE LECTURE•: Among anionic ndicators,methyl orange s the only

alternative to bromophenol blue that we have used. A wide range of

indicator types s available,but bromophenol lue has so few disadvantages

that there is little incentive to look elsewhere. With cationic indicators

the situation is quite different, and we have considered every coloured

organic ationiccompoundhat hasbeenbrought o our attention. Dimidium

bromidewas mentionedabove, and methyl yellow has also been usedby us.

Indicators such as methyl violet and methyl green gave less satisfactory

results than methylene blue; pinacyanol chloride and methylviologen

showedno promise. We think that the problem justifies attempts at the

special synthesisof an indicator, and some coloured organic compound

contairfingone quaternary ammoniumgroup and no other ionogenicgroup

in the moleculewould probably be suitable.

MR. J. S. LEAH¾: Has the use of thin layer chromatography een in-

vestigated n place of paper chromatographyn the qualitative analysisof

detergents It would appear o have advantages oth in time and possibly

conditions of detection.

THE L•C•URER: We havenot investigatedhe subjectand do not know

of any work on thin layer chromatography f detergents. In view of the

apparent advantageswe hope to look into the technique when time is

available.

A M•M•ER OF •H• AUDIENCE: How is phosphomolybdic cid used?

THE L•c•u•n•: Phosphomolybdicacid is slowly added to a dilute

acid solutionof the non-ionicsurfaceactive agent and of barium chloride,

and the non-ioniccompoundM is thereby precipitated as the complex

B%(PM%204o)2.xM.The precipitate s filtered off, dried, and weighed.

The compositionof the precipitate is then determined by dissolvinga

weighed portion in excessof alkali and back-titrating the excess. The

overall reaction is :--

B%(PMo•20•0)• 46 NaOH +3 Na•SO4 3BaSO•-.4-24Na•MoO•+

2 Na•HPO•+22 H20

For a preciseend-point we back-titrate to excesswith hydrochloric cid,

then add a little neutral sodiumsulphate,and titrate again with sodium

hydroxide. This reduces he interferencedue to carbon dioxide, which may

be appreciablewhen solublebarium salts are present. Since460 ml 0.1N

sodiumhydroxideare equivalent o 4057 mg of barium phosphomolybdate,


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THE ANALYSIS OF SYNTHETIC DETERGENTS •59.7

the inorganic ontentof the precipitate an be calculated. The rest of the

precipitate ompriseshe non-ionic urface ctiveagent he contentof which

in the originalsolution s thus determined. An analysisof the precipitate

is essential or every new type of non-ioniccompound,because he value

of x varies from one substance o another, and may even vary among com-

poundsof nominally the same composition.

Ml•. D. B^ss: Your method of analysis or ampho ytics s to estimate

as cationics under acid conditions. This method works well for the sub-

stituted aminoacid type, but do you obtain good esultsusing he betaine

type of ampholytic I am thinking n particularof difficulties hen here

is a degreeof internal compensation ithin the molecule s with the cyclo-

imidinium type.

T}m LECTURER: Yes, we find our normal method for cationics to be

satisfactory or the betaine type of surfaceactive agent. The two-phase

titration is performedn acid solutionwith chloroform s the organicphase,

sodiumdodecylbenzenesulphonates titrant, methyleneblue as indicator,

and we take complete ransferenceof colour to the organic phase as the

end-point.

BOOK REVIEW

Standard Methods of Chemical Analysis. Volume II (A and B). INDUSTRIAL &

NATURAL PRODUCTS & NONINSTRUMENTAL METHODS. Sixth Edition.

Editor: F. J. Welcher. Part IIA--Pp. xiv q- (1-1282) q- Ill. Part IIB--Pp. xi q-

(1283-2613) q- Ill. (1963). D. Van Nostrand Company, Inc., New York.

$25 each (not sold separately).

It is almost wenty-five years sincea revisededition of Standard Methodsof Chemical

Analysis has appeared. In 1939, the Fifth Edition was published as two volumes but

so great have been the modifications, efinementsand developmentsof the methods of

chemical analysissince hat time that the Sixth Edition appears n three volumes, with

Volume II expanded nto two parts, bound separately as Volume IIA and Volume IIB.

Despite its considerableexpansion the purpose of Volume II remains that it shall be a

collection of carefully selectedwell proved methodsof technical analysis, of practical

value to the professional chemist.

The lay-out of this edition is similar to the previous one, but the expansiondue to

the inclusionof new material adequately reflectssome of the important changes hat

have taken place in recent years in analytical techniques. The expansion includes

chapterson standard aboratory apparatus; detectionof cations and anions; mechanical

separation; separationsby filtration; separationsby electrolysis; solvent extraction;

separationsby distillation and evaporation; chromatography; ion exchange methods

in analysis; acid-base titrations in non-aqueoussolvents; statistical interpretations;

quantitative organic analysis; air pollutants; amino acid analysis of protein hydroly-

zates; chemicalanalysis n clinical medicine; fertilizers; gas analysiswith emphasison

vacuum techniques; pesticides; plastics; silicates,glasses, ocks, soils and vitamins.

There are numerous eferences o original papers and there is a good ndex at the

end of Part B only. It is somewhat annoying that Part B has to be consulted for work

that is known to be found in Part A, for these books are not lightweight ones. It is

difficult to understandwhy the index was not included n Part A as well; the book would

only be 22 pages larger than Part B had this been done.

Cosmetic chemists may be disappointed that the analysis of cosmetics does not

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pTHE ANALYSIS OF SYNTHETIC DETERGENTS - W. B. SMITH