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V O L U M E 27, NO. 7, J U L Y I 0 5 5ents for acid gases but also absorbed exorbitant amounts of car-bonyl sulfide. Therefore, th e gene fated gas is passed as rap id lya~ practical through the caustic scrubber a3 we11 as the Ascarite-f illed absorption tube. Repe ated scrubbing of the impure gasover Ascarite will effectively remove the remaining traces ofhydrogen sulfide, sulfur dioxide, and carbon dioxide.Various methods were tested for removing the carbon disul-f ide, repeated lon- tem perature fractionation being most success-ful. Evac uation of the product at liquid nitrogen temp eratureeliminates the remaining undesirables, oxygen and nitrogen,and mater ially shortens the time for purif ication without intro-ducing subsequent variable factors . With this prepara tion pro-cedure, approlimately 1 gram of p ure carbo nyl sulfide shou ld beobtained.Carbon?-1 sulf ide can be stored for several m onths a t 0 C.in a s tainless s teel bomb f itted with a s tainless s teel valve. Inth e ear ly stages of th e m-ork, a stainless s teel bomb f itted with abrass needle valve and connector was employed. Over a shortperiod of time th e composition of the gas had changed appreci-ably, the decomposition apparently being catalyzed by the brass.The reliability of the method is illustrated by thedata in Tablee I and 111. Analyses performed for the purpose ofchecking the performa nce of the method or evaluating v arious lotsof freshly prepared carbo nyl sulfide indi cated a maximum abso-

Accuracy.

1171lute deviation of 1 p.p .m. f rom the thCweticd v a h e with in therange of 2 t o 60 p.p .m. , or 3.1 when expressed as an es t imateds tandard devia t ion .

ACKNOWLEDGMENTAcknowledgment is made to Matt hew S. Norris for the u l t r a -v io le t measurements and to Nathan F. Kerr for conduc t ingthe carbonyl sulfide mass spectrom eter assays.

LITERATURE CITED1) Alvdeeva, A. V., Zavodskaya Lab., 7 , 279 (1938).(2) Brady, L. J., ANAL.C HEM. , 0, 512 (1948).3) Cornell, P. W., private comm unication.

(4) Hakewill, H., and Rueck, E. AI . , Am. Gas Assoc., Proc., 28, 5295) MacHattie , I. J. W., and McXiven, K. ., Can. Chern. ProcessG ) Riess, C . H., and Wohlberg. C.. Am. Gas Assoc. , Proc., 25, 259

(1946).Inds. , 30, 87, 92, 94 (1946).(1943).

RECEIVEDor review September 2 4 , 1954. Pre-sented before the Symposiuni on Methods f o r Testing Liquefied PetroleumGases, ASTAI Committee D-2. Sat ii ral Gasoline Association of America,and California Xatural Cramline .*ssociation, St. Louis, Ma. , September 27t o 29, 1954.

Accepted January 8, 1955,

etermination of l e a d in UrineWILL IAM M MCCORD and JOHN W. ZEMPD e p a r t m e n t o f C h e m is t r y T h e M e d i c a l C o l l e g e o f South Caro l i na Char les ton S. C.

A method is described for the determination of leadin urine which eliminates the necessity for time-con-suniing precipitation and ashing . Lead, as lead iodide,is extracted quantitatively from acid solution w-ithme th >l isopropyl ketone. The lead is the n removedfrom the ketone layer with an aqueous sodium hydrox-ide solution and is determined colorimetrically by thedithizone method of Snyder using the lead-bismuthseparation of Bambach and Burkey.

H E detection of lead poisoning is greatly facilitated by theT eterm inati on of micro quant itie s of lead in th e urine of theindividual 2 , 6, 10). Th e majo rity of methods currently in use(photo metr i c, polarographic, e tc.) 1,3-6,8, 11) nvolve precipita-tion of th e lead as the phosph ate, an d usually ashing, for the re-moval of 7-arious organic an d inorganic constit,uents which arepresent in relatively large amo unts in ur ine. In th e experienceof this lab orat ory , the initial precip it,ation of th e lead as t.he phos-pha te in alkalin e solution, with calcium and oth er ions, is thetedious a n d t ime-consuming part of the analytical procedure,especially when larger volumes of urine must be used n-hena m o u n t s of' lead present are small.T he introduction of n iethyl isopropyl ketone as an organic sol-vent for the quantitative extraction of lead as lead iodide byWest and Car l ton 12) furnishes a means for considerably re-duc ing the t ime required for an analysis . In the proposedmethod , lead, in an acid solution a nd in t he presence of excesspotassium iodide, is extracted quantitatively by methyl iso-propyl ketone. Thi s is followed by estraction from the ketoneint o basic solution and deveiopm ent of color n+h dithizone.

The d i th izone method is tha t of Snyder (9) using the lead-bis-mu th separation of Bam bach and Burkey 3 ) .REAGENTS AND APPARATUS

A blank m us t be run to de te rmine the amount of lead in thereagents an d distilled wa ter supply before their use. If t h e to ta la mo u n t i s mo re th a n 0.2 y, th e reagents must be purified. Allchemicals should be reagent grade.Si t r ic ac id , concentra ted .Die th y l e th e r .M e th y l i s o pr o p yl k e to n e , Ea s tm a n KO. 146.Potassi um iodide. Dissolve 155 granis of potassium iodide in100 ml. of distilled n-ater. Th is includes a slight excess t o ensuresa tura t ion .Sodium hydroxide, 0.5 . Dissolve 0.5 gram of sodium hydrox-ide in 100ml. of distilled wat er .Thymol b lue ind ica tor , 0.1 . Dissolve 0.1 gram of t h y mo lblue W n 100 ml. of distilled w ater.Ammonium citrate, 5 . Dissolve 5 grams of amm oniumcitra te in 100 ml. of distilled water.Sodium cyanide , 2 . Dissolve 2 gram s of sod ium cj-an ide in100 ml. of distilled wate r .Ammonium hydroxide, 14 . Mix equal volumes of concen-tra ted ammon ium hydros ide and d ist i lled wate r .Dithizone solution. Diseolve 25 mg. of dith izone (Eas tmanSo 3092) in 1 liter of chloroform. Sto re in a glass-stopperedbottle in the refr igerator .Dilu te 9.1 ml. of concentrated nitr ic acid toapproximate ly 500 ml. with d is t il led wate r . Adjus t the pH t o3.4 with ammonium hydroxide . Add to th is so lu t ion a mixtureof 25 m l. of 0.2M potass ium ac id phtha la te and 4.98 ml. of 0.231hydrochloric ac id . Dilu te to 1 iter with distilled w ater .Mix 5 volumes of 14 am-monium hydroxide , 1 volume of 1yosodium sulf ite , and 1 volumeof 201, sodium cyanide. [T he sodium su lf ite is added t o reduceoxidants which a t tack the d i th izone 7 ) .

Buffer , p H 3.4.

Ammoniacal cyanide solution.

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1172 A N A L Y T I C A L C H E M I S T R YStan dard lead solution. Dissolve 0.160 gram of lead nitratein 1 liter of 1 nitric ac id . Dilu te fur ther as needed with 1nitr ic acid.All t r aces of lead m us t be removed f rom th e appara tu s by r ins -ing with warm dilu te nitr ic acid and distilled water , then shakingwith ammoniacal cyanide solution and dithizone solution untilno pink color is seen in th e chloroform layer . Finally, rinse oncewith distilled water .

PREPARATION OF SAMPLEUrine. To 100 ml. of urine in a 500-ml. Florence flask, add10 ml. of concentrated nitric acid and reflux for 20 minutes.Cool under t a p water and transfer to a 250-ml. separatory funnel,r insing the f lask with warm dilute nitr ic acid. Ex tract w ith 25-ml.portions of diethyl eth er three times, discarding the eth er layers.

PROCEDURETo th e prepared sam ple in a 250-ml. separatory funne l, add10 ml. of sa tu ra ted potass ium iodide solu t ion an d ex trac t th reeti ne s with 10-ml. portions of me thy l isopropyl ketone satu ratedwith 5 hydrochloric ac id . Combine and save the ke tone layersin another separa tory funne l . Remove the lead f rom the ke toneby extracting with 50 ml. of 0.5 sodium hydroxide. Discardthe ke tone layers . Add 4 dropf of indicator to the sodiumhydroxide so lu t ion . Adjus t th e pH of th is so lu tion to the ac idside of t he alkaline range of th e indicator (p H 9.5 to 10.0) withnitr ic acid. Add 10 ml of 5 amm onium citrate and 10 ml. of

2 sodium cyanide . Read jus t the pH to 9 .5 to 10 .0 , f neceseary ,with amm onium hydroxide .Sha ke with 20-ml. portions of dithizone solution unti l thegreen color of the dithizone remains unchanged, saving thechloroform layers in a separatorv funnel containing 25 ml. of abuffer solution, pH 3 . 4 . (Each 20-ml. portion of dithiaone solu-tion represents 187 y of lead . ) Shake the separa tory funne l con-taining dithizone solution and buffer for 1 minute . Discard thechloroform layer. If more than 187 y of l ead are present, ueealiquots , diluting with buffer solution (pH 3 .4) t o k ee p t h e p Hunchanged. Add 75 ml. of ammoniacal cyanide solution tobring th e pH t o 11.5, add 25 ml. of dithizone solution, and sha kefor 1 minute. Filter the red chloroform layer containing leaddi th izona te in to a c lean dry co lorimeter tube .Carry a blank consisting of 25 ml. of 1 nitr ic acid throughthe procedure and ad jus t it t o 100 t r a n s mi t t a n c e a t a wa v elength of 510 mp. No te absorbance of the unknown, and , byreferr ing to a s tand ard curve, obta in the concentration of lead.RESULTS AND DISCUSSION

I n T a b l e I, the results are lis ted for analyses of know n concen-tratio ns of lead in urine using a Coleman Unive rsal spectrop hotom -eter an d a 22-mm. cell.Extraction of lead from acid solution by methyl isopropylketone presents several specific advantages. In th e extractionof lead with dithizone-chloroform a clear ammoniacal solution isnecessary. In t he presence of ma ny alkaline precipitates (cal-cium and magnesium phosphates, ferr ic hydroxide, etc. ) leadmay be occluded and troublesome emulsions may be formed.Some mater ials , such as ur ine, contain more of these substancestha n can be kept in solution with any reasonable a mo unt of citricacid (1). T he extraction of lead in acid solution wit h meth yl iso-propyl ketone accomplishes the initial isolation and concentra-tion of th e lead while avoidi ng th e tedious precipitation, en train-ment, a nd ashing necessary in some of the other m ethods andavoiding the formation of emulsions du e to alkaline precipitates.An important advantage also is th e ready adaptability of thisme thod t o larger volumes of urine.Furthermore, the time required for each analysis is reducedfrom hours to approximately 45 minutes. By using severalextractions with methyl isopropyl ketone, lead may be quantita-tively removed with out the waiting period of 1hour recommendedby West 12) for the complete separation of the ketone layers.Troublesome emulsions with m ethyl isopropyl ketone ma y occurin the analysis of ur ine bu t m ay be avoided by a preliminary acidhydrolysis and ether extraction of the urine.In the presence of sodium or potassium cyanide interfer ing

ions are limited to stannous tin, thallium, and bismuth 1).Stannous tin and thallium me rarely encountered in ur ine andma y usually be ignored. Th e bismuth m ay be removed by apreliminary acid-thiocyanate extraction 1 2 )or by a n acid chloro-form-dithizone extraction S ) , in which, a t a pH of 3.4 , t h elead is extracted into the aqueous layer , while bismuth remainscombined with dithizone in th e chloroform layer and is discarded.T h is p H j s critical. 4 t a higher pH , lead will remain in t he chlo-roform layer, giving low results; at a lower pH , bismu th will alsobe extrac ted into t he buffer, giving high results.

Table I . Recovery of Lead from UrineLead,

0.0 0 . 1 0.11 .0 1 .1 0 .12 0 2 . 0 0

Differencedded Found

-0 .3+ 0 . 2o 2-0 .30.8+0.3- 0 . 60- 0 . 5-0 .1- 0 . 8- 0 . 2- 0 3Standard deviation = 0 39.

By extracting an aqueou s solution of lead with dithizone solu-tion at a p H of 11.5, the lead as lead dithizonate is quantitativelytransferred to t he chloroform layer and the excess dithizone isconcentrated in the aqueous layer presumably as the ammoniumsalt (9). Thi s remova l of escess dithizon e results in a low, butcons tant, conce ntration of unreac ted dithizo ne in th e chloroformlayer , thus im proving the accuracy an d reliability of t he resultsas compared with the lower p H methods. This high pH ex-traction also permits the use of a s tandard dithizone solutionand eliminates the necessity for titr imetr ic extraction to esti-ma te concentration of lead in the sample. Th e preliminary ex-traction a t a pH of 9.5 to 10.0 enables the analyst t o make a roughestim ate of th e am ount of lead present.Th e range of sensitivity of t he m ethod, 0 to 70 y using a 22-mm.cell and a Coleman Universal spectrophotometer, is sufficient todeterm ine th e microquant ities of lead found in mild, chroniclead poisoning which would otherwise be difficult to detect. Byvarying cell size the range may be increased (9).I t is absolutely essential that the last traces of lead be re-moved from all equipment used in the analysis.

LITERATURE CITED(1) Assoc. Offic. Agr. Chemists, Washington, D. C., OfficialMethods of Analvsis. DD. 376-93. 1935.(2) Aub, J. C., Fairbail, L. T., Minot, A. S., and Reznikoff, P.,3) Bambach. I C . , and Burkey, R. E., IND.ESG.CHEM. , NAL. D.,

Medzcine, 4, (1925).11, 400 (1939).Toxicol.,30, 59 (1948).4) Cholak, J., Hubbard, D. SI. nd Burkey, R. E., J . Ind. Hug.5 ) Fairhall, L. T., and Keenan, R. G., J . Am. Chem. S o c . 63,3076 (1941).Paul B. Hober, Inc., New York, 1949.Blakiston, Philadelphia, Pa., 1941.

6) Hamilton, A., and Hard y, H. L., Industrial Toxicology, p. 49,(7) Mellan, I., Organic Reagents in Inorganic Analysis, p. 91,8) Ross, J. R., and Lucas, C. C., Can. Med. Assoc. J . , 29, 649 (1933).(9) Snyder, L. J., ANAL. HEW ,19, 684 (1947).(10) Thienes, C. H., Clinical Toxicology, p. 98, Lea and Febiger,

(11) Weber, H. J., J . Ind. Hyg Tosieol., 29, 188-67 (1947).(12) West, P. W., and Carlton, J. K.. Anal. Chim. Acta, 6 , 406 (1952)R E C E I V E Do r review April 13, 1954.

Philadelphia, Pa., 1940,

Accepted February 12, 1955.