V O L U M E 27, NO. 7, J U L Y I 0 5 5 ents for acid gases but also absorbed exorbitant amounts of carbonyl sulfide. Therefore, the genefated gas is passed as rapidly a~ practical through the caustic scrubber a3 we11 as the Ascaritefilled absorption tube. Repeated scrubbing of the impure gas over Ascarite will effectively remove the remaining traces of hydrogen sulfide, sulfur dioxide, and carbon dioxide. Various methods were tested for removing the carbon disulfide, repeated lon- temperature fractionation being most successful. Evacuation of the product a t liquid nitrogen temperature eliminates the remaining undesirables, oxygen and nitrogen, and materially shortens the time for purification without introducing subsequent variable factors. With this preparation procedure, approlimately 1 gram of pure carbonyl sulfide should be obtained. Carbon?-1 sulfide can be stored for several months a t 0" C. in a stainless steel bomb fitted with a stainless steel valve. I n the early stages of the m-ork, a stainless steel bomb fitted with a brass needle valve and connector was employed. Over a short period of time the composition of the gas had changed appreciably, the decomposition apparently being catalyzed by the brass. Accuracy. The reliability of the method is illustrated by the data in Tablee I and 111. Analyses performed for the purpose of checking the performance of the method or evaluating various lots of freshly prepared carbonyl sulfide indicated a maximum abso-
1171 lute deviation of 1 p.p.m. from the thCweticd v a h e within the range of 2 t o 60 p.p.m., or 3.1% when expressed as an estimated standard deviation. ACKNOWLEDGMENT
Acknowledgment is made t o Matthew S. Norris for the ultraviolet measurements and to Nathan F. Kerr for conducting the carbonyl sulfide mass spectrometer assays. LITERATURE CITED
(1) (2) (3) (4)
Alvdeeva, A. V., Zavodskaya Lab., 7, 279 (1938). Brady, L. J., ANAL.CHEM.,20, 512 (1948). Cornell, P. W., private communication. Hakewill, H., and Rueck, E. AI., Am. Gas Assoc., Proc., 28, 529
(1946). ( 5 ) MacHattie, I. J. W., and McXiven, K. L., Can. Chern. Process Inds., 30, 87, 92, 94 (1946). ( G ) Riess, C . H., and Wohlberg. C.. Am. Gas Assoc., Proc., 25, 259 (1943). RECEIVED for review September 24, 1954. Accepted January 8, 1955, Presented before the Symposiuni on Methods for Testing Liquefied Petroleum Gases, ASTAI Committee D-2. Satiiral Gasoline Association of America, a n d California Xatural Cramline .*ssociation, St. Louis, Ma., September 27 t o 29, 1954.
Determination of lead in Urine WILLIAM M. MCCORD and JOHN W. ZEMP Department o f Chemistry, The M e d i c a l College of South Carolina, Charleston,
A method is described for the determination of lead in urine which eliminates the necessity for time-consuniing precipitation and ashing. Lead, as lead iodide, is extracted quantitatively from acid solution w-ith meth>l isopropyl ketone. The lead is then removed from the ketone layer with an aqueous sodium hydroxide solution and is determined colorimetrically by the dithizone method of Snyder using the lead-bismuth separation of Bambach and Burkey.
T
HE detection of lead poisoning is greatly facilitated by the determination of micro quantities of lead in the urine of the individual ( 2 , 6, 10). The majority of methods currently in use (photometric, polarographic, etc.) (1,3-6,8, 11)involve precipitation of the lead as the phosphate, and usually ashing, for the removal of 7-arious organic and inorganic constit,uents which are present in relatively large amounts in urine. I n the experience of this laboratory, the initial precipit,ation of the lead as t.he phosphate in alkaline solution, with calcium and other ions, is the tedious and t ime-consuming part of the analytical procedure, especially when larger volumes of urine must be used n-hen amounts of' lead present are small. The introduction of niethyl isopropyl ketone as an organic solvent for the quantitative extraction of lead as lead iodide by West and Carlton (12) furnishes a means for considerably reducing the time required for an analysis. I n the proposed method, lead, in an acid solution and in the presence of excess potassium iodide, is extracted quantitatively by methyl isopropyl ketone. This is followed by estraction from the ketone into basic solution and deveiopment of color n+h dithizone.
S. C.
The dithizone method is that of Snyder (9) using the lead-bismuth separation of Bambach and Burkey ( 3 ) . REAGENTS AND APPARATUS
A blank must be run to determine the amount of lead in the reagents and distilled water supply before their use. If the total amount is more than 0.2 y, the reagents must be purified. All chemicals should be reagent grade. Sitric acid, concentrated. Diethyl ether. Methyl isopropyl ketone, Eastman KO.3146. Potassium iodide. Dissolve 155 granis of potassium iodide in 100 ml. of distilled n-ater. This includes a slight excess to ensure saturation. Sodium hydroxide, 0.5%. Dissolve 0.5 gram of sodium hydroxide in 100 ml. of distilled water. Thymol blue indicator, 0.1%. Dissolve 0.1 gram of thymol blue W S in 100 ml. of distilled water. Ammonium citrate, 5%. Dissolve 5 grams of ammonium citrate in 100 ml. of distilled water. Sodium cyanide, 2%. Dissolve 2 grams of sodium cj-anide in 100 ml. of distilled water. Ammonium hydroxide, 14%. Mix equal volumes of concentrated ammonium hydroside and distilled water. Dithizone solution. Diseolve 25 mg. of dithizone (Eastman S o . 3092) in 1 liter of chloroform. Store in a glass-stoppered bottle in the refrigerator. Buffer, p H 3.4. Dilute 9.1 ml. of concentrated nitric acid t o approximately 500 ml. with distilled water. Adjust the p H t o 3.4 with ammonium hydroxide. Add t o this solution a mixture of 25 ml. of 0.2M potassium acid phthalate and 4.98 ml. of 0.231 hydrochloric acid. Dilute t o 1 liter with distilled water. Ammoniacal cyanide solution. Mix 5 volumes of 14% ammonium hydroxide, 1 volume of 1 yosodium sulfite, and 1 volume of 201, sodium cyanide. [ T h e sodium sulfite is added to reduce oxidants which attack the dithizone ( 7 ) .]
1172
ANALYTICAL CHEMISTRY
Standard lead solution. Dissolve 0.160 gram of lead nitrate in 1 liter of 1% nitric acid. Dilute further as needed with 1% nitric acid. All traces of lead must be removed from the apparatus by rinsing with warm dilute nitric acid and distilled water, then shaking with ammoniacal cyanide solution and dithizone solution until no pink color is seen in the chloroform layer. Finally, rinse once with distilled water. PREPARATION OF SAMPLE
Urine. To 100 ml. of urine in a 500-ml. Florence flask, add 10 ml. of concentrated nitric acid and reflux for 20 minutes. Cool under t a p water and transfer t o a 250-ml. separatory funnel, rinsing the flask with warm dilute nitric acid. Extract with 25-ml. portions of diethyl ether three times, discarding the ether layers. PROCEDURE
To the prepared sample in a 250-ml. separatory funnel, add 10 ml. of saturated potassium iodide solution and extract three tines with 10-ml. portions of methyl isopropyl ketone saturated with 5% hydrochloric acid. Combine and save the ketone layers in another separatory funnel. Remove the lead from the ketone by extracting with 50 ml. of 0.5% sodium hydroxide. Discard the ketone layers. Add 4 dropf of indicator to the sodium hydroxide solution. Adjust the pH of this solution t o the acid side of the alkaline range of the indicator (pH 9.5 to 10.0) with nitric acid. Add 10 ml of 5% ammonium citrate and 10 ml. of 2% sodium cyanide. Readjust the pH to 9.5 to 10.0, if neceseary, with ammonium hydroxide. Shake with 20-ml. portions of dithizone solution until the green color of the dithizone remains unchanged, saving the chloroform layers in a separatorv funnel containing 25 ml. of a buffer solution, pH 3.4. (Each 20-ml. portion of dithiaone solution represents 187 y of lead.) Shake the separatory funnel containing dithizone solution and buffer for 1 minute. Discard the chloroform layer. If more than 187 y of lead are present, uee aliquots, diluting with buffer solution (pH 3.4) t o keep the p H unchanged. Add 75 ml. of ammoniacal cyanide solution to bring the pH to 11.5, add 25 ml. of dithizone solution, and shake for 1 minute. Filter the red chloroform layer containing lead dithizonate into a clean dry colorimeter tube. Carry a blank consisting of 25 ml. of 1% nitric acid through the procedure and adjust it to 100% transmittance a t a wave length of 510 mp. Note absorbance of the unknown, and, by referring to a standard curve, obtain the concentration of lead. RESULTS AND DISCUSSION
I n Table I, the results are listed for analyses of known concentrations of lead in urine using a Coleman Universal spectrophotometer and a 22-mm. cell. Extraction of lead from acid solution by methyl isopropyl ketone presents several specific advantages. In the extraction of lead with dithizone-chloroform a clear ammoniacal solution is necessary. I n the presence of many alkaline precipitates (calcium and magnesium phosphates, ferric hydroxide, etc. ) lead may be occluded and troublesome emulsions may be formed. Some materials, such as urine, contain more of these substances than can be kept in solution with any reasonable amount of citric acid (1). The extraction of lead in acid solution with methyl isopropyl ketone accomplishes the initial isolation and concentration of the lead while avoiding the tedious precipitation, entrainment, and ashing necessary in some of the other methods and avoiding the formation of emulsions due to alkaline precipitates. An important advantage also is the ready adaptability of this method t o larger volumes of urine. Furthermore, the time required for each analysis is reduced from hours t o approximately 45 minutes. By using several extractions with methyl isopropyl ketone, lead may be quantitatively removed without the waiting period of 1 hour recommended by West ( 1 2 ) for the complete separation of the ketone layers. Troublesome emulsions with methyl isopropyl ketone may occur in the analysis of urine but may be avoided by a preliminary acid hydrolysis and ether extraction of the urine. In the presence of sodium or potassium cyanide interfering
ions are limited to stannous tin, thallium, and bismuth (1). Stannous tin and thallium me rarely encountered in urine and may usually be ignored. The bismuth may be removed by a preliminary acid-thiocyanate extraction ( 1 2 )or by an acid chloroform-dithizone extraction ( S ) , in which, at a p H of 3.4, the lead is extracted into the aqueous layer, while bismuth remains combined with dithizone in the chloroform layer and is discarded. This p H js critical. 4 t a higher pH, lead will remain in the chloroform layer, giving low results; at a lower pH, bismuth will also be extracted into the buffer, giving high results.
Table I. Added 0.0
Recovery of Lead from Urine Lead, Y Found
Difference
0.1 1.1 2.0
1.0 2 0
+0.1 $0.1 0 -0.3
+0.2
+o
2 -0.3
+0.8 +0.3 -0.6 0 -0.5 -0.1 -0.8 -0.2 -0 3
Standard deviation = 0 39.
By extracting an aqueous solution of lead with dithizone solution at a p H of 11.5, the lead as lead dithizonate is quantitatively transferred t o the chloroform layer and the excess dithizone is concentrated in the aqueous layer presumably as the ammonium salt (9). This removal of escess dithizone results in a low, but constant, concentration of unreacted dithizone in the chloroform layer, thus improving the accuracy and reliability of the results as compared with the lower p H methods. This high p H extraction also permits the use of a standard dithizone solution and eliminates the necessity for titrimetric extraction to estimate concentration of lead in the sample. The preliminary extraction a t a p H of 9.5 to 10.0 enables the analyst to make a rough estimate of the amount of lead present. The range of sensitivity of the method, 0 to 70 y using a 22-mm. cell and a Coleman Universal spectrophotometer, is sufficient to determine the microquantities of lead found in mild, chronic lead poisoning which would otherwise be difficult to detect. By varying cell size the range may be increased (9). I t is absolutely essential that the last traces of lead be removed from all equipment used in the analysis. LITERATURE CITED
(1) Assoc. Offic. Agr. Chemists, Washington, D. C., “Official
Methods of Analvsis.” DD. 376-93. 1935. (2) Aub, J. C., Fairbail, L. T., Minot,‘ A. S., and Reznikoff, P., Medzcine, 4, 1 (1925). (3) Bambach. IC., and Burkey, R. E., IND.ESG.CHEM.,ANAL.ED., 11, 400 (1939). (4) Cholak, J., Hubbard, D. SI.,and Burkey, R. E., J . Ind. Hug. Toxicol., 30, 59 (1948). ( 5 ) Fairhall, L. T., and Keenan, R. G., J . Am. Chem. Soc., 63,
3076 (1941).
(6) Hamilton, A., and Hardy, H. L., “Industrial Toxicology,” p. 49,
Paul B. Hober, Inc., New York, 1949. (7) Mellan, I., “Organic Reagents in Inorganic Analysis,” p. 91, Blakiston, Philadelphia, Pa., 1941. (8) Ross, J. R., and Lucas, C. C., Can. Med. Assoc. J . , 29, 649 (1933). (9) Snyder, L. J., ANAL.CHEW, 19, 684 (1947). (10) Thienes, C. H., “Clinical Toxicology,” p. 98, Lea and Febiger, Philadelphia, Pa., 1940, (11) Weber, H. J., J . Ind. H y g . Tosieol., 29, 188-67 (1947). (12) West, P. W., and Carlton, J. K.. Anal. Chim. Acta, 6 , 406 (1952) I
RECEIVED f o r review April 13, 1954.
Accepted February 12, 1955.
