(and the other combinations with the one exception of cystine-cysteine) in a similar mixture of 20 amino acids appear frequently as homogeneous spots, when chromatographed by conventional techniques. However, this method indicates that there are sufficient differences in their R, values within a given spot to warrant the selective identification of each of the amino acids by their color complexes. This technique has been employed routinely in these laboratories for the identification of amino acids in hydrolyzates of the beta hemolytic streptococci fraction. It was of help in distinguishing between the troublesome leucine and isoleucine in amino acid mixtures. Maximum resolution is the most outstanding feature of two-dimensional chromatography. However, this degree of resolution is not required when the polychromatic procedure is employed, even though some of the amino acids possess relatively similar R, values. I n unidimensional chromatography lysine, histidine, and asparagine butyl alcohol-acetic acid-water, 4:1: 5 ratio), when sprayed with ninhydrin, appear as a homogeneous substance. Each amino acid, however, can be readily distinguished after a minimum of 6 hours of resolution when sprayed with N-CN. Other combinations of amino acids selected on the basis of the similarity of R, values, such as cystinecysteine, glycine-aspartic acid, arginine-
serine, threonine-glutamic acid-alanine, tyrosine-valine-methionine, tryptophanphenylalanine, and isoleucine-leucine also were studied to determine if they could likewise be detected after a minimum of 6 hours of resolution. These mixtures of amino acids would also appear as homogeneous mixtures and give singular spots when treated with the ninhydrin reagents. However, when treated as outlined, each amino acid could be characterized by its color complex. A single application provides a far superior chromatogram than using t F o sprays to effect only semipolychromatic results. Perhaps the most outstanding advantage of this method is that the interfering factors such as abnormalities occurring as a result of ionizable substances, cation concentration, the rate of movement of solvent, and temperature, are of no major significance; in two-dimensional chromatography they would be of considerable importance in the reproducibility of RI values for the identification of amino acids.
(2) Bentley, H. R., Whitehead, J. K., Bzochem. J . 46, 341 (1950). (3) Block R. J., Bolling, Diana, “Amino Acid ,$omposition of Proteins and Foods, p. 576, Charles C Thomas, Springfield, Ill., 1951. (4) Block, R. J., Durrum, E. L., Zweig, Gunter, “Manual of Paper Chromatog-
raphy and Paper Electrophoresis,” Academic Press, New York, 1955. (5) Consden, R., Gordon, A. H., Martin, A. J. P., Biochem. J . 38,224 (1944). (6) Hardy, T. L., Holland, D. O., Nayler, J. H. C., ANAL.CHEM.27,971 (1955). (7) Hird, F. J. R., Trikojus, V. M., Australian J . Sci. 10,185 (1948). (8) Levy, A. L., Chung, D., ANAL. CHEM.25,396 (1953). Miettinen, J. K.. Suomen Kemistilehti (9) ~,
26,49 (1953). ’ (10) Miller, H., Kraemer, D. M., ANAL. CHEM.24,1571 (1952). (11) Partridge, S. M., Biochem. J . 42, 238 (1948). (12) Patton, A. R., Chism, P., AKAL. CHEM.23,1683 (1951). (13) Redfield, R. R., Biochim. et Biophys. Acta 10, 344 (1953). (14) Redfield, R. R., Barron, E. S. G., Arch. Biochem. Biophys. 35, 443 (1952). (15) Rockland, L. B., Blatt, J. L., Dunn, M. S., ANAL.CHEM.23, 1142 (1951). (16) Smith, P. B., Pollard, A. L., J . Bacteriol. 63, 129 (1952). (17) Toennies, G., Kolb, J. J., ANAL. CHEM.23,723 (1951).
ACKNOWLEDGMENT
The authors express their appreciation to Jack H. Davis and Irwin Schultz, M C USNR, for helpful suggestions in the preparation of this manuscript. LITERATURE CITED
(1) Auclair, J. L., Dubreuil, Robert, Can. J . Zool. 30, 109 (1952).
RECEIVEDfor review April 9, 1958. Accepted November 14, 1958. From Research Project NM 52 06 04.4, Bureau of Medicine and Surgery, Navy Department, Washington 25, D. C. The views and opinions expressed herein are those of the authors and do not necessarily reflect those of the Navy Department or the Naval Service a t large.
Titrimetric Determination of AI kyl Mercaptan-Dial kyl Sulfide and AI kyl Mercaptan-AI kyl Disulfide Mixtures BRUNO JASELSKIS Department o f Chemistry, University o f Michigan, Ann Arbor, Mich.
Mixtures of n-alkyl mercaptans and dialkyl sulfides can b e determined titrimetrically using two aliquots. The first aliquot is titrated for mercaptan with iodine, and the second, after treatment with basic acrylonitrile, is acidified and titrated with bromatebromide solution. The amount of dialkyl sulfide is found by the difference. The results agree to better than 1%. Mixtures of n-alkyl mercaptans and alkyl disulfides are determined iodimetrically. Mercaptan alone is titrated first, and then the total mercaptan is titrated after the reduction of alkyl disulfide with zinc in an acetic-hydrochloric acid-alcohol mixture. Alkyl
928
ANALYTICAL CHEMISTRY
disulfides with higher molecular weights than propyl disulfide are recovered quantitatively.
A
for determination of mercaptans (thi01s) have been developed using iodine ( 7 ) or silver nitrate (3, 8, 11). The determination of alkyl sulfides by bromate-bromide standard solutions has been described by Siggia and Edsberg (10). However, samples containing a mixture of alkyl sulfide and alkyl mercaptan in excess of 10% cannot be analyzed satisfactorily, because of the slow and incomplete oxidation of CCURATE TITRIMETRIC METHODS
mercaptan and alkyl sulfide Kith bromine and the interference of alcohol in exhaustive oxidation. This difficulty can be overcome by using the addition reaction of acrylonitrile to alkyl mercaptan to yield sulfide, which is readily oxidized to sulfoxide. The reactions of acrylonitrile and alkyl mercaptans have been studied by Earle (2) and Hurd and Gershbein (4, and the determination of acrylonitrile and alpha-beta-unsaturated compounds has been described by Beesing et al. ( 1 ) . Mixtures of alkyl mercaptans and alkyl disulfides in the absence of alcohol have been determined by bromine oxidation as described by Siggia and Eds-
berg (IO),and in the presence of alcohol using a Jones reductor as described by Kolthoff et al. (9). The exhaustive oxidation method is not applicable in presence of alcohol. The results for disulfide obtained with a Jones reductor are about 4% low. Better results are obtained by reducing alkyl disulfides under refluxing conditions with amalgamated zinc and acetic-hydrochloric acid-ethyl alcohol mixtures. The reduction of alkyl disulfides by zinc in acetic acid has been described recently by Karchmer and Walker (6). This paper describes conditions under which mixtures of alkyl mercaptandialkyl sulfide and alkyl mercaptanalkyl disulfide can be determined accurately using standard iodine and bromate solutions. The results obtained by these methods agree to better than 1%. REAGENTS AND APPARATUS
Master solutions were prepared by weighing out approxiniately 0.025 mole of Eastman Khite Label alkyl mercaptan, dialkyl sulfide, or alkyl disulfide and diluting to 280 ml. with 95y0 alcohol or glacial acetic acid. The glacial acetic acid solutions were used for exhaustive oxidation titrations with bromate. Mixtures were prepared by pipetting out the desired amounts of the master solutions. The concentration of mercaptan in the master solution was determined iodometrically. The concentration of alkyl sulfide in the master solution was obtained using standard bromate-bromide titrant. The alkyl disulfide concentration was derived primarily from the weighed amount. However, the results were checked against the titration of the disulfide after reduction to mercaptan or by exhaustive oxidation in the absence of alcohol. Approximately 0.121' potassium triiodide solution was prepared by dissolving iodine in potassium iodide solution and standardizing against arsenious oxide. The standard O.lN bromate-bromide solution was prepared by m-eighing analytical grade potassium bromate and adding at least a sevenfold excess of potassium bromide. The normality was checked against arsenious oxide. Acrylonitrile used for the condensation reaction with alkyl mercaptans was obtained from the Matheson Co. It was used without further dilution. The alkyl disulfide solutions were reduced in a refluxing flask containing a water-cooled condenser and a cold finger cooled by a n ice-salt mixture. The latter attachment is necessary when using ethyl and propyl disulfides. PROCEDURE
Alkyl Mercaptan-Dialkyl Sulfide Mixtures. Two equal aliquots of the alkyl mercaptan-dialkyl sulfide mixture were placed in separate flasks. T h e contents were diluted with a sufficient amount (30 t o 50 ml.) of alcohol t o keep the alkyl mercaptan
and dialkyl sulfide in solution throughout the titration. One of the aliquots was acidified with approximately 2.0 ml. of acetic acid; mercaptan was then titrated with the standard iodine solution until t h e color of free iodine appeared. For small amounts of mercaptan a 10-mi. buret was used t o enable the titrant t o be measured within hO.01 ml. 41kyl mercaptans with higher molecular weights than propyl mercaptan could be titrated in the absence of oxygen in acidic potassium iodide solution with the standard bromate-bromide. This mercaptan solution was deaerated using pieces of dry ice. The results were somewhat lower than in the direct iodometric determination. Khen this method is used, only one standard solution is necessary for determination of mercaptan and sulfide. The contents of the second flask were made alkaline with approximately 3 drops of 10% potassium hydroxide, then acrylonitrile was added from a 1-ml. graduated pipet. The volume of acrylonitrile to be added was determined by the amount of mercaptan present. Approximately a twofold excess as compared to mercaptan was usually sufficient. However, the volume of acrylonitrile is not critical, as long as there is an excess and provided blank determinations are run using the same amount of acrylonitrile. After the addition of acrylonitrile the solution was stirred for about 2 minutes to ensure completion of the reaction. It was then acidified with approximately 15 ml. of glacial acetic acid containing about 3 ml. of concentrated hydrochloric acid and titrated with the standard bromate-bromide solution to the first appearance of free bromine throughout the solution for a t least 30 seconds. The end point could be observed best in a white light against a white background. Cnder these conditions the blank volume of 0.1N bromate-bromide necessary to impart a yellow coloration to the solution did not exceed 0.1 ml. I n the presence of approximately 0.2 ml. of acrylonitrile the blank required about 0.15 ml. The amount of alkyl sulfide present in the mixture was calculated from the two titrations as follows: Alkyl sulfide, grams =
rneq.~,03--~~ - 2(meq.18-) X E
tained using a mixture containing approximately 25 ml. of alcohol, 5 ml. of acetic acid, and 0.5 ml. of hydrochloric acid. The reduction of n-alkyl disulfides was complete in about 30 minutes. The refluxing flask was then chilled in an ice bath, after which the condenser and cold finger were rinsed and the contents transferred to the titration flask. Total mercaptan was then titrated with iodine. For the reduction of ethyl disulfide special precautions were taken to prevent the loss of ethyl mercaptan and ethyl disulfide by evaporation. The gases escaping from the cold finger were allowed to bubble through the iodine solution. However, the losses of ethyl mercaptan were considerable. Tertiary alkyl disulfides could not be reduced and determined by this method. Mercaptans boiling higher than ethyl mercaptan vere recovered quantitatively. The amount of disulfide in the mixtures was determined as follows: NI~ - (ml.? - mLl) X eq. wt. of disulfide = grama of disulfide
Results obtained by this method were low by approximately 1%. RESULTS AND DISCUSSION
The determination of alkj 1 mercaptans and dialkyl sulfides in the presence of alcohol cannot be performed using exhaustive oxidation with bromate-bromide in strongly acid solution because of the oxidation of alcohol. H o ~ e v e r ,in the absence of alcohol the oxidation proceeds slon ly to completion in the following manner:
+ 3Br2 + 2Hz0 = RSOz+ + 6Br- + 5H+ RSR + Br2 + HzO = RSOR + 2Br- + 2H+ RSOR + Brp + HzO = RSOzR + 2Br- + 2H+ RSH
(2)
(3)
The first and third reactions are slow and incomplete a t room temperature, but can be speeded by heating. I n the presence of alcohol the determination is based on the condensation reaction of alkyl mercaptan n-ith acrylonitrile RSH
n.here milliequivalents of bromine is for the second titration corrected for the blank, milliequivalents of iodine is for the first titration corrected for the blank, and E is the equivalent weight of sulfide. Alkyl Mercaptan-Alkyl Disulfide Mixtures. Two equal aliquots of the alkyl mercaptan-alkyl disulfide mixture were used; one was placed in a volumetric flask and the other in a refluxing flask. The first aliquot was titrated with standard iodine solution until the appearance of free iodine color. Alkyl disulfide in the second aliquot was reduced with 20-mesh granulated zinc under refluxing conditions in a mixture of alcohol and acetic and hydrochloric acids. Satisfactory results were ob-
(1)
+ CHs = CHCN (OH); RS-CHP-CHI-CN
(4)
The resulting sulfide is readily oxidized in dilute acid solution by bromine according to Equation 2 . It is titrated to the first appearance of free bromine throughout the solution. The double bond in acrylonitrile is not brominated readily. The end point can be determined to within 10.03 ml. The average values of five determinations for mixtures of alkyl mercaptans and dialkyl sulfides are summarized in Table I. The results for alkyl mercaptan in the absence of dialkyl sulfide determined by iodine or by bromateVOL. 31, NO. 5, MAY 1959
* 929
Table 1.
Titration of Alkyl Mercaptan-Dialkyl Sulfide Mixtures
(Results are average of five determinations) Millimoles of Alkyl Mercaptan Found bv Millimoles of Acrylonitrile .~ Dialkyl Sulfide condensation, Found by Iodometric and bromate bromate Added titration" Sample Added method titration Ethyl mercaptan 0.9574 0.956 0.957 0.9574 0.956 .. 0 .ilia 0.244 Mixture IAb Mixture IBb 0.4787 0.477 .. 0,6175 0.615 0.1915 0.190 .. 1.2350 1.227 Mixture ICb Diethyl sulfide .. 1.2350 1.236 n-Propyl mercaptan 1.1130 1.'io9 1.'ii5 Mixture IIA. 1.1130 1.107 .. 0.2469 0.245 Mixture IIBc 0.5665 0.556 .. 0,6172 0.616 Mixture IICc 0,2226 0.221 .. 1.2340 1.232 Dipropyl sulfide .. .. .. 1.2340 1.233 1.061 1.065 n-Butyl mercaptan 1.0640 Mixture IIIAd 1.0640 1.059 .. 0. i844 o .'i83 0.5320 0.531 .. 0.4611 0.460 Mixture IIIBd Mixture IIICd 0.2128 0.211 .. 0,9222 0.921 .. .. .. 0,9222 0.921 Dibutyl sulfide 0.901 0.901 n-Octyl mercaptan 0.9015 0,9015 0.901 .. 0 . is44 o .'1'83 Mixture IVAe 0.4507 0.449 .. 0.4611 0.460 Mixture IVB. 0.1803 0.179 .. 0.9222 0.921 hlixture IVCe Millimoles of dialkyl sulfide obtained from [(meq.)Bros- - 2(meq.)13-]/2. b Mixture I, ethyl mercaptan and diethyl sulfide. Mixture 11, n-propyl mercaptan and dipropyl sulfide. Mixture 111, n-butyl mercaptan and dibutyl sulfide. e Mixture IV, n-octyl mercaptan and dibutyl sulfide. Q
bromide titrations, after the condensation of mercaptan with acrylonitrile, are in good agreement. The end point can be reproduced readily to =t0.03 ml., yielding reproducibility better than 1% for the 10-ml. volume of titrant used. The results for dialkyl sulfide in the presence of mercaptan can be reproduced to approximately 1% or better if small amounts are present. The results are in better agreement with
Table 11.
higher molecular weight dialkyl sulfides than with diethyl sulfide. The presence of acrylonitrile affects the blank correction somewhat. The change of volume of acrylonitrile from 0.2 to 0.5 ml. increases the blank correction by approximately 0.1 ml. of 0.lN bromate. The condensation of acrylonitrile with mercaptan is rapid and complete in alkaline solution a t p H 12 or above. Normal and secondary mercaptans
Titration of Alkyl Mercaptan-Alkyl Disulfide Mixtures
(Results are average of five determinations) Millimoles of Disulfide Found by Millimoles of Mercaptan Exhaustive oxidation Found bv iodometrh Iodometric with Added method Added method bromatea 0.713 0.645 0.680 Ethyl disulfide .. .. 1.244 1.235 1.207 ?+Propyl disulfide .. *. .. 1.244 1.231 Mixture IAb 0.2226 0.221 0.248 0.245 .. Mixture IBb 1.1130 1.107 1.105 1.098 1.079 n-Butyl disulfide 1,105 1.096 .. Mixture IIAc o.ii28 0 :212 0.221 0.219 .. Mixture IIBc 1.0640 1.059 n-Octpl disulfide 1.175 1.170 1.145 Mixture IIIAd 0 . is03 o .'iig 1.175 1.169 .. Mixture IIICd 0,9015 0.901 0.235 0.232 .. Isopropyl disulfidee .. .. 1.251 1.238 1.215 tert-Butyl disulfide6 .. .. 0.978 0.592c 0.959 a Solutions have no alcohol. b Mixture I, n-propyl disulfide and n-prop 1 mercaptan. c Mixture 11, n-butyl disulfide and n-butyymercaptan. Mixture 111, n-octyl disulfide and n-octyl mercaptan. e Resulting tert-butyl mercaptan is titrated with silver nitrate. 930
ANALYTICAL CHEMISTRY
can be titrated with the standard iodine solution. Tertiary mercaptans should be titrated argentometrically. Hydrogen sulfide and all the substances which can be oxidized by iodine will interfere. Bromate-bromide titrations can be used in the absence of all the substances which can be oxidized by bromine and all unsaturated compounds prone to bromination. Dialkyl sulfides can be oxidized t o sulfoxides without difficulty, and the end points are rather sharp and reproducible. Rlixtures of hydrogen sulfide, mercaptan, and dialkyl sulfide can be titrated potentiometrically with alcoholic silver nitrate to yield the results for mercaptan and hydrogen sulfide simultaneously ( 5 ) . Dialkyl sulfide then can be determined by bromate-bromide titration after the separation of hydrogen sulfide and mercaptan as cadmium sulfide and cadmium mercaptide, respectively. This separation can be avoided by condensing hydrogen sulfide and mercaptan with acrylonitrile and titrating all the dialkyl sulfides with the standard bromate-bromide solution. However, the results for the dialkyl sulfide are continuously loa and reproducibility is rather poor. The difficulty arises in condensation of hydrogen sulfide with acrylonitrile. Ordinarily it is necessary to have about a fivefold excess of acrylonitrile and a condensation time of about 30 minutes instead of 2 minutes as is used for mercaptans. Alkyl disulfide in mixtures of alkyl mercaptan and alcohol cannot be determined by exhaustive oxidation with bromine. However, the resulting mercaptan can be determined after the reduction of the disulfide with zinc in an acetic-hydrochloric acid-alcohol mixture with an accuracy as good as for mercaptans alone. Determinations of mixtures of alkyl disulfide and alkyl mercaptan mixtures are summarized in Table 11. The results for butyl and octyl disulfides determined (after reduction with zinc) with the standard iodine solution can be readily reproduced to within d ~ O . 1ml. with a recovery better than 99%. The results for ethyl and propyl disulfides are low. The recovery for ethyl disulfide is about 94% and that for propyl disulfide about 98.5%. This is probably caused by the volatilization of mercaptans or disulfides and incomplete reduction of the corresponding disulfides, However, with proper care propyl disulfide can be determined iodometrically with better accuracy than by using exhaustive oxidation with bromine. Tertiary alkyl disulfides cannot be reduced satisfactorily and, therefore, cannot be determined by this method. The determination of mixtures of alkyl mercaptans, dialkyl sulfides, and
alkyl disulfides in the presence of alcohol cannot be achieved bv direct titrimetric methods Jvithout the removal of mercaptan and the reduced disulfide as silver mercaptides. In these mixtures the condensation of mercaptan Jvith acr\-lonitrile after the reduction of disulfide with zinc does not proceed even in presence of ethylenediaminetetraacetic acid, and tilus dialk\-l sulfide cannot be detprmined SatiSfaCtorilg by this method.
LITERATURE CITED
(1) Beesing, D. W., Tyler, R. P., Kurtz,
D. >I.. Harrison. S. A,. ANAL.CHEM.21. 1073 (1949).
(2) Earle, T.E., Zbid., 2 5 , i 6 9 (1953). (3) Haslam, J., Grossman, S., Squirrel, D. C. M., Loveday, S. F., Analyst 78,
92 (1953). (4) Hurd, C. D., Gershbein, L. L., J . Am. Chem. SOC. 69,2328 (1947). (5) Karchmer, J. H., - 4 ~ 4 CHEX ~ . 30, 80 (1958). (6) Karchmer, J. H., Ralker, -4. T., Zbid., 30, 85 (1958).
('7) Kimball, J. W., Kramer, R. L., Reid, E. E., J.Am. Chem. Soc.43,1199 (1921)
( 8 ) Kolthoff, I. M., Harris, W. E., IND.
E N G . CHEM.,!iNAL. ED. 18, 161 (1946). (9) Kolthoff, I. M., May, D. R., Morgan
P., Laitinen, H. A., O'Brien, A. S., Zbid., 18,442 (1946). (10) Siggia, S.,Edsberg, R. L., Zbid., 2 0 , 938 (1948). (11) Strafford, N., Cropper, F. R., Hamer, A., Analyst 75, 55 (1950).
RECEIVEDfor review June 25, 1958. Accepted December 3, 1958.
Spectrophotometric Determination of Traces of Nickel with 4-lso pro pyl-l ,2-cyclohexanedioned 10x1 me 1.
B. L. McDOWELL, A. S.
MEYER, Jr., R. E. FEATHERS, Jr., and J. C. WHITE
Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b The use of xylene rather than chloroform to extract the nickel(ll)-4-isopropyl 1,2 cyclohexanedionedioxime chelate results in increased sensitivity in the spectrophotometric deterrnination of nickel. The extraction coefficient in xylene is more than five times as great as that in chloroform, and the low solubility of xylene in aqueous solution permits the use of much larger phase ratios (aqueous to organic). The system conforms to Beer's law for concentrations of nickel from 1 to 12 y of nickel per ml. of xylene. The precision of the method is 2y0. Iron, cobalt, and copper interfere seriously; however, their interference can b e minimized so that weight ratios of metal to nickel of 20, 2, and 8, respectively, can b e tolerated. Concentrations of nickel from 0.005 to 100 p.p.m. were determined in water, alkali metals, and several analytical reagents. Recoveries in excess of 95% were obtained when known amounts of nickel were extracted from aqueous solutions of relatively high ionic strength a t aqueous-toorganic volume ratios as high as 300 to 1.
-
R
-
for the determination of nickel have been adequately reviewed by Hooker and Banks (S), who noted that the vicinal dioximes are examples of a nearly ideal reagent for the determination of nickel. Of the several substituted cyclohexanedionedioximes recommended as reagents for the determination of nickel by gravimetric, spectrophotometric, and titrimetric procedures, these authors suggested 4-isopropyl-l,2-cyclohexanedionedioxime as the hest reagent for the spectrophotoEAGENTS
metric determination of nickel. They suggested that extraction of the nickel chelate from large volumes of aqueous solution into chloroform offers the most sensitive method yet reported for the determination of nickel. This report is concerned with further studies of 4-isopropyl-1,2-cyclohexanedionedioxime as a reagent for nickel. With xylene as an extractant for the nickel chelate, the reagent has been applied to the determination of 10 y of nickel in as much as 500 ml. of aqueous solution with a coefficient of variation of 2%. This order of sensitivity makes the method ideally suited for application to such samples as liquid metals, purified water, and reagent chemicals. Following the completion of this investigation, Blundy and Simpson ( I ) published a method applying 4-methyl1,2-cyclohexanedionedioxime to the determination of nickel with toluene as the solvent for the nickel chelate. APPARATUS
All absorbance measurements were made in 1.00-cm. Cores cells. The absorption spectra were recorded with a Gary automatic recording spectrophotometer, Model 14-11, and absorbance measurements were made with a Beckman Model D U spectrophotometer. REAGENTS
Prepare a standard nickel(I1) solution by dissolving 5 grams of nickel shot in hydrochloric acid and diluting the resulting solution to 500 ml. Determine the concentration of nickel gravimetrically ( 3 ) . The solution used for this study contained 9.97 mg. per ml. Make appropriate dilutions of this stock solution to yield standard solutions of lower nickel concentration.
Prepare a 0.004M solution of the chromogenic reagent, 4-isopropyl-1,2cyclohexanedionedioxime [synthesized according to the procedure of Hooker and Banks (S)], by stirring 80 mg. of the reagent with 100 ml. of water for 24 hours and then filtering off the excess reagent. The 0.004M solution is a saturated aqueous solution of the diosime ( 6 ) . Xylene, hexane, chloroform, benzene, and toluene, all reagent grade. Ammonium acetate solution, approximately 10M. Sodium fluoride solution, 10 mg. of fluoride per ml. Sodium thiocyanate solution, 10% (W*/V.)*
Potassium (./.)
.
cyanide solution. 10%
Hydroxylamine hydrochloride solution, 10% (IV./T.). prepared fresh daily. Prepare a solution of Sulfi-Down (stabilized thioacetamide, distributed by A. Daigger and Co., Chicago, Ill.) by dissolving 2.5 grams of the solid reagent in 50 ml. of water and heating to 80" k 5" C. Cool immediately to prevent evolution of hydrogen sulfide. Store in a tightly stoppered flask and prepare fresh daily. PROCEDURE
Transfer a volume of solution which contains 10 to 150 y of nickel to a separatory funnel of appropriate size. Adjust to approximately p H 7 and add sufficient 1 O M ammonium acetate to make the final solution 1M with respect to acetate. For a final aqueous volume of 100 ml. or less, add 2 ml. of the saturated dioxime solution. For each additional 100 ml. of aqueous solution add another 2 nil. of diovime solution. After 30 minutes, add 10 ml. of xylene; a smaller volume may be used if the amount of nickel is very low. Shake the contents of the funnel VOL. 31,
NO. 5, MAY 1959
931
