558 BLC'KDY AXD SIMPSON: THE DETERMISATION OF The Determination of Nickel [Vol. 83 a Solvent-extraction Method BY P. D. BLUNDY AND 11, P. SIMPSON (Chemical Engineering Division, A .E. R.E., Harwell, 921. Didcot, Bevks.) A method is described for the rapid determination of nickel in solutions containing uranium, thorium, copper, iron and chromium. The aqueous insoluble 4-methylcyclohexane- 1 : 2-dionedioxime complex of nickel is ex- tracted with toluene, and the optical density of this phase is measured with a Spekker absorptiometer, a Hilger H556 filter being used. Interference by copper is suppressed with thioglycollic acid, and tartaric acid is used to prevent formation of iron thioglycollate. Tartrate also prevents the hydrolysis of thorium. A RAPID method for determining small amounts of nickel in solutions containing uranium, thorium, copper, iron and chromium was required.Methods in which ion-exchange tech- niques are used have been developed' for radioactive solutions containing these elements, but the procedures are extremely exacting and time-consuming. Many analogues of dimethylglyoxime have been suggested for colorimetric and gravi- metric determinations of nickel. The nickel complexcs can be extracted with organic solvents, e.g.) nickel has been determined absorptiometrically after extraction of its x-furildioxime complex with chloroform.2 This method was tried in our laboratories, but the results werc not reproducible, and further, the range of 0 to 20 pg was too limited for our requirements. Banks and Hooker3 described a reagent 4-methylcyclohexane-1 : 2-dionedioxime (Q-methyl- nioxime), for the gravimetric determination of nickel in the pH range 3 to 7.They studied the interference of some twenty-nine elements. rind tlicir results suggested that the reagent would he suitable for our purpose. I.: x PE KIM E ST AL Approximately SO pg of nickel were precipitated with a 0.1 per cent. aqueous solution of 4-methylnioxime from a solution buffered at pH 5 to 5.5 with ammonium acetate. The red precipitat e first appeared as a. colloid, which rapidly coagulntcd under thcsc conditions.Oct., 19581 NICKEI. BY A SOLVENT-EXTRACTION METHOD 559 Attempts were made to extract the precipitate with a variety of organic solvents; the results are shown in Table I. loluene was found to be the best solvent, extraction being rapid and complete in one stage.The organic phase was yellow, and, when measured with a Unicam spectrophotometer, showed a broad absorption band with a maximum a t 340 mp. (The molar extinction coefficient at 365 mp is 3340.) The colour WAS stable for at least 2 hours, and Beer's law was obeyed over a concentration range of 5 to 200 pg of nickel per 2.5 ml of toluene. TABLE 1 SOLUBILITY OF NICKEL - 4-METHYLNIOXIME COMPLEX I N VARIOUS ORGANIC SOLVENTS Extractions were carried out from solutions containing 100 pg of nickel and 1.0 ml of 10 per cent. w/v sodium acetate solution Solvcnt Solutility Colour of solvcnt phase isoUiityl nicthyl kctonc (industrial) . . Slightly soluble Faint ycllow ('hloroform . . .. .. . . . . Slightly soluble Pale yellow ('arlmn tctrachloride .. . . . . Slightly soluble Pale ycllow i.w.imyl alcohol . . .. .. . . Slightly solublc Red str.-Butyl alcohol . . . . .. . . Sliglitlv soluhle Red Di-n-btityl ether . . . . . . . . Insoluble - iaolhtyl methyl ketone (purc) . . .. Insoluble - rycloHcxane . . .. . . .. . . Insoluble - 7r-fIcxane . . .. .. .. .. Insoluble - Ethyl acetate . . .. . . .. Insoluble - Rcnzene . . . . . . .. . . Rcadily soluble Yellow 'Toluene . . .. .. . . . . IIighly soluble Yellow EFFECT OF ISTERFERINC IONS- Cations-For each of the ions expected to accompany nickel in sample solutions, the following procedure was used to determine individual and collective interference. .4 solution containing a suitable concentration of the interfering element or elements was buffered at pH 4 with ammonium acetate.One millilitre of 0.1 per cent. 4-methylnioxime solution was added and the solution was extracted with toluene. Precipitation was not apparent in any solution. Tartaric acid was added to the solution containing thorium to prevent hydrolysis. l'he absorption spectra of the tolueiie phases were examined; those derived from solutions containing uranium, thorium, iron and chromium showed no absorption in the region of 365 mp, the wavelength transmitted by a Hilger I-1556 filter. In this region, however, copper caused an absorption band similar to that of nickel. Various methods of masking were tried, e.g., ethylenediaminetetra-acetic acid, ammonia, citrate, tartrate, cyanide and ammonium tliiocyanate after reduction of copper to the cuprous form with sulphur dioxide, but none was satisfactory.Pellowe and Hardy4 described the use of thioglycollic acid for masking copper in the analysis of aluminium. I t was found that 1.0 ml of 10 per cent. thioglycollic acid solution prevented formation of the copper - 4-methylnioxime complex. I t was then necessary to add tartaric acid and to use sodium hydroxide instead of ammonium hydroxide for neutralising free acid to prevent interference from iron thioglycollate. In the presence of tartaric acid the optimum pH was 5 to 5.5. A12ions--.Extractioris were carried out in solutions containing a hundred-fold excess of sulphate, chloride and nitrate without interference. In the presence of citrate, precipitation was retarded and recoveries were low.METHOD KEAGESTS- Sodium Iydroxide, 2 X. Thioglycollic acid solution, 10 per cenf. ;~/v--Dissolve 10.0 ml of analytical-reagent grade thioglycollic acid in water and dilute to 100 ml. The solution is stable for about 1 month. Sodium acztate solution, 10 per cent. w/u. Tartaric acid solution, 20 per cent. wlv. Chfethylnioxime solution, 0.1 per cent. w/r!--l)issolve 0.1 g of 4-methylcyclohexane-1 : 2- Standard nickel solution-Dissolve approximately 24 g of nickel sulphate, NiS0,.7H20, dionedioxime in water and dilute to 100 ml. in water and dilute to 1 litre. The solution is stable indefinitely. Standardise the solution gravimetrically.560 BLUNDY AND SIMPSON: THE DETERMINATION OF [Vol. 83 Place an aliquot containing 5 to 100 pg of nickel in a 50-ml beaker, and add sufficient 20 per cent.w/v tartaric acid solution to prevent hydrolysis of thorium. Add 1.0 ml of 10 per cent. w/v sodium acetate solution, and adjust the pH to between 5 and 5.5 with 2 N sodium hydroxide. Transfer the solution to a 100-ml separating funnel, add 1.0 ml of 0.1 per cent. 4-methylnioxime solution, and dilute to 30 ml with distilled water. Add exactly 25 ml of sulphur-free toluene, and shake for 2 minutes. Allow the layers to separate and run off the aqueous layer. Pass the solvent layer through a Whatman No. 1 filter-paper, to remove the last traces of water, into a clean dry 2-cm absorptiometer cell, and cover the cell to prevent evaporation. Measure the optical density with a Spekker absorptiometer fitted with H556 PROCEDURE I N PRESENCE O F THORIUM, IRON AND CHROMIUM- 0.6 6 to Wavelength, IT u Fig.1. Absorption spectrum of the nickel - 4-methyl- nioxime complex in toluene: the complex was prepared from 105 pg of nickel and 1.0 ml of 0.1 per cent. 4-methylnioxime solution in 25 ml of toluene, and the optical densities were measured in a 1-cm cell TABLE I1 EFFECT OF OTHER ELEMENTS ON THE DETERMINATION OF NICKEL All solutions contained 1.0 ml of 10 per cent. w/v sodium acetate solution, 1-0 ml of 20 per cent. w/v tartaric acid solution and 1.0 ml of 10 per cent. v/v thioglycollic acid solution Uranium Thorium Copper Iron Chromium Nickel Nickel Solution present, present, present, present, present, added, found, mg mg mg mg mg mg mg 11.0 - 0.0 0.0 - 0.0 <0*001 1 2* - 46.0 0.0 0.0 3 - - 0.963 - 1.02 - 0.0 <0.001 4 - - 0.236 0.0 <0.001 5 - 0.132 0.132 6 - 0,0528 0.053 7 11.0 - 0.482 0.102 0,250 0,132 0.132 9 11.0 - 0.482 0.255 0.250 0.132 0.131 8 10 11.0 - 0.482 0.510 0.250 0.132 0.130 11 11.0 - 0.241 0.102 0.250 0.132 0.129 12 11.0 - 0.241 0.255 0.250 0.132 0.130 13 11.0 - 0.241 0.510 0.250 0.132 0.130 - - 0.250 0,132 0.130 14 11.0 - 15 11.0 - 0.241 0.102 0.025 0,0528 0.053 16* - 37.5 - 1.38 0.221 0.132 0.132 5.38 104.5 0.150 0.051 0.047 0.0504 0.050 5.38 104.5 0.150 0.051 0,047 0.1032 0.1035 17t 5.38 104.5 0.150 0.051 0.047 0,156 0.155 1st - - - - - - - - - - - - - - - - - - - 19t * Solution contained no thioglycollic acid.t Solution contained 2 ml of 20 per cent. w/v tartaric acid solution.Oct., 19581 NICKEL BY A SOLVENT-EXTRACTION METHOD 561 filters and a mercury-vapour lamp.Use a blank solution, prepared in a similar manner, in the comparison cell. PROCEDURE IN PRESENCE OF URANIUM, COPPER, IRON AND CHROMIUM- Place an aliquot containing 5 to 200 pg of nickel in a 50-ml beaker, and add 1.0 ml of 20 per cent. w/v tartaric acid solution. Add 1-0 ml of 10 per cent. v/v thioglycollic acid solution and 1.0 ml of 10 per cent. w/v sodium acetate solution. Adjust the pH to between 5 and 5.5 against a pH meter with 2 N sodium hydroxide, and continue as described under “Procedure in Presence of Thorium, Iron and Chromium.” PREPARATION OF CALIBRATION GRAPH- use the procedures described. Take aliquots of standard nickel solution to cover the range 5 to 200 pg of nickel and RESULTS AND CONCLUSIONS Fig. 1 shows the absorption spectrum of the nickel - 4-methylnioxime complex. Table I1 shows the effect of cations on the nickel determination. Eighteen replicate deter- minations were carried out at 50, 100 and 150-pg levels of nickel in the presence of 6 mg of uranium, 0.15 mg of copper, 104 mg of thorium, 0.05 mg of iron and 0.05 mg of chromium; the mean recovery was 99-8 per cent. and the standard deviation was k1.2 per cent. The proposed method is rapid, simple and accurate; it has been used constantly in our laboratories for the last 6 months. We thank Mr. R. Todd and Mr. W. H. Hardwick for helpful discussions during this work. REFERENCES 1. 2. 3. 4. Horton, A. D., Thomason, P. F., and Kelley, M. T., Anal. Chem., 1957, 29, 388. Taylor, C. G., Analyst, 1956, 81, 369. Banks, C. V., and Hooker, D. T., Anal. Chem., 1956, 28, 79. Pellowe, E. F., and Hardy, F. R. F., Analyst, 1954, 79, 226. Received February 26tk, 1958