April, 1945
ANALYTICAL EDITION
phase from the ligroin solution of the cobalt-nitrosocresol complex., If large amounts of copper are present the cupric nitrosocresol complex is easily adapted to a quantitative procedure. I t is usually desirable, however, to evaporate the aqueous phase to dryness with 1 ml. of perchloric acid and determine copper on the residue by the carbamate or other suitable method. The procedure described in this paper has been found satisfactory for the determination of cobalt in soils by R. S. Holmes, Bureau of Plant Industry, Soils, and Agricultural Engineering, U. S. Department of Agriculture, and has been incorporated in an analytical scheme for the determination of several micronutrient elements in soils and soil solutions (8).
257 LITERATURE CITED
(1) Baudisch, O.,J . Am. Chem. SOC.,63, 622 (1941). (2) Baudisch, O.,Science, 92,336 (19.10). (3) Baudisch, O.,and Karrzeff, N., Ber., 45,1164 (1912). (4) Baudisch, O.,and Rothschild, S., I b i d . , 48, 1660 (1915). ( 5 ) Cronheim, G., IND.ENCI. CHEM., A N A L . ED., 14,445 (1942). (6) Cronheim, G.,and Wink, W., Ibid., 14, 447 (1942). (7) Ellis, G.H., and McNall, F., “Application of a Modified Vance
Amplifier in Photoelectric Colorimetry, Fluorometry and Potentiometric Titration” (unpublished). (8) Holmes, R. S., Soil Sci. (in press). (9) Marston, H. R., and Dewey, D. W., Australian J. Ezptl. Biol.
Med. Sci., 18, 343 (1940). (10) Parks, R. Q . , Hood, S. L., Hurwitr, C., and Ellis,G. H., IND. ENG.CHEM.,ANAL.ED.,15,527(1943).
Colorimetric Determination of Minute Amounts
OF
Nickel
EMANUEL PASSAMANECK Analytical and Control Laboratory, Reed & Carnrick, Jersey City,
Small amounts of nickel, especially in the presence of great excess of iron and other common metals, may b e determined b y precipitating the nickel dimethylglyoxime from an ammoniacal citrate solution of a small volume of the prepared material, dissolving the precipitate in pyridine, and comparing its color with a known pyridine solution of nickel dirnethylglyoxime.
I
K T H E determination of minute quantities of nickel in a
material containing relatively large amounts of other metals, difficulties encountered in using available methods suggested the need for a simple, accurate method which would not require preliminary removal of other metals. The colorimetric determination of nickel by dithiooxalate (4) requires its previous separation from other metals. Since this reagent gives a color with cobalt, this metal must first be determined and its equivalent amount added to the standard to compensate for the final cobalt color. I n attempting separation of less than 0.1 mg. of nickel from a large excess of iron the author has had little success even after three reprecipitations by ammonia. In the more recent wet-extraction method using a-fury1 dioxime (1) copper must first be removed and the amount of tartaric acid added must be carefully controlled. Sandell and PerIich ( I f ) describe a method for determination of nickel in silicate rocks in which the nickel dimethylglyoxlme from an ammoniacal citrate solution of the prepared sample is extracted with chloroform, the chloroform solution treated with dilute acid, and the nickel determined colorimetrically by Rollet’s. method (IO). They state ,that the color intensity of fhe mckelic dimethylglyoxime solution increases slowly on standing and that the standard and the unknown should be treated yith reagents at the same time. I t would be desirable if the maximum color developed in a short time and remained stable thereafter. The nickel dimethylglyoxime in pyridine is stable; the standard concentrated stock solution shows no apparent change after many months. Furthermore, the author did not find the separations as outlined by Sandell and Perlich clear-cut on the solution he had to use wherein iron and several other metals were present in great excess. The difficulties involved in the complete (5) precipitation of pure nickel dimethylglyoxime on a macro scale from a solution in which iron, copper, and cobalt preponderate (3) are not encountered in the proposed micromethod wherein relatively large amounts of reagents are used. Since the precipitate from a f e r micrograms of nickel is too small to be weighed accurately, even on a microbalance, it cannot be too certain that the precipitate is not contaminated with iron and cobalt. However, after washing as directed the precipitate is “pure” red against a white as.bestos background, and in the final color comparison no more
N. J.
absorption was observed from a similar metal solution containing iron, copper, manganese, cobalt, and zinc without the nickel than from pure water similarly treated. When amounts of nickel were added to this metal solution satisfactory recoveries were obtained (Table 11). I n amounts ranging from 0.12 to 4 mg. of nickel, corresponding to 0.6 to 20 mg. of nickel dimethylglyoxime (2, Sl, respectively, Pollak (9) has reported gravimetric determinations. By keeping the volume low and other interfering metals in solution, and by allowing sufficient time for complete precipitation the author can quantitatively precipitate much smaller amounts than the above with nickel dimethylglyoxime. I t was found that the substitution of potassium citrate for tartaric acid for preventing precipitation of other metals gave much more consistent results. Nuka ( 7 ) has observed that the precipitate from small amounts of nickel should stand a t least an hour before filtering. The author finds that in amounts of 40 micrograms or more good recoveries may be obtained after 2 hours’ standing, but in much smaller amounts recoveries may be low and uncertain unlers more time is allowed (Table I). He is able to assure the precipitation of as low as 2 micrograms by overnight standing, probably even less. The “nonweighable” precipitate may be dissolved in a small volume of an appropriate solvent and determined colorimetrically in a suitable colorimeter. Among the organic solvents tried, it was found that nickel dimethylglyoxime dissolves readily in pyridine, giving a yellow to orange-red solution, depending upon its concentration. Ostroumov (8), in precipitating metals by hydrogen sulfide in the presence of pyridine, had found that unless steps were taken to overcome this difficulty, the subsequent determination of nickel as the dimethylglyoxime was low, owing to its solubility in pyridine.
Table
1.
Recovery of Nickel
(Solution containing per 10 cc. 16,000 micrograms of iron, 1200 microgram8 of copper, 800 micrograms of manganese, 600 micrograms of zinc, and 60 microrrrams of cobalt) Nickel Added Standing 10.38 y 20.76 y 31.14 y 41.52 Time of Pot. Nickel Recovered Houra Y Y ’I Y 0.5 2.0 16.3 27.6 39 8 1 5.7 17.6 27.8 39 8 6.7 1.5 16.5 24.2 39 5 2 3.7 14.9 25.5 30 4 3 6.6 15.6 27.8 1 7.0 15.7 29.4 39 8 5 8.0 17.8 29.7 40 6 Overnight 10.5 20.8 32.0 43.9
258
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol 17, No. 4
with a few drops of pyridine, using the rod to effect solution and collecting the solution and washings in the beaker containing the asbestos. :Fit a small suction Bask with a tube containing a m a l l graduated tube protected by a cushion from the bottom of the outer tube. Have the tip of a Hirsch funnel extend into the graduated tube (Figure 1). Transfer the asbestos and pyridine t o the fillrer. wash with small amounts of pyridine, and press as dry as possible with a flatt.ened glass rod. Add sufficient pyridine to adjust the volume to 3 t,o 5 cc. for the Duboscq colorimeter. or I O ec. for the pbotoelectric colorimeter. Campsre with standard nickel dimethyl-’ glyoxime solution. Make correction for B blank similarly tryted. Jsing. d 402-EF Lumetron colorimeter with a B-I light filter (peak Lransmission 364 millimicrons) in combination with a serondary light blue B-1 Glter (maximum tranumis4on 400 to 500 millimicrons) and B neutral gray filter in the ssmple holder compartment and an absorption cell of 10 mm., the author obtained for concentrations of 0 to 84 mioroflams of nickel per LO cc. of pyridine t.ransmissious oi I00 to 25%, respectively. A curve of microg.rams of nickel platted rtxainst minus 108s of transmission gave a straight line. The absorption cell may, of course, be vaned with a correspohding calibration of the photometer. With a 1-00, cell of IO-mm. thickness one may estimate 1 microgram or less.
-
Figure I. Filtering Apparatus for Pyridine
The particular substance under examination was a hydrochloric acid solution of the same concentration of metals as in Table I, but also containing 30 micragmms of nickel per 5 ec. The method is applicable to any solution of biological or mineral origin wherein iron and many other metals are present with relatively very little nickel. Where only a Duboscq colorimeter with microcups is available, the volume of pyridine solution, about 3 to 5 cc., may be eompared with a standard stock solution suitably diluted with pyridine. With a photoelectric colorimete? the author has been able ta determine a few micrograms of nickel even in the presence of the above large quantities of other metals.
The solutions used for, the results shown in Tahle I1 and I11 have the same metallic concentrations as in Table I. The author applied this method to the estimation of nickel in water. Using 10M)-ce. samples of Jersey City water and 100-cc. samples of water from the Coppercliff Nickel Mine District in Ontario. he obtained results of about 9 and 100 parts per billion, respectively.
Table II. Nickel Added
Determination of Nickel Nickel Found
SOLUTIONS REOUIRED
Pyridine A.R. recently distilled. Standard pyrihine solution of nickel dimethylglyoxime containing 0.06 ma. of nickel uer cc. 0.295 mx. of nickel dimethvlglyoxime per Cc. May 6e diluted with pyridine as necessab. Keep in glass-stoppered bottle in a dark place. The nickel dimethylglyoxime may he made from a pure nickel solution, filtered on a BOchner funnel snd dried at 100’ C. Potwium Fitrate, A.H., 0.5 gram per cc. l)~mrthylalyoxime, I‘;O 111 alcohol. Antnwniwn I.ydmxidc, A.R., wncentmted.
-
PROCEDURE
As in all minute metal assrtys the water used should be at l w b doubledktilled, and the final &stillation should be from an allPyrex apparatus. I n a 3% or SO-cc. besker evaporate almost to dryness, with low heat toward the end, an aliquot of the hydrochloric acid solution estimated to contain 20 to 50 micrograms if a microcur, Duboscq colorimeter is to bc used, or about 2 UI30 mirrogramsif a phot& electric rolorimeter is availa1,le. Dissolve tile rcriduc in 2 PC. of water. .idd I cc. of DOl%S3lUm citrate solution xnd 5 drum of concentrated ammonia.‘ Mix by rotatinc Eentlv. Add 1.6 bo. of ~~
~
~
~~
~~
~
~~
hot water, i u n n g each throu h~filter The solubilit~-if~ni
