V O L U M E 22, N O . 5, M A Y 1 9 5 0
723
Table 11. Determination of Benzylpenicillin by Three Methods % Benzylpenicillin NEP" UVb Sample 89.4 89.0 41,369 41,518 90.5 87.1 93.1 94.8 42,522 94.3 98.7 43.678 89.4 90.0 46,385 88.6 91 . o 46,574 92.0 89.5 46,975 91.0 88.8 48.623 89.1 48,743 88.5 92.0 94.6 48,774 91.0 93.8 48,949 93.4 92.9 50,233 92.5 95.8 50,345 93.9 93.3 50,346 92.4 95.8 49,523 88.3 92.9 49,038 91.3 92.3 Mean N-ethylpipendine. b Ultraviolet. C N(1-naphthyl) ethylenediamine dihydrochloride.
NEDC 89.7 96.8 96.8 97.1 95.2 87.2 91.2 91.1 86.8 96.2 92.0 94.0 97.0 95.2 94.8 95.1 93.5
trated sulfuric acid, cool, and add 1 ml. of 0.1% sodium nitrite and 1 ml. of 0.25% ammonium sulfamate, shaking well after the addition of each. Add 10 ml.. of 95% alcohol. Add 1 ml. of 1.5% N ( 1-naphthyl) ethylenediamine dihydrochloride, prepared fresh daily. Make to volume. Let stand a t least 1 hour and determine the density of the solution a t 560 mp in a Beckman quartz spectrophotometer. Crystalline penicillin may be used, or the residue from a 1-ml. aliquot of a solution of penicillin in water or buffer which has been taken to dryness in boiling water. The procedure may be interrupted after nitration, but once reduction has taken place the color must be developed within 1 to 2 hours. With many samples of penicillin color development is complete within 15 minutes, but some samples require 1 hour for maximum color development. The color is stable for at least 3 hours after the maximum color is reached. Though different brands of N ( 1 -
naphthyl) ethylenediamine dihydrochloride possess different physical properties, under the above conditions the same results are obtained. For refereme the author established a regression line using the above procedure and amounts of sodium benzylpenicillin varying from 0.05 to 0.5 mg. The 67 points used were determined on 5 days during a period of 2 weeks. Two brands of N ( 1-naphthyl) ethylenediamine dihydrochloride and two standard benzylpenicillins were used. The equation of'the line was Y = 0.399032 X 0,0059, where Y represents milligrams of benzylpenicillin and X is the density. The correlation coefficient was +0.995 and the standard error of prediction +0.014 mg. In Table I1 results obtained by this method on a number of commercial samples of penicillin are compared with results by the gravimetric N-ethylpiperidine ( 5 ) and the ultraviolet absorption ( 4 ) methods. Although these methods are based upon three different principles, they show good agreement. They vary greatly in the amount of time required, the size of sample used, and the precautions that must be observed. The choice of a method will depend upon the conditions existing in individual laboratories. ACKNOWLEDGMENT
The author wishes to thank Merck & Co. and Ayerst, McKenna & Harrison, Ltd., both of Montreal, for gifts of crystalline benzylpenicillin. LITERATURE CITED
(1) Boxer, G. E., and Everett, P. M., ANAL.CHEM.,21, 670 (1949). (2) Canback, T.,Farm. Rea., 46,97 (1947). (3) Del Vecchio, G., and Argenziano, R., BUZZ. soc. ital. biol. 8pcc.. 22, 1190 (1946). (4) Levy, G.B.,et al., ANAL.CHEM.,20, 1159 11048). ( 5 ) Mader, W. J., and Buck, R. R., Ibid., 20,254 (1948). (6) Page, J. E., and Robinson, F. A , , Nature, 158,910 (1946).
RECEIVED July 19, 1949.
Identification and Microdetermination of Nickel In Presence of Iron by Means of 1,Z-Cyclohexanedione Dioxime H. I. FEINSTEIN National Bureau of Standards, Washington, D . C . DVANTAGES and disadvantages in the use of 1,2cyclodioxime (called nioxime) as compared with dimethylglyoxime in the analytical chemistry of nickel and palladium have been reported (2-4). Voter, Banks, and Diehl (3) devised a procedure using this reagent for the gravimetric determination of nickel in the presence of a number of elements, but were not successful in preventing interference by iron. The cause of this difficulty was not explained, but i t seems likely that the masking agents did not form sufficiently stable complexes a t a p H of 4 to 5 to prevent oxidation of the reagent by ferric iron. Accordingly, a change in the pH of the solution a t the time of precipitation might eliminate the interference from iron. Therefore, experiments were performed using neutral or slightly ammoniacal solution a t room temperature followed by digestion a t 60" C. Furthermore, nioxime wag added to the already neutralized solution, whereas Voter, Banks, and Diehl (S) adjusted the p H after the reagent was added. The use of acetate as a buffer was eliminated, because tartrate could function both as buffer and masking agent. I t is believed that tartrate has no appreciable reducing action on ferric ion under the conditions of the procedure. The procedure finally adopted was tested on three National Bureau of Standards standard samples of iron and steel. The
A hexanedione
results of nickel determinations employing single and double precipitation on these samples are given in Table I. GRAVIMETRIC PROCEDURE
A weighed sample containing 10 to 25 mg. of nickel is tranaferred to a 400-ml. beaker and decomposed by accepted methods Table I.
Values Obtained for Nickel by Single and Double Precipitations
S.B.S. Standard Sample 33ca
Weight of Sample,
Nickel Present,
Nickel Found, % Single Double precipiprecipitation tation 3.32 3.27 3.32 3.26
0.
%
0.5
3.28
82ab
1.0
1.07
1 12 1.12 1 12 1.11
lOlbC
0.1
8.99
9.17 9.13 9.18
0.2
1.10 1.10
8.90 8.99 a Nickel steel (SAE 2335). M n 0.733; Cu 0.031; Cr 0.052; M o 0.032; AI 0.032. b Nickel-chromium cast iron. M n 0.65. Si 2.06. Cu 0.08; Cr 0.33. 0 18 Chromium-9 nickel steel (SAE '30905). 'Mn 0.597; Cu 0.168; Cr 18.49; V 0.049; Mo 0.078; Co 0.078; Cb 0.062; Sn 0.012.
ANALYTICAL CHEMISTRY
124 for niekcl in iron and s t t d :is when dimet,hylglyoxinrr ir uscd ( 1 ) . If an insoluble residue rcinnins, it is fikrred ON:tnd sashed thoroughly with hot mater. If this rcsidur is suriprrterl oi con-
taining nickel, the paper is hurncd, t r e n t d with hydroRuori
