Table I. Effect of Reagent Concentration on Absorbance of Nickel-Nicon Complex Mole
Reagent Molarity 1 . 7 x 10-8 3 . 4 x 10-3 5 . 1 x 10-3 8 . 5 x 10-3
Ratiobf Reagent to Nickel
Absorbance 0.167 0.303 0.313 0.315
1
2 3 5
unknown, 0.75 ml. of reagent was added. This volume provides the necessary excess when 250 pg. (25 p.p.m.) of nickel is present in a 10-ml. flask. Conformity to Beer’s Law. The complex follows Beer’s law with solutions containing from 1 t o 25 p.p.m. of nickel. Optimum Concentration Range. Since the absorbance readings show minimum error when they are made between 0.200 and 0.700 (7), the optimum concentration range for nickel is between approximately 6.0 and 22.5 p .p .ni . Sensitiviiy. T h e difference in concentration of nickel necessary t o produce a change in the absorbance reading of 0,001 is calculated as 0.027 Unknowns. T o test t h e accuracy of t h e method, 11 solutions of concentration unknown t o t h e analyst were prepared. These solutions were treated according to the recommended procedure. T h e results are recorded in Table 11, DISCUSSION
The determination of nickel with Nicon offers several advantages. The reagent is easily obtainable in sufficiently pure form. It dissolves readily in ethyl alcohol to give a stable color-
Table II. Determination of Nickel in Solutions of Unknown Concentration Siokel.
Applied 12.00
7.50 23 .oo
10.00 15.00
3.75 18.75 5.00 20.50 14.00 6.25
P.P.M. Found 10.90 6.90 22.30 9.25 15.25 3.90 18.62 4.90 20.70 13.75 6.10
-
212
ANALYTICAL CHEMISTRY
Figure 3. Continuous variation method applied to nickel-Nicon complex, X ml. of reagent added to 3 - X ml. of nickel solution A. B. C.
430mp 560mp 580mp
X ML. OF REAGENT
less solution which shows only negligible absorbance at the wavelength of the determination. Although the nickelNicon complex precipitates unless some protective colloid is used, gelatin readily stabilizes the solution, and no change in absorbance is observed u p to 24 hours. The broad p H range of 3 to 6 eliminates the need for close control of acidity, and the method is accurate over the concentration range of 1 to 25 p.p.m. The only diverse ions which cause serious interference a t any concentration are copper and iron. The removal of these ions with an anionic exchange resin is suggestcd (5). Copper may also be removed by paper chromatography ( 2 ) . Cobalt interferes at concentrations above 2.5 p.p.m. The determination of nickel in the presence of less than 2.5 p.p.m. of cobalt may be made by adjusting the pH of the solution between 5 and 6, Ivhich is the range of minimum absorbance for the cobalt-Kicon complex Remoml of greater conccntrations of cobalt may he effected by the sanic means suggested for iron and coppcr. If no interfering ions arc present, greater sensitivity in the dcterniiiiatioii of nickel may be obtained by making all measurements a t 430 nip. The molar absorptivity at 430 mp is 4.18 X l o 3 and a t 560 mp 2.14 X lo3. All absorbance measurements were made a t 560 nip rather than a t the more sensitive wavclength to eliminate as much interference due to cobalt as possible (I). ACKNOWLEDGMENT
Financial support from the Sntional Science Foundation is gratefully acknowledged.
LITERATURE CITED
(1) Frierson,
TV. J., Patterson, N., Harrill, H., Marable, N., ANAL.CHEM. 33,1096-7 (1961). (2) Frierson, W.J., Rearick, D. A., Yoe, J. H., Ibid., 30,468 (1958). (3) Gahler, A. R., Mitchell, A. &I., Mellon, & G., I.Ibid.,23, 500-3 (1951). (4) Johnson, TV. C., Simmons, hi., Analyst 71,55-1-6 (1946). ( 5 ) Kraus, K. A,, Moore, G. E., J . Am. Chem. SOC.75, 1460 (1953). (6) Pearse, G. ri., PHaum, R. T., ANAL. CHEM.32.213-15 119601. ( 7 ) Sandell,’ E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 97, Interscience, Ne-, York, 1959. (8) Vosburgh, IT. C., Cooper, R. C., J . .4m. C h e m Soc. 63,437 (1941). (9) Voter, R. C., Bank., C. Y., ANAL. CHEX. 21,1320-3 (1949). (10) Welcher, F. J., “Organic Analytical Reagents,” Vol. 3, p. 332, Van Nostrand, Princeton, iY.J., 1947. (11) Yoe, J. H., Jones, A. L , IVD. ESG. CHERI., h A L . E D . 16, 111 (1914). RECEIVEDfor review August 29, 1961. Accepted November 30, 1961.
Correct ion Extraction of the Elements as Q u a t e r n a r y ( P r o p y l , Butyl, a n d H e x y l ) Amine Complexes I n this article by R. J. blaeck, G. L. Booman, 11,E. Kussy, and J. E. Rein [ANAL. CHEM. 33, 1775 (196l)], on page 1776, column 1, line 5, hexylamine should be changed t o butylamine.
