Table 111.
Analyses of Standard Boron Solutions (Boron, p.p.m.)
Standard
Found
1 . 9 8 , " 1 . 9 9 , 2.00, 2.00 4 . 0 0 , a 3 . 9 9 , 4.01, 4.02 1 . 0 1 , b 1 . 0 0 , 1 . 0 1 , 1.00 2 . 0 0 , b 1 . 9 9 , 1 . 9 7 , 2.00 Using 530 mM. Using 355 mp.
2.0 4.0 1.o 2.0 b
Table
IV.
Comparison of
Methods
Molar Method Absorptivity Quinalizarina 262 Carminic acida 3040 Chromatropic Acida 4120h Curcumina 6010 Ba chloranilate, 530 nip 210b Ba chloranilate, 355 mp 245Ob n As calculated from Figure i (8). b Mean values.
This wavelength is really outside the range of maximum absorbance. I n spite of the limitations in ivorking a t
365 mp, the sensitivity has been increased to ten times that as compared t o observations made a t 530 mp (see Table IV). The absorbance values obtained a t 355 mp using a 1-em. cell and narrow slit on a Beckman DB spectrophotometer are given in Table 11. The plot of absorbance us. concentration is linear only a t low concentrations. .4t concentrations higher than 3 p.p.m., curvature is observed. At very high concentrations (more than 10 p.p.m.) the results are not consistant. The method is simple, sensitive, and covers a wide range of concentrations because of the two absorption bands n-hich could be used. The results of analyses using this method are shown in Table 111. Agreement between the standard and observed values indicates that the boron contents from 0.3 to 10.0 p . p m may be determined with an average deviation of h0.1p.p.ni. A comparison as given in Table Is' shows that the barium chloranilate method is sensitive when observations are made a t 355 in and is better than
methods utilizing quinalizarin and carminic acid. Obviously sulfate ions will interfere in such determination of boron. ACKNOWLEDGMENT
Grateful acknowledgment is made to the International Nickel Company of Canada Ltd., and the Sational Research Council of Canada for a research grant in support of this work. LITERATURE CITED
(1) Barney, J. E., 11, Bertolacini, R. J., AXAL.CHEY.29,1187-8 (1957). ( 2 ) Bertolacini, R. J., Barney, J. E., 11, Ibid., 29,281-3 (1957). (3) Ibid., 30, 202-5 (1958). (4) Bovalini, E., Piazzi, M., Ann. chim. (Rome)48, 305-9 (1958). (5) Broad, W. C., Ueno, K., Barnard, A. J., Jr., B u n s e k i Kagaku 9, 257-64 (1960). (6) Hayashi, K., Danzuka, T., Ceno, K., Talanta 4,244-9 (1960). \ - - - - ,
(T) Hensley, A. L., Barney, J. E., 11, BXAL.CHEM.32,828-31 (1960). (8) Pasztor, L., Bode, J. D., Fernando, Q., Ibid., 32,277-81 (1960).
RECEIVEDfor review August 2, 1961. Accepted December 7, 1961.
Spectrophotometric Determ nation of Nickel with 1,2,3-Cyclohexanetrione Trioxime W. JOE FRIERSON and NINA MARABLE Department of Chemistry, Agnes Scoff College, Decafur, Ga.
The stable red complex formed between nickel and 1,2,3-~yclohexanetrione trioxime (hereafter called Nicon) gives two absorption maxima, one at 560 and the other at 430 mp. Since the reagent gives essentially no absorbance at 560 mp, this wavelength was used in the following study. The optimum concentration range was between 6 and 22.5 p.p.m. of nickel. The pH for the formation of the complex may vary from 3 to 6.
V
for the spectrophotometric determination of nickel have been investigated: dimethylglgoxime ( I O ) , a-furildoxime ( 3 ) , oxamidosime ( 6 ) , 1,2-cycloheptanedione dioxime (9), 1,2-cyclohesanedione diosime (4). A recent study ( I ) of Kicon as a reagent for the quantitative determination of cobalt suggested that this compound may also be used as a reagent for nickel. This paper deals with the further study of the reagent 210
ARIOUS OXIME REAGENTS
ANALYTICAL CHEMISTRY
and with the procedure for the determination of trace amounts of nickel. EXPERIMENTAL
Reagents. The colorless solution of the reagent (1.7 X lO-*ilf) Tvas prepared by dissolving 0.2910 gram of Xicon (white label Eastman Organic Chemical No. 7660) in 100 ml. of 93% ethyl alcohol. Nickel chloride hexahydrate (NiC12. 6Hz0), Baker Analyzed, was dried a t 140' C. for 4 hours to convert the salt to its anhydrous form. The stock solution was prepared by dissolving 53.21 mg. of the dried salt in 250 ml. of redistilled water to obtain a 100-p.p.ni. solution of the nickel ion. A 1.0% solution of gelatin was used to stabilize the solution of the complex. Redistilled water was used throughout the inirestigation. All other chemicals used were of reagent grade purity. Apparatus. All absorbance measurements were made with a Beckman Model DU spectrophotometer
equipped with a multiplier phototube attachment and operated a t varying sensitivity \Tit11 a slit width of approximately 0.025 mm. Matched 1.00em. Corev cells were used. All p H measurements were made with a Beckman Zeromatic p H meter using glass electrodes. 9 syringe microburet, Model S o . SB2 (Xicrometric Instrument Co., Cleveland, Ohio) was used for measuring volumes of solution. Procedure. Solutions varying in concentration from 1.0 to 25 p.p.m. m-ere prepared by measuring a known volume of t h e 100-p.p.m. stock solution into 50-ml. beakers, adding 3.0 ml. of t h e 1.0% gelatin solution and 0.75 ml. of t h e reagent solution. The solutions ivere then transferred to 10-nil. volumetric flasks and diluted to t h e mark. Absorbance measurements were made against a reagent and gelatin blank a t 560 mp. S o adjustment of p H is necessary if the solution of the complex as prepared falls within the pH range of 3 to 6, however, if
0.7L
monium hydroxide. Absorption measurements were then made against a reagent-gelatin blank at 560 mp. No change in absorbance over this p H range was observed. Values above p H 6 and below p H 3 were not considered because the absorbance of the reagent increases in these ranges. The increase below pH 3, however, is small in comparison to that above p H 6. Since all solutions as prepared fell within the p H range of 3 t o 6, no adjustment of p H in the determination m-as necessary. Nature of the Color Reaction. TKO methods were used to determine the combining ratio of nickel and Nicon: the mole-ratio method of Yoe and Jones (11) and the continuous variation method of Job as modified by Vosburgh and Cooper (8) (Figures 2 and 3). Both methods indicate a ratio of one mole of nickel to two moles of Nicon. To be certain that only one species of complex was forming, the absorbance measurements for the continuous variation plots were made a t several different wavelengths. The ratios were the same a t all wavelengths; therefore, only one species was present, Figure 3. The following structure is postulated for the complex:
0.6
300
460 540 W A V E LENGTH, m y
620
Figure 1. Absorbance curve of nickel-Nicon complex, 10 p.p.m. nickel
adjustment is necessary, it may be made with dilute ammonia water or dilute hydrochloric acid. A buffer was not used since the adjustment could be made very quickly witli the acid or the base. RESULTS
The complex which is formed by the reaction between nickel and Xicon nil1 precipitate unless the nickel solutions are stabilized n i t h gelatin solution prior to the addition of the reagent. One milliliter of 1.0% gelatin solution is sufficient for stabilization of the solutions when the p H is approviniately 3 to 4. At higher pH values, 3 ml. of gelatin arc required. Absorbance readings made on the gelatin-stabilized solutions of the compltv are the Sam? before and after the solutions are allowd to stand 18 to 24 hours. The complev decomposes s l o ly ~ wlirn heated above 50" c. Rate of Reaction. Absorbance readings were made immediately after the reagent was added and after 10, 30, and 60 minutes. There was n o appreciable increase in absorbance after the initial reading indicating t h a t the reaction is essentially instantaneous. Wavelength. The absorption spectrum of the reagent was studied from 275 to 625 mp. The absorbance ~vaq negligible above 375 mp but showed a steady increase a t lower wavelengths without reaching a maximum. The absorption spectrum of the complex Color
Stability.
was studied from 375 to 625 nik. S o study was made below 375 mp because of the high absorbance of the reagent in this range. Two absorption maxima occur in the spectrum of the complex between 375 and 625 mp, one a t 430 and another a t 560 mp. The working portion of the curve is shown in Figure 1. ,411 absorbance measurements for this investigation were made a t 560 mp to minimize interfering absorbance of the cobalt-n'icon complex n-hich is lower at this wavelength than a t 430
Hz H,c'c'c=n-oH 1 1
Amount of Reagent. K h e n the reagent concentration is 1.7 X 10-2X, 0.2 nil. are required to supply the amount of reagent equivalent to 100 pg. of nickel. However, some excess of reagent is necessary to force the reaction to completion and therefore to obtain maximum absorbance readings. Table I indicates that the absorbance remains constant as long as the reagent concentration is three times that of the nickel present. To ensure a threefold excess of reagent in all succeeding dcterminations when the concentration v a s
m p.
Effect of pH. The effect of hydrogen-ion concentration on the absorbance of the complex was examined over a p H range of 3 t o 6. Solutions of equal concentration of the complev rrere prepared in the described manner and adjusted to the dmired pH n.ith dilutc hydrochloric acid or dilute am-
m-
1
0
0 W
z m a
I 0.0
0.1
0.2
i
I
I
0.3
0.4
I
0.5
ML. OF REAGENT
Figure 2.
Mole-ratio method applied to nickel-Nicon complex, 10 p.p.m. nickel VOL. 34, NO. 2, FEBRUARY 1962
211
Table I. Effect of Reagent Concentration on Absorbance of Nickel-Nicon Complex Mole
Reagent Molarity
Ratiobf Reagent to Nickel
1 . 7 x 10-8 x 10-3 5 . 1 x 10-3 8 . 5 x 10-3
1 2 3 5
3.4
Absorbance 0.167
0.303
0.313 0.315
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. The 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. The 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.
P.P.M.
Applied
Found
12.00 7.50 23 .oo 10.00 15.00 3.75 18.75 5.00 20.50 14.00 6.25
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 sobtion 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.
