Spectrophotometric Determination of Gold with 2,2'=Dipyridyll Ketoxime William J. Holland and John Bozic Department of Chemistry, University of Windsor, Windsor, Ontario, Canada VARIOUSpyridylketoxirnes have been used for the spectrophotometric determination of certain metals. Phenyl-apyridyl ketoxime was used by Sen (I, 2) as a reagent for the determination of palladium and gold. Guyon and Murmann (3) and Trusell and Diehl ( 4 ) reported the use of the same reagent for the dete rmination of rhenium and iron, respectively. Palladium has been determined by Pflaum, Wehking, and Jensen (5)using 2-pyridine aldoxime. In the present work, 2,2 '-dipyridyl ketoxime has been found to be highly selective for gold; it reacted to form a watersoluble chelate which is extractable into dichloromethane. A molar ratio plot showed that the gold and the reagent combined in the ratio of 1 mole to 3 moles, respectively. The molar absorptivity of the gold chelate in dichloromethane was 2 X 104. Absorbance measurements were made at the wavelength of maximum absorbance, 459 mp. EXPERIMENTAL
Instruments. Spectral studies were made with a Hitachi Perkin Elmer spectrop hotometer, a Beckman DB Spectrophotometer, and a recording Bausch and Lomb Spectronic 505. Measurements of pH were made with a Corning Model 12 pH meter. Preparation of Reagent. The procedure of Henze and Knowles (6) was employed to synthesize 2,2'-dipyridyl ketone. The crude ketone was converted directly to the oxime with hydroxylamine hydrochloride. Several recrystallizations from water gave 1 he pure oxime which melts at 141O142" C. The melting point reported in the literature (7) is 141"-142.5" C. Reagent Solution. A 1 solution of the reagent in 95 ethanol was used. This solution was stable for several months. Standard Solutions. All chemicals used were of reagent grade. The standard gold solution was prepared from H Au C1, 3H20 and standardized by precipitating the elemental gold with hydroquinone according to the method of Beamish, Russell, and Seath (8). Solutions of diverse cations were prepared from their chlorides or nitrates arid solutions of diverse anions from their sodium or potassium salts. Procedure. An aliquot of solution containing approximately 20 to 200 pg of gold was placed in a 50-1111 separatory funnel. To this was added 3 ml of a saturated KClO, solution, and the volume was made up t 3 approximately 15 ml with distilled water. The pH of the contents was maintained between 2.0 and 3.5 by addition of a few drops of dilute hydrochloric
z
z
(1) B. Sen, ANAL.CHEM., 31, 881 (1959). (2) B. Sen, Anal. Cliim. Acta, 21, 35 (1959). 36,1058 (1964). (3) J. Guyon and R. K . Murmann, ANAL.CHEM., (4) F. Trusell and H. Died, Zbid.,31, 1978 (1959). ( 5 ) R. T. Pflaum, M. W. Wehking, and R. E. Jensen, Talanta, 11, 1193 (1964). (6) H. R. Henze and M B. Knowles, J . Org. Clzem., 19, 1127 (1954). (7) E. Leete and L. Marion, Can. J . Clzem., 30, 563 (1952). (8) F. E. Beamish, J. J. Itussell, and J. Seath, IND. ENG.CHEM., A ~ A LED., . 9, 174 (1937).
Table I. Influence of pH (4.8 ppm gold) Absorbance
PH
0.198 0.507 0.520 0.519 0.510 0.483 0.308 0.088 0.039 0.019
0.5 1.4 2.5 3.5
4.0 4.7 6.5 7.9 8.2 9.6
Table 11. Precision and Accuracy Std Gold, ppm Re1 dev, Experiment Taken Found error ppm 1 2 3
1.20 3.60 6.00
1.23 3.60 6.05
+2.50 0.00
+0.83
0.03 0.01 0.06
Range, ppm
0.07 0.02 0.17
The result of experiment 1 is the average of 5 separate analyses and for experiments 2 and 3 the average of 10 separate analyses.
acid or potassium hydroxide. Two milliliters of reagent solution was added and the contents were shaken briefly, The yellow color was allowed to develop for a t least 10 minutes and then extracted three times with 5-ml portions of dichloromethane. The extracts were added to 25-1111, glass-stoppered, graduated cylinders containing 3 ml of methanol. The funnel stem contained a small plug of glass wool to remove any traces of water. The resulting solutions were made up to 25 ml with dichloromethane and the absorbance was measured at 459 mp. A blank was prepared in the same manner without addition of gold. No gold was found remaining in the aqueous layer on applying the 5-(p-dimethylaminobenzylidene)-rhodanine spot test. RESULTS
Influence of pH on Complex Formation and Extraction. The maximum yellow color intensity in the organic phase occurred between a pH of 1.5 and 4.0. The results are shown in Table I. Effect of Reagent. A large excess of reagent was used. There was no change in absorbance when 2 or 10 ml of the reagent solution was added. No absorbance due to reagent occurs a t 459 mp. Effect of Time. The yellow color was completely developed within 10 minutes and was stable for at least 24 hours. All color developments were made at room temperature. Effect of Solvent. The yellow-colored complex in the presence of KClO, is completely extracted into dichloromethane, partially extracted into chloroform, benzene, toluene, amyl VOL. 39, NO. 1, JANUARY 1967
109
alcohol, nitrobenzene, and not extracted into carbon tetrachloride, ethyl acetate, ethyl ether, or bromobenzene. Beer’s Law. A straight line was obtained over the range 1-10 ppm when absorbances were plotted against concentrations. Precision and Accuracy. The precision and accuracy of the method was studied by analyzing solutions containing known amounts of gold using the outlined procedure. The results are summarized in Table 11. Effect of Diverse Ions. Five milligrams of a foreign ion was added to a separatory funnel containing 90 pg of gold and the extraction was performed according t o the procedure outlined above. The following ions did not interfere: Na+, K+, Mg+2, Ca+2, VO+3, Cr+3, Mn+2,Zn+2, Ba+*, Sn+4, Cd+2, Pb+2, Al+3, NH4+,S04-2, Zr+4, UOz+2,T1+2, Pt+4, R u + ~Re+’, , Rhf3,
F-, NO3-, Clod-, Br-, acetate ion, citrate ion and EDTA. When 5 mg of a foreign ion interfered, masking agents were employed. The following ions did not interfere in conjunction with the corresponding masking agents: 5 mg of Be+* masked with 25 mg of F-; 5 mg of N P 2masked with 2 ml of a 1 EDTA solution; 5 mg of C u f 2 masked with EDTA solution; 0.5 mg of Fe+3masked with 5 mg of F-; 5 mg of Bi+3 masked with 200 mg of citrate. The system could also tolerate 0.5 mg of W04-2; 1 mg of Hg+2; 3 mg of Cr207-2; 1 mg of Ag+ or 5 mg of Ag+ if the major portion of the AgCl formed was filtered off. Interferences due to Pd+2 and Co+2 could not be eliminated. RECEIVED for review September 23, 1966. Accepted November 21, 1966. Work supported by the National Research Council of Canada.
Uniform Neutron Irradiation of Inhomogeneous Samples G . L. Priest, Forrest C. Burns, and Homer F. Priest U. S.Army Materials Research Agency, Watertown, Mass. 02172 THE USE OF NEUTRON generators utilizing the 3H(d,n)4He reaction to produce 16Mev neutrons for activation analysis has presented some special problems because such a source is neither isotropic nor exactly reproducible in flux configuration from irradiation to irradiation. Studies reported elsewhere (1-2) have shown that a n isotropic flux configuration is not realized near the target but only a t a distance of several inches away. Uniform irradiation of samples a t a distance of several inches could be achieved, but unfortunately the neutron flux a t this point is decreased by several orders of magnitude, a n intolerable reduction in most cases. If the samples are placed as near to the target as possible to expose them to the maximum neutron flux, the asymmetry of the flux distribution is severe. There are two generally accepted procedures for neutron activation analysis. In the first, the unknown and standard samples are irradiated separately with a flux monitor such as a neutron scintillator or a standard foil being used to determine the magnitude of the neutron flux for each. The flux monitor reading is used to normalize the data obtained for the sample and the unknown. This procedure has been quite successfully used by Anders (3) and his associates. In the second procedure the unknown and standard are irradiated simultaneously employing some kind of motion to ensure that they are both exposed to the same neutron flux. The authors prefer this second procedure. Planetary rotators designed t o simultaneously expose the unknown and the standard to the same neutron flux are available commercially ( 4 - 3 , but such devices give accurate results only for samples having a high degree of uniformity of distribution of the constituent being determined (6). A (1) H. F. Priest, F. C. Burns, and G. L. Priest, Nuclear Instruments and Methods, in press. (2) B. T. Kenna and F. J. Conrad, Health Physics, 12, 564 (1966). (3) 0. U. Anders and D. W. Briden, ANAL.CHEM., 37, 530 (1965). (4) Kaman Nuclear Corp., Colorado Springs, Colo., “Activation
Analysis Transfer System,” company bulletin.
( 5 ) Technical Measurements Corp., Ellison Division, Chamblee,
Ga., company bulletin.
(6) D. E. Wood, P. L. Jessen, and R. E. Jones, Kaman Nuclear,
Colorado Springs, Colo., 1966 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, February 1966. 110
ANALYTICAL CHEMISTRY
simple calculation shows that for the case where the level of irradiation at the ends of 1.5-inch long samples is one half that in the middle, inhomogeneity of the magnitude experienced in many metals and semiconductors can give rise to either negative or positive errors as large as 25 %. Various simple motions have been studied singly and in combination to determine what motion or combination of motions will ensure not only uniform irradiation of both unknown and standard but also that both receive an identical neutron dose. Two types of samples were considered: long, thin cylinders where radial effects are negligible, and disks where radial effects become important and longitudinal effects are minimized. EXPERIMENTAL
To simulate samples having a known distribution of impurities, a cylindrical configuration 0.31 3 inch in diameter and 1-2 inch long was chosen. The radioactive isotope chosen for the studies was 18F, 109.5 minute half life (7). The cross section for the reaction 19F(n,2n)18F(109.5min) is about 60 millibarns (8) so that for the size of samples considered adequate activity for good counting statistics is obtained by short irradiations. The half life is such that accurate corrections are easily made but is short enough that the radioactivity decays overnight permitting re-use of the samples. Allowing the samples to decay for 2 min eliminates interference due to z°F. Teflon (Du Pont) was used as the fluorine-containing material. Disks 0.313 inch in diameter and 0.125 inch thick were machined from Teflon rod. Each disk was numbered and weighed. Polyethylene disks of identical dimensions were prepared for use as inert fillers to enable preparation of cylinders having a variety of distributions of fluorine. By restricting sample diameter to 0.313 inch the radial neutron absorption was negligible obviating the need to rotate the cylinders on their own axes although such an addi(7) F. C. Burns, G. L. Priest, and H. F. Priest, U. S. Army Materials Research Agency, Watertown, Mass., unpublished data, 1965. (8) Texas Nuclear Corp., Austin, Texas, Table of Cross Sections for Fast Neutron Reactions, 2nd. ed., January 1964.
