Anal. Chem. 1983, 55, 1810-1817
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Spectrophotometric Determination of Palladium(I I ) with Propericiazine A. Thimme Gowda and H. Sanke Gowda Department of Post-Graduate Studies and Research in Chemistry, University of Mysore, Manasagangotri, Mysore-570 006, India N. M. Made Gowda* Division o f Biochemistry, Department of Human Biological Chemistry and Genetics, The University of Texas Medical Branch, Galveston, Texas 77550 A review of various methods reported for the determination of palladium and other noble metals (1-7) shows that no attempt has been made to use the reaction between palladium and 2-cyano- 10-[3-(4-hydroxy- 1-piperidinyl)propyl]phenothiazine or propericiazine (PPC) for the spectrophotometric determination of palladium. In this paper, we report our studies on the orange-red complex of palladium with PPC. An analytical method has been developed for the spectrophotometric determination of microgram amounts of palladium in solution. The advantages of the proposed method over the spectrophotometric methods reported in the literature (2-4) include high sensitivity, selectivity, wide determination range, simplicity, and rapidity of determination. Application of this method in the determination of palladium content in jewelry alloy has been discussed.
EXPERIMENTAL SECTION Apparatus. A Beckman spectrophotometer (Model DB) with stoppered silica cells of 1-cm optical path was used for absorbance measurements. The pHs of the solutionswere measured (vs.SCE) with pH meter, Model L1-10 (M/S. Electronic & Industrial Instruments, Hyderabad, India). Reagents. Palladium(II) Solution. A stock solution of palladium(I1) was prepared by dissolving 0.9840 g of palladium(I1) chloride (M/S. Johnson Matthey Chemicals Ltd., London) in 1 M hydrochloric acid (AnalaR) and diluted to 1 L to give 0.1 M with respect t o hydrochloric acid. It was standardized gravimetrically by using dimethylglyoxime (7). The working solutions were made by suitable dilution of this standardized stock solution. PPC Solution. A 0.2%solution was prepared in doubly distilled water containing few drops of hydrochloric acid (AnalaR) and stored in an amber bottle in a refrigerator. Buffer Solutions. Walpole buffer solutions (8)in the pH range 0.65-5.2 were prepared by employing 1 M sodium acetate and 1 M hydrochloric acid. All other reagents were of analytical grade and were used without further purification. Standard Procedure. To an aliquot of the sample solution containing 5-605 pg of palladium(II), 5 mL of sodium acetatehydrochloric acid buffer of pH 2.65 and 3.0 mL of 0.2% PPC solution were added. The solution was then diluted to 25 mL with doubly distilled water and shaken thoroughly, and the absorbance was measured at 474 nm against a reagent blank prepared identicallywithout palladium. The palladium concentration of the sample was then calculated from the standard calibration curve. RESULTS AND DISCUSSION The reagent, PPC, reacts instantaneously with palladium(I1) ion to form an orange-red complex in hydrochloric, sulfuric, phosphoric, or acetic acid or sodium acetatehydrochloric acid buffer medium at room temperature (25 f 2 "C). The study of palladium(I1)-PPC complex in hydrochloric, sulfuric, or acetic acid medium was not recommended because of the low sensitivity and stability of the complex. The sensitivity of the reaction was more in phosphoric acid but the A, of the complex changed with change in concentration of phosphoric acid. The buffer medium was, therefore, selected because of 0003-2700/83/0355-1816$01.50/0
good sensitivity, longer stability, and constancy in A, of the complex. Effects of pH and Reaction Time. The effective pH range for the orange-red complex was found to be 1.10-4.10. Below pH 1.10, the maximum color intensity was not attained and above pH 4.1, the absorbance of the complex decreased with increasing pH of the medium. Constant absorbance value was obtained immediately after adding PPC solution to palladium solution in the presence of sodium acetate-hydrochloric acid buffer and it remained constant for about 6 h. Absorption Spectra. The absorption spectra of palladium(I1)-PPC complex, reagent blank, and palladium(I1) in sodium acetate-hydrochloric acid buffer of pH 2.65 were recorded (concentration of Pd(I1) = 6 ppm). The maximum absorbance of the complex was found to be at 466-482 nm. The molar absorptivity was 4.1 X lo3 L mol-1 cm-l. The absorption spectra of the reagent blank and palladium(I1) solution, under similar conditions, showed no appreciable absorption around this wavelength, thus promoting excellent analytical conditions for the determination. All subsequent studies were carried out at 474 nm. Effect of Reagent Concentration and Temperature. The effect of PPC concentration was investigated by measwing the absorbance at 474 nm of solutions containing 10 ppm palladium(I1) and varying amounts of PPC. A 25-fold molar excess of the reagent over palladium(I1) was required for maximum absorbance. So 3.0 mL of 0.2% reagent solution in a final volume of 25 mL sufficed for less than 605 pg of palladium. The absorbance was not affected by temperature in the range of 8-54 "C. Above 54 "C the absorbance gradually decreased with the rise in temperature. Order of addition of reactants was not critical. Calibration, Range, and Sensitivity. The palladiumPPC complex obeys Beer's law over the concentration range of 0.2-24.2 ppm of palladium(I1). The optimum working range as evaluated by the Ringbom method (9) is 2-22 ppm. According to Sandell's expression ( 5 ) the sensitivity of the reaction is 26.19 ng cm-2. Precision and Accuracy. The precision and accuracy of the method were studied by analyzing solutions containing known amounts of palladium(I1). The results of determination of 2 to 10 ppm of palladium(I1) showed a maximum relative error of f1.2% and a maximum standard deviation of 0.016 ppm. Ten determinations were made for each of the five sample sizes. The sensitivity of the proposed method is more than that of all the phenothiazine derivatives so far investigated except the parent compound phenothiazine. Effect of Diverse Ions. In order to assess the possible analytical application of the reaction, the effects of some ions which often accompany palladium were studied. For these studies, different amounts of the ionic species were added to 150 pg of palladium(I1) in sodium acetate-hydrochloric acid buffer of pH 2.65 in 25-mL volumetric flasks and the color was developed as outlined in the standard procedure. The 63 1983 American Chemical Society
Anal. Chem. 1983, 55, 1817-1819
Application. Determination of Palladium in Jewelry Alloy. A typical jewelry alloy contains 95.5% palladium and 4.5% ruthenium. With the increasing use of palladium for jewelry alloy, a need has arisen for a simple, rapid, and accurate method for determining palladium in its alloys. Synthetic mixtures corresponding to jewelry alloy were prepared and their palladium content was determined by the recommended procedure. The results are presented in Table I.
Table I. Determination of Palladium(I11)in Synthetic Mixtures Corresponding to Jewelry Alloy
a
amt of Pd(I1) amt of Ru(III), amt of Pd(I1) PPm found,a ppm present, ppm 2.00 0.090 2.01 4.00 0.19 4.00 6.00 0.26 6.10 8.00 0.38 7.98 0.480 9.96 10.00 12.00 0.520 12.03 Average of five determinations.
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following amounts (Kg/mL) of foreign ioins were found to give less than 2% error in the determinatioin of 6 pg/mL of palladium(I1): Cu(II), 8210; Ni(II), 650; Co(II), 720; Fe(III), 3.0; Ru(III), 6.0; Pt(IV), 10; Os(VIII), 22; Rh([II), 26.0; Ir(III), 32.0; Hg(II), 850; U(VI), 1100; Zr(IV), 960; Zn(III), 1100; Cr(IlI), 280; fluoride, 2600, chloride, 4800; bromide, 3600; iodide, 10.0; nitrate, 8000; sulfate, 10000; phosphate, 2100; acetate, 1200; oxalate, 850; citrate, 820. ETDA, thiosulfate, Ag(I), Au(IXI), iodate, permanganate, dichromate, and vanadate interferred even in small amounts. Also, alkali metal and alkali earth metal ions caused no interference. Efforts to increase the tolerance limit of cations by the addition of masking agents were unsuccessful. Composition and Stability Constaint of the Complex. The composition of palladium-PPC complex was studied by continuous variations (10, II), mole ratio (12),and slope ratio (13)methods. These methods showed the formation of a 1:1 complex between the metal ion and the reagent. The apparent stability constant of the complex evaluated by the mole ratio method was log K = 4.78 f 0.1 at 27 V. Nature of the Complex. The nature of the complex was studied by passing am aliquot of solution of the complex through cation exchange resin, Dowex 50W-X8, and anion exchange resin, Dowex 1-X8. The orange-red complex was retained by Dowex 50W-X8 and not by Dowex 1-X8. This indicated that the complex was cationic in nature.
ACKNOWLEDGMENT The authors are grateful to L. Julou and J. Molle, Rhone-Poulenc-Centre, Nicolas Grillet, Paris, for supplying pure PPC. Registry No. PPC, 2622-26-6;palladium, 7440-05-3;palladium base, ruthenium alloy, 12727-67-2. LITERATURE CITED (1) Borisova, R.; Mosheva, P.; Ivanova, 7.; Topalova, E. Z . Anal. Chem. 1975. 2 7 4 . 31-34. (2) Sanke G w d a , H.; Thimmaiah, K. N. Z . Anal. Chem. 1976, 208, 279. (3) Sanke Gowda, H.; Thimmaiah, K. N. Indian J . Chem., Sect. A 1976, 74A, 821. (4) Sanke Gowda, H.; Thimmalah, K. N. Rev. Roum. Chim. 1977, 22 (5), 745. (5) Sandell, E. B. "Colorimetrlc Determination of Traces"; Interscience, New York, 1944; Pp 358-360. (6) Beamish, F. E.; Van Loon, J. C. "Recent Advances in Analytical Chemistry of Noble Metals"; Pergamon Press: Oxford, 1972; pp 306-345. (7) Vogei, A. I."A Text Book of Quantitative Inorganic Analysis"; The ELBS and Longmans: London, 1968; p 512. (8) Britton, H. T. S. "Hydrogen Ions"; Chapman and Hall: 1955; Vol. I , p 353. (9) Rlngbom, A. 2.Anal. Chem. 1939, 775, 332-343. (10) Irving, H.; Pierce, T. B. J . Chem. SOC. 1959, 2565-2574. (11) Job, P. C . R. Hebd. Seances 1925, 780, 928-930. (12) Yoe, J. H.; Jones, A. L. Ind. Eng. Chem., Anal. Ed. 1944, 111-115. (13) Harvey, A. E.; Manning, D. L. J . Am. Chem. SOC. 1950, 72, 4488-4493.
RECEIVED for review March 28,1983. Accepted June 8, 1983. A.T.G. thanks the University Grants Commission, New Delhi, India, for the a.ward of a Teacher Fellowship under the Faculty Improvement Program.
Preparation of Electrodeless Discharge Lamps for Atomic Fluorescence Spectrometry M. D. Seltzer and EL. G. Michel* Department of Chemistry, University of Connecticut, Storrs, Connecticut 06268 Electrodeless discharge lamps (EDLts) have been studied for many years as potential sources foy atomic fluorescence spectroscopy (AFS).The early work was reviewed by Haarsma et al. (1).Michel et al. (2-4) have more recently concentrated on improving the reproducibility of preparation of these lamps. A continuation of the latter work is reported here. Michel et al. (2-4) showed that the reproducibility of the manufacture of EDLs depends primarily on carefully identifying and controlling the variablles which are inherent in the preparation of the lamps. This approach was successful for cadmium (2, 3) and selenium ( 4 ) when ten variable$ were identified and rigorously optimized by using the Simplex algorithm (5, 6). The classical method of preparation of EDLs (1)was very simple. Usually the lamp blank was cleaned by flame heating the quartz to white heat under vacuum. Then the appropriate metal or metal halide 'was put in the lamp and sublimed while in the lamp by flame heating to drive off volatile impurities. Then a few torr of an inert gas (usually argon) was added and the lamp sealed. Some variables were obvious and almost
always carefully optimized, for example, the weight of material and pressue of the inert gas put in the lamp. The method of Michel et d. (2-4) demonstrated, however, that the sublimation process was critical. In that work, the required amount of material was put in the lamp and the sublimation was then brought about in a controlled manner by initiating a microwave discharge in the lamp blank while it was on the vacuum system. The variables that were controlled were the duration and applied power of the discharge and the fill pressure of argon during the discharge. This procedure worked fine for the relatively volatile cadmium and selenium EDLs but here it did not work for manganese EDLs. This was because the heat provided by the microwave field was not sufficient to sublime the manganese iodide that was introduced into the lamp. Two approaches are described here which were designed to facilitate the sublimation of less volatile materials. First, the EDL was thermostated (7) while it was on the vacuum system prior to and during the sublimation stage and, second, ground silica chips of approximately 0.5 mm average
0003-2700/83/0355-1817$01.50/00 1983 American Chemical Soclety
