490 AfiaZyst, August, 1968, Vol. 93, $9. 490-493 Di-2-pyridyl Ketoxime, a New Reagent for the Rapid Gravimetric Determination of Palladium BY WILLIAM J. H O L L A N D , JOHN ROZIC AND JESSE GERARD (Department of Chemistry, University of Windsor, Windsor, Ontario, Canada) Di-2-pyridyl ketoxime is proposed for the gravimetric determination of palladium. The chelate is precipitated over a pH range of between 3 and 11 and weighed as Pd(C,1H,0N,)2. An extensive study of foreign ions and analytical conditions for precipitation indicates the procedure to be widely applicable, rapid and simple. NUMEROUS precipitating reagents have been proposed for the gravimetric determination of palladium, and have recently been excellently reviewed by Beamish.l The most important reagents for palladium contain the oxime grouping, C=N-OH.Dimethylglyoxime,2 cyclohexane-1 ,2-dione dioximeS (nioxime) and /3-furfuraldoxime4 are among the well estab- lished reagents in this class. More recently 2-selenophene aldoxime,b di-2-thienyl ketoxime6 and 8-mercapt~quinoline~ have been proposed as new gravimetric reagents for palladium. The purpose of the present work was to extend the application of di-2-pyridyl ketoxime to other analytical problems. This reagent has been investigated previously, and subsequently proposed for the spectrophotometric determinations of gold,* palladi~m,~ cobaltlo and iron.ll Further studies indicated that over a wide pH range, di-2-pyridyl ketoxime and bivalent palladium formed bis(di-2-pyridyl ketoxime) - palladium( 11) in quantitative yield- In this paper, the above reaction has been applied to the gravimetric determination of bivalent palladium in the presence of many diverse cations and anions.The palladium chelate is insoluble in hot water, while the reagent is completely soluble. Consequently, filtration from a hot solution, after a brief digestion period, results in a procedure that is rapid, with no loss of accuracy. Pd2+ + 2C11H90N, -+ Pd(C11H,ON3), + 2H+. EXPERIMENTAL PREPARATION OF THE REAGENT- Di-2-pyridyl ketoxime was synthesised by the method outlined in a previous publi~ation.~ A 1 per cent. solution in 95 per cent. ethanol, which is stable indefinitely, was used as the reagent. Conversion of di-2-pyridyl ketone (available from the Aldrich Chemical Co., Milwaukee, Wisconsin) into the oxime proceeds rapidly and gives a high yield.PREPARATION OF PALLADIUM SOLUTION- A stock solution was prepared by dissolving purified palladium(I1) chloride in concen- trated hydrochloric acid and diluting to 1 litre in a calibrated flask. The concentration of palladium(I1) was 1*002 mg per ml, as determined by the dimethylglyoxime method.12 'All other chemicals used were of analytical-reagent quality. RECOMMENDED PROCEDURE FOR THE DETERMINATION OF PALLADIUM- Transfer an aliquot of palladium solution, containing up to 50 mg of palladium(II), into a 250-ml beaker. Add about 2.5 ml of 40 per cent. sodium citrate (1 g) and adjust the pH to between 4 and 11. Heat the contents to about 80" C and add an excess of reagent solution (10 to 200 per cent. excess).Digest the hot solution for about 10 minutes, filter through a sintered-glass crucible of medium porosity, and wash the precipitate well with hot water. Dry it at 125" C to constant weight and weigh as Pd(C,lH,0N3)2. The gravimetric factor for palladium is 0.2116. 0 SAC and the authors.HOLLAND, BOZIC AND GERARD 491 EFFECT OF pH ON PRECIPITATION- The yellow chelate was precipitated from solutions of various pH values according to the procedure outlined, and dilute potassium hydroxide or hydrochloric acid used to make the pH adjustments. pH of solution . . . . 3.0 4.0 5.0 6-0 7.0 9.0 11.0 Palladium taken, mg . . 8-80 8.80 8-80 8.80 8.80 8.80 8-80 Palladium found, mg . . 8-82 8.79 8.80 8.79 8.81 8-83 8.76 The results indicate that the optimum pH conditions are between 3 and 11.However, because the precipitate was difficult to filter at pH 3, it is recommended that the pH be maintained above 4.0. EFFECT OF PALLADIUM CONCENTRATION- Analyses conducted on a series of different sample weights, as indicated below, showed that palladium could be successfully determined over the range of 4 to 50mg without co- precipitation of reagent. Because of the voluminous nature of the precipitate, the amount of palladium should not exceed 50mg. Palladium taken, mg . . . . 4.402 13.21 17.61 22.01 30.81 44.02 Palladium found, mg . . . . 4.395 13.19 17.60 22.03 30.83 44.06 Deviation, mg . . .. . . -0.007 -0.02 -0.01 +0.02 +0*02 +0*04 Each result is the average of six separate analyses. EFFECT OF REAGENT EXCESS- Various amounts of di-2-pyridyl ketoxime in excess were added to 13-21 mg of palladium.The results indicated that no co-precipitation occurs, even with 200 per cent. excess of reagent. EFFECT OF DIGESTION TIME AND TEMPERATURE- Recoveries of palladium for various digestion temperatures and times indicate that precipitation and filtration can be carried out at room temperature, or at elevated temperatures up to 100" C, with a brief digestion period of 5 to 10 minutes. DRYING CONDITIONS- A weighed amount of the chelate was isolated according to the procedure and dried at various oven temperatures and time periods. No significant weight change occurred when the chelate was dried for 1+ hours at temperatures between 118" and 210" C, or for I& hours at 125" C. Drying times of 1 hour, or less, resulted in slightly high results.COMPOSITION AND STRUCTURE OF THE PALLADIUM CHELATE- An aliquot of palladium solution, containing 25-05 mg of palladium(II), was transferred into a 250-ml beaker and the above procedure followed. Results of analyses of the precipitate for carbon, hydrogen and palladium and those calculated for the empirical formula, Pd(CllH,0N3) 2, are as follows- Palladium Carbon Hydrogen Percentage found . . .. . . 21.27 52.60 3.33 Percentage calculated . . . . 21.16 62.56 3.2 1 The palladium was determined gravimetrically by ignition to the metal, a few drops of formic acid being added to eliminate any palladium(I1) oxide formed. A probable structure for the chelate, based on infrared evidence reported previou~ly,~ is given below.492 HOLLAND et d.: DI-2-PYRIDYL KETOXIME, A NEW REAGENT [Analyst, VOl. 93 PRECISION AND ACCURACY- Pure anhydrous palladium chloride was dried over sulphuric acid for 5 hours and the amount of palladium determined twelve times according to the outlined procedure. The results obtained are listed below. They agree favourably with similar results obtained for dimethylglyoxime reported in a previous publication,6 in which di-2-thienyl ketoxime was used as a gravimetric reagent for palladium. Theoretical Palladi urn Relative mg mg per cent. palladium taken, found, standard deviation, 17-97 17.98 0.28 35-98 35.98 0.19 EFFECT OF DIVERSE IONS- Many foreign ions were studied to make the procedure as diversified as possible. Sodium citrate and EDTA were conveniently used as masking agents.In one series of test solutions 100 mg of a foreign ion were added to 15.03 mg of palladium and the outlined procedure followed. The recoveries gave a standard deviation of 0.02 mg for the following extraneous ions: Zn(II), Mn(II), Cu(II), Ni(II), Fe(II), Co(III), Al(III), Hg(II), Cd(II), Mg(II), Ca(II), Ba(II), Sr(II), Pb(II), Sb(V), Bi(III), As(III), Na, K, Ti(IV), U(VI), Mo(VI), Os(VIII), Ru(II1) , ammonium, oxalate, vanadate, chloride, pyrophosphate and dichromate. The ions of copper, nickel, cobalt and iron form soluble complexes with di-2-pyridyl ketoxime, and hence consume reagent. This effect was eliminated by masking these metals with 1 g of EDTA. In another series of test solutions, 100mg of the following foreign ions were added to 13.21 mg of palladium (the recoveries gave a standard deviation of 0.03 mg): Ag(I), Re(VII), Sn(IV), Te(IV), Ir(III), Zr(IV), Hf(IV), Ga(III), Se(IV), Ce(IV), Th(IV), In(III), Ta(V), Tl(I), iodide, thiourea, nitrite, nitrate, sulphite, sulphate, persulphate, carbonate, phosphate, tungstate, bromide, fluoride, perchlorate and thiocyanate.A silver complex was formed with ammonia at pH 10 to 11, and iridium was masked with 1 g of potassium thiocyanate at pH 8 to 9. The limit for rhodium was 50mg. There was no interference from 10mg of platinum in the regular procedure, and up to 50mg could be tolerated if the precipitation was carried out at room temperature. Gold interfered but was easily separated by reduction to the metal with sodium nitrite13 and filtration. Cyanide interfered severely in the procedure and must be absent.Cations were added as chlorides, nitrates or sulphates, and anions as sodium or potassium salts. Molybdenum, osmium, arsenic, rhenium and selenium were added as their oxides. DISCUSSION Di-2-pyridyl ketoxime is recommended for the gravimetric determination of palladium. The reagent has several advantages; it is stable indefinitely and is very water-soluble, thus eliminating co-precipitation, even up to a 200 per cent. excess of reagent. The ketone is commercially available and can readily be converted into the oxime. It is also possible to use the ketone directly and generate the oxime with hydroxylammonium chloride, thus allowing the precipitation of palladium from homogeneous solution. The chelate has a large molecular weight and hence a favourable gravimetric factor, which makes the reagent more sensitive than the classical reagent, dimethylglyoxime.Further, the di-2-pyridyl ketoxime procedure is much faster, producing comparable palladium recoveries in much less time. In the dimethylglyoxime method it is recommended that the precipitate be allowed to cool and stand overnight.2 The di-2-pyridyl ketoxime palladium precipitate is easy to handle during filtration, thus allowing up to 50 mg of palladium to be accurately determined over a wide pH range of between 3 and 11. There are no isomers to contend with because of the symmetrical structure of this oxime, and there are few interferences in the method. The applicability of this reagent to the determination of palladium was shown in a previous publi~ation,~ in which trace amounts of the chelate were extracted into chloroform, and the palladium subsequently determined by a spectrophotometric method.This work was supported by a grant from the National Research Council of Canada and a Province of Ontario Fellowship.August, 19681 FOR THE RAPID GRAVIMETRIC DETERMINATION OF PALLADIUM 493 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. REFERENCES Beamish, F. E., Talanta, 1966, 13, 773. Furman, N. H., Editor, “Standard Methods of Chemical Analysis,” Sixth Edition, D. Van Nostrand Company Inc., Princeton, N.J., New York, Toronto and London, 1962, Volume 1, p. 883. Voter, R. C., Banks, C. V., and Diehl, H., Analyt. Chem., 1948, 20, 652. Hayes, J. R., and Chandlee, G. C., Ind. Engng Chem. AnaZyt. Edn, 1942, 14, 491. Bark, L. S., and Griffin, D., Analyst, 1967, 92, 162. Holland, W. J., and Gerard, J., Analyt. Chem., 1966, 38, 919. Dalziel, J . A. W., and Kealey, D., Analyst, 1964, 89, 411. Holland, W. J., and Bozic, J., Analyt. Chem., 1967, 39, 109. -__ , Ibid., 1968, 40, 433. -- , Talanta, in the press. Holland, W. J., Bozic, J., and Gerard, J., Aizalytica Chim. Ada, in the press. Vogel, A. I ., “A Text-book of Quantitative Inorganic Analysis, including Elementary Instrumental Analysis,” Third Edition, Longmans, Green & Co. Ltd., London, 1961, p. 511. Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis, with Special Reference to the Analysis of Metals, Minerals and Rocks,” Second Edition, Revised by Lundell, G. E. F., Bright, H. A., and Hoffman, J. I., John Wiley and Sons Inc., New York; Chapman & Hall, Ltd., London, 1953, p. 367. Received March 15th, 1968