Analyst, June, 1968, Vol. 93, pp. 371-374 37 1 A Radiometric Procedure for the Micro Determination of Palladium and Iodide with Iodine131 BY MRS. USHA PURKAYASTHA AND H. P. MAITY (Nuclear Chemistry Division, Saha Institute of Nuclear Physics, 92 Acharya Prafulla Chandva Road, Calcutta, 9) A method is described for the micro determination of palladium and iodide in which the radioisotope iodine-131 is used as a tracer. The principle of the method depends on the formation of labelled palladium(I1) iodide by the addition of an excess of a solution of potassium iodide containing iodine-131 to the palladium, the palladium(I1) iodide being then carried by zirconium hydrogen orthophosphate, Zr(HPO,),, formed in the solution. From the loss of iodine-131 by the solution, the amount of palladium can be determined.By using the same principle, iodide can be determined if a known amount of palladium is added. The adsorption of palladium(I1) iodide by zirconium hydrogen orthophosphate has been found to be selective. Amounts of palladium in the range 4 x 10-8 to 2 x lO-'g have been determined so far, and errors are always within statistical fluctuations in activity measurements. The effect of the presence of some foreign ions has also been studied. The method is simple and can be completed within 30 minutes. THE determination of iodide as palladium(I1) iodide is well kn0wn.l Palladium is usually determined with dimethylglyoxime. An attempt has been made to determine palladium as palladium(I1) iodide by using iodine-131 as a radioactive indicator. The basis of the method is as follows.An excess of labelled potassium iodide solution is added to the palladium solution and the palladium(I1) iodide formed is carried with zirconium hydrogen orthophosphate. The radioactivity of the iodine left in solution is then measured. From the loss of radioactive iodine the amount of palladium can be calculated, assuming that all of the iodide is carried in the form of palladium(I1) iodide. By the same principle, micro amounts of iodide can be determined if a known weight of palladium, which is insufficient to combine with all of the iodide, is added after the addition of the tracer iodide. EXPERIMENTAL The canier-free iodine-131 used in this investigation was obtained from the Atomic Energy Establishment Trombay. The chemical reagents used, viz., palladium(I1) chloride, potassium iodide, zirconium nitrate and acids, were all of analytical-reagent quality. The procedure adopted in a typical determination is described below. A solution of carrier-free iodine-131 was thoroughly mixed with a solution containing a suitable amount of potassium iodide. A known volume of the mixed labelled solution containing two to four times the theoretical amount of iodide, as required by the equation was mixed with the solution of the palladium to be determined and a solution of zirconium nitrate, containing 0.5 to 1.0 mg of zirconium, then added. Orthophosphoric acid, equivalent to about ten times that required by the formula Zr(HPO,),, was added, dropwise, and the palladium( 11) iodide carried by the zirconium hydrogen orthophosphate formed.The mixture was thoroughly stirred and gently warmed until coagulation occurred. The volume of the solution at this stage was 12 to 14 ml, and the solution about 0.5 N with respect to sulphuric acid. It was then transferred into a 25-ml calibrated flask and the volume made up to the OSAC and the authors Pd2+ + 2KI -+ PdI2,372 PURKAYASTHA AND MAITY: A RADIOMETRIC PROCEDURE FOR THE MICRO [Artalyst, Vol. 93 mark. An aliquot was removed by pipette, with a filter-paper cap at its tip, and its activity measured with a liquid counter. From the loss of iodine-131 from the solution, the amount of palladium precipitated was calculated, assuming that zirconium hydrogen orthophosphate carries 100 per cent. of the insoluble iodide.For the determination of iodide, a solution containing the unknown iodide was thoroughly mixed, in a beaker, with carrier-free iodine-131. A solution containing palladium(I1) chloride, which was insufficient to combine with all of the iodide, was added, and the remaining operations were as previously described. TABLE I MICRO DETERMINATION OF PALLADIUM AND IODIDE WITH IODINE-131 Experiment No. 1 2 3 4 6 6 7 8 9 10 11 12 *13 14 15 16 17 *18 19 20 21 *22 23 *24 25 26 27 *28 29 30 *31 32 * 33 Experiment Nos. 1 to 3 4 and 5 6 to 33 14 to 18 19 to 24 25 to 28 29 to 31 32 and 33 Palladium taken, mg 4.55 2.28 1-14 0.100 0~0100 0~0100 0.00455 0.00273 0.001 14 0.000465 0.000228 0.000228 0.0001 14 0.001 14 0.001 14 0.001 14 0.00 1 14 0.00114 0-001 14 0-00114 0.001 14 0.001 14 2-28 2-28 0.001 14 0.00114 0-00114 0.00114 0.0 100 0~0100 0~0100 0~0100 0~0100 Palladium found, mg 4.67 2.2 1 1.1 1 0.0986 0.0101 0~0101 0.00455 0.00269 0~00110 0.000438 0.000223 0.000219 0.0000857 0.00113 0.001 11 0.001 11 0.00115 0.00 106 0.00115 0.00115 0.00112 0.000982 2.211 1.98 0.001 16 0.001 12 0.00115 0*000953 0.00973 0.00988 0.00890 0-00979 0.00880 Iodine, added as potassium iodide, mg 24.4 13.7 6-84 0.760 0.0760 0.0760 0.0367 0.0220 0.01 10 0.00367 0.00183 0.00183 0.001 10 0.01 10 0.0110 0.01 10 0.0110 0.0110 0~0110 0.01 10 0.0110 0.0110 13.7 13.7 0.0110 0.01 10 0.01 10 0.01 10 0.0760 0.0760 0-0760 0.0760 0.0760 Iodine found, mg 23.8 14-1 7-05 0.773 0.0758 0.0757 0.0367 0.0223 0.01 1 0.00381 0.00187 0~00190 0.00146 0.01 11 0.01 13 0.01 13 0.0109 0.0118 0.0109 0.0109 0.01 12 0-0128 14.1 15.7 0-0108 0.01 12 0.0109 0-0131 0.0783 0.0771 0.0854 0-0778 0.0865 Standard deviations of activity measurements , per cent.f 2-7 f3.1 f3.1 f2.0 f0.6 f 0.6 f 0-5 f 1-7 f 3.3 f 4.0 f 2-2 & 3.9 f3-6 f 1-3 f2.7 f 2.6 f 1.2 f 3.2 *1a1 f 1-4 f 1.7 f3-1 f 3.0 54.1 f 2.2 f 2.2 f 1.2 f 3.4 f 3.2 f 1.6 f 3.7 f2.7 k4.1 No carrier used. Amount of zirconium (as zirconium nitrate) used was 0.5 mg. Amount of zirconium (as zirconium nitrate) used was 1.0 mg. Amounts of nickel present were 0.011, 0-221, 0.554, 0-831 and 1-108 mg. Amounts of platinum present were 0.004, 0.008, 0.015, 0.023, 29.98 and 39-98 mg. Amounts of gold present were 0.0025, 0.005, 0.012 and 0.019 mg. Amounts of chlorine present were 2-20. 2.29 and 2-47 mg.Amounts of bromide present were 0-37 and 0-74 mg. * These results indicate that chemical errors are far greater than those caused by standard deviations in activity measurements. In these determinations, both palladium and iodide were calculated from the known iodine activity left in solution. Palladium was determined from knowledge of the amount of iodide added as potassium iodide, and the iodide determined from knowledge of the amount of palladium chloride added. It is evident from Table I that the errors in the determinationJune, 19681 DETERMINATION OF PALLADIUM AND IODIDE WITH IODINE-131 373 of palladium and iodide are equal in magnitude, but opposite in sign, because the values for both have been calculated from the same iodine activity left in solution in any operation.For the determination of palladium or iodide in the presence of foreign ions, a solution containing palladium or iodide was thoroughly mixed with the solution of the foreign ion and the palladium or iodide determined as already described, except that in the presence of gold and platinum, sodium sulphite (about 0.2g) was added to keep the medium in a reducing condition. To correct for any error caused by adsorption of iodide ions, a blank experiment was carried out without palladium, and this served as a standard for comparison. Experiments were also carried out to study the carrying of micro concentrations of various iodides on zirconium hydrogen orthophosphate (see Table 11). All of the results recorded in Tables I, I1 and I11 were obtained under the experimental conditions described above.TABLE I1 RESULTS WITH ZIRCONIUM HYDROGEN ORTHOPHOSPHATE AS A CARRIER OF VARIOUS IODIDES IN MICRO CONCENTRATION, WITH IODINE-131 AS A RADIOACTIVE INDICATOR Cations Iodine, added as Zirconium, contained in Uptake, Cations taken, potassium iodide, zirconium nitrate, per cent. x 10-6g x 10-6g mg Palladium . - .. 1.0 7.6 1.0 96.0 10.0 76.0 1.0 100.0 100.0 760.0 1.0 100.0 Silver .. .. 1.18 13.7 0.5 100.0 11.8 27.0 0.5 100.0 118.0 274.0 1.0 100.0 Thallium(1) . . .. 1.2 6.8 0.5 0.0 12.0 15.2 0.5 0.0 123.0 152.4 1.0 0.0 Copper(1) . . .. 1.0 5.4 0.5 0.0 10.5 54.8 0.5 0-0 105.0 648.0 1.0 0.0 Lead .. .. .. 1.1 2.7 0.6 0.0 11.5 27.4 0.5 0.0 115.0 274.0 1.0 0.0 Mercury(1) . . .. 1.3 1.5 0.5 0.0 13.0 15.2 0.5 0.0 131.0 152.0 1.0 0.0 Mercury(I1) .. . . 118.0 274.0 1.0 0.0 Cadmium .. .. 1.4 7.6 0.5 0.0 14.0 76.0 0.6 0.0 140.0 760.0 1.0 0.0 DISCUSSION Table I11 shows that the extent of adsorption of iodide ion, in a carrier-free state at a limited concentration, on zirconium hydrogen orthophosphate is negligibly small. Zirconium hydrogen orthophosphate takes up an appreciable amount of iodine activity in the presence of palladium. Table I shows that the iodide is carried as palladium(I1) iodide. Although TABLE I11 ADSORPTION OF VARYING AMOUNTS OF IODIDE IONS ON DIFFERENT AMOUNTS OF ZIRCONIUM HYDROGEN ORTHOPHOSPHATE IN 0-5 N ACID Zirconium taken, mg 0.5 0.5 0.5 0-5 1.0 Iodine, added as potassium iodide, mg 0.00 (without carrier) 0.0076 0.076 0.76 7.60 Iodide ion adsorbed, per cent.* 1.2 1-1 1.8 2.0 1.5 * Although the extent of adsorption is negligibly small, the blanks prepared, as mentioned in the Discussion, under identical conditions were used to give greater accuracy.374 PURKAYASTHA AND MAITY the adsorption of free iodide ion on zirconium hydrogen orthophosphate was negligibly small, blanks were made under identical conditions, so that errors caused by adsorption could be rendered insignificant (see Table 111).In Table I, typical results for the micro determination of palladium with iodine-131 are given, from which it is evident that palladium in the range 4 x to 2 x g can be determined with a fair degree of accuracy. It may be further observed that 2 x 10-6g of iodide can also be determined with the same degree of accuracy. Zirconium hydrogen orthophosphate can therefore be regarded as a reliable carrier in the system under investigation.The detemination of palladium has also been carried out in the presence of some inter- fering elements. It was found that it could be determined in the presence of about 750 times its weight of nickel and about twelve times its weight of gold and platinum, the latter metals being taken as their complex chlorides. It was also found that iodide could be determined in the presence of thirty times its weight of chlorine and five times its weight of bromine. The results in Table I1 show that only silver and palladium(I1) iodide are taken up quantitatively by zirconium hydrogen orthophosphate. In the presence of thallium(I), copper( I) , mercury( I), mercury( 11) , cadmium and lead, the recovery of palladium( 11) iodide was low, so that the determination of palladium in the presence of these elements was not successful.Palladium(I1) iodide probably formed complexes with the iodides of these metals. Adsorption of silver iodide on zirconium hydrogen orthophosphate has been re- ported in an earlier paper.2 It is of interest to note that silver and iodide can be determined in the presence of most of the iodides mentioned above by using zirconium hydrogen ortho- phosphate as a ~arrier.~ It will not be out of place to mention that cadmium is the only element in the group that interferes in the determination of silver by the m e t h ~ d . ~ In the present study, we observed that palladium(I1) iodide is adsorbed on zirconium hydrogen orthophosphate. The selective nature of this adsorption, which may be caused by anomalous mixed crystal formation, requires further study for its clarification. It is shown by experiment that the concentrations of palladium and iodide that can be determined are lower than 2 x 10-8 and 2 x lO-7g per ml, respectively. This method has various advantages over the classical procedures. It does not require more than half an hour to complete a full set of determinations ; filtration, washing and weighing are not required; and solubility factors, the use of which is necessary in radiometric analysis, are dispensed with by the application of a carrier. The authors express their thanks to Professor B. C . Purkayastha for his help and valuable suggestions. REFERENCES 1. 2. 3. Furman, N. H., Editor, “Standard Methods of Chemical Analysis,” Volume I, Sixth Edition, D. Van Nostrand Company Inc., Princeton, New York, Toronto and London, 1962, p. 616. Purkayastha, B. C., and Pai Verneker, V. R., J . Indian Chem. SOL, 1967, 31, 487. Purkayastha. Usha, and Maity, H. P., Indian J . AppZ. Chem., 1968, 31, in the press. First received August 22nd, 1966 Amended December 28th, 1967