Pyridine was first used by WILLISI in the polarographic determination of palladium. Later, PANTANI found that the methylpyridines were also suitable and showed, by coulometric measurements, that the complexes are reduced to the meta.12. DOUGLAS AND MAGEE~ have presented a method for the determination of palladium and rhodium with pyridine, while the methylpyridines have recently been used in the determination of palladium, rhodium and osmium4.
The reduction of the pyridine complex has recently been re-investigated by PARRY AND OLDHAM~. Their results indicated that the reduction was irreversible, in contrast to earlier reports. This paper discusses some of the reduction characteristics of the pyridine, 2methyl, 3-methyl and 4-methylpyridine complexes of palladium. In particular, the capabilities of polarography and chronopotentiometry for the determination of palladium with pyridine bases are discussed. EXPERIMENTAL Eqfcij%ne?tt A Davis Differential A1660 cathode-ray polarograph was used in this investigation. The single-cell technique was used throughout and the instrument was calibrated by injecting a small current into the input sockets and measuring the deflection produced. The dropping mercury electrode had an m value of 0.50 mg set-1. Chronopotentiograms were obtained with a Beckman Electroscan 30. A IBeckman platinum electrode, type 39007, was also used as a working electrode in the chronopotentiometric experiments. The cell used in the chronopotentiometric experiments with the mercury electrode (area 1.53 ems) is shown in Fig. I. Transition times were determined by the method of DELAHAY AND RERZINSO. Transition times in this paper are the average of at least three separate values. Experiments were carried out at a temperature of 28 _I I'. A x0-2 M stock solution of palladium chloride, 8.69 -10-3 M in hydrochloric acid was used. Pyridines were purified by refluxing over molecular sieves before distillation. Analar potassium chloride served as supporting electrolyte.