Catalytic Polarographic Determination of Trace Amount of Rhodium(Ⅲ)

A stable complex between rhodium and the new reagent, 2-(5-iodo-2-pyridylazo)-5-dimethylaminoaniline (5-I-PADMA) was formed in 1 mol·L-1 acetate buffer solution of pH 4.8, and a sensitive catalytic polarographic wave of this complex was observed at the potential of -1.01 V (vs.SCE) in 3 mol·L-1 HClO4 medium. Based on this fact, a method of catalytic polarography for the determination of trace amount of Rh(Ⅲ) was proposed. Linear relationship was kept between values of 1st derivative of peak current and mass concentration of Rh(Ⅲ) in the range of 40.0-400 ng·L-1 with detection limit (3s/k) of 14.2 ng·L-1. It was found that the polarographic wave was a catalytic hydrogen wave, and the electrode process was an irreversible reduction process, with number of electron transfer of 1. The proposed method was used in the analysis of samples of Rh-C catalyst and a CRM of GBW 07198, giving values of recovery and RSD (n=6) of 100% and 0.70% for the sample of Rh-C catalyst, and 101% and 1.8% for the CRM of GBW 07198.