Electrochemistry of platinum complexes. Part I. Polarographic reduction mechanism with reference to electrochemical detection

The polarographic behaviour of cis-diamminedichloroplatinum(II) (cisplatin) and eight analogue diammineplatinum complexes was studied. In the potential region 0 to -1 V (vs. Ag/AgCl), an adsorption facilitated current was observed for cisplatin which decreased after the potential of zero charge due to decreased adsorption. Adsorption of cisplatin obeyed a linear adsorption isotherm. After the minimum at -1 V, a second, irreversible wave reached a diffusion-controlled plateau at -1.6 V. The reduction of trans-diamminedichloroplatinum(II), (1,1-bis(aminomethyl)cyclohexane)dichloroplatinum(II) (= TNO-1) and the hydrolysed derivatives of cisplatin and TNO-1 reached the plateau value of the diffusion-limited current between 0 and -1 V. At potentials negative to about -1.5 V, catalytic H⁺-reduction currents were observed for all complexes except cis-dichloro-trans-dihydroxo-cis-bis(isopropylamine)platinum(IV) (= iproplatin, the only platinum(IV) complex investigated). In 0.1 M ammonium chloride solutions, these catalytic currents were increased and appeared at less negative potentials for all the platinum complexes, including iproplatin. A linear calibration plot was obtained for cisplatin up to 1.4×10^-4 M. It is anticipated that differential pulse polarographic detection in HPLC effluents containing ammonium ions will provide a sensitive analytical method for a large range of ammineplatinum complexes, including their metabolites.