Polarographic and Voltammetric Determination of meso-Tetrakis(4-sulfonatophenyl)porphyrin Tetrasodium Salt at Mercury Electrodes

The electrochemical behavior of meso-tetrakis(4-sulfonatophenyl) porphyrin tetrasodium salt (TPPS4) was investigated in aqueous media of BR buffer in pH range 2-12. Modern electroanalytical methods, i.e DC tast polarography (DCTP) and differential pulse polarography (both at a dropping mercury electrode), differential pulse voltammetry, adsorptive stripping voltammetry, and cyclic voltammetry (all at a hanging mercury drop electrode) were used for this purpose. TPPS4 gives three cathodic signals for pH 2 - 12, first of them corresponding to a two electron quasireversible process. From these signals, the first two are suitable for the determination of TPPS4 using both polarographic methods with limit of determination about 2·10-6 mol L-1 in BR buffer, pH 10. At concentration higher than 3·10-6 mol L-1, the calibration curve of the first signal deviates from the linear course due to formation of aggregates of TPPS4 in solution. The lowest limit of determination, 5.1·10-7 mol L-1 was achieved by AdSV due to strong adsorption of TPPS4 at the electrode surface. However, for concentrations higher than 1·10-6 mol L-1, the strong adsorption prevents the use of HMDE for voltammetric measurements conducted at low scan rates due to deformation of voltammetric curves and non-linearity of calibration dependences. On the other hand, at higher scan rates used in CV the linear dynamic range for voltammetric determination of TPPS4 is 4·10-7 - 1·10-5 mol L-1.