Exploiting ion-pair formation for the enhancement of electroanalytical determination of pyridoxine (B6) onto polyurethane-graphite electrodes

The present study reports some aspects of ion-pair formation between pyridoxine and dodecyl sulphate under suitable conditions of pH, and its application with analytical purposes. Electrochemical behavior of the analite onto a graphite-polyurethane electrode was assessed by both cyclic and square-wave voltammetries under different conditions (pH from 1.2 to 13.0, with and without surfactant), aiming to study its mechanisms and to define best parameters for such determination exploiting the association of electroanalytical variables and ion-pair formation; besides these, electrochemical impedance spectroscopy was also applied to evaluate ion-pair formation and its influence on interfacial fenomena. Best conditions were reach by square-wave voltammetry in pH 4.2 acetate buffer sweeping from + 0.7 to + 1.2 V (vs. Ag|AgCl_sat) in pulses of 50 mV amplitude and 10 mV step, in a frequency of 10 Hz. The concentration of sodium dodecyl sulphate was optimized being the optimal value a constant submicelar concentration of 3 mmol L^-1. Under such conditions a linear dynamic range from 2 to 18 μmol L^-1 was observed, providing faster, more selective and sensitive system. Interference studies were also carried out showing no relevant influence of thiamine, riboflavine and nicotinamide over the analysis of pyridoxine. The system was successfully applied to commercial parenteral samples containing thiamine and pyridoxine as purchased, without further treatment.