Ion-exchange voltammetry at a surfactant-doped electrode: model of mass transfer kinetics to an anionic surface-charged electrode and its application for the sensitive determination of alkaline phosphatase

A theoretical model of mass transfer kinetics was developed for investigating the accumulation of cationic compounds at an anionic surfactant-doped screen-printed electrode. It was extended to an enzyme-generated cationic product for the indirect determination of alkaline phosphatase (AP). The model takes into account the analyte depletion, the kinetics of the ion-exchange reaction-diffusion and the kinetics of the enzymatic reaction. The relationship between the ion-exchange voltammetric anodic peak current and the enzyme incubation/accumulation time for a given concentration of AP was established and the validity of the theoretical model was verified experimentally using a new AP substrate/product couple. It was shown that the theoretical and experimental data are in agreement. The combination of the catalytic enzyme generation of the cationic product with its simultaneous preconcentration at a cation-exchanger-doped electrode allows one to envision the indirect determination of AP at femtomolar levels.