Alkaline phosphatase assay using a redox procationic labeled substrate and a renewable Nafion‐loaded carbon paste electrode

The indirect electrochemical determination of alkaline phosphatase was achieved with a detection limit of 2 Ul−1 at a fresh surface of a renewable Nafion‐loaded carbon paste electrode, without preconditioning. [N‐ferrocenoyl]‐4‐aminophenyl phosphate was used as substrate and the enzyme reaction proceeded for 15 min in Tris buffer at pH 9.0. [N‐ferrocenoyl]‐4‐aminophenol was thus generated, which was further preconcentrated at the modified carbon paste electrode during a 5 min accumulation step in neutral medium. A potential of 0.35 V was applied during this step, and so the substituted phenol was irreversibly entrapped as a ferrocenium salt within Nafion before being detected by square wave voltammetry.