Potentiometric determination of alkaline phosphatase in blood serum using a hordenine-sensitive membrane electrode

A hordenine-sensitive membrane electrode was constructed and applied for the determination of alkaline phosphatase (ALP) in blood serum. The method is based on the detection of hordenine formed by the enzymatic reaction of 4-O-phosphonohordenine (hordenine phosphate) with ALP. The hordenine electrode was constructed by incorporating sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate as an ion-exchanger and 2-fluoro-2-nitrodiphenyl ether as a solvent mediator in a poly(vinyl chloride) membrane matrix. This is the first attempt to apply an ion-selective electrode for the assay of serum ALP. The results were compared with those obtained by colorimetry using phenyl phosphate as a substrate.