ENZYME IMMUNOASSAYS USING FLOW INJECTION ANALYSIS WITH ELECTROCHEMICAL DETECTION

Abstract

The utility of FIAEC for enzyme immunoassaysof low detection limit can be constrained bythe existence of a nonfaradaic capacitance current that records with the analytical faradaic signal. Since the magnitudeof this unwanted signal diminishes with smaller potential, conditions can be found where the interference becomes unimportant. This was done here by developing p-aminopheny] phosphate as a substrate for alkaline phosphatase, which yields p-aminophenol as product, oxidizable at between +100 and +300 mV. Additional advantageis gained by matching the compositions of the sample and mobile phase solutions. The useof p-aminopheny] phosphate as a substratefor electrochemical enzyme immunoassay was demonstrated by sensitive assays for theophylline, IgG and alpha-fetoprotein.