Amperometric detection of purine nucleotides utilizing immobilized enzyme reactors and on‐line amplification by substrate recycling

Flow‐injection systems with an immobilized enzyme reactor are proposed for the amperometric detection of purine nucleotides. One system studied is based on the combined use of an alkaline phosphatase (AlP) immobilized reactor and a purine nucleoside phosphorylase (PNP)‐xanthine oxidase (XO) coimmobilized reactor, which responds to purine nucleotides With high selectivity. Another system with a coimmobilized AlP‐PNP‐XO reactor gives responses amplified by substrate recycling. When carrier solution was pumped at a flow rate of 0.5 mL min−1, purine nucleotides could be detected with 9 to 26 times the sensitivity in the latter system compared with the former, with the detection limit of 4 × 10−8 M for a 20 μL injection.