AN APOENZYME THERMISTOR MICROANALYSIS FOR ZINC(II) IONS WITH USE OF AN IMMOBILIZED ALKALINE-PHOSPHATASE REACTOR IN A FLOW SYSTEM

Calorimetric microdetermination of zinc(II) ions with use of an apoenzyme thermistor in a flow stream is proposed. Alkaline phosphatase as the selective recognition element was immobilized onto oxirane-acrylic beads (Eupergit-C) and packed into a small polymer column. The flow-injection biosensing system was assembled with the immobilized enzyme reactor and a thermistor device for monitoring the enzyme activity. Zinc(II) ions were calorimetrically determined in the range 0.01-1.0 mM for 0.5 ml samples through their activation of the immobilized metal-free alkaline phosphatase (apoenzyme) reactor. The activity of the reactor was assessed by injecting 0.1 ml of 100 mM p-nitrophenyl phosphate solution. Regeneration of the reactor was performed by pumping 20 mM 2,6-pyridine dicarboxylate (pH 6.0) between successive samples. The system could be repeatedly used at least 120 times during 2 months of operation.