CHEMILUMINOMETRIC FLOW-INJECTION METHOD FOR DETERMINATION OF FREE L-MALATE IN WINE WITH CO-IMMOBILIZED MALATE-DEHYDROGENASE NADH OXIDASE

A flow-injection system with a co-immobilized malate dehydrogenase/red uced nicotineamide adenine dinucleotide (NADH) oxidase reactor and a c hemiluminometer is described for the determination of free L-malate in wine. Malate dehydrogenase and NADH oxidase were co-immobilized on po ly(vinyl alcohol) beads and packed into a stainless-steel column (5 cm x 4 mm i.d.). The hydrogen peroxide produced was detected chemilumino metrically via a luminol-hexacyanoferrate(III) reaction. The calibrati on graph was linear from 3 x 10(-7) M to 2.5 x 10(-4) M (the linear co rrelation coefficient was 0.9998); the detection limit (signal-to-nois e ratio, 3) was 8 x 10(-8) M. The sample throughput was 30 h(-1) witho ut carryover. The reactor was renewed every 2 weeks.