Determination of branched-chain L-amino acids by flow-injection analysis with co-immobilized leucine dehydrogenase/NADH oxidase and chemiluminescence detection

A method for the determination of branched-chain L-amino acids in plasma is described. Leucine dehydrogenase and NADH oxidase were co-immobilized on aminated poly(vinyl alcohol) beads and incorporated in a flow-injection system with chemiluminescence detection. 20 μ1 sample solution was injected into the system. The hydrogen peroxide produced was detected chemiluminometrically via a luminol-hexacyanoferrate(III) reaction. The calibration graph was linear for 5 × 10−7-6 × 10−4 M; the detection limit (signal-to-noise ratio = 3) was 3 × 10−7 M and the sample throughput was 15 h−1 without carryover.