POSTCOLUMN IMMOBILIZED TYROSINASE REACTOR FOR DETERMINATION OF L-3,4-DIHYDROXYPHENYLALANINE AND L-TYROSINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH FLUORESCENCE DETECTION

Immobilized tyrosinase was used as a reactor in a liquid chromatograph ic system for the selective detection Of L-3,4-dihydroxyphenylalanine (L-DOPA) and L-tyrosine. Tyrosinase was immobilized on controlled-pore glass beads. The compounds were separated on an ODS column with 0.1 M phosphate buffer (pH 7.2) as mobile phase. The fluorescent dihydroxyi ndol formed was detected at 490 nm (excitation at 360 nm). For L-DOPA the linear working range was 0.005-15 muM, with a detection limit of 1 nM (6 pg in a 30-mul injection); for L-tyrosine the range was 0.01-30 muM, with a detection limit of 5 nM (27 pg in a 30-mul injection). Th e reactor was stable for at least 2400 injections. Its usefulness for simultaneous determination Of L-DOPA and L-tyrosine in serum is descri bed.