HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF ASCORBIC-ACID IN SOFT DRINKS AND APPLE JUICE USING TRIS(2,2'-BIPYRIDINE)RUTHENIUM(II) ELECTROCHEMILUMINESCENCE

The electrochemiluminescence of tris(2,2'-bipyridine)ruthenium(II) [Ru(bpy)(3)(2+)] was applied to high-performance liquid chromatographic determination of ascorbic acid. Ascorbic acid was separated by a C-18 reversed-phase column with a mobile phase containing 15 mM NaH2PO4-K2HPO4 (pH 6.5). The eluted ascorbic acid was mixed with 0.5 mM Ru(bpy)(3)(2+) within the flow tube. The solution then passed through a thin layer flow cell equipped with a glassy carbon electrode and both ascorbic acid and Ru(bpy)(3)(2+) were oxidized at +1.5 V (vs. Ag/AgCl). The reaction of electrolytically formed Ru(bpy)(3)(3+) with oxidized ascorbic acid emitted light. The detection limit was 10 pmol for ascorbic acid at an S/N ratio of 3, and the linear calibration range was 0.06 - 80 nmol. The method was successfully applied to determination of ascorbic acid in soft drinks and apple juice.