Simultaneous determination of cysteine, ascorbic acid and uric acid by capillary electrophoresis with electrochemiluminescence

Capillary electrophoresis was applied for the separation of three charged compounds, cysteine (Cys), ascorbic acid (AA) and uric acid (UA). These compounds were then simultaneously determined using an electrochemiluminescence (ECL) system of tris(2,2′-bipyridyl) ruthenium (II) in the presence of tri-n-propylamine. The presence of Cys in the solution enhanced ECL intensities while the presence of AA and UA inhibited ECL intensities. Experimental conditions for their separation and detections were optimized. The optimal conditions were: an ECL detection potential of 1.2 V; a 50 mM pH 7.1 phosphate buffer in the detection cell containing 2.5 mM Ru(bpy)32+ and 200 μM TrPA; a separation voltage of 15 kV; a 10 mM pH 7.1 phosphate buffer as the running buffer solution; an injection voltage of 12 kV, and an injection time of 9 s. Under these conditions, the ECL intensities were linear with the concentrations of three compounds over the ranges from 2.0 μM to 100 μM. The detection limits (S/N = 3) for Cys, AA, and UA were 0.5, 0.4, and 0.02 μM, respectively. The relative standard deviations of their ECL intensities in the presence of 50 μM Cys, AA, and UA were 2.9%, 3.0%, and 2.9%, respectively. The method was applied successfully for monitoring three compounds in the human serum and urine samples.