Determination of melatonin and pyridoxine in pharmaceutical preparations for health-caring purposes by capillary electrophoresis with electrochemical detection

Melatonin (MT) and pyridoxine (PN) in pharmaceutical preparations for health-caring purposes were determined by capillary electrophoresis (CE) with electrochemical detection (ED). The effects of several factors such as acidity and concentration of running buffer, separation voltage and injection time on CE were investigated to acquire the optimum conditions. CE was performed in 0.025 mol/l phosphate buffer (pH 8.3). The two compounds were separated and detected within 12 min. The working electrode used was a 500-μm diameter carbon electrode operated in a wall-jet configuration. Excellent linearity was observed between peak current and concentration of analytes in the range from 2.5 × 10−6 to 1.0 × 10−3 mol/l for MT and from 5.0 × 10−6 to 1.0 × 10−3 mol/l for PN. The detection limits (S/N = 3) for MT and PN were 1.3 × 10−6 mol/l and 2.7 × 10−6 mol/l, respectively. The proposed method was successfully applied to analyze the actual samples with satisfactory assay results.