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

Melatonin (MT) and pyridoxine (PN) in pharmaceutical preparations for healt h-caring purposes were determined by capillary electrophoresis (CE) with el ectrochemical detection (ED). The effects of several factors such as acidit y and concentration of running buffer, separation voltage and injection tim e on CE were investigated to acquire the optimum conditions. CE was perform ed in 0.025 mol/l phosphate buffer (pH 8.3). The two compounds were separat ed and detected within 12 min. The working electrode used was a 500-mu m di ameter carbon electrode operated in a wall-jet configuration. Excellent lin earity was observed between peak current and concentration of analytes in t he range from 2.5 x 10(-6) to 1.0 x 10(-3) mol/l for MT and from 5.0 x 10(- 6) to 1.0 x 10(-3) mol/l for PN. The detection limits (S/N=3) for MT and PN were 1.3 x 10(-6) mol/l and 2.7 x 10(-6) mol/l, respectively The proposed method was successfully applied to analyze the actual samples with satisfac tory assay results. (C) 2000 Elsevier Science B.V. All rights reserved.