Analysis of ethambutol and methoxyphenamine by capillary electrophoresis with electrochemiluminescence detection

A capillary electrophoresis (CE) coupled with electrochemiluminescence (ECL) detection method for the analysis of ethambutol (EB) and methoxyphenamine (MP) has been investigated. Complete separation of EB and MP was achieved in 8 min using a background electrolyte of 20 mM sodium phosphate at pH 10.0 and a separation voltage of 9 kV. ECL detection was performed with an indium/tin oxide (ITO) working electrode biased at 1.4 V (versus a Pt wire reference) in a 200 mM sodium phosphate buffer (pH 8.0) containing 3.5 mM Ru(bpy)32+ (where bpy = 2,2′-bipyridyl). Linear correlation (r ≥ 0.993) between ECL intensity and drug concentration was obtained in the range 2–50 ng/ml. The limits of detection (LODs) for EB and MP in water were 1.0 and 0.9 ng/ml, respectively. The relative standard deviation values on peak size (10 ng/ml level) and migration time for the two drugs were in the ranges 5–8 and 0.2–0.7% (n = 7), respectively. Applicability of the CE–ECL method to the analysis of human plasma spiked with EB and MP was examined. The LODs for EB and MP in plasma were 0.4 and 0.3 μg/ml, respectively.