Separation of theophylline, caffeine and related drugs by normal-phase capillary electrochromatography

A capillary electrochromatography (CEC) method has been developed for the s eparation of theophylline, caffeine and five related drugs on a normal-phas e column with UV or photodiode array detection, Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable or ganic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris ( 52:40:8, pH 8), with an efficiency of 63 000 theoretical plates per meter a t room temperature. Detection limits are typically at the low mu g/mL level . The developed method is simple to use and it gives acceptable day-to-day reproducibility.