Fast determination of diphenhydramine, pyridoxine, and 8-chlorotheophylline by capillary electrophoresis with capacitively coupled contactless conductivity detection

Abstract

This work reports a new and fast method for the simultaneous determination of diphenhydramine (DIP), pyridoxine (PYR), and 8-chlorotheophylline (CTP) by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D). Samples containing DIP as the cation and both PYR and CTP as anions were analysed simultaneously in a single run (in less than 3 minutes). The separation by CE-C⁴D was achieved on a fused silica capillary (50 cm length – 40 cm effective, 50 μm i.d.) using an optimized background electrolyte (BGE) composed of 20 mmol L⁻¹ boric acid + NaOH (pH 9.0). Detection limits were 0.6, 1.3 and 1.3 μmol L⁻¹ for DIP, PYR and CTP, respectively. The proposed CE-C⁴D method is inexpensive, simple, fast (20 injections per h), environmentally friendly (minimal waste generation) and accurate (recovery values between 98 and 100%). The results obtained by the CE-C⁴D method were statistically similar to those obtained by HPLC (95% confidence level).