Quantitation of acetaminophen and salicylic acid in plasma using capillary electrophoresis without sample pretreatment improvement of precision

Capillary electrophoresis has become one of the most attractive techniques in the analysis of biological samples. Pharmaceuticals in human plasma can easily be determined on uncoated fused-silica capillaries without any sample pretreatment. Intra- and inter-day precision values of about 1–2% R.S.D. ( n=20) and 2–3% R.S.D. ( n>80) respectively are obtained using a sodium dodecyl sulfate-containing borate buffer, pH 10 and acetonitrile as a between-run rinsing reagent. This method is highly robust, no breakdowns of the current or capillary blockings were observed for several weeks. The general applicability is demonstrated for several model drugs. The effectiveness of other rinsing procedures including enzyme-containing solutions, different organic solvents and hydrofluoric acid is discussed.