Indirect laser-induced fluorescence detection of valproic acid in human serum by capillary electrophoresis

Abstract

A capillary electrophoresis (CE) method with indirect laser-induced fluorescence detection for the analysis of valproic acid in human serum has been explored. The buffer system was optimized with 2.5 mM borate-phosphate at pH 8.4; fluorescein sodium was used to generate background signal at a concentration of 6 μM. Hexanoic acid was selected as internal standard. Serum sample was deproteinized by acetonitrile. Analysis was performed by direct injection of the supernatant. CE separation was carried out at 30 kV and the total analysis time was less than 15 min, including sample treatment and electrophoresis time. No interference from other common anticonvulsant drugs occurred under the experimental conditions used. The interference of human serum matrix was reduced by using a high ratio of acetonitrile to serum (minimum 5:1) for deproteinization. Interference of ionic components in serum could occur, depending on the sample source. The linear range of concentrations for standard drug was between 4.5-144.0 μg/mL (r= 0.9947). The limit of detection was 0.9 μg/mL at S/N ≥ 3; the limit of quantitation at S/N ≥ 20 was 3 μg/mL. The recoveries of valproic acid spiked into serum were 69.2% and 60.2% for concentration levels of 90 and 54 μg/mL, respectively. This CE method was shown to be successful in the analysis of valproic acid in standard solutions. However, interference from the matrix was observed in the analysis of this compound in serum samples. Additional work should be done to develop a highly selective sample preparation technique.