A rapid and highly sensitive UPLC–MS/MS method using pre-column derivatization with 2-picolylamine for intravenous and percutaneous pharmacokinetics of valproic acid in rats

A rapid, highly sensitive and specific ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS/MS) for the detection of valproic acid (VPA) in rat plasma following the topical application was developed and validated. This method was carried out with pre-column derivatization using 2-picolylamine (PA) which reacts with the carboxylic acid group of VPA. The derivatization was completed in 10 min and the resulting PA-VPA derivative enabled the sensitive detection of VPA in selected reaction monitoring (SRM) mode. Sample preparation was done with simple liquid–liquid extraction and chromatographic separation was achieved within 5 min on a C18 column using a gradient elution with the mobile phase of 2 mM ammonium formate containing 0.1% formic acid and methanol. The standard curves were linear over the concentration range of 0.07–200 μg/mL with a correlation coefficient higher than 0.99. The limit of detection (LOD) and the lower limit of quantification (LLOQ) was 0.03 and 0.07 μg/mL, respectively with 100 μL of plasma sample. The intra- and inter-day precisions were measured to be below 10.7% and accuracies were within the range of 94.1–115.9%. The validated method was successfully applied to the pharmacokinetics of VPA in the rat following topical and intravenous applications.