A selective ultraperformance liquid chromatographic (UPLC) method for the quantification of valproic acid and its known related impurities using ion pair reagent has been developed. The method includes reversed-phase Acquity HSS T3 column with 100？mm？×？2.1？mm i.d. and 1.7？μ particle size. The mobile phase consists of acetonitrile, 5？mM 1-hexanesulphonic acid sodium salt, flow rate is 0.6？mL/min, and UV detection is performed at 215？nm. A system suitability test (SST) was developed to govern the quality of the separation. The developed method has been validated further with respect to linearity, accuracy, precision, selectivity, LOD, LOQ, and Robustness. 1. Introduction Valproic acid is chemically known as 2-propylpentanoic acid. Chemical structures of valproic acid and its pharmacopeial-related impurities are given in Figure 1. Valproic acid (VPA) is a chemical compound that has found clinical use as an anticonvulsant and mood-stabilizing drug, primarily in the treatment of epilepsy, bipolar disorder, and less commonly, it is also used to treat migraine headaches and schizophrenia [1–4]. To our knowledge, there is no paper describing an ultraperformance liquid chromatographic (UPLC) method that allows the separation of valproic acid and its related known impurities in bulk drugs. However, there are the UPLC-MS/MS method for the simultaneous determination of valproic acid and other 21 antiepileptic drugs for the routine therapeutic drug monitoring [5]. Furthermore we have used an ion pair reagent to resolute the valproic acid and its impurities more specifically, that is 2-isopropylpentanoic acid which is a structural isomer of valproic acid. Some articles are available on isocratic HPLC methods for the determination of valproic acid [6–10]. Gas chromatographic and colorimetric methods are also available in the literature for quantification of valproic acid [11–15]. Methods for determination of valproic acid by HPLC, LC-MS, or LC-MS/MS from biological matrix have also been published [16–26]. In addition, the capillary electrophoresis methods for the determination of valproic acid in different biological samples are also available [27–30]. Applying the above methods for quantification of impurities in a bulk valproic acid sample gives poor separation. Hence, the objective of this study is to develop a more selective LC method for the analysis of valproic acid and its related impurities. Besides this, it is accurate, precise, selective, robust, and linear with a reasonable analysis time. Furthermore, the developed method is applicable for the analysis of
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