Development and validation of a capillary electrophoresis method with ultraviolet detection for the determination of the related substances in a pharmaceutical compound

A capillary electrophoresis (CE) method was successfully developed to quantify the impurity profile of a new substance of pharmacological interest: LAS 35917. CE method was developed in order to separate the chloromethylated, monomethylated and hydroxylated impurities (molecules with very similar chemical structures) having the three coelution in the reversed-phase LC method initially established. Taking into account the structure of the impurities of LAS 35917, separation by conventional liquid chromatography (LC) methods would be longer and tedious than separation by CE, which is an appropriate and versatile technique giving easier and quicker methods. Among the three potential impurities mentioned of LAS 35917, two are due to the synthesis route of this drug, and the third arises from degradation. These drug-related impurities were separated using a capillary of 56 cm of effective length and 50 μm I.D., a 60 mM tetraborate buffer, at pH 9.2, and a positive voltage of 20 kV. The optimised CE method was preliminary validated with regard to specificity, linearity, limits of detection and quantitation, repeatability and solution stability. The method allows the detection and quantitation of impurities above 0.04 and 0.08% level, respectively. All three related substances were separated, detected and quantified from their parent drug in the analysis of real samples of LAS 35917, stressed or not stressed, with this simple and fast CE method.