Sensitive CE–MS analysis of potentially genotoxic alkylation compounds using derivatization and electrokinetic injection

• Analysis of potentially genotoxic impurities in active pharmaceutical ingredients.
• CZE separation of derivatized alkylating PGI prior to on line MS detection.
• CE–MS detection limits at 0.1–0.4 mg kg−1 API; ∼μg L−1 level in sample solution.

A CE–MS method has been developed to detect trace levels of potentially genotoxic alkyl halides. After derivatization of the target components with 4-dimethylaminopyridine (DMAP) or butyl 1-(pyridinyl-4yl) piperidine 4-carboxylate (BPPC), the natively positively charged derivatives are pre-concentrated by applying electrokinetic injection and separated by a highly efficient CZE method using a background electrolyte (BGE) consisting of 100 mM of TRIS adjusted to pH 2.5 with phosphoric acid. Using a sheath liquid interface, subsequent MS detection allows highly specific and sensitive analysis of alkyl halides.Conditions for electrokinetic injection were optimized to allow selective and effective injection. Injection of samples with low water content at 10 kV for 150 s using a high concentration of buffer in the BGE resulted in optimum sample stacking during injection and a highly efficient CE separation. At the sample pH applied, neutral and negatively charged components are shown to be selectively discarded, resulting in injection of positively charged ions only. The sample matrix influences the efficiency of the injection, but when using an internal standard, reproducibilities better than 10% RSD are obtained. Relative recoveries of the derivatives spiked to different types of model API between 85 and 115% demonstrate that the method can be applied for quantitative analysis. Detection limits of lower than 1 mg kg−1 for the tested alkyl halides obtained in CE–MS at least equal the sensitivity obtained in LC–MS. The CE–MS method is a valuable alternative for the LC–MS method used for analysis of alkylation compounds.

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