Simultaneous determination of alkyl mesilates and alkyl besilates in finished drug products by direct injection GC/MS

We report a specific, fast and feasible method for the simultaneous determination of methyl mesilate (MMS), ethyl mesilate (EMS), isopropyl mesilate (IMS), methyl besilate (MBS) and ethyl besilate (EBS) in finished drug products by GC/MS. Sample preparation was carried out by liquid extraction. The analytes were directly injected into the chromatographic system and quantified with the internal standard method using methyl tosylate (MTS) as internal standard (ISTD). The method gives excellent sensitivity for all the alkyl and aryl esters at typical target analyte level, according to the acceptance criteria that are described in the Guideline on the Limits of Genotoxic Impurities which has been issued in 2007 by the European Medicines Agency (EMA). The average recovery for methanesulfonic acid esters (mesilates) was not lower than 71 %, for benzenesulfonic acid esters (besilates) not lower than 94%. A linear range with R2 ⩾ 0.9998 has been established for concentrations between 0.01 and 1.33 μg/ml. Validation of the method was carried out on a sample matrix containing MMS, EMS, IMS, MBS and EBS at relevant levels and was further confirmed on finished products containing APIs as mesilate salts (Bromocriptine mesilate, Doxazosin mesilate).