An LC-MS/MS based candidate reference method for the quantification of carbamazepine in human serum

A validated LC-MS/MS-based candidate reference measurement procedure for the quantification of carbamazepine is presented in order to be used for standardization and harmonization of routine assays applied for therapeutic drug monitoring. Sample preparation was based on protein precipitation using acetonitrile followed by sample dilution. Since the previously listed certified reference material (CRM) SRM 1599 (anticonvulsant drug level assay standard) is no longer available, an ISO certified calibration material was used in this assay. As internal standards deuterated analyte congeners were applied. The method allows the measurement of carbamazepine, carbamazepine-10,11-epoxide and 10-hydroxy-10,11-dihydrocarbamazepine in the concentration range of 0.1 to 22.0 μg/ml with LODs and LOQs of < 0.1 μg/ml and 0.1 μg/ml, respectively. Comparative measurement of 105 native patient samples using the here presented method showed a good agreement between two independent laboratories with a mean bias of 0.6%.