Quantification of carbamazepine and its active metabolite by direct injection of human milk serum using liquid chromatography tandem ion trap mass spectrometry

This work reports the use of a liquid chromatography ion trap tandem mass spectrometry (LC–IT-MS/MS) system for quantification in human milk samples of both carbamazepine (CBZ) and its active metabolite, carbamazepine 10,11-epoxide (CBZE). An octadecyl restricted-access media bovine serum albumin column (RAM-BSA C18) was used in single-column mode. Selectivity, extraction efficiency, accuracy and precision were achieved employing 100 μL of the sample, without preparation, with detection limits of 20.0 ng/mL for CBZ and 40.0 ng/mL for CBZE. The matrix effect was investigated for the compounds by post-column infusion (qualitative) and by on-line extraction (quantitative). It was observed suppression effect for CBZ and CBZE by post-column infusion, ion suppression of 0.80 for CBZ, and enhancement of 1.28 for CBZE by on-line extraction. The developed method was validated and applied to analyze breast milk samples from one nursing mother. CBZ and CBZE were quantified in the concentrations of 2.26 μg/mL and 1.54 μg/mL, respectively. To our knowledge, this is the first report on the simultaneous determination of CBZ and its active metabolite by direct injection of human milk serum.