Chiral analysis of metoprolol and two of its metabolites, α-hydroxymetoprolol and deaminated metoprolol, in wastewater using liquid chromatography-tandem mass spectrometry.

A LC-MS/MS method for the chiral separation of metoprolol and two of its main metabolites, α-hydroxymetoprolol (α-OH-Met) and deaminated metoprolol (COOH-Met), in environmental water samples has been developed. The target bases, metoprolol and α-OH-Met, as well as the acidic metabolite (COOH-Met) were extracted from water samples by a solid phase extraction method employing Oasis HLB cartridges. The extraction recoveries were ≥ 73% for all compounds in surface water. Four different types of chiral stationary phases were investigated for the separation of the eight stereoisomers of metoprolol and its metabolites, Chiralcel OD-H, Chirobiotic V, Chiral AGP and Chiral CBH. In the final method, the enantiomers of metoprolol and four stereoisomers of α-OH-Met were separated using Chiral CBH, the enantiomers of COOH-Met were separated employing Chiral AGP. The analytes were detected in SRM mode by triple quadrupole mass spectrometry. The method was applied for the chiral analysis of the analytes in treated wastewater samples from Uppsala, Sweden. The enantiomers and diastereoisomers of α-OH-Met were detected and analyzed in the samples. The concentrations of the three first eluting stereoisomers of α-OH-Met were between 54 and 61 pM. Interestingly, the last eluting stereoisomer was found to be present at a concentration of 151 pM at the same sampling occasion. This is, to the best of the authors' knowledge, the first time the stereoisomers of α-OH-Met have been detected in wastewater samples. The enantiomers of metoprolol were determined to be 1.77 and 1.86 nM in the same matrix. The enantiomers of COOH-Met were not detected above the method detection limit (42 pM) in treated wastewater samples. The developed LC-MS/MS methods were validated in wastewater samples.