Rapid chiral separation of atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid using supercritical fluid chromatography–tandem mass spectrometry – Application to wetland microcosms

• Modern SFC using dual columns and MS/MS, used for fast enantioselective analysis.
• Baseline separation of three β-blocking agents and the zwitterionic metoprolol acid.
• Application to wetland microcosm samples, monitoring enantiomeric fraction.

A method for enantiomeric separation of the three β-blocking agents atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid, a major metabolite of both metoprolol and in environmental matrices also atenolol, has been developed. By use of supercritical fluid chromatography and the polysaccharide-based Chiralpak® IB-3, all four compounds were simultaneously enantiomerically separated (Rs > 1.5) within 8 min. Detection was performed using tandem mass spectrometry, and to avoid isobaric interference between the co-eluting metoprolol and metoprolol acid, the achiral column Acquity® UPC2 BEH 2-EP was attached ahead of to the chiral column. Carbon dioxide with 18% methanol containing 0.5% (v/v) of the additives trifluoroacetic acid and ammonia in a 2:1 molar ratio were used as mobile phase. A post column make-up flow (0.3 mL/min) of methanol containing 0.1% (v/v) formic acid was used to enhance the positive electrospray ionization. Detection was carried out using a triple quadrupole mass spectrometer operating in the selected reaction monitoring mode, using one transition per analyte and internal standard. The method was successfully applied for monitoring the enantiomeric fraction change over time in a laboratory scale wetland degradation study. It showed good precision, recovery, sensitivity and low effect of the sample matrix.