CHIRAL BIOANALYSIS BY NORMAL-PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY-ATMOSPHERIC PRESSURE IONIZATION TANDEM MASS-SPECTROMETRY

A highly sensitive and specific chiral high-performance liquid chromat ographic tandem mass spectrometric (HPLC-MS-MS) technique has been dev eloped for the determination of several chiral drugs and their metabol ites. Examples include enantiomers of verapamil and its most abundant active metabolite, norverapamil, enantiomers of oxybutynin and its met abolite, N-desethyloxybutynin, enantiomers of doxazosin and those of s otalol. These drugs are marketed as racemates although their optical i somers possess different pharmacological activities. Drug enantiomers and their respective chiral metabolites were separated by isocratic no rmal-phase chiral chromatography on a small-bore (100X2.1 mm I.D.) Chi ralpak AD column. Post-column reagent addition of an aqueous mobile ph ase was introduced to enable direct coupling of hexane-based mobile ph ases chiral chromatography with the heated nebulizer interface of the SCIEX API 300 tandem mass spectrometer. Quantification of individual d rug and metabolite enantiomers was obtained by multiple reaction monit oring. This novel approach was developed and used in bioanalytical stu dies. It successfully combines the convenience of normal-phase chiral separations on small-bore HPLC columns with high specificity and low l imits of quantification achieved by atmospheric pressure ionization MS -MS detection.