Comparative HPLC methods for β-blockers separation using different types of chiral stationary phases in normal phase and polar organic phase elution modes. Analysis of propranolol enantiomers in natural waters

The enantioselectivities of β-blockers (propranolol, metoprolol, atenolol and pindolol) on four different types of chiral stationary phases (CSPs): Chiralpak AD-H, Lux Cellulose-1, Chirobiotic T and Sumichiral OA-4900 were compared using polar organic (PO) elution mode and normal phase (NP) elution mode. Method optimizations were demonstrated by modifying parameters such as organic modifier composition (ethanol, 2-propanol and acetonitrile) and basic mobile phase additives (triethylamine, diethylamine, ethanolamine, and buthylamine). In normal phase elution mode with Lux Cellulose-1, the four pairs of enantiomers can be separated in the same run in gradient elution mode. Additionally, a simple chiral HPLC–DAD method using a newly commercialized polysaccharide-based CSP by Phenomenex (Lux Cellulose-1) in NP elution mode for enantioselective determination of propranolol in water samples by highly selective molecularly imprinted polymers extraction was validated. The optimized conditions were a mobile phase composed by n-hexane/ethanol/DEA (70/30/0.3, v/v/v) at a flow rate of 1.0 mL min−1 and 25 °C. The method is selective, precise and accurate and was found to be linear in the range of 0.125–50 μg mL−1 (R2 > 0.999) with a method detection limit (MLD) of 0.4 μg mL−1 for both enantiomers. Recoveries achieved with both enantiomers ranged from 97 to 109%.