Abstract
Solid phase extraction (SPE)-chiral separation of the important drugs pheniramine, oxybutynin, cetirizine, and brinzolamide was achieved on the C-18 cartridge and AmyCoat (150 x 46mm) and Chiralpak AD (25cm x 0.46cm id) chiral columns in human plasma. Pheniramine, oxybutynin, cetirizine, and brinzolamide were resolved using n-hexane-2-PrOH-DEA (85:15:0.1, v/v), n-hexane-2-PrOH-DEA (80:20:0.1, v/v), n-hexane-2-PrOH-DEA (70:30:0.2, v/v), and n-hexane-2-propanol (90:10, v/v) as mobile phases. The separation was carried out at 25 +/- 1oC temperature with detection at 225nm for cetirizine and oxybutynin and 220nm for pheniramine and brinzolamide. The flow rates of the mobile phases were 0.5 mLmin(-1). The retention factors of pheniramine, oxybutynin, cetirizine and brinzolamide were 3.25 and 4.34, 4.76 and 5.64, 6.10 and 6.60, and 1.64 and 2.01, respectively. The separation factors of these drugs were 1.33, 1.18, 1.09 and 1.20 while their resolutions factors were 1.09, 1.45, 1.63 and 1.25, and 1.15, respectively. The absolute configurations of the eluted enantiomers of the reported drugs were determined by simulation studies. It was observed that the order of enantiomers elution of the reported drugs was S-pheniramine>R-pheniramine; R-oxybutynin>S-oxybutynin; S-cetirizine>R-cetirizine; and S-brinzolamide>R-brinzolamide. The mechanism of separation was also determined at the supramolecular level by considering interactions and modeling results. The reported SPE-chiral high-performance liquid chromatography (HPLC) methods are suitable for the enantiomeric analyses of these drugs in any biological sample. In addition, simulation studies may be used to determine the absolute configuration of the first and second eluted enantiomers. Chirality 26:136-143, 2014. (c) 2014 Wiley Periodicals, Inc.