LAUSR

A method for simultaneous separation and determination of four enantiomeric pairs of β‐blockers in waters by chiral CE has been developed. Off‐line SPE was employed using functionalized ordered mesoporous silica as sorbent. Separation by CE was achieved using a BGE composed by methylated‐β‐CD (1.25% w/v) dissolved in a 50 mM phosphate buffer (pH 2.5) and 30°C, with good chiral resolution for all enantiomers. Mesoporous silica functionalized with octadecyl groups (denoted SBA15‐C18) was prepared by a postsynthesis method and applied for the preconcentration of atenolol, propranolol, metoprolol, and pindolol enantiomers in waters by off‐line SPE. Under optimized conditions, a preconcentration factor of 300 was achieved, employing 100 mg of SBA15‐C18 as sorbent, with recoveries between 96 and 105% in tap water and good repeatability (% RSD = 7–11%, n = 6). Commercial C18 amorphous silica (ExtraBondR C18) was also tested as sorbent for SPE, but results revealed better extraction capacity with higher recoveries for the SBA15‐C18 material. The analytical characteristics of the off‐line SPE‐chiral CE method were evaluated, showing good precision, linearity, and accuracy with method quantification limits between 5.3 and 13.7 μg/L for all enantiomers. The SBA15‐C18 material allowed the extraction of four enantiomeric pairs of β‐blockers spiked in tap water, river water, and ground water with recoveries between 58 and 105%.