Environmental chiral analysis of β-blockers: evaluation of different n-alkyl-modified SBA-15 mesoporous silicas as sorbents in solid-phase extraction

Environmental context β-Blockers are important chiral pharmaceuticals found as micropollutants in environmental waters as a result of incomplete removal during wastewater treatment. Because they display enantioselective toxicity, it is necessary to include chiral information in an environmental risk assessment. We have developed an analytical method using mesoporous silica for extracting β-blockers in water samples before their specific chiral analysis. Abstract The extraction and preconcentration of chiral β-blockers in environmental water was evaluated by solid-phase extraction (SPE) employing an SBA-15 ordered mesoporous silica functionalised with alkyl chains of different length. The materials were characterised by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption–desorption isotherm measurements and elemental analysis. Important parameters influencing extraction efficiency, including the type and amount of sorbent and the breakthrough volume, were optimised. The results obtained showed that the organic chain length played an important role in the behaviour of these sorbents. Under optimised conditions, using 200 mg SBA-15-C8 as sorbent, a simple analytical method based on off-line SPE coupled to chiral capillary electrophoresis with diode array detection (SPE-chiral CE-DAD) was developed. Method detection and quantification limits were lower than 0.6 and 1.9 µg L −1 respectively for all enantiomers, with a preconcentration factor of 500-fold. The method was successfully applied to the chiral analysis of atenolol, metoprolol, pindolol and propranolol in river and sewage water samples. Satisfactory recoveries (between 86 ± 2 and 98 ± 1 %) and repeatability (relative standard deviation (RSD) < 9 %, n = 3) were obtained. Metoprolol was detected in sewage water at a concentration of 10.7 and 9.9 µg L−1 and an enantiomeric fraction of 0.52 and 0.48 for the first- and the second-migrating enantiomers respectively. These results emphasise the importance of enantioselective analysis for environmental risk assessment.