Membrane assisted micro-solid phase extraction of pharmaceuticals with amino and urea-grafted silica gel

Individual polar sorbents with surface-displayed amino groups (APS) and non-nucleophilic urea-groups (UPS), were prepared by chemical modification of granular silica gel with bifunctional silane coupling reagents. In this preliminary study, they were separately employed for micro-solid phase extraction (μ-SPE) of the quarternary salt of Amitriptyline (Ami), Carbamazepine (Cbz), Ketoprofen (Ket) and Diclofenac (Dfn) from aqueous samples in conjunction with high performance liquid chromatography. The resulting enrichment factors for both APS and UPS are comparable and exceeded those of μ-SPE involving commercial C18-silica gel sorbents. The presence of highly polar, but non-basic and non-nucleophilic surfaces on UPS prompted the development of a UPS-based μ-SPE method. Good linear correlation was found over a concentration range of 0-50 μg L−1 with limits of detection ranging from 0.66 to 2.36 μg L−1). Limits of quantification between 1.61 and 7.88 μg L−1 were obtained. HPLC analyses indicated that relative recoveries of 123% for Ami, 65.6% for Cbz, 71.2% for Ket and 66.5% for Dfn were obtained during μ-SPE of spiked (10 μg L−1) environmental water samples with percentage relative standard deviations (%RSD) of between 2.1% and 12.6%.