Sol–gel molecular imprinted ormosil for solid-phase extraction of methylxanthines

A organically modified molecularly imprinted silica (MIS), selective for methylxanthines, was prepared using a simple sol–gel procedure. Caffeine was used as template; 3-aminopropyltrimethoxysilane (APTMS) as functional monomer and tetraethyl orthosilicate (TEOS) as reticulating agent. The material was packed on solid-phase extraction (SPE) cartridges and evaluated with aqueous test samples, natural water and human urine; a quantitative method for methylxanthines in water, using SPE cartridges packed with the MIS coupled with HPLC–UV was developed. The MIS was highly specific for methylxanthines, with an imprinting factor of (20.5 ± 1.9). The analytical method resulted in detection limits of 85 μg L−1 for theobromine, 44 μg L−1 for theophylline and 53 μg L−1 for caffeine.