Evaluation of bi-functionalized mesoporous silicas as reversed phase/cation-exchange mixed-mode sorbents for multi-residue solid phase extraction of veterinary drug residues in meat samples

A SBA-15 type mesoporous silica was synthesized and bi-functionalized with octadecylsilane (C18) or octylsilane (C8), and sulfonic acid (SO3-) groups in order to obtain materials with reversed-phase/strong cation-exchange mixed-mode retention mechanism. The resulting hybrid materials (SBA-15-C18-SO3 and SBA-15-C8-SO3-) were comprehensively characterized. They showed high surface area, high pore volume and controlled porous size. Elemental analysis of the materials revealed differences in the amount of C18 and C8. SBA-15-C18-SO3- contained 0.19 mmol/g of C18, while SBA-15-C8-SO3- presented 0.54 mmol/g of C8. The SO3- groups anchored to the silica surface of the pore walls were 0.20 and 0.09 mmol/g, respectively. The bi-functionalized materials were evaluated as SPE sorbents for the multi-residue extraction of 26 veterinary drug residues in meat samples using ultra-high-performance liquid chromatography coupled to mass spectrometry detector (UHPLC-MS/MS). Different sorbent amounts (100 and 200 mg) and organic solvents were tested to optimize the extraction procedure. Both silicas showed big extraction potential and were successful in the extraction of the target analytes. The mixed-mode retention mechanism was confirmed by comparing both silicas with SBA-15 mesoporous silica mono-functionalized with C18 and C8. Best results were achieved with 200 mg of SBA-15-C18-SO3- obtaining recoveries higher than 70% for the majority of analytes.