Preparation of restricted-access material precolumns by grafting δ-gluconolactone onto a hybrid silica monolithic column for on-line solid-phase extraction of tetracycline residues from milk.

A restricted-access material-hybrid monolithic column was prepared based on single-component organosiloxane and dynamic grafting of δ-gluconolactone for on-line solid phase extraction of tetracycline antibiotic residues from milk. The hybrid monolithic column was prepared in a stainless-steel chromatographic column using methyltrimethoxysilane as the single precursor. δ-Gluconolactone was covalently coupled to aminopropyl derivatized hybrid monolithic column, which formed hydrophilic structures on the surface of the pore of the restricted-access material-hybrid monolithic column. The columns were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption, contact angle analysis, dynamic adsorption, and chromatographic performance evaluation. The restricted-access material-hybrid monolithic column was applied to the on-line extraction of tetracycline residues from milk. An enrichment factor of 15.8 and a good sample clean-up effect were obtained under the optimized conditions. The recoveries of the three spiked milk samples were between 81.7 and 102.5% with relative standard deviations (n = 3) in the range of 2-5%. The limits of detection (S/N = 3) for target compounds were in the range of 3.80-9.03 μg/kg. The results show that the on-line extraction using the restricted-access material-hybrid monolithic column was powerful for food sample pretreatment with high selectivity and good clean-up effect.