Zeolite imidazolate framework-8 as sorbent for on-line solid-phase extraction coupled with high-performance liquid chromatography for the determination of tetracyclines in water and milk samples.

Zeolite imidazolate framework-8 (ZIF-8) was used as the novel sorbent for on-line solid-phase extraction coupled with high-performance liquid chromatography (HPLC) for the determination of oxytetracycline (OTC), tetracycline (TC) and chlorotetracycline (CTC) in water and milk samples. 390mg of ZIF-8 was packed into a stainless steel column (3cm long×4.6mm i.d.) which was mounted on the HPLC injector valve to replace the sample loop. On-line solid-phase extraction of OTC, TC and CTC was achieved by loading sample solution at a flow rate of 3.0mLmin(-1) for 10min with the aid of a flow-injection system. The extracted analytes were subsequently eluted into a C18 analytical column (25cm long×4.6mm i.d.) for HPLC separation under isocratic condition with a mobile phase (10% MeOH-20% ACN-70% 0.02molL(-1) oxalic acid solution) at a flow rate of 1.0mLmin(-1). Under optimized conditions, the developed method gave the enhancement factors of 35-61, the linearity range of 5-1000μgL(-1), the detection limits of 1.5-8.0μgL(-1), quantification limits of 5.0-26.7μgL(-1), uncertainties of 0.9-1.1μgL(-1), and the sample throughput of 4 samples h(-1). The recoveries of OTC, TC and CTC at 50μgL(-1) in water and milk samples ranged from 70.3% to 107.4%.