Analysis of tetracyclines in chicken tissues and dung using LC–MS coupled with ultrasound-assisted enzymatic hydrolysis

The accurate measurement of tetracycline antibiotics (TCs) in complex matrices related to chicken raising is important for food control. It was experimentally demonstrated that conventional acid deproteination methods led to high losses of TCs because TCs were strongly bounded to protein aggregates. To eliminate this effect, an ultrasound-assisted enzymatic hydrolysis method was developed to break the three-dimensional structures of proteins and release the bound TCs. This not only significantly improved the recovery of TCs but also shortened the pretreatment time from 960 to 6 min. By combining this new deproteination method and a solid phase extraction clean-up, a suitable sample preparation was achieved for the analysis of TCs with LC–MS/MS. The established LC–MS/MS analysis of TCs provided good linear ranges in the order of 20–1000 μg L−1 with the limits of detection ranging from 1.05 to 3.50 μg L−1 for the tested TCs. The new method yielded recoveries of TCs in spiked chicken-related samples as high as 89.1%–102.4%, being much higher than those (23.5%–36.2%) obtained using the acid deproteination process. When this method was used to analyze five practical samples of manures, it gave residual concentrations of 0.9–4.2 and 1.3–4.0 mg kg−1 for oxytetracycline and chlortetracycline, respectively.