Development of a quantitative multiclass/multiresidue method for 21 veterinary drugs in shrimp

A multiclass/multiresidue method has been developed and validated for the determination of 21 veterinary drug residues in shrimp, including sulfonamides (sulfadiazine, sulfamerazine, sulfamethazine, sulfachloropyridazine, sulfadimethoxine, and sulfaquinoxaline); tetracyclines (oxytetracycline, tetracycline, and chlortetracycline); (fluoro)quinolones (norfloxacin, ciprofloxacin, enrofloxacin, sarafloxacin, difloxacin, flumequine, oxolinic acid, and nalidixic acid); and cationic dyes (malachite green, gentian violet, leucomalachite green, and leucogentian violet), using HPLC/MS/MS. All drugs were quantifiable over a no less than 10-fold range with matrix-matched standards for linear external calibration, except for oxytetracycline, tetracycline, norfloxacin, and ciprofloxacin, for which norfloxacin-d5 was used as an internal standard. Two grams of preground shrimp sample was extracted twice with extractant at two different pH values. The combined supernatant was further diluted with an aqueous internal standard solution, and 50 microL extract was injected into the HPLC instrument. An online SPE system was set up for automated sample cleanup. A triple quadrupole mass spectrometer equipped with an electrospray ionization source was operated in the multiple-reaction-monitoring mode to acquire data. The method has been validated at three levels within the designated linear ranges for each drug, with accuracies between 77 and 115%, and most CV values below 15%.