A simple, sensitive, scientific and reproducible liquid chromatography-tandem mass spectrometric method was developed to determine 3-methylquinoxaline-2-carboxylic acid (MQCA) of olaquindox marker residue in chicken muscle tissues. The chickens were administered orally with olaquindox and used as positive samples. The approaches, enzyme, acid, and base hydrolysis, were adopted to digest MQCA in the medicated chicken muscles. The amounts of MQCA in the medicated chicken were determined and compared using different hydrolysis approaches. It was shown that the highest amount of MQCA was obtained for the base hydrolysis approach. Here, the sample was hydrolyzed with 1.0 mol/L NaOH solution, defatted with n-hexane, and purified with a mixed anion-exchange solid-phase extraction cartridge. The chromatographic separation was performed on a reversed-phase C18 column and detected using mass spectrometry in selected reaction monitoring mode. The analyte showed good linearity in the range 1.0-100 μg/L. The correlation coefficient (r2) was greater than 0.99. The limit of detection of the proposed method was 0.4 μg/kg. At the three spiked levels of 1.0, 5.0 and 50.0 μg/kg, the average recoveries of MQCA were in range 71.7%-82.4% obtained using external standard calibration, and in range 96.3%-103.7% for internal standard calibration, with relative standard deviations below 6.0%. The proposed method is suitable for routinely monitoring of MQCA residues in animal-derived foods.
Keywords: 3-methylquinoxaline-2-carboxylicacid; base hydrolysis; liquid chromatography-tandem mass spectrometry (LC-MS/MS); medicated chicken; residue; solid-phase extraction (SPE).