Simultaneous Screening Analysis of 3-Methyl-quinoxaline-2-carboxylic Acid and Quinoxaline-2-carboxylic Acid Residues in Edible Animal Tissues by a Competitive Indirect Immunoassay

Immunoassays contribute greatly to food safety. Yet there are no reported immunoassays that simultaneously detect MQCA and QCA, the marker residues for olaquindox and carbadox, respectively. Here, a broad-specificity mAb was successfully produced, and the mAb showed good cross-reactivity with both MQCA and QCA, having IC50 values in buffer of 4.8 and 9.6 ng/mL, respectively. The calibration curves ranged from 0.3 to 81 μg/kg. The average recoveries ranged from 76% to 108% at different spiked levels (2, 4, and 8 μg/kg for MQCA; and 4, 10, and 20 μg/kg for QCA), and the intra-/interday coefficients of variation were 4.2-13.3%. The limits of detection of MQCA and QCA in chicken, fish, pork, and shrimp were 1.76, 1.32, 1.90, and 1.18 μg/kg, respectively. This method was verified by LC-MS/MS, with a correlation coefficient above 0.98. The immunoassay was rapid and reliable for simultaneous screening analysis of MQCA and QCA residues.