Development and validation of an indirect competitive enzyme-linked immunosorbent assay for monitoring quinoxaline-2-carboxylic acid in the edible tissues of animals

Multi-residue determination of five quinoxalines and three their metabolites in poultry feathers and its application for depletions of olaquindox and quincetone in chickens

A method for the simultaneous determination of eight quinoxalines and their metabolites in poultry feathers was developed in this study using ultra-performance liquid chromatography combine with quadrupole linear ion trap electrostatic field orbit trap high resolution mass spectrometer. Specificity, matrix effect, linearity, trueness, repeatability, reproducibility, and stability using the Commission of the European Communities, Regulation (EU) 2021/808. The correlation coefficients were all greater than 0.99. The average recoveries of the eight compounds ranged from 76.1% to 112.8%, with coefficient of variation of less than 15%. The limits of detection and quantification of the method were 0.04-0.1 μg/kg and 0.12-0.3 μg/kg, respectively. The method has been successfully applied to depletions of olaquindox and quincetone in feathers of laying hens. Methylquinoxaline-2-carboxylic acid and quincetone are the main metabolites in olaquindox and quincetone in feather, respectively.

A sensitive and selective immunoaffinity column clean up coupled to UPLC-MS/MS for determination of trace methyl-3-quinoxaline-2-carboxylic acid in animal tissues

This paper described a reliable and simple method for the selective determination of MQCA in animal tissues using ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). A highly targeted immunoaffinity column was used for sample purification after enzymatic hydrolysis. The purified extracts were analyzed by reversed-phase HPLC-MS/MS in positive ESI and multiple reaction monitoring mode. The calibration curves showed good linearity with correlation coefficient (r²) larger than 0.995. The average recoveries at the spiked levels of 0.5, 2.0 and 20μgkg^-1 were 90.2% to 103.5% with intra-day and inter-day relatives standard deviations (RSD, n=6) ranging from 1.8% to 6.7% and 3.5% to 7.6% respectively. The limit of quantification (LOQ) was 0.5μgkg^-1, which can fulfil the maximum residue level (MRL) of 4.0μgkg^-1 stipulated by the Agricultural Minister of China and the requirement of the confirmatory criteria according to the European Commission Decision 2002/657/EC. The method is sensitive, accurate, convenient and rapid, and has been successfully applied in real samples.

In vivo studies to highlight possible illegal treatments of rabbits with carbadox and olaquindox

For the treatment of rabbit dysentery and bacterial enteritis, veterinary practitioners often adopt veterinary medicinal products authorised for other food-producing species, but in some cases non-authorised drugs frequently used in the past, such as carbadox and olaquindox, might be illegally adopted. To verify the carbadox and olaquindox distribution and persistence in rabbit tissues, two independent in vivo studies were carried out. In the first study, 24 healthy rabbits received water medicated with carbadox at 100 mg l(-1) over a period 28 days, whereas in the second one, 24 healthy rabbits were administered water containing olaquindox at 100 mg l(-1). In each study rabbits were randomly assigned to four groups to be sacrificed respectively at 0, 5, 10 and 20 days from treatment withdrawal, for depletion studies. A control group of six animals was adopted for control and as a reservoir of blank tissues. Muscle and liver samples collected from each treated animal were stored at -20°C pending the analysis. Sensitive and robust liquid chromatography-tandem mass spectrometry analytical methods were set up for the parent compounds and their main metabolites quinoxaline-2-carboxylic acid, desoxycarbadox and 3-methylquinoxaline-2-carboxylic acid to verify their residual. Data collected demonstrate that the combination of liver as target matrix, quinoxaline-2-carboxylic acid and 3-methylquinoxaline-2-carboxylic acid as marker residue and enzymatic digestion is strategic to evidence carbadox and/or olaquindox illegal treatments in rabbits, even 20 days after treatment withdrawal at concentration levels higher than 0.5 µg kg(-1). This findings suggests that liver should be proposed as target matrix for official control in national monitoring plan.

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.

A sensitive and specific ELISA for determining a residue marker of three quinoxaline antibiotics in swine liver

Methyl-3-quinoxaline-2-carboxylic acid (MQCA) is a possible residue marker for three quinoxaline veterinary medicines (olaquindox, mequindox, and quinocetone). The wide application of mequindox/quinocetone or the illegal use of olaquindox leads to MQCA residue in animal's original food, thereby threatening the safety of human food. The indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) with a specific coating antigen and monoclonal antibody (MAB) was established and optimized for detecting MQCA in swine liver. Samples were acidified with 2 mol l(-1) hydrochloric acid, extracted with ethyl acetate-hexane-isopropanol (8 + 1 + 1, v/v/v) and then detected by IC-ELISA. The logarithm correlation of standards to OD values ranged from 0.2 to 200 μg l(-1), with IC(50) of 6.46 μg l(-1). Negligible cross-reactivity happened to five quinoxaline antibiotics (olaquindox, mequindox, quinocetone, carbadox, and cyadox) and the metabolite of carbadox and cyadox (quinoxaline-2-carboxylic acid). When spiked with 1 to 100 μg kg(-1) of MQCA, the recoveries ranged from 85.44 to 100.02 %, with the intra-assay coefficient of variation (CV) of 6.64-10.57 % and inter-assay CV of 7.29-10.88 %. The limit of detection for MQCA was 1.0 μg kg(-1) in swine liver. Furthermore, incurred samples were detected by the IC-ELISA and then conformed by a reported LC/MS/MS method, it shown that there was good correlation between the two methods. All these results indicated that the IC-ELISA method is appropriate for surveillance MQCA residue in animal tissues.