ABSTRACT
Objective To establish a reliable pretreatment method for the detection of mequindox and its metabolite in pork luncheon meat by ultra-performance liquid chromatography/triple qudrupole tandem mass spectrometry. Methods Samples were extracted with ethyl acetate, and the results of purification and enrichment by PAX and PEP solid-phase extraction columns were analyzed. Acetonitrile/methanol (3:11) - 0.1% formic acid water was used as the mobile phase, and Shimadzu Inertsil ODS-3-column (3µm, 2.1 × 100mm) chromatographic columns were used for qualitative and quantitative analysis using the multi-reaction detection positive ion mode. Results The results showed that PEP cartridge had good recovery rate. The detection limit of mequindox was 0.10µg/kg, and limit of quantitation was 0.30µg/kg. The average recoveries for spiked levels of 0.33, 0.83, and 1.65µg/kg were 127%, 72.0%, and 60.1%, respectively. The detection limit of 2-quinoxalinecarboxylic acid was 0.10µg/kg, and limit of quantitation was 0.40µg/kg. The average recoveries for spiked levels of 0.42, 1.05, and 2.1µg/kg were 125%, 99.0%, and 60.9%, respectively. Conclusion This method is suitable for the determination of mequindox and its metabolite 2-quinoxalinecarboxylic acid in luncheon meat.
ABSTRACT
The chemical structures of mequindox related metabolites in chicken plasma had been investigated using high performance liquid chromatography combined with linear ion trap quadrupole(LC-ESI/LTQ) and high performance liquid chromatography combined with ion trap-time of flight-mass spectrometry (LC-ESI/IT-TOF).Samples were separated by Hypersil BDS C_(18) and symmetry Shield columns, respectively, and 0.01% formic acid aqueous(A) and methanol(B) were used as mobile phase with gradient elution.Electros pray ionization mass spectrometric(ESI) source was used and operated in positive ion mode.When chickens were orally administered with mequindox at dosage of 20 mg/kg, blood samples were collected from the brachi al vein.Mequindox and its metabolites were extracted by the mixture of acetonitrile and acetoacetate (3:2, V/V).After solvent evaporated, the residue was dissolved in 30% methanol aqueous and the solution was detected by LC/IT-TOF MS and LC-ESI/LTQ.The molecule weight from LC-ESI/IT-TOF was analyzed by software Shimadzu's Composition and the mass chromatogram from LC-ESI/LTQ was analyzed by software Xcalibur 2.0.7.According to the molecular weight and MS~n data, referring the metabolic reaction rules, five chemical structures of mequindox related metabolites in chicken plasma were identified.Metabolites (M1-M4) were synthesized to verify the structure of metabolites.The metabolites are 3-methyl-2-(1-hydroxy) ethyl-qui-noxaline-N~1,N~4-dioxide(Ml), 3-methyl-2-(1-hydroxy) ethyl-quinoxaline-N~4-oxide(M2), 3-methyl-2-acetyl-quinoxaline-N~4-oxide, 3-methyl-2-acetyl-quinoxaline (M4), 3-hydroxymethyl-2-(1-hydroxy) ethyl-quinoxa-line-N~1,N~4-dioxide (M5).