[Determination of 3-methylquinoxaline-2-carboxylic acid of olaquindox marker residue in chicken muscles by liquid chromatography-tandem mass spectrometry].

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.

Quick Multi-Class Determination of Residues of Antimicrobial Veterinary Drugs in Animal Muscle by LC-MS/MS.

On the basis of the highly sensitive and selective liquid chromatography-tandem mass spectrometry technique, a generic extraction solvent and a sample dilution method was developed for the residue analysis of different polar veterinary drugs known as fluoroquinolones, sulfonamides, macrolides, and tiamulin in chicken muscle. The results showed that the matrix-matched calibration curves of all 10 compounds were in an effective linear relationship (r² ≥ 0.997) in the range of 0.2⁻100 µg L-1. At three spiking levels of 2 (5), 50, and 100 µg kg-1, average recoveries of analytes were between 67.1% and 96.6% with relative standard deviations of intra-day and inter-day below 20%. The limits of detection and limits of quantification of the method were in the range of 0.3⁻2.0 µg kg-1 and 2.0⁻5.0 µg kg-1, respectively, which were significantly lower than their maximum residue limits. In addition, the intensity of the target analytes and its corresponding matrix effects were obviously related to the sample dilution times (matrix concentration). There were no significant differences (p > 0.05) in the average content of almost any of the analytes in medicated chickens between this method and the method in the literature for determining analytes. Lastly, the proposed method was successfully applied for the simultaneous analysis of 10 common veterinary drugs in food animal muscle tissues.

Freeze-thaw approach: A practical sample preparation strategy for residue analysis of multi-class veterinary drugs in chicken muscle.

Seven drugs from different classes, namely, fluoroquinolones (enrofloxacin, ciprofloxacin, sarafloxacin), sulfonamides (sulfadimidine, sulfamonomethoxine), and macrolides (tilmicosin, tylosin), were used as test compounds in chickens by oral administration, a simple extraction step after cryogenic freezing might allow the effective extraction of multi-class veterinary drug residues from minced chicken muscles by mix vortexing. On basis of the optimized freeze-thaw approach, a convenient, selective, and reproducible liquid chromatography with tandem mass spectrometry method was developed. At three spiking levels in blank chicken and medicated chicken muscles, average recoveries of the analytes were in the range of 71-106 and 63-119%, respectively. All the relative standard deviations were <20%. The limits of quantification of analytes were 0.2-5.0 ng/g. Regardless of the chicken levels, there were no significant differences (P > 0.05) in the average contents of almost any of the analytes in medicated chickens between this method and specific methods in the literature for the determination of specific analytes. Finally, the developed method was successfully extended to the monitoring of residues of 55 common veterinary drugs in food animal muscles.

Chromatographic separation of racemic praziquantel and its residual determination in perch by LC-MS/MS.

An enantioselective depletion study of praziquantel (PZQ) in perch muscle was done using a simple, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Two cyclic polypeptides and two cyclic saccharide chromatographic columns were evaluated. The new hydroxypropyl ß-cyclodextrin (HP-RSP) superficially porous particle (SPP) column produced the optimum separation and was selected for the study. Deuterium labeled PZQ-d11 was used as the internal standard. The method was linear over concentration ranges of 5.00-5.00×102µgL-1 (r2≥0.99) for (-)-R-PZQ and (+)-S-PZQ. The average recoveries of R-PZQ and S-PZQ at three spiked levels of 5.00, 50.00 and 5.00×102µgkg-1 ranged from 86.1% to 98.2%, and the intra-day and inter-day relative standard deviations were less than 5%. The decision limit (CCα) and detection capability (CCß) of R-PZQ and S-PZQ in perch muscle matrices were all 1.0µgkg-1 and 5.0µgkg-1, respectively. The method was successfully applied in monitoring the depletion of praziquantel enantiomers in perch muscle following oral administration. The elimination rate of R-PZQ and S-PZQ in perch muscle tissue is equivalent.