Abstract:

An analytical method was developed to determine colistin A (CLA), colistin B (CLB), polymyxin B (PLB), bacitracin A (BTA), virginiamycin M (VGM) by combined quadrupole/orbitrap high resolution mass spectrometry (Q/Exactive) in meat, liver, kidney, milk and egg. Animal-origin foods were extracted with acetonitrile containing 1% (v/v) acetic acid and water under the ultrasonic assisted condition. The samples were analyzed directly on a C₁₈ column. The charged ion in positive electrospray ionization (ESI⁺) mode entered quadrupole mass limited to isolation window m/z 1.2. Product ion scan was performed on 35000 resolution of orbitrap mass. According to some parameters of molecular ion, isotopic ion ratios, characteristic product ion, the searched database was built with the Trace Finder 3.0 software. To solve the problem of poor reproducibility of the detected results, this method evaluated systematically some critical operation procedures. Finally, contributory factors of degradation were discovered including extraction time, adsorption of glass vessels, storing period. Under the experimental conditions, accuracy errors of the five analytes were all less than 5×10^-6. The limits of quantification (LOQs) were 0.5 μg/kg for virginiamycin M and 10 μg/kg for the other four analysts. The good linear relationship was obtained in the range of 0.25-500 μg/kg (correlation coefficient (R²)≥0.9931). The method recoveries were 67.4%-108.9% and the relative standard deviations (RSDs) were 4.5%-17.2%. This method showed that it was simple, accurate and reliable. It will be applicable for high throughput determination of polypeptide antibiotic residues in animal-origin foods.

Key words: animal-origin foods, colistin, high performance liquid chromatography (HPLC)-quadrupole/orbitrap high resolution mass spectrometry (MS), polymyxin, polypeptide drugs, residues, targeted product ion full scan (targeted-MS²)