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1.4 CHEMICAL SCIENCES, Analytical chemistry
A confirmatory method has been developed to allow for the analysis of eleven nitroimidazoles and also chloramphenicol in milk and honey samples. These compounds are classified as A6 compounds in annex IV of council regulation 2377/90 and therefore prohibited for the use in animal husbandry. Milk samples are extracted by acetonitrile with addition of NaCl, while honey samples are first dissolved in water before a similar extraction. Honey extracts undergo a hexane wash to remove impurities. Both milk and honey extracts are evaporated to dryness and reconstituted in initial mobile phase. These are then injected onto an LC-MS/MS system and analysed in less than 9 minutes. The MS/MS is operated in MRM mode with positive and negative electrospray ionisation. The method is validated in accordance with Commission Decision 2002/657/EC and is capable of analysing for metronidazole, dimetridazole, ronidazole, ipronidazole and there hydroxy metabolites MNZ-OH, HMMNI and IPZ-OH. The method is also able to analyse for carnidazole, ornidazole, ternidazole, tinidazole and chloramphenicol. A level of 3 μg L-1 / μg kg-1 (RL) for MNZ, DMZ and RNZ has been recommended by the community reference laboratory responsible for this substance group and this method can easily detect all nitroimidazoles at this level. A minimum required performance level of 0.3μg L-1 / μg kg-1 is in place for chloramphenicol which the method can also easily detect. For nitroimidazoles the decision limits (CC) and detection capabilities (CC) range from 0.41 to 1.55μg L-1 and 0.70 to 2.64μg L-1 respectively in milk and from 0.38 to 1.16μg kg-1 and 0.66 to 1.98μg kg-1 respectively in honey. For chloramphenicol the values are 0.07 and 0.11μg L-1 in milk and 0.08 and 0.13μg kg-1 in honey. Validation criteria of accuracy, precision, repeatability and reproducibility along with measurement uncertainty are calculated for all analytes in both matrices.
Cronly, M. et al:Rapid multi-class multi-residue method for the confirmation of chloramphenicol and eleven nitroimidazoles in milk and honey by liquid chromatography tandem mass spectrometry.Food Additives and Contaminants, Part A; (2010)27:1233-1246