Liquid chromatographic determination of chloramphenicol residues in meat: interlaboratory study

A liquid chromatographic (LC) method for the determination of chloramphenicol (CAP) residues in meat at the 10 microgram/kg level was tested in an interlaboratory study. The method used, based on aqueous extraction and sample cleanup with a cartridge containing Extrelut, was published earlier. A prestudy to familiarize collaborators with the method was performed before the actual interlaboratory precision study. The meat samples used in the precision study were prepared by diluting dosed chicken and pig muscle tissues with blank tissues from other species. Fourteen laboratories received 20 meat samples; 13 laboratories actually participated in the study. Two blank samples and 2 positive samples each of pig, calf, chicken, lamb, and cow meat were tested. The chloramphenicol concentrations in the positive samples ranged from 6.5 to 21 micrograms/kg. The overall mean reproducibility coefficient of variation was 17.9% after the results per laboratory were corrected for the mean recovery obtained within each sample series. The overall mean recovery was 55.1% with a coefficient of variation of 18.0% at the 10 micrograms/kg level. The limit of detection, based on chromatograms of blank samples, was estimated to be 1.5 micrograms/kg of chloramphenicol. No false positives or false negatives were observed in the concentration range tested; only 2 false positive results above the detection limit (1.7 and 6 micrograms/kg) on a total number of 60 blank analyses (3.3%) were observed.