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The confirmation of the commercial kits used in the detection of antibiotics in milk with HPLC (high pressure liquid chromatography)
In this study, Charm II Assay was confirmed by HPLC for B-lactam, sulphonamide and tetracycline residues in milk. These antibiotics were chosen because they are most frequently used veterinary drugs and their detection have importance for milk quality and consumer's health. The results for confirmation of Charm II Assay showed that the test was very sensitive to all groups that were investigated and showed %100 true results for blank samples and spiked samples that were fortified with mixed standards at MRL (maximum residue limit) for each group. Average recoveries of HPLC used for confirmation were between 47% to 97% for beta-lactams, 61.5% to 84.8% for tetracyclines and 50.4% to 54.6% for sulphonamides. The results of analysis with the naturally contaminated milk samples showed that Charm II Assay may give false positive results. But this might be because of the high sensitivity of the test that sometimes HPLC may not reach that detection limit of Charm II assay or the milk samples may contain other compounds of investigated antibiotics that HPLC method can not detect.In samples that were collected for B-lactam determination, only 2 out of 81 samples were detected above MRL where the amounts were 6.5 ppb penicilin-G and 23.8 ppb ampicillin. The MRL for these B-lactam antibiotics are specified as 4 ppb by European Union regulations. The samples investigated for tetracycline residues which were found as positive and confirmed by HPLC were below MRL or negative. In samples investigated for sulphonamides only one sample out of 44 was above MRL where the amount was 119 ppb sulfamethazine.Analysis with 5 commercial milk samples showed none antibiotic residues. Only 4 samples out of 5 for sulphonamides were screened positive but after confirmation no residues were detected in these samples.