SENSITIVE SPECTROFLUOROMETRIC DETERMINATION OF TETRACYCLINE RESIDUES IN BOVINE-MILK

A novel, sensitive, high-performance liquid chromatographic method for the residue determination of tetracyclines in bovine milk has been de veloped. Clean-up of the sample extracts is performed with metal chela te affinity chromatography. Detection is based upon the measurement of fluorescence induced by complexation of tetracyclines with the zircon ium cation, which is added post column to the high-performance liquid chromatographic eluate. The method has been validated for oxytetracycl ine, tetracycline and chlortetracycline. Calibration curves using 'bla nk' milk fortified at the 10-200 ng ml(-1) level showed good linear co rrelation. Accuracy was measured at the 100 ng ml(-1) level and was fo und to be within acceptable limits using a t-test (alpha = 0.05). At t his level both within- and between-day precision, as measured by relat ive standard deviation (s(r)), were less than 16% for oxytetracycline and chlortetracycline, and less than 20% for tetracycline. The most st riking advantages of the proposed method, over previously reported met hods, are the higher sensitivity and specificity achieved. Using a sig nal-to-noise ratio of 4:1, the detection limits of the assay were 1 ng ml(-1) for oxytetracycline, 2 ng ml(-1) for tetracycline and 4 ng ml( -1) for chlortetracycline.