GENTAMICIN IN TISSUE AND WHOLE MILK - AN IMPROVED METHOD FOR EXTRACTION AND CLEANUP OF SAMPLES FOR QUANTITATION ON HPLC

A new, inexpensive, and rapid procedure for the extraction of gentamicin from animal tissue and whole milk samples is described. Tissue samples from gentamicin-treated calves were homogenized in a pH 8.8 extraction buffer, mixed, filtered, and centrifuged. The resulting supernatant fractions were extracted using bifunctional hydrophobic/ion exchange solid phase cartridges. The isolated gentamicin was derivatized with a chromophore and analyzed using high-performance liquid chromatography. Whole milk samples were similarly extracted and analyzed. The resulting chromatograms showed exceptionally clean samples with no interfering peaks in the area of gentamicin elution. This allowed good separation and detection of all four isomers of gentamicin. The detection limit for gentamicin was 0.6 mu g/mL in whole milk and 1 mu g/g in tissue samples. The coefficients of variation were 2.5% for whole milk and 8.1% for tissue samples. The efficiency of recovery was greater than 90%.