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 gentamic in from animal tissue and whole milk samples is described. Tissue samp les from gentamicin-treated calves were homogenized in a pH 8.8 extrac tion buffer, mixed, filtered, and centrifuged. The resulting supernata nt fractions were extracted using bifunctional hydrophobic/ion exchang e solid phase cartridges. The isolated gentamicin was derivatized with a chromophore and analyzed using high-performance liquid chromatograp hy. Whole milk samples were similarly extracted and analyzed. The resu lting chromatograms showed exceptionally clean samples with no interfe ring peaks in the area of gentamicin elution. This allowed good separa tion and detection of all four isomers of gentamicin. The detection li mit for gentamicin was 0.6 mu g/mL in whole milk and 1 mu g/g in tissu e samples. The coefficients of variation were 2.5% for whole milk and 8.1% for tissue samples. The efficiency of recovery was greater than 9 0%.