Gas Chromatographic/Mass Spectrometric Determination of Oxolinic, Nalidixic, and Piromidic Acid in Fish

Abstract

Abstract A gas chromatographic/mass spectrometric (GC/MS) method using selected ion monitoring (SIM) mode has been developed for determination of oxolinic, nalidixic, and piromidic acid in fish. Drugs are extracted with ethyl acetate from a sample homogenized with phosphate buffer (pH 6.0). The extract is partitioned into 3% sodium bicarbonate solution, and the aqueous phase is re-extracted with ethyl acetate after neutralization. After evaporation, the residue is dissolved in methanol and reduced with sodium tetrahydroborate. The reaction mixture is treated with acid, extracted with ethyl acetate, and re-extracted with ethyl acetate after alkalinization. The combined ethyl acetate extract is passed through an alumina cartridge column, concentrated, and analyzed by GC/MS in SIM mode. Percent recoveries and coefficients of variation (CV%) from silver salmon fortified at the 0.1 ppm level were 92.2 (4.4) for oxolinic, 100.6 (12.8) for nalidixic, and 92.1 (3.8) for piromidic; at the 0.01 ppm level, they were 80.5 (6.2) for oxolinic, 81.5 (8.2) for nalidixic, and 69.6 (8.5) for piromidic. The detection limit is 0.003 ppm