Determination of piromidic acid residues in trout muscle tissue and in urine by liquid chromatography with post-column modification of pH and fluorimetric detection.

A rapid high-performance liquid chromatographic method has been developed to determine piromidic acid in trout muscle tissue and in urine, in the presence of nalidixic, 7-hydroxymethylnalidixic, oxolinic and pipemidic acids and cinoxacin. A Nova-Pak C18 column was used with acetonitrile-4x10(-4) M oxalic acid (40:60, v/v) as the mobile phase. A post-column change of pH was made with NaOH. Fluorimetric detection at 456 nm (lambda ex 275 nm) was used. The instrumental detection limit was 5.91 ng/ml, based on height of peak. Pretreatment of the urine samples was not necessary and fish samples were extracted with sodium hydroxide solutions and cleaned by means of an extraction with chloroform. Detection limit was 147 ng/ml for urine and 5.91 ng/g for trout muscle. Good separation without interference from any other components was obtained. Recovery was better than 87% in urine and better than 72% in trout muscle tissue.