Determination of oxolinic acid in feeds and cultured fish using capillary electrophoresis

A capillary electrophoretic method was developed for the determination of the antibiotic oxolinic acid. The electrolyte composed of a buffer solution (10 mM phosphate, pH 9.00) and methanol (9:1) was found to be the most suitable for this separation. The effect of type of buffer, its pH and concentration as well as injection times and applied voltage on the migration of oxolinic acid was also studied. Key analytical characteristics of the method are as follows: detection limit (signal-to-noise ratio 3), 0.08 μg ml−1; linear range, 0.5–40 μg ml−1; migration time, 5.3 min; relative standard deviation for within-day and day-to-day variation of 1.67 and 2.24%, respectively. The method, in conjunction with a solid phase extraction procedure, was successfully applied for the analysis of spiked oxolinic acid in fish feeds and fish muscles. The recoveries of oxolinic acid from spiked feeds and muscle tissues were 81.15 and 84.80%, respectively.