DETERMINATION OF METHYLENE-BLUE IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS) TISSUE BY LIQUID-CHROMATOGRAPHY WITH VISIBLE DETECTION

Methylene blue (MB) is a thiazine dye that, although not regulated for use with edible fish, may sometimes be used as a chemotherapeutic age nt in the aquaculture industry, A liquid chromatographic (LC) method w as developed for the determination of MB in fish muscle, MB was extrac ted from catfish tissue with an acetonitrile-acetate buffer solution c ontaining hydroxylamine and toluene-sulfonic acid, partitioned into me thylene chloride, and cleaned up on alumina and carboxylic acid solid- phase extraction cartridges, MB concentrations were determined by LC w ith visible detection at 660-665 nm, Recoveries of MB from catfish for tified at 10-50 ng/g were 75-90% (RSDs, 5-12%), Leucomethylene blue al so can be recovered from catfish tissue as the MB colored form at low levels with similar recoveries, Analysis of catfish exposed to MB in a bath treatment at 5 ppm MB for 1 h recovered 10-20 ppb of the drug in the muscle tissue, The low tissue concentration suggests poor absorpt ion of this drug compared with other antifungal dyes that tend to conc entrate and remain in fish tissue at high levels.