Determination of tricaine residues in fish by liquid chromatography

Tricaine methanesulfonate (MS-222) is approved by the U.S. Food and Drug Administration, Center for Veterinary Medicine (CVM), as an anesthetic drug for select aquaculture species. It was approved for use as a handling aid with a 3 week withdrawal time. The drug is rapidly metabolized and excreted; therefore, CVM approved its use without requiring a regulatory method for drug residues in tissues. However, there are concerns that the drug may be used to sedate fish during transport to slaughter. A regulatory method will enable monitoring for unsafe residues of this drug resulting from extralabel use. We present a quantitative method, using LC at a target level of 0.1 mg/kg (ppm), for three different farmed species: salmon (Salmo salar); tilapia (Oreochromis spp.); and catfish (Ictalurus punctatus). The assay begins with an acetonitrile extraction, followed by filtration and mixed-mode cation-exchange solid-phase extraction cleanup. The extracts are analyzed by reversed-phase LC with UV detection at 320 nm. The method was validated by using fish fillets with incurred residues, control fish fillets, and fish fillets fortified at half the target level, the target level, and twice the target level (0.05, 0.1, and 0.2 ppm, respectively). For all species, accuracy is > or =80% and the RSD is < or =10%. The method complies with CVM performance criteria for the determination of veterinary drug residues.