Determination of sulfadimethoxine and sulfamethazine residues in animal tissues by liquid chromatography and thermospray mass spectrometry.

A simple, sensitive, and rapid method for simultaneous determination of sulfamethazine and sulfadimethoxine residues in animal tissues by liquid chromatography (LC) with on-line confirmation by thermospray mass spectrometry is reported. Tissue extracts, after cleanup on C18 cartridges, were injected into a reversed-phase C18 column, and the sulfa drugs were determined by ultraviolet (UV) detection at 265 nm. On-line confirmation of sulfamethazine and sulfadimethoxine in the extracts by mass spectrometry was obtained by feeding the sulfa drugs eluting from the chromatographic column after UV detection directly into the ion source of a mass spectrometer with a thermospray ionization LC interface. Analytical results obtained with the LC method, which has detection limits of 2 and 10 ng/g of tissue, for sulfamethazine and sulfadimethoxine, respectively, compared favorably with those obtained with the official thin-layer chromatographic-densitometric method.