Gas chromatographic–mass spectrometric determination of sulfamethazine in animal tissues using a methyl/trimethylsilyl derivative

Abstract

A method is described for the determination of sulfamethazine in swine tissues by GC–MS. Samples are extracted with chloroform-acetone, followed sequentially by two solid-phase clean-up steps using silica gel and SCX ion exchange. The extracts are then partitioned between sodium dihydrogenphosphate (0.1 mol l^–1) and methyl tert-butyl ether, the organic phase is evaporated to dryness and the sulfamethazine subjected to a double derivatization via methylation and silylation and determined by GC–MS in the selected-ion monitoring mode. Quantification is achieved by measuring the ratio of the abundances of the M —65 (—HSO₂) ions of the derivatives of sulfamethazine and the internal standard, [phenyl-¹³C₆] sulfamethazine, at m/z 299 and 305, respectively. The presence of sulfamethazine can be confirmed using the abundance ratios of the ions of m/z 299, 300 (—SO₂) and 349 (—CH₃). Recovery values from muscle, kidney and liver spiked at 0.05, 0.2 and 0.4 ppm ranged from 86 to 114% with RSDs between 2.8 and 9.0%. The limit of detection for the assay is 0.01–0.02 ppm. The methyl/trimethylsilyl derivatives exhibited better chromatography than the commonly used N¹-methyl derivatives; for the same conditions, the peak was sharper and tailing was significantly reduced.