A Liquid Chromatography−Mass Spectrometry Assay for Analyzing Sulfonamide Antibacterials in Cattle and Fish Muscle Tissues

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Abstract
A simple and rapid method able to determine residues of 12 sulfonamide (SAs) antibacterials in cattle and trout muscle tissues is presented. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography−mass spectrometry (LC−MS). The LC−MS instrumentation was equipped with an electrospray source and a single quadrupole. After 0.8 g of a flesh sample containing the analytes is deposited on sand (crystobalite), this material is packed into an extraction cell. SAs are extracted by flowing 4 mL of water through the cell heated at 80 °C. A 0.5-mL aliquot of the bovine tissue extract is then directly injected into the LC column, while the fish tissue extract is filtered prior to LC−MS analysis. MS data acquisition was performed in the positive-ion mode and monitoring at least three ions for each target compound. Confirmatory ions were produced by the in-source collision-induced dissociation process. At the tolerance levels issued by the EU and U.S. Food and Drug Administration, i.e., 100 ppb, recovery of the analytes in bovine and trout muscle tissues was 75−98% with RSDs ranging between 1 and 8%. Estimated limits of quantification (S/N = 10) were 6−15 ppb for SAs in bovine muscle tissue and 3−13 ppb in trout fillet. When trying to reduce the analysis time by using a short chromatographic run time, severe ion signal suppression was experienced for the early-eluted SAs. This effect was traced to competition effects by polar endogenous coextractives, maybe proteinaceous species, which are eluted in the first part of the chromatographic run. This unwelcome effect was removed by simply adopting more selective chromatographic conditions.