Rapid confirmatory assay for determining 12 sulfonamide antimicrobials in milk and eggs by matrix solid-phase dispersion and liquid chromatography-mass spectrometry

A rapid confirmatory method for determining 12 sulfonamide (SAs) antibacterials in whole milk and eggs is presented. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography (LC)-mass spectrometry (MS). The LC-MS instrument was equipped with an electrospray ion source and a single quadrupole. After 4 mL of a milk sample containing the analytes had been deposited on sand (crystobalite), this material was packed into an extraction cell. SAs were extracted by flowing 4 mL of water through the cell heated at 75 degrees C. With some modifications, this procedure was applied also to eggs. After pH adjustment and filtration, 0.5 mL of the final extracts was then injected into the LC column. MS data acquisition was performed in the positive-ion mode and by monitoring at least three ions for each target compound. The in-source collision-induced dissociation process produced confirmatory ions. At the 50 ng/g level, recovery of the analytes in milk and eggs was 77-92% with relative standard deviations ranging between 1 and 11%. Estimated limits of quantification (S/N = 10) were 1-3 ng/g of SAs in milk and 2-6 ng/g in eggs. With both matrices, attempts to reduce the analysis time by using a short chromatographic run time caused severe ion signal suppression 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 almost completely removed by simply adopting more selective chromatographic conditions.