Nano-liquid chromatography coupled with mass spectrometry: Separation of sulfonamides employing non-porous core–shell particles

In this paper, nano-liquid chromatography coupled with mass spectrometry was used for the simultaneous determination of 18 sulfonamides. Preliminary experiments were carried out to investigate selectivity of three different stationary phases. Best results were achieved utilizing a capillary column (100 μm I.D.) packed in our laboratory following the slurry packing procedure with a recent commercialized stationary phase, Kinetex® C18 core–shell. A binary mobile phase, consisting of water and acetonitrile and both containing 0.1% (v/v) formic acid, was employed in a gradient mode at a low flow rate (190 nL/min). Applying these conditions, baseline separation of studied compounds was obtained in about 35 min. Although sulfathiazole and sulfapyridine were resolved from the other drugs, they were not separated from each other. Sensitivity was improved by on-column focusing evaluating the appropriate sample solvent and establishing the maximum injection volume. Comparison between UV and mass spectrometric detection was done. Milk samples spiked with sulfonamides were subjected to a rapid pre-treatment by means of acidic deproteinization followed by solid-phase extraction, and analyzed with the developed method. The detection limits obtained in milk were in the range of 8–96 μg/kg, however they were low enough according to the regulations set-up by the European Commission. Calibration curves showed good linearity (R2 > 0.995) in the studied concentration ranges.