Evaluation of ionic liquids supported on silica as a sorbent for fully automated online solid‐phase extraction with LC–MS determination of sulfonamides in bovine milk samples

Sulfonamides are antibiotics widely used in the treatment of diseases in dairy cattle. However, their indiscriminate use for disease control may lead to their presence in tissues and milk and their determination requires a sample preparation step as part of an analytical approach. Among the several sample preparation techniques available, those based upon the use of sorptive materials have been widely employed. Recently, the application of ionic liquids immobilized on silica surfaces or polymeric materials has been evaluated for such an application. This manuscript addresses the evaluation of silica‐based ionic liquid obtained by a sol–gel synthesis process by basic catalysis as sorbent for online solid‐phase extraction with liquid chromatography and electrospray ionization time‐of‐flight mass spectrometry for sulfonamides determination. Infrared vibrational spectroscopy confirmed the presence of the ionic liquid on the silica surface, suggesting that the ionic liquid was anchored on to the silica surface. Other sorbents varying the ionic liquid alkyl chain were also synthesized and evaluated by off‐line solid‐phase extraction in the sulfonamide extraction. As the length of the alkyl chain increased, the amount of extracted sulfonamides decreased, possibly due to a decrease in the electrostatic interaction caused by the reduction in the polarity, as well as the presence of a hexafluorophosphate anion that increases the hydrophobic character of the material. The use of 1‐butyl‐3‐methylimidazolium hexafluorophosphate as a selective ionic liquid sorbent enabled the isolation and sulfonamide preconcentration in bovine milk by online solid‐phase extraction with liquid chromatography and electrospray ionization time‐of‐flight mass spectrometry. The limit of quantification for the method developed was 5–7, 5 μg/mL, with extraction recoveries ranging between 74 and 93% and intra‐ and interassay between 1.5–12.5 and 2.3–13.1, respectively.