Ultrasound-assisted ionic liquid/ionic liquid-dispersive liquid–liquid microextraction for the determination of sulfonamides in infant formula milk powder using high-performance liquid chromatography

Ultrasound-assisted ionic liquid/ionic liquid-dispersive liquid–liquid microextraction (UA-IL/IL-DLLME) high-performance liquid chromatography was developed and applied to the extraction, separation and determination of sulfonamides in infant formula milk powder samples. The hydrophobic IL and hydrophilic IL were used as extraction solvent and dispersion solvent, respectively. The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C6MIM][PF6] dispersed entirely into sample solution with help of [C4MIM][BF4]. The purification of sample and concentration of target analytes were performed simultaneously. The introduction of ion-pairing agent (NH4PF6) was beneficial to the improvement of recoveries for IL phase and analytes. The experimental parameters of the UA-IL/IL-DLLME, including concentration of [C6MIM][PF6] and [C4MIM][BF4] in sample solution, ultrasound extraction time, pH value of sample solution and amount of ion-pairing agent (NH4PF6), were evaluated. The limits of detection for sulfamerazine, sulfamethizole, sulfachlorpyridazine, sulfamonomethoxine, sulfmethoxazole and sulfisoxazole were 2.94, 9.26, 16.7, 5.28, 3.35 and 6.66 μg kg−1, respectively. When the present method was applied to the analysis of infant formula milk powder samples, the recoveries of the analytes ranged from 90.4% to 114.8% and relative standard deviations were lower than 7.5%. The proposed method was compared with the ionic liquid-homogeneous liquid–liquid microextraction, ionic liquid-ultrasound-assisted emulsification–microextraction and ionic liquid-temperature-controlled-DLLME. The results indicated that the proposed method is effective for the extraction of the sulfonamides in milk powder samples.