Separation and concentration of sulfonylurea herbicides in milk by ionic‐liquid‐based foam flotation solid‐phase extraction

The ultrasound‐assisted ionic liquid foam flotation solid‐phase extraction of sulfonylurea herbicides in milk was developed and validated. The proteins and lipids were isolated from the sample matrix by adding salt and adjusting the pH value. The target analytes eluted from the solid‐phase extraction cartridge were determined by high‐performance liquid chromatography. Some experimental parameters, including the pH value of sample solution, amount of NaCl, ionic liquid type, extraction time, flow rate of carrier gas, flotation time, and solid‐phase extraction cartridge type were investigated and optimized. Under the optimized experimental conditions, the limits of detection for metsulfuron, pyrazosulfuron, chlorimuron‐ethyl, and nicosulfuron were 1.3, 0.6, 0.7, and 1.1 μg/L, respectively. When the present method was applied to the analysis of milk samples the recoveries of the analytes ranged from 84.3 to 105.2% and relative standard deviations were >5.7%.