Determination of ten sulfonylurea herbicides in soil samples by liquid chromatography with electrospray ionization mass spectrometric detection

A multi-residue method has been developed for the confirmation and quantitation of ten sulfonlylurea herbicides including nicosulfuron, thifensulfuron-methyl, metsulfuron-methyl, sulfometuron-methyl, chlorsulfuron, ethametsulfuron-methyl, tribenuron, bensulfuron-methyl, pyrazosulfuron-ethyl and chlorimuron:ethyl in soil. Samples were extracted from soil with methanol-phosphate buffer (2:8, V/V) (pH 7.8) under ultrasonic bath. Then the extracts were brought, to pH 2.5 with 85% H3PO4 and passed under vacuum through a solid-phase cartridge. Different types of sorbents were evaluated: silla-based Cleanert C-18 and two polymeric sorbents, namely Oasis HLB and Cleanert HXN. The best results were obtained with Cleanert C-18, and was performed by high performance liquid chromatography ( HPLC) -electrospray mass spectrometry( LC-ESI-MS) instrumentation equipped with ion trap mass filter. The HPLC column used was a 4.6 mm x 250 mm XDB C-18 column, 5 mu m particle size. The mobile phase was acetonitrile-methanol-0.2% acetic acid. The elution gradient was as follows: the mobile phase started with 10% of acetonitrile and 10% methanol, which was increased linearly to 45% in 14 min, to 48% in the next 2 min and then returned to initial conditions in 2 min. The column was equilibrated for 5 min. The column temperature was kept at 30 degrees C and flow rate was 1.0 mL/min. The retention times of 10 herbicides were between 10 - 16 min. The ten sulfonylurea compounds above mentioned were measured in fortified soil at 0.01 - 1.0 mg/kg levels. Average recoveries were in the range of 80.2% - 104.5% with relative standard deviations ( RSDs) of 0.02% 14.9%. The limit of detection(LOD) was 0.6 - 3.5 mu g/kg.