Determination and Quantitation of Ten Sulfonylurea Herbicides in Soil Samples Using Liquid Chromatography with Electrospray Ionization Mass Spectrometric Detection

A multiresidue method was developed for confirmation and quantitation of ten sulfonylurea herbicides including nicosulfuron, thifensulfuron-methyl, metsulfuron-methyl, sulfometuron-methyl, chlorsulfuron, ethametsulfuron-methyl, tribenuron, bensulfuron-methyl, pyrazosulfuron-ethyl, and chlorimuron-ethyl in soil. Analytes were extracted from the soil sample with methanol-phosphate buffer (2:8, v/v) (pH 7.8) in an ultrasonic bath. The extracts were adjusted to pH 2.5 with 85% H3PO4 and passed, under vacuum, through a solid-phase extraction cartridge. Several types of adsorbents were evaluated, including silica-based Cleanert C18 and two polymeric adsorbents (Oasis HLB and Cleanert HXN). Cleanert C18 showed good cleanup effects in the study. Determination and quantitation were performed by high performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) instrumentation equipped with an ion trap mass filter. Analytes were eluted on a HPLC column of 4.6 mm × 250 mm XDB C18, 5 × particle size, in the mobile phase of the acetonitrile (solvent A)-methanol (solvent B)-0.2% acetic acid (solvent C). The elution gradient was as follows: the mobile phase started with 10% of acetonitrile and 10% methanol, which increased linearly to 45% in 14 min, to 48% in the next 2 min and then returned to the initial condition in 2 min. The column temperature was kept at 30°C with a flow rate of 1.0 ml/min. Thus the retention time of nine herbicides was in the range of 10 to 16 minutes. Spiked soil at 0.01–1.0 mg/kg levels was checked. Average recoveries were in the range of 80.2%–104.5% with relative standard deviations (RSDs) of 0.02%–14.90%. The limit of detection (LOD) of this method was in the range of 0.6 to 3.5 μg/kg.