Solid-phase extraction of sulfonylurea herbicides from water samples with single-walled carbon nanotubes disk

This study presents a new, easily made and practical solid-phase extraction disk, a single-walled carbon nanotubes (SWCNTs) disk. The properties of the disk were evaluated by extracting large volumes of aqueous solution (500-3,000 mL) spiked with trace levels of sulfonylurea herbicides, metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl, pyrazosulfuron-ethyl, and chlorimuron-ethyl. The adsorption of analytes on the SWCNTs disk was more favorable at pH 3.0, and the adsorbed sulfonylurea herbicides could be eluted completely with acetonitrile (1% acetic acid) solvent. The disks were stacked to enhance their extraction ability to analytes. The triple layered SWCNTs disks system showed excellent extraction efficiency when the sample volume was up to 3,000 mL. A comparative study was conducted with a commercial C-18 disk and an activated carbon disk. The SWCNTs disks showed an adsorption capacity comparable to sulfonylurea herbicides to the C-18 disk and activated carbon disk, but the analytes retained on the activated carbon disk were hardly desorbed. Finally, the triple layered SWCNTs disks system was used to pretreat 1,000 mL of several environmental water samples spiked with the analytes, and satisfactory recoveries (79-102%) were obtained. Detection limits of 1.1-7.2 ng L-1 for analytes were achieved under the optimized conditions.