Coated capillaries with highly charged polyelectrolytes and carbon nanotubes co-aggregated with sodium dodecyl sulphate for the analysis of sulfonylureas by capillary electrophoresis

• SC-SWCNTs were found to be strongly absorbed on the PDADMAC.
• A very stable double layer PDADMAC/SC-SWCNTs was obtained.
• Four sulfonylureas were separated by CE in mineral and underground waters.
• Excellent peak efficiencies superior to 110,000 theoretical plates were obtained.
• Coating was very stable at high pH and tolerates aggressive organic solvents.

Sulfonylureas (SUs) are one of the most widely used herbicides to control weeds in crops. Herein, capillary electrophoresis (CE) was used to determine four sulfonylureas in natural waters, namely chlorsulfuron (CS), iodosulfuron methyl (IM), metsulfuron methyl (MSM) and mesosulfuron methyl (MSS). First of all, a bare silica capillary was chosen with 10 mM of 1-butyl-3-methylimidazolium tetrafluoroborate (bminBF4) as electrophoretic buffer (pH 9.6) containing 2 mg L−1 of surfactant-coated single-wall carbon nanotubes (SC-SWCNTs). A dramatic deviation in migration times was observed. Therefore, a poly(diallyldimethylammonium) chloride (PDADMAC) statically coated cationic capillary was used to improve repeatability and to alter the selectivity of the separation. The electroosmotic flow (EOF) measurement revealed that the SC-SWCNTs were strongly adsorbed at the surface of the PDADMAC coating even in the absence of the surfactant-coated nanotubes in the electrolyte buffer. Consequently, a stable strong cathodic EOF and excellent repeatabilities were obtained with relative standard deviations (RSDs) on migration times and on corrected peak areas below 0.9 and 1.5%, respectively. The separation of the SUs was conducted in only 6 min. No regeneration of the coating between analyses was necessary, and high peak efficiencies up to 173,000 theoretical plates were obtained. The bi-layer coating was subsequently used to analyze sulfonylureas in tap water, in several mineral waters as well as in underground waters spiked with SUs and directly injected into the CE capillary.