Micellar electrokinetic chromatography with amperometric detection and off-line solid-phase extraction for analysis of carbamate insecticides |
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Authors: | Apichai Santalad Lin Zhou Fengjun Shang Dara Fitzpatrick Rodjana Burakham Supalax Srijaranai Jeremy D. Glennon John H.T. Luong |
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Affiliation: | 1. Irish Separation Science Cluster (ISSC), Department of Chemistry and Analytical and Biological Chemistry Research Facility (ABCRF), University College Cork, Cork, Ireland;2. Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand;3. Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec H4P 2R2, Canada |
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Abstract: | Six selected primary carbamate insecticides, methomyl, carbaryl, carbofuran, propoxur, isoprocarb, and promecarb, were hydrolyzed in alkaline solution, resulting in electroactive derivatives detectable at a platinum (Pt) electrode poised at +0.8 V vs Ag/AgCl (3 M NaCl). The Pt electrode was inserted into a small electrochemical cell and positioned close to the capillary outlet as an end-column detector to detect the carbamate derivatives after electrophoretic separation. Based on their predicted pKa values and aqueous solubilities, micellar electrokinetic chromatography (MEKC) was optimized for baseline separation of the derivatives using 20 mM borate, pH 10.2 containing 20 mM sodium dodecyl sulfate as a running buffer. When combined with solid-phase extraction (SPE) on octadecyl silica, a preconcentration factor of 100-fold achieved detection to 0.5 μM methomyl and to 0.01 μM for the remaining five pesticides, significantly below the level regulated by government agencies of most countries. The SPE-MEKC method when applied to the separation and analysis of spiked river water and soil samples, yielded results with excellent reproducibility, recovery and selectivity. |
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Keywords: | Micellar electrokinetic chromatography Amperometric detection Platinum electrode Solid-phase extraction Carbamates Hydrolyzed carbamates |
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