Methods development for separation of fungicides using micellar electrokinetic chromatography

摘要

In this study, micellar electrokinetic chromatography (MEKC) was used for the simultaneous separation of three different classes of fungicides. Separations were done at 210 nm with on-column UV detection. Two different types of separation buffer system (borate and formate) were used. The influence of separation buffer concentration and pH, surfactant concentration, separation voltage and addition of organic solvents and modifiers on migration time, efficiencies and resolutions were investigated. Four fungicides from three different classes viz. carbendazim and thiabendazole (benzimidizole), propiconazole (triazole) and vinclozolin (dicarboximide) were successfully separated in less than 15 min using both separation buffer systems with propiconazole giving two stereoisomer peaks. A buffer system consisting of 4 mM borate buffer at pH 10, with 60 mM sodium cholate (SC) gave the best separation result. On the other hand, good separation was also achieved with a running buffer composed of 20 mM formate buffer at pH 7, containing 60 mM SC and 5 mM ß-cyclodextrin (ß-CD). The limit of detections (LODs) of fungicides in borate buffer system were in the range of 9 – 23 ppm and 29 – 52 ppm for formate buffer system. In an effort to reduce the LODs, two on-line preconcentration techniques with formate buffer system were used because of its higher LODs. The two on-line preconcentration techniques, sweeping and stacking with hydrodynamic (HDI) and electrokinetic (EKI) injection were contrasted. The effect of sample matrix, injection time and injection voltage on fungicides separation was studied using the two online preconcentration techniques. Using on-line preconcentration techniques, height and area sensitivity enhancement factor (SEFheight and SEFarea) were found to be between 10 to 99. LODs in the sub-ppm (0.3 – 4 ppm) level were obtained. At least 10-times improvement in detector response was achieved with normal stacking mode MEKC using hydrodynamic injection, NSM-MEKC-HDI. The proposed method was applied to the analysis of spiked fungicides in lake water samples at 2 – 4 ppm. The recovery was between 46.22 % to 93.30 % with RSDs of 10 % to 27 %.