Normal Stacking as an Online Concentration in Micellar Electrokinetic Chromatography for the Separation of Different Classes of Fungicides
Neutral analytes can be separated using micellar electrokinetic chromatography (MEKC), a method initially developed by Terabe and co-workers. MEKC offer higher efficiencies and faster analysis times than those achieved with high performance liquid chromatography (HPLC). However, one drawback of MEKC is the poor sensitivity due to a short path length in on-column UV detection and minute injection volumes (nL). In this study, an on-line concentration method called stacking with
electrokinetic injection (SEKI) and stacking with hydrodynamic injection (SHDI) were explored to improve the detection sensitivity of three classes of fungicides, viz. benzimidazoles (carbendazim, thiabendazole), triazoles (propiconazole) and dicarboximide (vinclozolin). Optimized separation of these four fungicides was achieved using 20 mM ammonium formate at pH 7, 60 mM sodium cholate, 5 mM β-cyclodextrin (CD), 25 kV separation voltage, and on-column UV detection at 210 nm. All four fungicides were successfully separated in less than 15 minutes. It was found that SEKI at 5 kV injection voltage for 20s injection time produced the highest sensitivity enhancement factor in terms of area (SEFarea) of about 40-68. A value of 10 for SEF corresponds to 1 order of magnitude improvement in concentration detection limit. The LOD of these four fungicides was found to be in the sub-ppm range (0.6-2.6 ppm).