Normal stacking mode (NSM) in improving the detection sensitivity of dioxin related compounds using micellar electrokinetic chromatography

Abstract

Micellar electrokinetic chromatography (MEKC) with diode array detection (DAD) was used to separate two dioxin related compounds viz. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzo-p-furan (TCDF) using 20 mM sodium cholate, 20 mM sodium tetraborate-decahydrate with 5% v/v organic modifier (3:1 acetonitrile-methanol). To enhance sensitivity of detection, normal stacking mode (NSM-MEKC) which is the simplest stacking mode was used just by dissolving the analytes in water and injected into the capillary as a long plug. The hydrodynamic injection time was optimized by varying the injection time length in the ranges of 1s, 4s, 10s, 20s, 30s, 40s and 50s at constant hydrodynamic pressure of 50 mbar. From the optimum injection time obtained, calibration graphs of both TCDF and TCDD were constructed to calculate the detection limit obtained. A detection sensitivity enhancement factor (SEFLOD) of 330 was achieved for 2,3,7,8-TCDD achieving a detection sensitivity of 0.05 ppm while for 2,3,7,8-TCDF the SEFLOD was 65 with a detection sensitivity of 0.34 ppm. Stacking efficiencies were compared to that of normal mode (NM- MEKC) whereby no stacking is involved.