Analysis of dioxin and furan related compounds and organophosphorous pesticdes using micellar electrokinetic chromatography

Abstract

Micellar electrokinetic chromatography (MEKC) is increasingly popular in the analysis of organic pollutants in the environment due to its high separation efficiency, less solvent usage and shorter analysis time. In this study, MEKC was used for the separation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8- tetrachlorodibenzo-p-furan (TCDF) with a separation buffer consisting of 20 mM sodium cholate, 20 mM sodium tetraborate decahydrate and 5% v/v organic modifier acetonitrile-methanol (3:1 v/v) at a final buffering pH of 9.16-9.22. Separation voltage was at 25 kV with anodic injection and optimum wavelength set at 225 nm. To improve the limit of detection (LOD), five on-line preconcentration techniques were evaluated. The techniques were normal stacking mode (NSM-MEKC), reversed electrode polarity stacking mode (REPSM-MEKC), high conductivity sample stacking mode (HCSSM-MEKC), sweeping and field enhanced sample injection (FESI-MEKC). High conductivity sample stacking method-MEKC (HCSSMMEKC) that gave an LOD of 46 ppb for TCDF and 18.5 ppb for TCDD was chosen. Solid phase disc extraction (SPDE) was used to further improve the LOD during the extraction of TCDF and TCDD from water thus reducing the LODs by 1000 fold. LODs in the ppt range were achieved for both analytes. This is the first study conducted using MEKC for 2,3,7,8-TCDF and 2,3,7,8-TCDD. Selected hydrophilic organophosphorous pesticides were also included in this study. They were dicrotophos, monocrotophos and phosphamidon. Separations were carried out using acidic buffer (pH 2.3) with a buffering system consisting of 10 mM sodium dodecyl sulphate, 20 mM sodium dihydrogen phosphate and 10% v/v methanol. Optimum detection wavelength of 225 nm with separation voltage at -25 kV was used. MEKC separation gave LODs of 32.1 ppm for dicrotophos, 3.75 ppm for monocrotophos and 18.6 ppm for phosphamidon. Stacking with reverse migrating micelles (SRMM) gave better LODs of 0.15 ppm for dicrotophos, 0.39 ppm for monocrotophos and 0.22 ppm for phosphamidon. SPDE was able to reduce the LOD further by 250 fold. Sample matrix used was spiked pond water. MEKC was successfully used to separate the test analytes in pond water sample. These analytes consisted of 2,3,7,8- TCDF and 2,3,7,8-TCDD under basic conditions and three hydrophilic organophosphorous pesticides under acidic conditions with analysis time of less than 10 minutes.