Electrically driven microseparation methods for pesticides and metabolites Part VII: Capillary electrophoresis and electrochromatography of derivatized and underivatized phenol pesticidic metabolites. Preconcentration and laser induced fluorescence detection of dilute samples

Abstract

In this report, the electrophoretic migration and electrochromatographic retention behaviors of underivatized and derivatized phenol pesticidic metabolites were evaluated over a wide range of conditions in capillary electrophoresis (CE) and capillary electrochromatography (CEC), respectively. Also, a precolumn derivatization for these environmental pollutants with a fluorescent tag, namely carbazole-9-N-acetic acid (CRA), was evaluated in their detection at low levels by laser induced fluorescence (LIF) detection after CE and CEC separation. Due to the fact that underivatized phenols are very weak acids and also relatively nonpolar compounds, they were readily separated by either capillary zone electrophoresis (CZE) at alkaline pH or by surfactant-mediated electrokinetic capillary chromatography (SM-EKC). SM-EKC was performed in the presence of hydro-organic electrolyte systems based on mixtures of the surfactant dioctyl sulfosuccinate sodium salt (DOSS) and acetonitrile. Upon derivatization with CRA, the phenols become neutral species and their nonpolar character increases. The retention behaviors of the CRA-phenol derivatives were evaluated and compared in both CEC and SM-EKC. Although the separation mechanism in both CEC and SM-EKC is based primarily on hydrophobic interaction, the two separation approaches yielded different selectivity. Using LIF detection, the LOD's of the CRA-phenol derivatives were in the range 10–7 to 10–9 M in SM-EKC and CEC for most phenols. However, polychlorinated phenols (containing 3 or more chlorine atoms) did not derivatize with CRA to a sufficient extent and also their derivatives did not fluoresce due to the quenching effect of halogen substitution. In order to overcome this shortcoming, an on-column preconcentration procedure based on field amplified sample stacking (FASS) for underivatized phenols prior to CZE separation was demonstrated. FASS permitted LOD's at low levels in the range 10–7 to 10–9 M in deionized and tap waters.