Use of Triethylenetetraminehexaacetic Acid Combined with Field-Amplified Sample Injection in Speciation Analysis by Capillary Electrophoresis

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Abstract
Simultaneous speciation of lead, mercury, and selenium was carried out by capillary electrophoresis. The method used a polyaminocarboxylic acid, triethylenetetraminehexaacetic acid (TTHA), as an off-column complexing agent to form UV-absorbing complexes with the analytes for direct UV detection. TTHA was also added to the background electrolyte for the on-column complexations of the analytes, as well as for improving resolution and detection. To describe the migration behavior of the complexes, a theoretical model, considerating pH value and the concentrations of TTHA and SDS, was proposed. The parameters in the model were calculated on the basis of the experimental data, by nonlinear regression. The results were in good agreement with those from the literature. The model can be used for the prediction of migration behavior and for the optimization of the separation conditions. Field-amplified stacking injection was performed because the complexes were charged. Up to 1500-fold on-line enrichment and down to sub-nanogram-per-milliliter detection limits were obtained for the analytes under the optimal stacking conditions. Finally, the applicability of the method was evaluated on seawater samples.