On-column complexation and simultaneous separation of vanadium(IV) and vanadium(V) by capillary electrophoresis with direct UV detection

An on-column complexation method has been developed for the simultaneous determination of V(IV) and V(V). Vanadium species were chelated with aminopolycarboxylic acids to form anionic complexes which were separated by capillary zone electrophoresis (CZE) with direct UV detection. Ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetric acid (DTPA), nitrilotriacetic acid (NTA), and N-2-hydroxyethylethlendiaminetriacetric acid (HEDTA) were investigated as both ligand and running electrolyte. Of the ligands studied the complexes of EDTA with V(IV) and V(V) resulted in the highest selectivity and UV response. The conditions used for on-column complexation and separation, including pH, and electrolyte ligand concentration, were examined to achieve reasonable separation selectivity and detection sensitivity. The optimum separation of the anionic forms of V(IV) and V(V) was obtained by use of CZE with UV detection at 185 nm and an electrolyte containing 5 mmol L-1 EDTA at pH 4.0. Linear calibration plots were obtained in the concentration range 10-300 mumol L-1; detection limits were 3 mumol L-1 for V(IV) and 1 mumol L-1 for V(V). The proposed method was demonstrated for the determination of vanadium in groundwater spiked with V(IV) and V(V).