Improving sensitivity in simultaneous determination of copper carboxylates by nonaqueous capillary electrophoresis.

A new method of nonaqueous capillary electrophoresis (NACE) with UV spectrophotometric detection was developed and optimized for the simultaneous determination of seven carboxylates (trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), nitrilotriacetic acid (NTA), 1,3-diaminopropane-N,N,N',N'-tetraacetic acid (PDTA) and triethylenetetraaminehexaacetic acid (TTHA)) as copper complexes. The method development was carried out by using a fused silica capillary. Background electrolyte (BGE) was optimized and the best separation achieved by using 30mmolL(-1) potassium bromide in N-methylformamide (NMF) at apparent pH (pH(app)) 10.2. A voltage of +30kV and direct UV detection at 280nm were used in all measurements. Large-volume sample stacking using the electroosmotic flow pump (LVSEP) was tested in addition to basic capillary electrophoresis (CE) and observed to improve the separation of the analyte zones in the capillary. All the peaks in the electropherograms were properly separated, the calibration plots gave excellent correlation coefficients (R(2)>or=0.994) and all seven copper carboxylate complexes were detected in less than 20min using both the basic measurements and the large-volume sample stacking method. The new NACE method was tested with lake water and proved to be reliable.