Determination of alternative and conventional chelating agents as copper(II) complexes by capillary zone electrophoresis—The first use of didecyldimethylammonium bromide as a flow reversal reagent

A capillary zone electrophoresis (CZE) method for analyzing 11 chelating agents [alaninediacetic acid ((beta)-ADA), trans-1,2diaminocyclohexane-N,N,N,N-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N,N-triacetic acid (HEDTA), N-(2-hydroxyethyl)iminodiacetic acid (HEIDA), iminodiacetic acid (IDA), methylglycinediacetic acid (MGDA), nitrilotriacetic acid (NTA), 1,3-diaminopropane-N,N,N,N-tetraacetic acid (PDTA) and triethylenetetraaminehexaacetic acid (TTHA)] as negatively charged copper(II) complexes has been established. Both conventional and alternative chelating agents were included in this study, because they are used side by side in industrial applications. In this study, didecyldimethylammonium bromide (DMDDAB) was successfully used as a flow reversal reagent for the first time in an aqueous CZE method based on phosphate BGE with UV spectrophotometric detection. In addition this new flow modifier was compared to common TTAB. Method development was done using a fused silica capillary (61 cm × 50 (mu)m i.d.). The optimized BGE was a 105 mmol L^-1 phosphate buffer with TTAB or DMDDAB in the concentration 0.5 mmol L^-1 at pH 7.1. The measurements were done with -20 kV voltage using direct UV detection at 254 nm. In both CZE methods all 11 analyte zones were properly separated (resolutions (less than or equal)2.4), and the calibrations gave excellent correlation coefficients ((less than or equal)0.998; linear range tested 0.5–2.0 mmol L^-1). The limits of detection were (less than or equal)34 and (less than or equal)49 (mu)mol L^-1 with the method of DMDDAB and TTAB, respectively. A clear benefit of both methods was the short analysis time; all 11 complexes were detected in less than 6 and 5.5 min with the methods of TTAB and DMDDAB, respectively. The two methods were tested with dishwashing detergents and paper mill wastewater samples and proved to be suitable for practical use.