Anion-exchange capillary electrochromatography with indirect UV and directcontactless conductivity detection

Conductivity detection is applied to ion-exchange capillary electrochromato graphy (IE-CEC) with a packed stationary phase, using a capacitively couple d contactless conductivity detector with detection occurring through the pa cked bed. Columns were packed with a polymeric latex-agglomerate anion-exch anger (Dionex ASS-SC). A systematic approach was used to determine suitable eluants for IE-CEC separations using simultaneous indirect UV and direct c onductivity detection. Salicylate and p-toluenesulfonate were identified as potential eluant competing anions having sufficient eluotropic strength to induce changes in separation selectivity, but salicylate was found to be u nsuitable with regard to baseline stability. It was also found for both ind irect UV and direct conductivity detection that homogenous column packing w as imperative, and monitoring of the baseline could be used to assess the h omogeneity of the packed bed. Using a p-toluenesulfonate eluant, the separa tion of eight common anions was achieved in 2.5 min. Direct conductivity de tection was found to be superior to indirect UV detection with regard to bo th baseline stability and detection sensitivity with detection limits of 4- 25 mug/L being obtained. However, the calibration for each anion was not li near over more than one order of magnitude. When using conductivity detecti on, the concentration of the eluant could be varied over a wider range (2.5 -50 mM p-toluenesulfonate) than was the case with indirect UV detection (2. 5-10 mM), thereby allowing greater changes in separation selectivity to be achieved. By varying the concentration of p-toluenesulfonate in the eluant, the separation selectivity could be manipulated from being predominantly i on-exchange in nature (2.5 mM) to predominantly electrophoretic in nature ( 50 mM).