On-capillary ion-exchange preconcentration of inorganic anions using open-tubular capillaries followed by elution with a transient isotachophoretic gradient

A new method is described for the elution of inorganic anions in open-tubul ar capillary electrochromatography (in which an anion-exchange stationary p hase is adsorbed to the capillary wall) after preconcentration via ion-exch ange interactions. The method utilises a transient isotachophoretic gradien t, established using two electrolytes. The first contains a low mobility, w eak ion-exchange competing anion, with the second containing a higher mobil ity strong ion-exchange competing anion. Analytes are adsorbed onto the sta tionary phase in the weakly eluting electrolyte, but are efficiently desorb ed in the stronger eluting electrolyte. By selecting the appropriate mobili ties and concentrations of the competing anions, it is possible to obtain h ighly efficient elution of the analytes from the concentrator column, resul ting in a peak compression/focusing effect. The principle of this method fo r peak compression and elution from the column was demonstrated for iodide, which could be eluted as a peak of width less than 0.1 s, correlating to a n elution volume of approximately 40 nL. The potential of this method was d emonstrated using bromide and nitrate, which were preconcentrated on a coat ed section of the capillary, eluted with an isotachophoretic gradient, and separated by capillary zone electrophoresis. Detection limits obtained for iodide, bromide and nitrate using this method were 2.24 nM, 0.86 mu M, and 0.32 mu M, respectively.