Direct determination of bromide, nitrate, and iodide in saline matrixes using electrostatic ion chromatography with an electrolyte as eluent

A new ion chromatographic method that is applicable to the direct determination of UV-absorbing inorganic anions in saline matrixes is described. An octadecylsilica column modified with a zwitterionic surfactant (3-(N,N-dimethylmyristylammonio)propanesulfonate) is used as the stationary phase, and an electrolytic solution is used as the eluent. Under these conditions, the matrix species (such as chloride and sulfate) are only retained weakly and show little or no interference. It is proposed that a binary electrical double layer (EDL) is established by retention of the eluent cations on the negatively charged (sulfonate) functional groups of the zwitterionic surfactant (forming a cation-EDL) and by retention of eluent anions on the positively charged (quaternary ammonium) functional groups of the zwitterionic surfactant (forming an anion-EDL). Sample anions are able to distribute into the cation-EDL and to form ion pairs with the EDL cations, while at the same time experiencing repulsion from the anion-ED...