Chromate as a Mobile Phase for the Determination of Anions Using Cetyl-Trimethylammonium-Coated Columns and Indirect Photometric Detection

Abstract

Abstract A suitable indirect photometry chromatographic system for the separation and detection of common inorganic and organic anions was made by dynamically coating an octadecyl-bonded silica column with cetyltrimethylammonium ions and using potassium chromate as the eluent. The effect of chromate ion concentration on the capacity factor indicates an ion-exchange mechanism. The detection limit of the anions F−, Cl−, NO2 −, Br−, and NO3 −, corresponding to a signal-to-noise ratio of 3, were 0.29, 0.55, 0.72, 0.83 and 0.97 ppm, respectively. A linear response was observed between peak heights and injection volume of a solution with 1.19 ppm F−, 2.22 ppm Cl−, 2.88 ppm NO2 −, 4.99 ppm Br− and 3.88 ppm NO3 −. This can further lower the detection limit of the anions by about 9 fold when a volume of 175 μL is injected. This system has been applied to the trace analysis of NO3 − in tap water. A concentration of 1.97 ± 0.10 ppm NO3 − was detected. This system was also found applicable for the separation of organic acids (formate, acetate, propionate and butyrate) and may also be used for the separation of a mixture of organic and inorganic anions.