Determination of inorganic anions by capillary ion-exchange chromatography using polyethylenimine-coated octadecyl-bonded phases.

The utility of a cationic polymer polyethylenimines (PEI) for coating some commercially available silica-based stationary phases packed in capillaries of 0.32 mm i.d. and 10 cm long was studied for the separation and direct UV detection of inorganic anions (iodate, bromate, nitrite, bromide, and nitrate ions). With a super-endcapped octadecylated silica stationary phase, which yielded the best separation in terms of resolution and retention time of individual anions, the effect of the pH and composition of the eluent on the elution behavior of individual anions was studied. The relative standard deviations of the retention time, peak area and peak height for 60 successive injections (running time of more than 10 h) were not more than 1.32, 2.30 and 1.94, respectively, with the exceptions of the peak area and peak height of the bromate ion. The detection limits at 210 nm ranged from 1 to 7 ppm. This method was successfully applied to determine concentrations of nitrate ions present in pills and beverage samples.