Influence of the sample matrix composition on the accuracy of the ion chromatographic determination of anions

The influence of high concentrations of chloride on the accuracy of the determination of nitrite and nitrate by suppressed ion chromatographic analysis was studied using UV-Vis and conductivity detectors. It was found that in the presence of high concentrations of chloride between 0.1 and 10.0 g/l, the retention times of nitrite and nitrate were significantly increased, and co-elution of the two anions was observed at chloride concentrations greater than 15.0 g/l. The nitrite response (absorbance) was found to decrease with increased chloride concentration, whereas the nitrate response did not change significantly. Calibration graphs for nitrite (1-10 mg/l) in solutions containing chloride were linear but their slopes decreased exponentially with increase in chloride concentration. At the same time the slopes of the calibration graphs for nitrate under similar conditions did not vary significantly. It was found that the decrease in the nitrite peak area was the result of a decrease in the absorptivity (210 nm) caused by the protonation of NO; in the suppressor column, The increase in the retention times of the anions can be explained by the self-elution effect of the chloride present in the sample and on-column changes in eluent composition.