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 th e determination of nitrite and nitrate by suppressed ion chromatograph ic analysis was studied using UV-Vis and conductivity detectors. It wa s found that in the presence of high concentrations of chloride betwee n 0.1 and 10.0 g/l, the retention times of nitrite and nitrate were si gnificantly increased, and co-elution of the two anions was observed a t chloride concentrations greater than 15.0 g/l. The nitrite response (absorbance) was found to decrease with increased chloride concentrati on, whereas the nitrate response did not change significantly. Calibra tion graphs for nitrite (1-10 mg/l) in solutions containing chloride w ere linear but their slopes decreased exponentially with increase in c hloride 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 resu lt of a decrease in the absorptivity (210 nm) caused by the protonatio n 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 chlo ride present in the sample and on-column changes in eluent composition .