Determination of Purity of Sodium Chlorite and Its Anion Impurities by Replacement-Ion Chromatography

As an attachment to the conventional suppression ion chromatograph, two self-prepared ion replacement columns were installed in series between the suppressor and the UV-detector successively. The former is a cation replacement column of Li⁺-type and the latter is an anion replacement column of IO₃^--type. Dionex IonPac AS 18 anion exchange column was used for separation in IC analysis, and 30 mmol·L^-1 NaOH solution was used as mobile phase. In the determination of purity of sodium chlorite and its impurityanions, when the sample solution (prepared by dissolving 0.100 0 g of the sample in water, making its volume to 50.0 mL, and still-further by diluting an aliquot of the solution 100 times quantitatively) was separated through the anion-exchange column and then passed through the 2 ion-replacement columns, the anions, i.e., ClO₂^- and the other 4 anions, were all replaced to the same anion of IO₃^-, and determined at the wavelength of 210 nm by the UV-detector. As shown by the results, linear relationships between values of peak area and concentration of chlorite and other impurity ions were obtained in definite ranges, with detection limits (3S/N) in the range of 6.09-19.66 μg·L^-1. Test for recovery was made by standard addition method and the values of recovery were found in the range of 96.0%-101%, with RSDs (n=6) ranged from 1.1% to 3.0%.