CARBONATE INTERFERENCES BY ION-CHROMATOGRAPHIC DETERMINATION OF ANIONS IN MINERAL WATERS

The high content of hydrogen carbonate anions and dissolved CO2 in som e mineral waters interfere with the determination of anions in such sa mples by ion chromatography. It was found that the irreproducibility o f retention times of all anions present in the samples was caused by o n-column neutralisation of CO32- to HCO3- by CO2. Microbubbles of CO2 released downstream by the suppressor inhibited exchange of Na+ with H 3O+ resulting in lower conductivity and consequently in the decrease o f chloride peak. To avoid peak deformation and overlapping caused by c arbonate species, they should be removed by acidification followed by CO2 elimination in a gas separation unit. To prevent sample contaminat ion by the anion of the added acid, the electrodialytic clean-up proce dure was applied. The liberated CO2 was removed in a microporous Gore- Tex semipermeable tubing connected in series with the dialytic cell. T he developed dialytic clean-up procedure was applied to the analysis o f some typical mineral waters.