Isotachophoretic analyses of anions at high pH

In isotachophoretic analyses of anions, performed in operational systems at high pH (pH > 7) disturbances due to carbon dioxide from the air can be expected. Even at neutral pH the isotachophoretic features can be obscured by this disturbance, because the pH of the sample zones has a tendency to increase from the leading zone towards the terminating zone in anion analysis 1,2. This disturbance, according to the principles of zone electrophoresis, can be caused by carbon dioxide dissolved in the terminating electrolyte. A minor disturbance can be expected from carbon dioxide dissolved in the leading electrolyte. It was found very convenient to prepare both the leading and terminating electrolytes under nitrogen. Barium hydroxide (analytical-reagent grade) was added to the terminating electrolyte to prevent carbonate from entering the separation compartment. The terminator compartment still needed to be refreshed completeley after each analysis. Complex formation between Ba2 + with sample anions was minimized by careful injection. Addition of barium hydroxide to the leading electrolyte is not recommended. Unwanted complex formation often occurs and precipitation of barium carbonate can block the capillary column. In this paper it is shown that isotachophoretic analyses of anions at pH >7 can be carried out by closing the separation compartment with semi-permeable membranes of cellulose polyacetate (0.1 mm thick) and having solely doubly distilled water in the electrode compartments. Both the leading and terminating electrolytes are consequently not in direct contact with air. Carbon dioxide already dissolved in the electrolyte during preparation still has to be taken into account.