Ion-chromatographic measurements of ammonium,fluoride, acetate,formate and methanesulphonate ions at very low levels in antarctic ice

Ion chromatography is used to determine the concentrations of organic (formate, acetate and methanesulphonate) and inorganic (fluoride and ammonium) ions present in Antarctic ice at less than 10⁻⁹ g g⁻¹ levels. With suitable columns, the simultaneous measurement of these ions requires only 6 min. A sample volume of 5 ml is sufficient to reach the 10⁻¹⁰ g g⁻¹ level. The determination of such low concentrations requires stringent contamination-free techniques. For formate and acetate, the samples should never come into contact with plastics. Except for methanesulphonate, all the ions studied can be produced by dissolution of the various gaseous compounds present in a polluted atmosphere. Therefore a glass device with pure nitrogen circulation was designed for air-free melting of samples. To prevent possible biological activity on organic matter, samples were analysed immediately after melting. Measurements of ammonium ion in these Antarctic ice samples demonstrate that the problem of contamination by surrounding ammonia was not completely eliminated in previous studies. The serious contamination problems encountered, particularly for carboxylic acids, cast doubt on some earlier results for remote areas.