DETERMINATION OF DISSOLVED ARGON AND NITROGEN IN WATER BY DIRECT AQUEOUS INJECTION GC-HID

A gas chromatography-based automated method was developed for direct a queous injection analysis of trace gases dissolved in water samples to support studies on air-water exchange processes of chemicals. Initial efforts were focused on the determination of dissolved gases such as Ar and N-2 because of their potential to serve as ''tracer'' species ( or as ''surrogates'') for the air-water exchange process. Direct injec tion of water samples eliminated time-consuming sample preparation pro cedures and enabled short analysis cycles. The method employed a GC eq uipped with a helium ionization detector (HID) to achieve sensitivity sufficient for water analysis with direct injection of 10 mu L water v ia a liquid sample valve. Analytes were isolated from the water matrix using a column switching technique prior to the separation and detect ion. Chromatographic separation of Ar, O-2 and N-2 was achieved with a long, 30-foot molecular sieve column. However, a short, 6-foot column combined with a chemical scrubber for O-2 was selected in order to en sure accurate quantitation of Ar and shorten the analysis cycle to 15 minutes. The precision for determination of Ar and N was 1% RSD, with a method detection limit of ca. 30 mu g/L Ar or N-2 in water and a lin ear range of ca. 2.5 orders of magnitude.