| Abstract: | Interest in monitoring halogenated organics in drinking water and natural surface and ground water in the low ppb range continues to grow. There is a tendency to include still more volatile halocarbons, the trace determination of which is known to be rather demanding. This prompted us to re-examine the feasibility of large-volume direct aqueous injection onto capillary columns, coupled with ECD. A primary problem was to avoid simultaneous elution of water with halocarbons, since water suppresses the ground current of the ECD. The following measures contributed to the solution of this problem. Apolar, extremely inert, columns are required to elute water completely, and even before very light halocarbons. Their coatings have to be far thicker (≈? 5 mUm) than commonly employed thick films since they must permit isothermal analysis at a column temperature around 100°C in order to ensure rapid and complete elution of water. Finally, it is essential that sampling be carried out on-column for two reasons: diffusion of water vapor in the injector, resulting in delayed elution, is then eliminated, and peak distortion during splitless injection is avoided. Although we now know that persilylated columns with immobilized coatings withstand routine water injections, more longterm experience is needed to provide detailed recommendations for the handling of these columns. |
