Introduction of large volumes of methylene chloride in capillary GC with electron capture detection

In this paper we present a system that allows direct introduction of large volumes of methylene chloride in capillary gas chromatography using electron capture detection. The system is based on a two-dimensional (one-oven) GC instrument equipped with a programmed temperature injector. The methylene chloride sample is introduced into the liner of the programmabie injector at a controlled speed. During sample introduction the solvent is eliminated via the split line by applying a high flow of purge gas at a reduced iniet pressure. In this stage of the sample introduction process the pre-column is back-flushed in order to prevent transfer of methylene chloride into the column. After completion of the solvent elimination the components retained in the liner of the injector are transferred to the pre-column in the splitless mode. Traces of methylene chloride eluting from the pre-column are eliminated via a column-switching device placed between the pre-column and the analytical column. The method described in this paper was used for the analysis of pesticides and polychlorinated biphenyls (PCBs) in methylene chloride at ultra low concentration. Using the system described here the solvent exchange, normally required when ECD detection is used, was eliminated. Moreover , the detection limits were significantly improved by the introduction of large sample volumes.