The perfluorocarbon tracers (PFTs) are usually analysed using packed columns and an electron capture detector (ECD), which provides extremely low detection limits (ca. 0.2-1.0 femtograms of PFT). The ambient background of these compounds can easily be measured using less than a litre of air. This sensitivity is achieved only with considerable sample processing involving removal of VOCs, freons, oxygen and water. The hardware modification to the sample inlet of the GC is extensive, including a complicated heart-cutting step, a catalytic reduction column and Nafion drying. The GC once modified is dedicated to PFT analysis, necessitating a considerable cost and reduced use of the instrument for other applications. A simple, sensitive method for analysis of these compounds that can be easily set-up and removed would permit more extensive use of the technology.
The advent of capillary columns utilising a microporous carbon layer has enabled the rapid and efficient separation of these compounds using a simple benchtop GC-MS system operating in EI or NCI modes for the detection of PFTs without the need for extensive sample processing as is required when using the ECD. The selection of ionisation mode determines the limit of detection of the method, NCI permitting considerably greater selectivity and sensitivity than EI. We have shown that the carbon layer capillary column adequately resolves the perfluorocarbons and easily separates them from oxygen, hydrocarbons and water. The remaining interferences are due to chlorofluorocarbons (CFCs), which are present in ppb concentrations in the atmosphere, and dominate analyses using ECD without catalytic removal, but respond quite differently to Negative Ion Chemical Ionisation. The ambient background concentration has been measured at several sites in NSW using this method, and atmospheric dispersion experiments using the tracer PMCH have been successfully undertaken.