From Tech Trends November 1994

Site Search to Evaluate Soil-Gas Monitor

The EPA is adapting the U.S. Army's hand-held chemical agent monitor (CAM) to the area of environmental risk assessment analysis. The monitor is now ready for a field demonstration and evaluation; and, EPA's Environmental Monitoring Systems Laboratory at Las Vegas (EMSL-LV) is searching for a site to field evaluate this innovative technology. EMSL-LV, together with Washington State University, built the prototype field monitor that couples gas chromatography with a Fourier transform ion mobility spectrometer (GC-FTIMS). The monitor is a good candidate for on-site detection of vinyl chloride, other chlorinated gases and many chlorinated solvents that are regulated at concentrations near the one part per billion level in soils and water. These compounds are frequently trapped in the soil-gas spaces and are difficult to analyze because of the physical problems of obtaining and preserving the sample as well as the challenges inherent in the subsequent analysis. The GC-FTIMS is particularly well suited for this type of analysis because it merges the separation power of capillary gas chromatography with the sensitivity of ion mobility spectrometry and incorporates a Fourier transform to achieve ruggedness for in situ analysis. The GC-FTIMS offers an alternative to 100% laboratory analysis of samples. The GC-FTIMS has been tested in the laboratory and has turned out good results.

If you think your site is a good candidate for a field evaluation of the monitor, call Ken Brown at the EMSL-LV Technology Support Center at 702-798-2270.

Here's how it works. Reactive ions are formed from air or carrier gas molecules by using either a nickel-63 (continued from page 2) beta source or a photoionization source. These ions then react with analyte molecules, after having been separated by GC, to form ion clusters which are then measured by atmospheric pressure time of flight (IMS). The ions enter a drift region where they move through an applied field toward a collector electrode. The electrode current is monitored continuously, allowing a mobility spectrum to be measured. The specificity is imparted by the ionization preferences of analytes and the mobility differences of the ion clusters. Separations are a function of ion size.

Selectivity of IMS for various analytes is based on the atmospheric pressure ionization events themselves, which relate to the proton and electron affinities of the analytes, the polarity of the products (i.e., positive or negative ions) and the mobility of those ions. Analytes with higher proton or electron affinities than other constituents of the ambient environment are differentiated and detected easily. Analytes with low affinities can be measured when competing chemicals with higher affinities are not present. Thus, compounds such as benzyl chloride, halogenated compounds, hydrogen cyanide, nitro-compounds (explosives), organophosphorus compounds, phenols, phosphorus trichloride, toluene diisocyanate and vinyl chloride are better suited to analysis by IMS than are compounds like hexane and benzene.

If your site is used to evaluate the GC-FTIMS, you will get immediate on-site data that will enable you to make immediate decisions. In order to determine the performance of the GC-FTIMS system during field measurement, a selected number of split samples should be sent to an approved laboratory for confirmatory analysis, using approved laboratory methods or a gas chromatography-mass spectrometry.

For more technical information, call Tammy Jones at EMSL-LV at 702-798-2270. But, call Ken Brown at 702-798-2270 if you want to discuss field evaluation of the monitor at your site.