The analyte concentration is less than the 340 ppbv vapor pressure of NG and includes a separation of the NG from volatile impurities. This separation illustrates both the connection of the EVM II to existing IMS application bases for detection of explosives and drugs, and the potential of the technique as a screening tool for pharmaceuticals in a process environment. Figure 4 illustrates the detection of acetaldehyde from a low ppm level vapor standard. This separation was performed using N2 carrier gas and provides the dry conditions required for the detection of small somewhat polar, molecular species and non-polar analytes. Vapor analytes with a broad range of volatiles and functionalities may be rapidly detected by sub ppmv levels.
Vapor analytes with hetero-atom functionality can in some cases be detected at single ppbv levels.
Addition of N2 carrier gas allows the low H2O levels to be obtained for consistent detection of non-polar aromatic species and other species with low proton affinities. Overall analytical performance of the EVM II exceeds that of its predecessors in terms of sensitivity, IMS peak shape and low volatility compound detection. A broad range of volatilities may be addressed using this technology, but future advances in the realm of low power temperature programming may extend the volatility range of analyses suitable for determination during a single analysis. While this technique has shown the strength of a hyphenated system, it is not yet suitable to the direct detection of unknown analyses, since sufficiently large standardized libraries have not been developed. However, when screening for a set of known analytes, this approach has unsurpassed interferant rejection capabilities for a hand held instrument.