PERFORMANCE ADVANCES IN ION MOBILITY SPECTROMETRY THROUGH COMBINATIONWITH HIGH-SPEED VAPOR SAMPLING, PRECONCENTRATION AND SEPARATION TECHNIQUES

Rugged, low weight, hand-held ion mobility spectrometry devices, initi ally developed for chemical warfare detection purposes, possess attrac tive characteristics as field-portable instruments for paramilitary (t reaty verification, chemical demilitarization, drug interdiction, coun terterrorism operations) and civilian (environmental monitoring, foren sic characterization, process control) applications. Generally, howeve r, such devices tend to exhibit limited resolution, narrow dynamic ran ge, nonlinear response and long clearance times which severely limit t heir usefulness for qualitative and quantitative analysis of mixtures. To overcome these restrictions a prototype combined gas chromatograph y-ion mobility spectrometry (GC-IMS) unit was constructed by replacing the membrane inlet of a military LMS device known as the CAM (chemica l agent monitor) with suitable front-end modules. These modules enable high speed automated vapor sampling (AVS), microvolume preconcentrati on/thermal desorption, and isothermal GC preseparation of analytes usi ng a short capillary column while operating the IMS source and cell at subambient pressures as low as 0.5 atm. The AVS-GC-IMS methodology sh arply reduces competitive ionization and facilitates identification of mixture components, thereby enabling quantitation of volatile and sem ivolatile compounds over a broad range of concentrations in air. At hi gher concentration levels (e.g. >1 ppm) using the AVS inlet in automat ic attenuation control (AAC) mode maintains excellent linear response. At ultralow concentration levels, e.g. < 10 ppb, a microvolume, trap- and-desorb type preconcentration module, maintains adequate signal to noise levels, thereby expanding the effective dynamic range of the met hod to approx. 6 orders of magnitude (100 ppt-100 ppm). The resulting ''hyphenated'' GC-IMS technique has the potential of evolving into the first hand-portable, combined chromatography-spectroscopy instruments for field screening applications.