Gas Chromatography (GC) is routinely used in the laboratory to temporally separate chemical mixtures into their constituent components for improved chemical identification. This paper will provide a overview of more than twenty years of development of one-dimensional field-portable micro GC systems, highlighting key experimental results that illustrate how a reduction in false alarm rate (FAR) is achieved in real-world environments. Significantly, we will also present recent results on a micro two-dimensional GC (micro GCxGC) technology. This ultra-small system consists of microfabricated columns, NanoElectroMechanical System (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator. The separation of a 29-component polar mixture in less than 7 seconds is demonstrated along with peak widths in the second dimension ranging from 10-60 ms. For this system, a peak capacity of just over 300 was calculated for separation in about 6 s. This work has important implications for field detection, to drastically reduce FAR and significantly improve chemical selectivity and identification. This separation performance was demonstrated with the NEMS resonator and bench scale FID. But other detectors, suitably fast and sensitive can work as well. Recent research has shown that the identification power of GCxGC-FID can match that of GC-MS. This result indicates a path to improved size, weight, power, and performance in micro GCxGC systems outfitted with relatively non-specific, lightweight detectors. We will briefly discuss the performance of possible options, such as the pulsed discharge helium ionization detector (PDHID) and miniature correlation ion mobility spectrometer (mini-CIMS).
Sandia National Laboratories has a long tradition of technology development for national security applications. In
recent years, significant effort has been focused on micro-analytical systems - handheld, miniature, or portable
instruments built around microfabricated components. Many of these systems include microsensor concepts and target
detection and analysis of chemical and biological agents. The ultimate development goal for these instruments is to
produce fully integrated sensored microsystems. Described here are a few new components and systems being explored:
(1) A new microcalibrator chip, consisting of a thermally labile solid matrix on an array of suspended-membrane
microhotplates, that when actuated delivers controlled quantities of chemical vapors. (2) New chemical vapor detectors,
based on a suspended-membrane micro-hotplate design, which are amenable to array configurations. (3) Micron-scale
cylindrical ion traps, fabricated using a molded tungsten process, which form the critical elements for a micro-mass
analyzer. (4) Monolithically integrated micro-chemical analysis systems fabricated in silicon that incorporate chemical
preconcentrators, gas chromatography columns, detector arrays, and MEMS valves.
Environmental fate and transport studies of explosives in soil indicate that 2,4,6-trinitrotoluene (TNT) and similar products such as dinitrotoluene (DNT) are major contributors to the trace chemical signature emanating from buried landmines. Chemical analysis methods are under development that have great potential to detect mines, or to rapidly classify electromagnetically detected anomalies as mines vs. 'mine-like objects'. However, these chemical methods are currently confined to point sensors. In contrast, we have developed a method that can remotely determine the presence of nitroaromatic explosives in surface soil. This method utilizes a novel distributed granular sensor approach in combination with uv-visible fluorescence LIDAR (Light Detection and Ranging) technology. We have produced prototype sensor particles that combine sample preconcentration, explosives sensing, signal amplification, and optical signal output functions. These particles can be sprayed onto soil areas that are suspected of explosives contamination. By design, the fluorescence emission spectrum of the distributed particles is strongly affected by absorption of nitroaromatic explosives from the surrounding environment. Using ~1mg/cm2 coverage of the sensor particles on natural soil, we have observed significant spectral changes due to TNT concentrations in the ppm range (mg TNT/kg soil) on 2-inch diameter targets at a standoff distance of 0.5 km.