Through an internally funded research program, Defiant Technologies has developed a compact chemical detector that
can be tailored for a range of target analytes. The system uses a preconcentrator (PC) to collect and screen samples from
the air, and a surface acoustic wave (SAW) microbalance to detect analytes when they are released from the PC. This
PC-SAW system serves as a trigger for a secondary analysis channel that uses a micro-gas chromatographic (micro-GC)
column to perform a more detailed analysis of the air. This combined approach provides high-confidence results while
conserving power and minimizing response time. By properly selecting coatings on the PC, micro-GC and SAW, the
unit can be designed for optimum performance in detecting specific target gases while ignoring interferents. This paper
presents test results from our research and discusses some of the applications for this type of system.
R. Cernosek, A. Robinson, D. Cruz, D. Adkins, J. Barnett, J. Bauer, M. Blain, J. Byrnes, S. Dirk, G. Dulleck, J. Ellison, J. Fleming, T. Hamilton, E. Heller, S. Howell, R. Kottenstette, P. Lewis, R. Manginell, M. Moorman, C. Mowry, R. Manley, M. Okandan, K. Rahimian, G. Shelmidine, R. Shul, R. Simonson, S. Sokolowski, J. Spates, A. Staton, D. Trudell, D. Wheeler, W. Yelton
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.
Sandia's hand-held MicroChemLabTM system uses a micromachined preconcentrator (PC), a gas chromatography channel (GC) and a quartz surface acoustic wave array (SAW) detector for sensitive/selective detection of gas-phase chemical analytes. Requisite system size, performance, power budget and time response mandate microfabrication of the key analytical system components. In the fielded system hybrid integration has been employed, permitting optimization of the individual components. Recent improvements in the hybrid-integrated system, using plastic, metal or silicon/glass manifolds, is described, as is system performance against semivolatile compounds and toxic industrial chemicals. The design and performance of a new three-dimensional micropreconcentrator is also introduced. To further reduce system dead volume, eliminate unheated transfer lines and simplify assembly, there is an effort to monolithically integrate the silicon PC and GC with a suitable silicon-based detector, such as a magnetically-actuated flexural plate wave sensor (magFPW) or a magnetically-actuated pivot plate resonator (PPR).
KEYWORDS: Chromatography, Diffusion, Computer simulations, Chemical analysis, Data modeling, Coating, Chemical detection, Etching, Silicon, Microsystems
The gas chromatography (GC) column is a critical component in the microsystem for chemical detection ((mu) ChemLabTM) being developed at Sandia. The goal is to etch a `meter-long' GC column onto a 1-cm2 silicon chip while maintaining good chromatographic performance. Our design strategy is to use modeling and simulation approach. We have developed an analytical tool that models the transport and surface interaction process to achieve an optimized design of the GC column. This analytical tool has a flow module and a separation module. The flow module considers both the compressibility and slip flow effects that may significantly influence the gas transport in a long and narrow column. The separation module models analyte transport and physico-chemical interaction with the coated surface in the GC column. It predicts the column efficiency and performance. Results of our analysis will be presented in this paper.
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