µChemLab: twenty years of developing CBRNE detection systems with low false alarm rates

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)

Comprehensive multidimensional gas chromatography and modulator development for portable instrumentation.

The goal of this research was to develop technology that will facilitate high-speed, multidimensional, low-resource, and portable gas chromatography (GC) instrumentation. Current commercial GCxGC instruments are very powerful but are large and require expensive cryogenic consumables. Developing a portable GCxGC will reduce the instrument footprint and consumable requirements in addition to providing onsite analysis capabilities to expand the potential application range for GCxGC analysis. The combined separation power of a microfabricated separation column and microfabricated differential mobility spectrometer (DMS) is demonstrated. The additional separation mechanism inherent in the DMS provides increased peak capacity and produces further information for chemical identification. The microfabricated components demonstrate the separation of 45 components in 400 s with vast decreases in system footprint compared to conventional systems. A model was developed for the prediction of band elution times for GCxGC systems consisting of a primary column, secondary column, and modulator with independent inner diameters. Comparisons between modeled and experimental data are provided for alkane species which show excellent model prediction of retention time for low-molecular weight compounds, while increasingly underestimating the retention time for heavier compounds. A low-resource thermal modulator requiring no cryogenic liquids is evaluated for its performance in regards to the flow rate through the modulator and modulation period. The modulator was used in a GCxGC system to successfully analyze headspace samples of U.S. currency by detecting a select group of ink decomposition marker compounds. Attempts to create high-speed modulators capable of producing sub-20 ms peak width plugs of analyte for very fast (∼100 ms) second column separations to achieve truly high-speed GCxGC separations are described. Two styles of high-speed modulators are presented; a narrow-bore, uncoated steel tube modulator and a microfabricated channel modulator. Both employed cold-jet cooling with resistive heating to provide narrow band slices (17 ms peak width achieved with steel tube modulator). Valve modulators capable of sub-300 ms modulation periods for high-speed GCxGC separations were investigated using Sandia-proprietary valves. Experiments demonstrating the modulation of methane, peak area conservation, and an 18-component separation completed in 9 s are described. Additional analyses regarding modulated-band peak-width and overall peak capacity are included.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127106/2/3354151.pd

A high-speed, high-performance, microfabricated comprehensive two-dimensional gas chromatograph

A small, consumable-free, low-power, ultra-high-speed comprehensive GC×GC system consisting of microfabricated columns, nanoelectromechanical system (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble holdup time is demonstrated with a downstream FID. The analysis time of the second dimension was 160 ms, and peak widths in the second dimension range from 10–60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20 000 runs of the GC×GC columns with the NEMS resonators using a 4-component test set is presented. The GC×GC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector

A high-speed, high-performance, microfabricated comprehensive two-dimensional gas chromatograph

A small, consumable-free, low-power, ultra-high-speed comprehensive GC×GC system consisting of microfabricated columns, nanoelectromechanical system (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble holdup time is demonstrated with a downstream FID. The analysis time of the second dimension was 160 ms, and peak widths in the second dimension range from 10–60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20 000 runs of the GC×GC columns with the NEMS resonators using a 4-component test set is presented. The GC×GC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector