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Gary A Eiceman

Publications and source records attributed to Gary A Eiceman.

8 recordsLinked to original sources
PubMed2006

Pressure effects in differential mobility spectrometry.

A microfabricated planar differential ion mobility spectrometer operating from 0.4 to 1.55 atm in a supporting atmosphere of purified air was used to characterize the effects of pressure and electric field strength on compensation voltage, ion transmission, peak width, and peak intensity in differential mobility spectra. Peak positions, in compensation voltage as a function of separating rf voltage, were found to vary with pressure in a way that can be simplified by expressing both compensation and separation fields in Townsend units for E/N. The separation voltage providing the greatest compensation voltage and the greatest resolution is ion-specific but often occurs at E/N values that are unreachable at elevated pressure because of electrical breakdown. The pressure dependence of air breakdown voltage near 1 atm is sublinear, allowing higher E/N values to be reached at reduced pressure, usually resulting in greater instrumental resolution. Lower voltage requirements at reduced pressure also reduce device power consumption.

Air Pressure↗
PubMed2006

Analysis of bacterial strains with pyrolysis-gas chromatography/differential mobility spectrometry.

Eight vegetative bacterial strains and two spores were characterized by pyrolysis-gas chromatography with differential mobility spectrometry (py-GC/DMS) yielding topographic plots of ion intensity, retention time, and compensation voltage simultaneously for ions in positive and negative polarity. Biomarkers were found in the pyrolysate at characteristic retention times and compensation voltages and were confirmed by standard addition with GC/MS analyses providing discrimination between Gram negative and Gram positive bacterial types, but no recognition of individual strains within the Gram negative bacteria. Principal component analysis was applied using two dimensional data sets of ion intensity versus retention time at five compensation voltages including the reactant ion peaks all in positive and negative ion polarity. Clustering was observed with compensation voltage (CV) chromatograms associated with ion separation in the DMS detector and little or no clustering was observed with the reactant ion peaks or CV chromatograms where ion separation is poor. Consistent clustering of Gram positive B. odysseyi and Gram negative E. coli in both positive and negative polarities with the reactant ion peak chromatograms and key CV chromatograms suggests common but unknown common chemical compositions in the pyrolysate.

Bacteria↗
PubMed2006

Miniature differential mobility spectrometry using atmospheric pressure photoionization.

Positive and negative ion spectra have been obtained with a miniature differential mobility spectrometer equipped with a photoionization source operating at atmospheric pressure. With benzene as a dopant, providing C6H6+ as reactant ion, protonated molecular ions and proton-bound dimer ions were obtained with dimethyl methylphosphonate and butanone. The spectra obtained from gas chromatographic injections of aromatic hydrocarbons, benzene, toluene, and the xylenes, produced the molecular ions when the moisture level was very low, but at a high level the hydrated proton was also present. Possible mechanisms for the formation of protonated products are discussed. Negative ions were produced from electron capture by sulfur hexafluoride using benzene or acetone as dopant. Photoionization of nitrogen dioxide led to the formation of the nitrate ion whose yield was a nonlinear function of concentration. The use of a suitable dopant enhanced ion formation by up to 2 orders of magnitude, and limits of detection in both the positive and negative modes were all at the sub ppm(v) level. The study makes a strong case for the use of a photoionization source as an alternative to the radioactive 63Ni source.

Journal Article↗
PubMed2004

Microfabricated differential mobility spectrometry with pyrolysis gas chromatography for chemical characterization of bacteria.

A microfabricated drift tube for differential mobility spectrometry (DMS) was used with pyrolysis-gas chromatography (py-GC) to chemically characterize bacteria through three-dimensional plots of ion intensity, compensation voltage from differential mobility spectra, and chromatographic retention time. The DMS analyzer provided chemical information for positive and negative ions simultaneously from chemical reactions between pyrolysis products in the GC effluent and reactant ions of H+(H2O)n and O2-(H2O)n in air at ambient pressure. Authentic standards for chemicals formed in the pyrolysis of bacteria showed favorable matches with plots from py-GC/DMS analysis and were supported by py-GC/MS results. These and other yet-unidentified constituents provided a means to distinguish Escherichia coli from Micrococcus luteus. A Gram-positive spore former (Bacillus megaterium) was distinguished by an abundant peak for crotonic acid evident in positive and negative ions and not observed with M. luteus. In contrast, plots from py-GC/DMS of lipid A and lipoteichoic acid showed poor matches to plots for a Gram-negative (E. coli) bacterium and a Gram-positive (M. luteus) bacterium and the differences were attributed to differences in genus sources of the biopolymers. A significant percentage of the chemical information available in py-GC/DMS is unidentified, and the analytical utility must be established. Precision in the chemical measurement was determined as +/- 0.2 V, 10% relative standard deviation (RSD), and +/- 0.05 min for compensation voltage, peak intensity, and retention time, respectively. The minimum number of total bacteria (cell forming units) detected was 6000 though detection limits and resolution could be varied by the magnitude of the separation voltage in the differential mobility spectrometer.

Anions↗
PubMed2004

Gas chromatography.

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Chromatography, Gas↗
PubMed2002

Gas chromatography.

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Chromatography, Gas↗