Microfabricated Differential Mobility Spectrometry with Pyrolysis Gas Chromatography for Chemical Characterization of Bacteria

Abstract

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.

Scaling of the resolving power and sensitivity for planar FAIMS and mobility-based discrimination in flow- and field-driven analyzers

“…The operational simplicity, small size, and low cost make FAIMS attractive for field analyses that require rugged, portable, inexpensive sensors. Recent commercialization of FAIMS technology, alone and in conjunction with LC/MS or GC, has enabled its expansion into proteomics [15][16][17], structural biology [13,18,19], pharmaceutical analyses [10,20], environmental monitoring [4,14], and security applications such as detection and classification of fire sources [8], explosives [9,11], chemical warfare agents [9], illicit drugs [9], and bacterial pathogens [12].Ions in FAIMS are separated using a periodic asymmetric field E D (t) that comprises short segments of high E and long segments of low E of opposite polarity such that the average E is zero but absolute positive and negative E are unequal [1]. Hypothetical ions with constant K would oscillate in that field with no separation.…”

“…Under typical operating conditions, the spread of elimination rates for commonly analyzed ions is reduced from Ͼ5 times in flow-driven to 1.6 times in field-driven FAIMS while the difference in resolving power decreases from ϳ60% to ϳ15%. ield asymmetric waveform ion mobility spectrometry (FAIMS) has emerged as a powerful new analytical technique [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. All IMS methods separate ions using their transport in a gas under the influence of electric field [21]: conventional IMS is based on absolute ion mobility (K) at particular field intensity (E) and FAIMS works with the difference between K at high and low E. So FAIMS is also known as differential mobility spectrometry (DMS) [11,12].…”

Fast gas chromatography-differential mobility spectrometry of explosives from TATP to Tetryl without gas atmosphere modifiers

“…In previous studies with DMS, favorable response was obtained for chemicals spanning a broad range of volatilities [26][27][28][29] and this experience suggested that DMS or GC DMS could be extended to improvised explosives such as triacetone triperoxide (TATP) or hexamethylene triperoxide diamine (HMTD) and to volatile explosive related compounds (ERCs) such as nitrobenzene and nitrotoluene. There has been to date little reported on DMS response to improvised explosives or ERCs and no unified method for GC IMS or GC DMS which is suitable for simultaneous determination of all organic explosives spanning the volatilities from TATP to RDX or Tetryl.…”

“…There has been to date little reported on DMS response to improvised explosives or ERCs and no unified method for GC IMS or GC DMS which is suitable for simultaneous determination of all organic explosives spanning the volatilities from TATP to RDX or Tetryl. In studies here, the goal was a single measurement for explosives from this broad range of volatilities by controlling instrument parameters for each component [7,[26][27][28][29][30]. An additional intention was to achieve determinations using DMS as a chromatographic detector, i.e., as a differential mobility detector, without the addition of reagent gases or gas modifiers to the supporting gas atmosphere.…”

Optimum waveforms for differential ion mobility spectrometry (FAIMS)

“…The introduction of commercial DMS instruments and particularly their integration with mass spectrometry (MS) andI or liquid or gas chromatography since 2003 has enabled rapid growth of the number and diversity of applications that include environmental analyses [6,7], food and water quality assurance [8][9][10], bacterial typing [11,12], forensic investigations [13], proteomics and metabolomics [14][15][16][17], pharmaceutical studies [18][19][20], and protein folding research [21][22][23][24][25]. Since its earliest days, DMS has been employed to detect explosives, drugs, and chemical warfare agents, and its role in defense, security, and law enforcement settings continues expanding [26][27][28][29][30][31].…”