Cycloidal sector mass analyzers have, in principle, perfect focusing due to perpendicularly oriented uniform electric and magnetic fields, making them ideal candidates for incorporation of spatially ...coded apertures. We have previously demonstrated a proof-of-concept cycloidal-coded aperture miniature mass spectrometer (C-CAMMS) instrument and achieved a greater than 10-fold increase in throughput without sacrificing resolution, compared with a single slit instrument. However, artifacts were observed in the reconstructed mass spectrum due to nonuniformity in the electric field and misalignment of the detector and the ion source with the mass analyzer focal plane. In this work, we modified the mass analyzer design of the previous C-CAMMS instrument to improve electric field uniformity, improve the alignment of the ion source and the mass analyzer with the detector, and increase the depth-of-focus to further facilitate alignment. A comparison of reconstructed spectra of a mixture of dry air and toluene at different electric fields was performed using the improved C-CAMMS prototype. A reduction in reconstruction artifacts compared to our proof-of-concept C-CAMMS instrument highlights the improved performance enabled by the design changes.
A recently developed prototype mobile laboratory mass spectrometer, incorporating an atmospheric pressure ionization (API) interface, is described. This system takes advantage of the small size, ...lower voltage requirements, and tandem MS abilities of the cylindrical ion trap mass analyzer. The prototype API MS uses small, low-power pumps to fit into a 0.1-m
3 self-contained package weighing <45 kg. This instrument has been adapted to allow rapid interfacing to electrospray ionization, desorption electrospray ionization, and direct analysis in real-time sources. Initial data indicate that these techniques provide rapid detection and identification of compounds for quality control, homeland security, and forensic applications. In addition, this instrument is self-contained and compact, making it ideally extensible to mobile laboratory and field analyses. Initial MS and MS/MS data for analyses of drugs, food, and explosives are presented herein.
A mobile-lab API-MS capable of ESI, DESI, and DART enables analysis of bulk and trace materials for chemical fingerprinting and MS/MS identification.
The concentrations of a suite of halogenated volatile organic compounds (HVOCs) were measured near Barrow, Alaska, from January to April 2005. The HVOCs are produced from the reaction of bromine and ...chlorine atoms with ethene and propene. During periods of decreasing ozone concentration, increases in the HVOC concentrations allowed for the calculation of the ratio of bromine to chlorine radical concentrations, based on available kinetic data. We use these concentration data to interrogate the chemistry that results in tropospheric ozone depletion in the Arctic, the possible sources of ozone depleting halogen molecules, and the spatial scale in which ozone depletion occurs. We report calculated halogen atom concentration ratios (Br/Cl) during partial ozone depletion events. The concentration ratio was observed to range from 80 ± 30 to 990 ± 300 when ozone concentrations were above 15 ppb. These data make it clear that chlorine and bromine atom chemistry is active in the Arctic troposphere beginning at twilight, even absent large‐scale ozone depletion, and that the sources of the chlorine atoms are poorly understood.
Despite many potential applications, miniature mass spectrometers have had limited adoption in the field due to the tradeoff between throughput and resolution that limits their performance relative ...to laboratory instruments. Recently, a solution to this tradeoff has been demonstrated by using spatially coded apertures in magnetic sector mass spectrometers, enabling throughput and signal-to-background improvements of greater than an order of magnitude with no loss of resolution. This paper describes a proof of concept demonstration of a cycloidal coded aperture miniature mass spectrometer (C-CAMMS) demonstrating use of spatially coded apertures in a cycloidal sector mass analyzer for the first time. C-CAMMS also incorporates a miniature carbon nanotube (CNT) field emission electron ionization source and a capacitive transimpedance amplifier (CTIA) ion array detector. Results confirm the cycloidal mass analyzer’s compatibility with aperture coding. A >10× increase in throughput was achieved without loss of resolution compared with a single slit instrument. Several areas where additional improvement can be realized are identified.
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The vertical extent and impact of halogen chemistry in the Arctic springtime was investigated through balloon‐based measurement of several atmospheric chemical components. Various chemical species, ...including volatile organic compounds (VOCs), ozone, and elemental mercury, that are modified by halogen chemistry were measured from the surface to ∼300 m during late March through mid‐April 2005 in Barrow, Alaska. It is observed that the halogen chemistry appears to be most active in the lowest 100–200 m of the atmosphere. The Hg vertical concentration profiles are consistent with destruction by chemistry that evolves from a species emitted from the snowpack, most likely Br2 and BrCl, and the VOC profiles also demonstrate the limited vertical scale of halogen‐initiated chemistry taking place above the Arctic snowpack.
A novel chemical ionization (CI) source has been developed based on a carbon nanotube (CNT) field emission electron source. The CNT-based electron source was evaluated and compared with a standard ...filament thermionic electron source in a commercial explosives trace detection desktop mass spectrometer. This work demonstrates the first reported use of a CNT-based ion source capable of collecting CI mass spectra. Both positive and negative modes were investigated. Spectra were collected for a standard mass spectrometer calibration compound, perfluorotributylamine (PFTBA), as well as trace explosives including trinitrotoluene (TNT), Research Department explosive (RDX), and pentaerythritol tetranitrate (PETN). The electrical characteristics, lifetime at operating pressure, and power requirements of the CNT-based electron source are reported. The CNT field emission electron sources demonstrated an average lifetime of 320 h when operated in constant emission mode under elevated CI pressures. The ability of the CNT field emission source to cycle on and off can provide enhanced lifetime and reduced power consumption without sacrificing performance and detection capabilities.
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Gaseous ammonia, a common toxic industrial compound, is not detected readily in ion trap mass spectrometers because its molecular ion falls below the low-mass cutoff (~m/z 40) normally used when ...examining organic compounds. Instead, reactions of ammonia with halobenzene radical cations were used with internal electron ionization in two cylindrical ion trap miniature mass spectrometers to create a characteristic product ion by which to identify and quantify ammonia. Ammonia showed a linear response over the concentration range studied (parts per million ppm to parts per billion ppb) with limits of detection of 17 ppm and 220 ppb for experiments involving direct introduction and thermal desorption after pre-concentration, respectively. These values are comparable to ammonia's permissible exposure limit (50 ppm) and odor threshold (5 ppm). Receiver operating characteristic (ROC) curves were used to describe the method sensitivity, the probability of true positives, and the false positive rate for ammonia. A customized reaction scan function was created to select the species available for the ion/molecule reaction and set the amount of time the product ion could be accumulated in the trap. Product ion identity was verified using tandem mass spectrometry. Similar reactions with methylamine, ethylamine and the two nitriles, acetonitrile and benzonitrile, were explored.
This work compares the coded aperture imaging performance of thermionic filament and carbon nanotube (CNT) field emitter-based electron sources in cycloidal-coded aperture mass spectrometers. The use ...of spatially coded apertures in mass spectrometry enables miniaturization by improving throughput without sacrificing resolution. CNT-based electron ionization sources for mass spectrometers provide several potential benefits over conventional thermionic emitters, including low voltage and low power consumption, room temperature operation, long lifetime, and ability to emit electrons in a pulsed mode. However, spatiotemporal variation in electron emission from CNTs is a major disadvantage. In this study, electron emission stability and spatiotemporal stability of the coded aperture image were compared for coded aperture cycloidal mass analyzers with either a CNT-based ion source or a thermionic filament-based ion source. We found that the thermionic filament-based ion source produced a significantly more stable coded aperture image than the CNT based ion source. The aperture image fluctuations in the CNT-based source are likely a result of adsorption and desorption of molecules on the CNT surface that cause local work function changes and induce spatiotemporal variation in electron emission and subsequent ion generation.
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•Aperture coding improves performance; enables miniaturization of mass spectrometers.•Higher electron emission variation from carbon nanotubes over thermionic filaments.•Adsorption and desorption of gases cause work function changes in carbon nanotubes.•Thermionic filament-based ion sources produce a more stable coded aperture image.
This report compares the coded aperture imaging performance of thermionic filament and carbon nanotube (CNT) field emitter-based electron sources in cycloidal-coded aperture mass spectrometers. The ...use of spatially coded apertures in mass spectrometry enables miniaturization by improving throughput without sacrificing resolution. CNT-based electron ionization sources for mass spectrometers provide several potential benefits over conventional thermionic emitters, including low voltage and low power consumption, room temperature operation, long lifetime, and ability to emit electrons in a pulsed mode. However, spatiotemporal variation in electron emission from CNTs is a major disadvantage. In this study, electron emission stability and spatiotemporal stability of the coded aperture image were compared for coded aperture cycloidal mass analyzers with either a CNT-based ion source or a thermionic filament-based ion source. We found that the thermionic filament-based ion source produced a significantly more stable coded aperture image than the CNT based ion source. The aperture image fluctuations in the CNT-based source are likely a result of adsorption and desorption of molecules on the CNT surface that cause local work function changes and induce spatiotemporal variation in electron emission and subsequent ion generation.
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