Autonomous in situ analysis and real-time chemical detection using a backpack miniature mass spectrometer: concept, instrumentation development, and performance.

A major design objective of portable mass spectrometers is the ability to perform in situ chemical analysis on target samples in their native states in the undisturbed environment. The miniature instrument described here is fully contained in a wearable backpack (10 kg) with a geometry-independent low-temperature plasma (LTP) ion source integrated into a hand-held head unit (2 kg) to allow direct surface sampling and analysis. Detection of chemical warfare agent (CWA) simulants, illicit drugs, and explosives is demonstrated at nanogram levels directly from surfaces in near real time including those that have complex geometries, those that are heat-sensitive, and those bearing complex sample matrices. The instrument consumes an average of 65 W of power and can be operated autonomously under battery power for ca. 1.5 h, including the initial pump-down of the manifold. The maximum mass-to-charge ratio is 925 Th with mass resolution of 1-2 amu full width at half-maximun (fwhm) across the mass range. Multiple stages of tandem analysis can be performed to identify individual compounds in complex mixtures. Both positive and negative ion modes are available. A graphical user interface (GUI) is available for novice users to facilitate data acquisition and real-time spectral matching.

Hand-held mass spectrometer for environmentally relevant analytes using a variety of sampling and ionization methods.

A recently developed hand-held, rectilinear ion trap mass spectrometer, capable of performing in situ analysis, has been evaluated for a variety of environmentally relevant analytes. Different sampling and ionization methods were implemented, demonstrating the considerable versatility of this instrument. A discontinuous (viz. pulsed) atmospheric pressure inlet (DAPI) was used to introduce externally-generated analyte ions. Nitro compounds were ionized by electrosonic spray ionization (ESSI) yielding the protonated and sodiated forms of the molecular ion, as well as fragment ions. The amines 2,2,6,6-tetramethylpiperidine, triethylamine and 2,6-diphenylpyridine showed low parts per billion (ppb) detection limits. Vapor phase external ionization was used to examine the chemical warfare simulant dimethyl methylphosphonate and the insect repellant N,N-diethyl-m-toluamide. Membrane introduction mass spectrometry (MIMS) was used as the introduction system for hydrophobic analytes using a selectively permeable (polydimethylsiloxane) membrane placed within the vacuum manifold with subsequent ionization of the thermally desorbed neutral compounds inside the ion trap. MIMS allowed the quantitation of trace levels (a few ppb) of fluorinated compounds in the vapor phase. MIMS was also applied to the quantitation of aqueous polycyclic aromatic hydrocarbons (PAH's) with limits of detection again in the low ppb range for naphthalene, acenaphthene, anthracene and phenanthrene.

Multiplexed rectilinear ion trap mass spectrometer for high-throughput analysis.

A multichannel mass spectrometer based on the rectilinear ion trap (RIT) analyzer was designed and constructed for simultaneous high-throughput analysis of multiple samples. The instrument features four parallel ion source/mass analyzer/detector channels assembled in a single vacuum chamber and operated using a common set of control electronics, including a single rf amplifier and transformer coil. This multiplexed RIT mass spectrometer employs an array of four millimeter-sized ion traps (x(o) = 5.0 mm and y(o) = 4.0 mm, where x(o) and y(o) are the half-distances in the x and y dimensions, respectively). Mass spectra are acquired from four different samples simultaneously. The available mass/charge range is m/z 15-510 with excellent linearity of the mass calibration (R2 = 0.999 999). The peak width is less than 0.3 mass/charge units at m/z 146, corresponding to a resolution of approximately 500. Simultaneous MS/MS of ions due to four compounds (3-fluoroanisole, 4-fluoroanisole, 2-fluorobenzyl alcohol, 2,6-dimethylcyclohexanone) with the same nominal molecular radical cation but distinctive fragmentation patterns was demonstrated. Isolation and fragmentation efficiencies were approximately 25 and approximately 75%, respectively, measured in the typical case of the molecular radical cation of acetophenone. Preacquisition differential data were obtained by real-time subtraction of the ion signals from two channels of the multiplexed mass spectrometer. The differential experiment presented offers proof of principle of comparative mass spectra in high-throughput screening applications while reducing data storage requirements.