Molecular beams mass spectrometer

FIGURE 12.1. Schematic of tubular reactor setup for pyrolysis/catalytic/oxidation studies coupled to a molecular-beam mass spectrometer sampling system. 

A. Me Ilroy, T.D. Hain, H.A. Michelsen, and T.A. Cool. A Laser and Molecular Beam Mass Spectrometer Study of Low-Pressure Dimethyl Ether Flames. Proc. Combust. Inst., 28 1647-1653, 2000. 

Figure 2. Molecular beam mass spectrometer. Key A, nozzle-skimmer chamber B, middle chamber C, mass spectrometer chamber D, sampling nozzles E, skimmers F, choppers G, gate valve assembly H, mass spectrometer and I, nylon flanges permitting electrical biasing for detection of ions from coal burner.

Freedman, A., Wormhoudt, J., and Stewart, G., "ARI Modulated Molecular Beam Mass Spectrometer," Aerodyne Research, Inc. Bedford, MA 01730, Report No. TM-13, Feb. 1981. 

Studied pyrolysis/reforming of several types of common plastics using a micro-reactor interfaced with a molecular-beam mass spectrometer (MBMS). 

ICEV Internal Combustion Engine Vehicle MBMS Molecular-Beam Mass Spectrometer... 

Figure 1. Molecular beam mass spectrometer flame sampling...

The UNIQUE sorption experiments reported here [107] were performed under packed bed conditions at atmospheric pressure. The experimental setup, illustrated in Figure 11.27, consisted of a tube furnace with five independent heating zones encasing the sorbent sample bed through which the gas in all sorption tests flowed at a temperature of 700-900 °C progressively saturating the sorbent the cleaned gas composition being determined by a molecular beam mass spectrometer (MBMS). 

The most common separators include the Ryhage or jet diffusion separator (74), the Watson-Biemann or pore diffusion separator (75), and the membrane solution diffusion separator originally developed by Llewellyn (75). The first two separators involve direct passage of the sample into the mass spectrometer the low molecular weight helium diffuses more readily and is pumped away. The membrane separator involves diffusion of the sample through a silicone membrane while the carrier gas vents to the atmosphere carrier gas is thus not confined to helium. There is no best separator the choice depends on the nature of the compounds, the temperature range over which it will be operated, and most usually what is available in a particular laboratory. A convenient configuration for a double-beam mass spectrometer such as the AEI MS-30 is two different separators, one into each beam, which permits rapid evaluation of separator performance. 

Impressed by the information provided by Py-FIMS, another research group developed pyrolysis-molecular beam mass spectrometry (Py-MBMS) by coupling a quartz pyrolysis chamber to the inlet of a triple-quadrupole mass spectrometer. This group wished to study the organic matrix of forest soils and saw two limitations for the application of Py-FIMS to their study first, that the very small sample used in Py-FIMS might not be representative of the macro soil sample, and second, that the time required for each sample analysis by Py-FIMS was relatively long if one wished to examine and compare a large number of soil samples. 

Other methods of sample introduction that are commonly coupled to TOP mass spectrometers are MALDI, SIMS/PAB and molecular beams (see section (Bl.7.2)). In many ways, the ablation of sample from a surface simplifies the TOP mass spectrometer since all ions originate in a narrow space above the sample surface. 

The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine. 

This chapter should be read in conjunction with Chapter 3, Electron Ionization. In electron ionization (El), a high vacuum (low pressure), typically 10 mbar, is maintained in the ion source so that any molecular ions (M +) formed initially from the interaction of an electron beam and molecules (M) do not collide with any other molecules before being expelled from the ion source into the mass spectrometer analyzer (see Chapters 24 through 27, which deal with ion optics). 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

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