Spectrometer continued mass

Mass Spectrometer. The mass spectrometer is the principal analytical tool of direct process control for the estimation of tritium. Gas samples are taken from several process points and analy2ed rapidly and continually to ensure proper operation of the system. Mass spectrometry is particularly useful in the detection of diatomic hydrogen species such as HD, HT, and DT. Mass spectrometric detection of helium-3 formed by radioactive decay of tritium is still another way to detect low levels of tritium (65). Accelerator mass spectroscopy (ams) has also been used for the detection of tritium and carbon-14 at extremely low levels. The principal appHcation of ams as of this writing has been in archeology and the geosciences, but this technique is expected to faciUtate the use of tritium in biomedical research, various clinical appHcations, and in environmental investigations (66). 

Mass, infrared, ultraviolet, and mnr spectrometry have been highly developed as aids to identification. In some gas-chromatographic techniques some of the sample corresponding to a peak must be condensed and examined in others the effluent can be monitored continuously with an instrument such as the time-of-flight mass spectrometer, whereby mass spectra corresponding to each peak can be recorded as it is eluted. Developments in the mass-spectrometric analysis of gas chromatography effluents have been reviewed by McFadden. ... 

The CO-TPD measurements were performed in a flow reactor, described elsewhere [12]. A quadropole mass spectrometer continuously analysed the gas composition after the monolith... 

Dissolved Gases in Biochemical Systems with the Quadrupole Mass Spectrometer, Continuous Measurement of (Degn, Cox, and Lloyd). .. Electrochemical Detection, Biomedical Uses of High-Performance Liquid... 

Beeause an electrospray source transfers ions continuously to the gas phase, it is most easily coupled to a continuous mass analyzer. From the time of the first successful applieations of this technique, linear quadrupoles proved to be of great praetical use. In triple-quadrupole mass spectrometers, a linear multipole guides the ions to a first quadrupole mass filter, followed by a second ion guide leading to a seeond quadrupole mass filter. Finally, an ion multiplier deteets the ions. Differential pumping reduces the pressure from atmospheric pressure (API region, ESI source) to 10 mbar in the mass analyzer. 

For use in GC-MS systems, attention should be paid to the injection at the necessary high flow rates in connection with the maximum permitted carrier gas loading of the mass spectrometer. As the injection system is always cold, moisture can accumulate from samples or insufficiently purified carrier gas (Figure 2.75). Because of this, the sensitivity of the mass spectrometer could be compromized. The effect is easy to detect because the mass spectrometer continually registers the water background and because the on-column injector can easily be opened at a particular time so that the carrier gas can pass out via the splitter. 

Instead of the fast-atom beam, a primary ion-beam gun can be used in just the same way. Generally, such an ion gun emits a stream of cesium ions (Cs ), which are cheaper to use than xenon but still have large mass (atomic masses Cs, 139 Xe, 131). Although ion guns produce no fragment ions in the primary beam, they can contaminate the mass spectrometer by deposition with continued use. 

By passing a continuous flow of solvent (admixed with a matrix material) from an LC column to a target area on the end of a probe tip and then bombarding the target with fast atoms or ions, secondary positive or negative ions are ejected from the surface of the liquid. These ions are then extracted into the analyzer of a mass spectrometer for measurement of a mass spectrum. As mixture components emerge from the LC column, their mass spectra are obtained. 

A major advantage of the TOF mass spectrometer is its fast response time and its applicability to ionization methods that produce ions in pulses. As discussed earlier, because all ions follow the same path, all ions need to leave the ion source at the same time if there is to be no overlap between m/z values at the detector. In turn, if ions are produced continuously as in a typical electron ionization source, then samples of these ions must be utihzed in pulses by switching the ion extraction field on and off very quickly (Figure 26.4). 

By allowing any solution, but particularly the eluant from a liquid chromatographic column, to flow continuously (dynamically) across a target area under bombardment from fast atoms or ions (FAB or FIB), any eluted components of a mixture are ionized and ejected from the surface. The resulting ions are detected and recorded by a mass spectrometer. The technique is called dynamic FAB or dynamic LSIMS. 

If samples are introduced continuously, then the measurement of isotope ratios can also be continuous as long as sample is flowing into the flame, and several m/z ratios can be examined with almost any kind of mass spectrometer,... 

Most electrical signals flowing between a mass spectrometer and an attached computer are of the analog type viz., the associated voltage varies continuously with time. 

Continuous inlet. An inlet in which sample passes continuously into the mass spectrometer ion source, as distinguished from a reservoir inlet or a direct-inlet probe. 

Direct liquid introduction interface. An interface that continuously passes all, or a part of, the effluent from a liquid chromatograph to the mass spectrometer the solvent usually functions as a chemical ionization agent for ionization of the solute. 

GC/MS interface. An interface between a gas chromatograph and a mass spectrometer that provides continuous introduction of effluent gas from a gas chromatograph to a mass spectrometer ion source. 

Nonfractionating continuous inlet. An inlet in which gas flows from a gas stream being analyzed to the mass spectrometer ion source without any change in the conditions of flow through the inlet or by the conditions of flow through the ion source. This flow is usually viscous flow, such that the mean free path is very small in comparison with the smallest dimension of a traverse section of the channel. The flow characteristics are determined mainly by collisions between gas molecules, i.e., the viscosity of the gas. The flow can be laminar or turbulent. 

Thermospray interface. Provides liquid chromatographic effluent continuously through a heated capillary vaporizer tube to the mass spectrometer. Solvent molecules evaporate away from the partially vaporized liquid, and analyte ions are transmitted to the mass spectrometer s ion optics. The ionization technique must be specified, e.g., preexisting ions, salt buffer, filament, or electrical discharge. 

The part that marries the plasma to the mass spectrometer in ICPMS is the interfacial region. This is where the 6000° C argon plasma couples to the mass spectrometer. The interface must transport ions from the atmospheric pressure of the plasma to the 10 bar pressures within the mass spectrometer. This is accomplished using an expansion chamber with an intermediate pressure. The expansion chamber consists of two cones, a sample cone upon which the plasma flame impinges and a skimmer cone. The region between these is continuously pumped. 

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