Mass spectrometer simultaneous

Hint To distinguish these compounds without elemental composition or standards for GC retention time, split the GC effluent to a FID, a nitrogen-phosphorus detector, and the mass spectrometer, simultaneously. Using this splitter system, it is easy to determine if the GC peak contains nitrogen. Also, the analyst can differentiate between azobenzene and benzophenone by using the methoxime derivative. 

Mass spectrometers are among the most selective detectors, but they are still susceptible to interferences. Isomers have identical spectra, whereas many other compounds have similar mass spectra. Heavy petroleum products can contain thousands of major components that are not resolved by the gas chromatograph. As a result, multiple compounds enter the mass spectrometer simultaneously. Different compounds may share many of the same ions, confusing the identification process. The probability of misidentiflcation is high in complex mixtures such as petroleum products. 

Internal Calibration The process by which one or more calibrant is introduced into the mass spectrometer simultaneously with the unknown sample, and the mass calibration is continuously updated during analysis. Considered the most effective means of obtaining highly accurate mass analysis (provided the calibrant does not interfere with the analysis of the unknown) (Hemiman et al., 2004). 

Perhaps the greatest attribute that TOF-MS may apply to elemental mass spectrometry is the ability to provide simultaneous multielemental analysis. Of course, a TOF-MS does not record all the masses in the spectrum simultaneously the time difference between adjacent masses is typically in the nanosecond regime. However, all masses are sampled into the mass spectrometer simultaneously and an entire spectrum is generated from each injected ion pulse. Because successively recorded mass spectra are obtainable in short periods in a TOF-MS, especially in instances in which there is a small, well-defined mass range of interest, thousands of mass spectra can be obtained each second. 

For pyrolysis at high temperatures (dD or d 0 analysis) the gaseous reaction products H2 and CO are allowed to enter the mass spectrometer simultaneously. For D/H it is possible to remove CO ciyo-genically using, for instance, a piece of capillary molecular sieve column immersed in liquid nitrogen. 

All mass spectrometers analyze ions for their mass-to-charge ratios (m/z values) and simultaneously for the abundances of ions at any given m/z value. By separating the ions according to m/z and measuring the ion abundances, a mass spectrum is obtained. 

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight. 

A multipoint ion collector (also called the detector) consists of a large number of miniature electron multiplier elements assembled, or constructed, side by side over a plane. A multipoint collector can be an array, which detects a dispersed beam of ions simultaneously over a range of m/z values and is frequently used with a sector-type mass spectrometer. Alternatively, a microchannel plate collector detects all ions of one m/z value. When combined with a TOP analyzer, the microchannel plate affords an almost instantaneous mass spectrum. Because of their construction and operation, microchannel plate detectors are cheaper to fit and maintain. Multipoint detectors are particularly useful for situations in which ionization occurs within a very short space of time, as with some ionization sources, or in which only trace quantities of any substance are available. For such fleeting availability of ions, only multipoint collectors can measure a whole spectrum or part of a spectrum satisfactorily in the short time available. 

Mixtures passed through special columns (chromatography) in the gas phase (GC) or liquid phase (LC) can be separated into their individual components and analyzed qualitatively and/or quantitatively. Both GC and LC analyzers can be directly coupled to mass spectrometers, a powerful combination that can simultaneously separate and identify components of mixtures. 

In a mass spectrometer, ions can arrive at a multipoint collector as a spatially dispersed beam. This means that all ions of different m/z values arrive simultaneously but separated in space according to each m/z value. Each element of the array, depending on its position in space, detects one particular m/z value (see Chapter 29, Array Collectors ). 

Alternatively, the ions in a mass spectrometer can also arrive at a multipoint collector as a temporally dispersed beam. Therefore, at any point in time, all ions of the same m/z value arrive simultaneously, and different m/z values arrive at other times. Ail elements of this collector detect the arrival of ions of one m/z value at any one instant of time. This type of detector, which is also an array, is called a microchannel plate collector of ions. 

Powerful mass spectrometer/computer systems can achieve simultaneous foreground/background operation, especially if transputers are used to provide the advantage of parallel processing. 

A computer attached to a mass spectrometer is used both to acquire data and to control the operation of the spectrometer. Powerful transputer systems can be used to ensure that both modes of operation can be carried out almost simultaneously. 

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-... 

Simultaneous Differential Thermal-Mass Spectrometer Analysis of Nitrate Salts of Mono-methylhydrazine and Methylamine , SAMSO TR-70-117(1970) 54) Anon, Propellants,... 

The mass spectrometer sampling capillary or the dispersive infra-red analyzers used for continuous analysis and monitoring of the gas phase composition are situated between the reactor and the sampling valve, as close to the reactor as possible, in order to avoid any delay in the recording of changes in the composition of reactants or products. This delay should be taken into account when plotting simultaneously the time dependence of catalyst potential or current and gas phase concentration of the reactants or products. 

Figure 5.35 Schematic of a system which allows eluates from four HPLC columns to be introduced simultaneously into a mass spectrometer. From de Biasi, V., Haskins, N., Organ, A., Bateman, R., Giles, K. and Jarvis, S., Rapid Commun. Mass Spectrom., 13, 1165-1168, Copyright 1999. John Wiley Sons Limited. Reproduced with permission.

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