Quadrupole mass, generally analyzer

An extensive and detailed coverage of the MS of expls in general has been documented (Ref 163). Volatile constituents of Comp A-3, Comp B, pressed TNT and cast TNT were surveyed with a residual gas analyzer MS (Ref 40). The mass spectra of all possible TNT (except for 3,4,5-TNT) and DNT isomers in the vapor phase were obtained as a function of ionizing voltage (Refs 65 84). The use of membrane inlet systems for the separation of TNT vapor in trace vapor detection is described and an analysis of the membrane inlet system for quadrupole mass spectroscopy is presented (Refs 95 113). Estimations of the vapor pressure of TNT were made mass spectrometrically in the range of 50—... 

All major mass spectral data collections consist of El mass spectra, mostly recorded under accepted standardized conditions such as an ionization voltage of 70 eV, an emission current of 100-200 xA, and an ion source temperature of 150-200°C. Several types of GC/MS systems may be applied, for instance, magnetic sector, quadrupole, or ion trap analyzers. Ion trap systems are considered less applicable, when data comparison is required with spectra from a reference library. In particular, basic compounds related to VX or the three nitrogen mustards tend to produce protonated molecular ions by self-protonation. Magnetic sector and quadrupole mass spectrometers suffer less from interference of self-protonation, and spectra produced with these types of instruments are generally reproducible. 

Ions exiting the drift tube are mass analyzed in mass spectrometer MS2, an important feature if reactions are occurring in the drift cell. Ions are generally detected after MS2 by ion counting techniques. The mass spectrometers MSI and MS2 are typically quadrupole mass filters, and either one or the other can be run in RF-only mode for better signal but without mass selection, if desired. 

Tandem mass spectrometry (MS-MS) using quadrupole mass analyzers or ion-trap analyzers facilitate the conducting MS-MS experiments and increases the sensitivity of detection. Fragmentation patterns of anthocyanins generally show the loss of a glycoside or... 

In a quadrupole mass analyzer, only a single mass-to-charge ratio m/z) value is transmitted to the detector for any given combination of radio frequency (RF) and direct current (DC) potentials. Typically, the RF/DC ratio is held constant and scanned to provide a mass spectrum. If, for example, a quadrupole is scanned from m/z 1 to 1000 in 1 second, then any particular m/z is transmitted to the detector for only 1 millisecond, representing a duty cycle of 0.1 %. Thus, a quadrupole mass analyzer has a low transmission duty cycle in the full-scan mode, which results in limited full-scan sensitivity. In contrast, ion-trap and TOF mass analyzers have the theoretical potential to transmit all ions that enter the mass analyzer and yield far better sensitivity across the entire mass spectrum. In reality, the pulse sequences associated with these analyzers devote significant time to functions such as ionization and detection. The actual duty cycles are generally between 10 and 25%, still far better than a scanning quadrupole mass spectrometer. 

Multiple Knudsen cells for the determination of chemical activities have been reported by Chatillon and coworkers [148-151], Fraser and Rammensee [134], Zimmermann [152], Paulaitis and Eckert [153], and Hackworth et al. [154]. Multiple cells have practically the same temperature. One cell contains a reference material, the other for instance samples of different compositions. A comparison of the vapor in the different cells is generally rendered possible by their displacement from outside so that the molecular beams originating in the different cells can be analyzed successively. The quadrupole mass spectrometer and not the multiple Knudsen cell is displaced in the Knudsen cell-mass spectrometer system described by Ref. 153. No displacement of the mass spectrometer or the cell is necessary if the triple cell by Hackworth et al. [154] is used. Backdiffusion through the orifice has, however, to be considered for the two cells containing sample and reference. 

In general a mass spectrometer consists of an ion source, a mass-selective analyzer, and an ion detector. Since mass spectrometers create and manipulate gas-phase ions, they operate in a high vacuum system. The magnetic-sector, quadrupole, and time-of-flight designs also require extraction and acceleration ion optics to transfer ions from the source region into the mass analyzer. Tables 2 and 3 provide brief descriptions of the most commonly used ionization techniques and the different types of mass spectrometers available, respectively [163,232-235,241,242,244-246]. 

Developments in two general areas have spurred this progress. Sector and quadrupole mass analyzers, the traditional methods of separation of ions in mass spectrometry, have recently been complemented by the development of powerful Foiuier transform (FT-MS) and time-of-flight (TOF-MS) instruments. The TOF analyzers are particularly well-suited for detecting higher molar-mass species present in polymers. 

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