Quadrupole mass, generally

Generally FAB produces protonated, MH+, or depro-tonated, (M — H) , quasi-molecular ions with a little excess energy which will sometimes produce fragment ions of low intensity. FAB is therefore a mild to soft ionisation technique which produces primarily molecular weight information and some structural information. Positive and negative ionisation mass spectra are produced with equal facility. FAB was originally used with magnetic sector mass spectrometers, but lately mainly with quadrupole mass spectrometers (Table 6.10). 

Quadrupole mass spectrometers are generally bench-top instruments, of relatively low cost, easy to manage and widely used for routine analysis. 

Quadrupole mass filters can easily be combined with chromatographic techniques so are often the analysers used in GC-MS and LC-MS instruments (see Section 5.6). In general, quadrupole mass filters are often used to provide low-resolution spectra and are much cheaper and require less space than magnetic sector instruments. 

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—... 

Both of the above examples illustrate that the sensitivity of the MDF method, in general, is comparable to PIS analysis and better than NLS methods (Figs 6.9 and 6.10). The sensitivity of the MDF method is attributed at least in part to the full-scan capability of high-resolution mass spectrometers such as the Q-TOF and LTQ-FTICR, which could be several times more sensitive than full-scan analysis by a triple-quadrupole mass spectrometer (Kostiainen et al., 2003). 

Plasma MS is usually based on quadrupole mass analysers. The atmospheric ICP, optimised for ion formation, is placed on its side facing a sample cone (Fig. 4.3). The mass spectrometer operates at reduced pressure and therefore a two- or three-stage differentially pumped interface is needed to transfer the ions from the plasma to the mass analyser. The interface for GC-ICP-MS is generally the same as for ICP emission systems. In one of the earliest GC-MS speciation studies (Chong and Houk, 1987) a packed GC column was used to obtain mass spectra of organic compounds with detection limits in the range 0.001-500 ngs The effects of isotopic fractionation by natural physico-chemical processes were also studied. 

In general, triple stage quadrupole mass spectrometer with ESI in positive ion mode is perceived as the most appropriate MS technique available at present for small—mostly basic—molecules and was used for the assay of nilotinib [112], sorafenib [115,116], lapatinib [117], sunitinib [113,114], bosutinib [88], vatalanib [119] axitinib [120], vandetanib [118] neratinib [87], and crizotinib [125], The latter assay for crizotinib was developed for preclinical experiments and does not contain... 

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. 

Figure 2.10 shows the general diagram of an instrument with three quadrupoles [8], Quadrupole mass spectrometers are symbolized by upper case Q, and RF-only quadrupoles with a lower case q. A collision gas can be introduced into the central quadrupole at a pressure such that an ion entering the quadrupole undergoes one or several collisions. 

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... 

Electrospray mass spectra were recorded on a Perkin-Elmer Sciex API-Ill triple quadrupole mass spectrometer (Thornhill, Canada) with general MS and LC setup as previously described (5-8). Modifications of the instrument which improve sensitivity for negative-ion mode detection of phosphorylation and sulfation have also been described before (7,8). Because phosphorylated or sulfated peptides produce predominantly negatively charged marker ions while glycosylation or acylation yield positively charged species, these two classes of modification cannot both be detected in a single LCMS experiment. 

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