Recording Mass Spectra

In a GC/MS combination, passage of the separated components (A, B, C, D) successively into the mass spectrometer yields their individual spectra. 

Slow scanning (i) of the mass spectrum over a GC peak for substance A gives spectrum (a), but rapid scanning (ii) gives spectrum (b), which is much closer to the true spectrum (c). 

10 sec). Thus, scan follows scan right through the chromatogram, and hundreds of mass spectra 

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The mass spectrometer tends to be a passive instrument in these applications, used to record mass spectra. In chemical physics and physical chemistry, however, the mass spectrometer takes on a dynamic function as a... 

The mass spectrometry of diazo compounds was reviewed by Zeller (1983) and by Lebedev (1991). It is difficult to record mass spectra of diazonium salts using conventional techniques. With the water thermospray method, however, Schmelzeisen-Redeker et al. (1985) observed the diazonium ion and various fragments such as [Ar+ - N2 + 2H]+ and [Ar + N2 + H20]+. Ambroz et al. (1988) applied the fast atom bombardment (FAB) technique using a 3-nitrobenzylalcohol matrix. Peaks for ArNJ, Ar+, and [M + ArN2]+ and further peaks due to solvated ions were found. 

There are different methods of recording mass spectra ... 

The photoplate detector is one of the oldest types of MS detectors (Fig. 2.21a). J.J. Thompson used photoplates to record mass spectra [4], Photoplates were for a... 

We recorded mass spectra of MYKO relatives in order to check if the simplicity of the fragmentation j thway found in the MYKO 63 spectrum was also observed with other kinds of substituent on the phosphorus atoms, or when the central ring system was modified. 

Most recorded mass spectra show a parent ion (1 89,90 major fragmentation process, as with 2//-imidazoles, is loss of RCN, which can and frequently does occur in two different ways this often leads to the base peak. Loss of a 4-substituent to give a delocalized cation can also compete as the primary process ... 

It is unlikely that the laboratory organic chemist will be required to record mass spectra of compounds produced in the laboratory as they will normally be obtained through a centralised service. This section therefore concentrates on the interpretation of spectra rather than on the techniques for obtaining the spectra. For further information on this aspect of mass spectrometry the reader should consult the sources listed in the references at the end of this chapter.4... 

A DuPont model 21-492B GC/MS with an Incos data system was used to confirm the presence of thiazolidine and nitrosated thiazolidine. A 30 m x 0.24 mm id glass capillary column coated with SP-2250 was used for GC/MS analyses with a 30 1 split ratio (with the larger fraction vented to atmosphere through a charcoal trap). Electron impact ionization was used at 70 eV. The data system generated total ion current chromatograms and recorded mass spectra. 

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. 

Using SIFT-MS it is possible to record mass spectra in the full-scan mode (FS) of quadrupole MS or in multiple ion monitoring mode (MIM) when ions are passed thorough the quadrupole with a certain m/z ratio. FS mode allows the full mass spectrum of analytes in a defined range of m/z values to be registered within a specified time period. In the case of MIM, precursor ions and selected ions, formed during reaction of the reagent ion and the analyte, are scanned. 

The mass spectrum (MS) of chitin was recorded using a VG Micro-mass 7070 F gas chromatography mass spectrometer imit. The electron paramagnetic resonance (EPR) spectra were recorded using a Varian EPR spectrometer. The MS recorded at a temperature of 300 °C is shown in Eig. 2.22. This temperature was used to obtain a more stable and rich fragmentation pattern. Table 2.13 presents the list of fragments that can be attributed to the ions detected in the recorded mass spectra (MS). 

An AEI MSIO Residual Gas Analyzer was used to record mass spectra of permanent gases. Spectra of other gaseous products were obtained using an AEI MS12 Instrument. 

Fractions 1-4 can be analyzed by ESI-direct infusion recording mass spectra in negative ionization mode. Due to the higher complexity of fractions 8-10, for these samples direct ESI-MS analysis does not provide useful information, and for their characterization LC/ESI-MS and MSn analyses have to be performed. Compounds identified are reported in Table 3.8 with the analytical conditions used. 

On-line computerization has the advantage that the computer can interact closely with the GG MS. For example, the computer can monitor the gas chromatogram and record mass spectra as the compounds elute. 

Much more challenging than recording mass spectra of pure CyDs are applications of MS for characterization of stoichiometry, physicochemical properties, and even gas-phase reactions of the inclusion complexes of CyDs with a broad variety of ligands, both organic and inorganic. Since the mid-1990s several extensive review articles [20, 21, 56-58) and the chapter in Vol. 8 of the Comprehensive Supramolecu-lar Chemistry [59] have been published on these subjects. Almost all of them con-... 

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