Magnetic sector mass spectrometers double-focusing

Peak matching can be done on quadrupole and magnetic-sector mass spectrometers, but only the latter, particularly as double-focusing instruments, have sufficiently high resolution for the technique to be useful at high mass. 

Fig. 1. Schematic diagram of a double-focusing Nier-Johnson magnetic sector mass spectrometer where ( " ) represents paths of ions having slightly...

The dwelltime of ions within the ion source is defined by the extraction voltages applied to accelerate and focus them into an ion beam and by the dimensions of that ion source. In standard El ion sources the freshly formed ions dwell about 1 ps before they are forced to leave the ionization volume by action of the accelerating potential. [41] As the ions then travel at speeds of some 10 m s they pass the mass analyzer in the order of 10-50 ps (Fig. 2.9). [9] Even though this illustration has been adapted for a double focusing magnetic sector mass spectrometer, an ion of m/z 100, and an acceleration voltage of 8 kV, the effective time scales for other types of instruments (quadrupole, time-of-flight) are very similar under their typical conditions of operation (Table 2.4). 

Magnetic sector mass spectrometers (and double-focusing mass spectrometers). 

Magnetic Sector Mass Spectrometers (and Double Focusing Mass Spectrometers)... 

A small fraction of the reactant ions collide with Cm molecules, and product ions scattered into the forward hemisphere in the laboratory frame are collected by the octapole. Product and unscattered reactant ions are mass selected by a double focusing electric and magnetic sector mass spectrometer, and detected by an on-axis Daly detector [16]. In the following we give only relative cross sections, due to uncertainties in the absolute pressure of Cm, the product collection efficiency, and the alkali-metal ion beam intensities in the scattering cell. 

All positive ion DCI mass spectra were obtained from a Finnigan MAT 90 double focusing magnetic sector mass spectrometer. The electron energy was set at 150 eV. The instrument was set to scan from 100-850 amu at 2 seconds per decade with a 1 second InterScan time. Ammonia was used as the reagent gas at a source pressure of lxlO 4Torr. 

Magnetic deflection mass analyzer Double focusing sector spectrometer Quadrapole mass analyzer Triple quadrapole analyzer... 

Double-focusing magnetic sector mass spectrometers and Fourier transform (FT) mass spectrometers (described in Chapter 9) are capable of mass measurements with high resolution. The most important use of high-resolution MS is the direct determination of molecular formulas by exact mass measurements. 

FIGURE 2.33 Double-focusing high-resolution magnetic sector mass spectrometer. 

FIGURE 1.24 (a) Schematic presentation of aquadrupolemass spectrometer. (FromBlaum, K. et al., Int. J. Mass Spectrom., 181,67,1998. With permission.) (b) Schematic of a double-focusing magnetic sector mass spectrometer with variable dispersion. (From Belshaw, N.S. et al, Int. J. Mass Spectrom., 181,51,1998. With permission.)... 

FIGURE 8.1 Schematic of a reverse Nier-Johnson double-focusing magnetic sector mass spectrometer (from U. Geismann and U. Greb, Fresnius Journal of Analytical Chemistry, 350,186-193, 1994). 

FIGURE 8.4 The principles of the Mattauch-Herzog double-focusing magnetic sector mass spectrometer with a simultaneous detector plane. (Courtesy of SPECTRO Analytical Instruments GmhH, Kleve, Germany.)... 

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