Accelerating potential

Most instruments are configured with a fixed value for the radius of curvature, r, so changing the value of B selectively passes ions of particular values of momentum, mv, tlirough tlie magnetic sector. Thus, it is really the momentum that is selected by a magnetic sector, not mass. We can convert this expression to one involving the accelerating potential. 

At the other extreme, ions with initial velocities in the direction opposite to the accelerating potential must first be turned around and brought back to their initial position. From this point their behaviour is the same as described above. The time taken to turn around in the ion source and return to the initial position is given by ... 

In this mode, ions are formed continuously in the ion source (a), but the electrostatic accelerating potential is applied in pulses (b). Thus, a sample of ions is drawn into the drift region (c) with more ions formed in the source. As shown in Figure 26.1, the ions separate according to m/z values (d) and arrive at the detector (e), the ions of largest m/z arriving last. 

If an ion has to travel from one end of a quadmpole to the other, it must have some kinetic energy in the z-direction. This kinetic energy can be induced by application of an accelerating potential to the ions before they enter the quadrupole field. 

Show that the wavelength X associated with a beam of electrons accelerated by a potential dilference Fis given by 1 = h(2eVmgy. Calculate the wavelength of such a beam for an accelerating potential difference of 36.20 kY... 

This sequence of events is quite rapid. If we take typical instrumental conditions of the LIMA 2A, where the UV laser pulse duration is 5-10 ns, the fight path is "2 m, and the accelerating potential is 3 kV, then an ion arrives at the detector i n approximately 3 ps, and a ion arrives at the detector in approximately 40 ps. Since the time width of an individual signal can be as short as several tens of nanoseconds, a high speed detection and digitizing system must be employed. 

For efficient production of X-rays by electron bombardment, exciting electron energies that are at least an order of magnitude higher than the line energies must be used, so that in Mg and A1 sources accelerating potentials of 15 kV are employed. Mod-... 

Nonetheless, the absence, from even the high range of the accelerating potential, of even very weak peaks corresponding to NbF5 ions was especially mentioned in [383]. 

The threshold curves obtained when the accelerating potential between OR and Q2 was changed over a wide range from the onset of a given production to its maximum intensity were fitted with the theoretical cross section program, CRUNCH, developed by Armenrout and coworkers,67-69 which leads to a determination of the threshold energies (see Section IV.C). 

The opportunity of creation of oscillating system in the structure with braking potential field, which were made by the distributed potentials and accelerating potential, is shown. The particle in such the field will make fourfold process of braking and accelerating. 

Continuous ion sources, such as ESI, can be connected to the TOF analyzers through orthogonal acceleration (oa-TOF) [205-209]. In oa-TOF, the ions generated by the source enter the TOF analyzer perpendicular to its main axis (Fig. 2.11). The acceleration potential is initially set to zero and the start pulse is generated instantaneously as the potential is raised and the ions are accelerated into the field-free flight tube. 

B is the magnetic field intensity, r is the radius of the ion path, and V is the accelerating potential. In analytical mass spectrometers either B or V is varied systematically so that ions of different m/z are sequentially focused on the collector and the spectrum recorded. Such whole molecule mass spectrometers have been employed occasionally for isotope ratio measurements but their use is restricted to samples... 

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). 

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