Transmission of the analyzer

Similarly to Eq. (2.6), fCis a proportionality constant containing fixed operating conditions, for example incident electron current density, transmission of the analyzer at the kinetic energy Ea, efficiency of the detector at the kinetic energy Ea, and the probability of the Auger transition XYZ. 

Increasing resolution does not affect the relative intensities of the peaks, i.e., the intensity ratios for m/z 28 32 40 44 in the spectrum of air basically remain constant (Fig. 3.18). However, an increase of resolution is usually obtained at the cost of transmission of the analyzer, thereby reducing the absolute signal intensity (Chap. 4.3.4). Accordingly, isotopic patterns are not affected by increasing resolution up to / = 10,000 beyond, there can be changes in isotopic patterns due to the separation of different isotopic species of the same nominal mass (Chap. 3.4). 

The intensity of a given photoelectron line is proportional to the X-ray flux, cross-section for exciting the particular level, density of the particular atom in the lattice x, the escape depth for electrons of the resulting kinetic energy, asymmetry factor in the angular distribution of the photoionization event, transmission of the analyzer, which includes the acceptance angle and area, and the efficiency of the electron detector. In addition, there are several secondary factors, some of which depend on the matrix. The intensity of line is given by... 

After post-ionization in the 3 cm long cylindrical plasma space between sample surface and the opposite wall, SN" enter a 90° electrostatic ion energy analyzer (ion optics) suppressing ionized plasma gas particles to a degree of 10 -10 noise levels are correspondingly low (1 cps). The transmission of the electrostatic ion optics is in the range of a few per cent. 

Mass bias, or the instrumental mass fractionation, is the variable transmission of the ion beam into the mass spectrometer. A variety of phenomena create conditions that lead to variable transmission of ion beams. For modem instmments, the transmission in the flight tube and the efficiency of ion conversion to electrons at the collector are almost quantitative. Most fractionation processes, therefore, take place within the source, namely in the area where the analyte is introduced into the mass spectrometer and ionized, or at the interface between the source and the mass analyzer. 

According to the above definition, sensitivity does not only depend on the ionization efficiency of El or any other ionization method. Also relevant are the extraction of ions from the ion source, the mass range acquired during the experiment, and the transmission of the mass analyzer. Therefore, the complete experimental conditions have to be stated with sensitivity data. 

We must also take into account two further factors. First, the fact that the transmission efficiency of the analyzer is a fimction of the kinetic energy (K.E.) of the photoelectrons in the ESCA-3 Vacumn Generators instrument the transmission is inversely proportional to the K.E. of the electrons (3a). Second, photoelectron yields must refer to total yield from a particular ionization process and this need not, for example, be just the area of the relevant peak. Account must be taken of all processes that divert electrons from the primary peak, e.g., shake-up, shake-oflF, and plasmon peaks. In some cases, e.g., emission from the Cu 2P3/2 level, the contribution of additional processes is small but in others, and emission from the Al(2p) shell is an example, the no-loss peak is substantially less than the true Al(2p) emission. 

This is a development of the above where a fiber-optic linked hqnid sample transmission cell is integrated with the sample fast loop cabinet (Figures 5.24 and 5.25). There can be multiple sample streams, take-offs and fast loops, each with its own separate fiber-optic transmission cell. The analyzer can either be local with short fiber-optic runs to the sampling cabinet(s), or remote, where a safe area location for the analyzer module may be feasible, but at the cost of longer, potentially less stable fiber-optic runs. This system avoids physical stream switching. 

The standard mass analyzer of ICP-MS is still the quadrupole. He allows the resolution of nominal mass units clown to 0.2-0.5 mass units and is therefore a low-resolution device. The performance of all ICP-MS instruments is limited by the transmission of the interface and mass analyzer unit, the background count rate clue to photons and the remaining gas pressure and the background count rate caused by molecular ions or doubly charged ions. Typical quadrupole instruments offer instrumental background count rates of 10 cps, newer instruments with an off-axis quadrupole show less than 1 cps like high-resolution instruments. 

In aes, the resolution is largely independent of the characteristics of the analyzer or source and is dictated by the natural linewidth of the Auger line (usually several eV). Therefore, in using a CMA for aes, the analyst is more concerned with transmission (and hence, sensitivity) than with resolution. In contrast to xps, the optimization of variables is achieved for aes in the CRR mode of operation. The large transmission of the CMA relative to the CHA make it the more desirable analyzer for aes. 

Figure 6J2A. Position of polarization analyzer (polarizer) in 180° geometry. Double-headed arrows indicate direction of laser electric field vector and direction of maximum transmission of the polarizers.

Transmission. The transmission of the wavelength analyzer is the fraction of light of a given wavelength entering the entrance slit that reaches... 

The secondary ion current (Im) of chemical species m is collectively determined by the primary ion flux (Ip), the sputter yield (Ym) and the ionization probability. a+ represents the probability for positive ions, 9m is the fractional concentration of species m in the surface layer and rj is the transmission of the detection system. The transmission is defined as the ratio of the ions detected to ions emitted, and it varies from 0 to 1 depending on the analyzer. The sensitivity of SIMS to element m is controlled by the factors Ym, a+ and rj. Ym generally increases with beam energy and with the primary ion mass. It also varies with the types of atomic bonding in target samples. 

The pressure calibration factor k takes into account losses of species caused for example by the intensity distribution of the molecular beam from the Knudsen cell or the transmission of the ion source and the analyzer. Three different methods are generally used [86] ... 

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