Ion optics and transmission

A computer program, MacSimion, [92] can be used to model the ion trajectories in ion optics after various assumptions. From these considerations it becomes dear that when dealing with several dements any optimization will also lead to compromises. Thus there will always be a difference in performance in mass spectrometry with respect to sensitivity and to the lowest matrix influences between single-element optimization and compromise conditions. 

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The importance of surface and chemical analysis techniques in electronics corrosion testing cannot be overstated. These powerful tools contribute to solving problems and elucidating corrosion mechanisms in simple and complex systems. Chemical analysis techniques include infrared (IR), ultraviolet (UV), and RAMAN spectroscopy X-ray diffraction atomic adsorption emission and mass spectroscopy gas and liquid chromatography and optical and transmission electron microscopy. Surface analytical techniques include electron spectroscopy for chemical analysis (ESCA), Auger, secondary ion mass spectroscopy (SIMS), and ion scattering spectroscopy (ISS). These important techniques used in conjunction with corrosion tests are described in another section of this manual. 

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. 

The other very important function of the ion optics is to shape the ion beam. Voltages on the various lenses should be set to avoid chromatic aherration, which causes energy-dependent transmission of ions in the instrument, and as a result erroneous lEDs [161, 163]. The correct lens settings have been found by simulations of ion trajectories in the EQP using the simulation program SIMION [329], In addition, an experimental method to find the correct settings has been presented [161, 163]. 

Carburization of rhenium filaments has been used to optimize Th and Pa ionization efficiency for TIMS analysis on single filaments (Esat 1995). ReC has a greater work function than Re metal, and elemental oxidation state is maintained in the reduced or metal state by the presence of carbon in the filament. Using this method and a mass spectrometer with improved ion optics, Esat (1995) was able to improve Th transmission and ionization efficiency by about a factor of 30 over conventional methods. Using more conventional mass spectrometry, Murrell et al. (personal communication) were able to improve ionization efficiency for Pa and Th by a factor of 5-10 over conventional graphite sandwich loads on Re filaments (Goldstein et al. 1989 Pickett et al. 1994). For Pa analysis, one drawback is that Pa and U ionization commonly overlap using this... 

In order to maintain the number of ions arriving at the ion trap, it is necessary to multiply the number above with the transmission factor TF(m), which will be dependent on mass, in order to take into account the permeability of the separation system for atomic number m (analogous to this, there is the detection factor for the SEMP it, however, is often already contained in TF). The transmission factor (also ion-optical transmission) is thus the quotient of the ions measured and the ions produced. 

Continued advances in source/interface designs for the coupling of LC and MS/MS have increased ion formation and transfer into the mass spectrometer. Improved optics (focusing lenses, etc.) have increased ion transmission through the MS and to the detector. These improvements have resulted in a significant increase in sensitivity, and as a result, quantification at the parts per trillion concentration level is routine today and was not possible a decade ago. Advances in source/interface design to increase the abundance of ion formation, transfer, and transmission through the MS may lead to even more sensitive instruments. In addition, the use of smaller particle sizes in LC (e.g., UPLC) also increases resolution, selectivity, and sensitivity. 

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