Ion population

As expected, the addition to the flame of the electronegative species Cl (from HC1) or CN (from CH3CN) produces Cl or CN. At low pressures, the total negative ion population may be increased (9) while at 1 atm. all the negative ions can be replaced by Cl (14). Thus, both direct attachment and charge transfer are involved. 

Cold plasma with reduced temperature is another way to cope with the most annoying problems from interferences, even in the case of low-resolution instruments [394], The effect consists of weaker ionisation conditions coming close to chemical ionisation [395]. In particular, argides are reduced by orders of magnitude in comparison to conventional ICP operation. However, at lower plasma temperatures, evaporation of analyte material is considerably reduced. Reducing the plasma temperature also has a dramatic effect on the ionisation (and therefore sensitivity) of many elements. Table 8.65 shows the ion population as a function of plasma temperature and ionisation potential. As a result, the cold plasma technique is only advantageous for a rather small number of elements and applications. 

Table 8.65 Ion population (%) as a function of plasma temperature and ionisation potential...

Senko, M. W. Beu, S. C. McLafferty, F. W. Determination of monoisotopic masses and ion populations for large biomolecules from resolved isotopic distributions. J. Am. Soc. Mass Spectrom. 1995, 6,229-233. 

Fig. 7.2. Calculated [40] relative ion population as a function of ion charge state in solid Ti heated at temperatures ranging from 10 to lOOeV. Also shown in the same plot is the separation energy of the 2p-ls transitions as a function of the ion charge. Higher ionization stages from B-like Ti to O-like Ti are expected to emit in the range between 4,550 and 4,750 eV...

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

For our method of monitoring the ion population in the reaction mixtures, we chose electrical conductivity because the concentrations of ions involved were far too low for any kind of spectroscopic facility available to us at the time, and it was desirable to keep the reaction vessel attached to the vacuum line so that solvent and monomer could be added to or distilled out of it. 

This is the expression for the capacity of an interface in the presence of contact adsorption. Note how the differential capacity is affected by contact-adsorbed ions populating the IHP through the quantity dqcfJdqM. 

Would ions populating only the OHP explain the constancy of capacity It will tend to do so because when it is considered that the ions are in the OHP, the d term in Eq. (6.262) will become r( plus other terms connected with the radii of water molecules separating the ions from the electrode [see Fig. 6.88(a)]. The total separation distance would be much less dependent on the radius of the ion because it consists also of the water molecules around the ion and those hydrating the electrode. The variation in rf would affect d to a lesser degree. Constant capacity means, then, that ions do not contact adsorb on the electrode, but populate the OHP. 

TABLE 12. Encaged ion population (IVion), HOMO and LUMO energies (eV) and stabilization energies (AE, kcalmol-1) of endohedral complexes of Ygo (Y = C, Si and Ge) with various ionsaA.c... 

Temporal Variation of Ion Signal of an Inert Ion. 1. Problem Definition Several assumptions are required if correct correlations between ion signal and chemical reactivity are to be made from ion kinetic studies using FTMS. The first assumption must be that the sensitivity of the ion trap remains constant with time so that ion signals are representative of the ion population with time. The second assumption is that losses of reactant ions are due to consumption of those ions in a chemical reaction and not by physical processes. 

The observations that there is an "optimum" orbit size and that peaks split for orbits not too much larger than the optimum orbit suggest that the optimum orbit occurs because of special circumstances. One possible circumstance is a coincidence of frequencies for ions with low and high z-mode amplitudes so that if there are mass discriminating differences in the way the ions populate the trap or in the way ions are excited, then systematic mass measurement errors can be expected. Excitation of the cyclotron mode does produce a spread in cyclotron radii, and mass discriminating z-mode excitation is discussed elsewhere in this chapter. Thus, frequency variations that cause systematic mass errors are due in part to trap field inhomogeneities. These effects are evident at low ion populations and may be due in part to excitation induced ion cloud deformation which increases with ion number. 

The hyperbolic cell offers several advantages for accurate mass determinations. 1) The frequencies of fundamental modes of the ion motion are independent of the location of the ion in the cell at least for the low ion limit. This is important because frequencies are known to be influenced by the location of the ions in cubic cells. 2) The excitation electric field has a simple form identical to that of the trapping field. Thus, the operation of the trap is the same everywhere in the interior permitting most of the volume to be used for storage of larger ion populations with reduced space charge effects. 3) Harmonic effects (31,13b) that complicate spectra are removed. 

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