Role of the Ion Optics

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

FIGURE 6.1 Position of ion optics relative to the plasma torch and interface region. 

As mentioned in Chapters 4 and 5, the plasma discharge and interface region have to be designed in concert with the ion optics. It is absolutely critical that the composition and electrical integrity of the ion beam be maintained as it enters the ion optics. For this reason, it is essential that the plasma be at zero potential to ensure that the magnitude and spread of ion energies are as low as possible.  

FIGURE 6.2 An ion-focusing system that uses a hollowed-out ion mirror to deflect the ion beam 90° to the mass analyzer, while allowing photons, neutrals, and solid particles to pass through (courtesy of Varian Inc.). 

FIGURE 6.2 Extreme pressure drop in the ion optic chamber produces diffusion of electrons, resulting in a positively charged ion beam. 

FIGURE 6.3 The degree of ion repulsion will depend on the kinetic energy of the ions— those with high kinetic energy (heavy masses) will be transmitted in preference to those with medium (medium masses) or low kinetic energy (light masses). 

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It is also important to understand that an additional role of the ion optic system is to stop particulates and neutral species from making it through to the detector, which would increase the noise of the background signal. This will certainly impact the instrument s detection capability in the presence of complex matrices. Therefore, it is definitely worth carrying ont a DL test in a difficult matrix such as lead or uranium, which tests the ability of the ion optics to transport the maximum number of analyte ions while rejecting the maximum number of matrix ions, neutral species, and particulates. 

This enzyme has been studied extensively by x-ray, kinetic, NMR, optical, circular dichroic, and fluorescence techniques. Thus, many approaches have been used to explore the role of the metal ions in catalysis and of other protein residues in substrate binding and catalysis. The review of this enzyme will serve to point out the information to be gained from using multiple biophysical approaches in understanding metalloenzyme catalysis. 

Optical detection of intermediates produced in the reactions of triplet carbonyl compounds with electron donors has some obvious limitations. However, the technique of CIDNP is proving particularly effective at elucidating the reaction pathways in these systems. The outstanding work of Hendriks et al. (1979) illustrates the power of the technique. Not only was the role of radical ions in the reactions of alkyl aryl ketones with aromatic amines defined but the rate constants for many of the processes determined. The technique has been used to show that trifluoracetyl benzene reacts with electron donors such as 1,4-diazabicyclo[2.2.2]octane and 1,4-dimethoxy-benzene by an electron-transfer process (Thomas et al., 1977 Schilling et al., 1977). Chemically induced dynamic electron polarisation (CIDEP) has been... 

Some of the most definitive studies of Mg(II)-activated enzymes have been performed by mangetic resonance (NMR, ESR) methods with the Mn(ll)-substituted species. An integrated picture of the role of the metal ion in catalysis in almost all cases also includes data from kinetics (steady state and pre-steady state), equilibrium binding, and optical spectroscopic methods. As stated above, there are but a few examples of true Mn-containing enzymes, especially in mammalian sytems. Table 1 provides a non-exhaustive list of examples of both Mn-specific and Mn/Mg-activated enzymes. Within the latter category are enzymes that show a preference for but not absolute specificity for one ion or the other. The distinction between these categories is not simple, often being dependent upon the source or form of the enzyme and various parameters as the type of assay used, temperature, pH, and others. 

The development of fluorescent probes which can selectively sense metal ions has received increasing interests in recent years.1 The significant attention attracted in this research field is not only because of the important roles of metal ions in biological, clinical and environmental chemistry, but also due to the advantages of fluorescence technology simple instrumentation suitable for field analysis, and optical signals observable by the naked eye. 

Tetrahedral coordination of the metal ion is not an essential requirement for formation of this type of helical structure. Two-coordinate silver(I) ion plays an important role in the formation of a helical framework, that is, the stereoconformation of the ligand itself is maintained on coordination to Ag(I) and arranged in a onedimensional helical chain. Reaction of the bidentate optically active ligands (4R,5R)- and (4S,5S)-4,5-bis(2-(2-pyridyl)ethyl)-l,3-dioxolane (RJl-Lis or S,S-L3) with silver(I) trifluoromethanesulfonate in metha-... 

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