Ion flow

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

FIGURE 6.3 Extreme pressure drop in the ion optic chamber produces diffusion of electrons, resulting in a positively charged ion beam. 

FIGURE 6.4 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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Figure A3.5.5. Rate constants for the reaction of Ar with O2 as a fiinction of temperature. CRESU stands for the French translation of reaction kinetics at supersonic conditions, SIFT is selected ion flow tube, FA is flowing afterglow and HTFA is high temperature flowing afterglow.

Figure A3.5.7. Schematic diagram of a selected ion flow drift tube with supersonic expansion ion source.

These days, remarkably high-resolution spectra are obtained for positive and negative ions using coaxial-beam spectrometers and various microwave and IR absorption teclmiques as described earlier. Infonnation on molecular bond strengths, isomeric fonus and energetics may also be obtained from the teclmiques discussed earlier. The kinetics of cluster-ion fonuation, as studied in a selected-ion flow tube (SIFT) or by high-pressure... 

Adams N G and Smith D 1976 The selected ion flow tube (SIFT) a technique for studying ion-neutral reactions Int J. Mass Spectrom. Ion Phys. 21 349... 

Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Adv. At Mol. Phys. 24 1-49... 

Figure Bl.7.12. A schematic diagram of a typical selected-ion flow (SIFT) apparatus. (Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Advances in Atomic and Molecular Physics vol 24, ed D Bates and B Bederson p 4. Copyright Academic Press, Inc. Reproduced with pennission.)...

This volume eontains exeellent diseussions of the various methods for studying ion-moleeule reaotions in the gas phase, ineluding high pressure mass speotrometry, ion eyelotron resonanee speotrosoopy (and FT-ICR) and seleeted ion flow tube mass speotrometry. 

This method relies on the simple principle that the flow of ions into an electrolyte-filled micropipette as it nears a surface is dependent on the distance between the sample and the mouth of the pipette [211] (figure B 1.19.40). The probe height can then be used to maintain a constant current flow (of ions) into the micropipette, and the technique fiinctions as a non-contact imaging method. Alternatively, the height can be held constant and the measured ion current used to generate the image. This latter approach has, for example, been used to probe ion flows tlirough chaimels in membranes. The lateral resolution obtainable by this method depends on the diameter of the micropipette. Values of 200 nm have been reported. 

Among the three-dimensional silicates are the zeolites, which contain cavities or tunnels in which Na+ or Caz+ ions may be trapped. Synthetic zeolites with made-to-order holes are used in home water softeners. When hard water containing Ca2+ ions flows through a zeolite column, an exchange reaction occurs. If we represent the formula of die zeolite as NaZ, where Z represents a complex, three-dimensional anion, the water-softening reaction can be represented by the equation... 

Hydrogen ions flow through the membrane, but since the electrolyte is nonconductive to electrons, it forces the electrons to flow through an external electrical circuit to complete the reaction. This flow of... 

Taking into account the variation in the oxidized area as a function of the overpotential, and the counter-ion flows, the charge consumed during the potential sweep in those regions where the structure was previously opened under conformational relaxation control, is given by... 

Barcilon, V, Ion Flow Through Narrow Membrane Channels Part I, SIAM Journal of Applied Mathematics 52, 1391, 1992. 

The second factor is the type and concentration of chemicals in soil. Soils with low initial ionic strengths favor high EO efficiencies. A lower initial ionic strength is responsible for a higher conductivity of the specimen, which in turn results in a decrease in the resistance offered to current flow, and hence the ion flow is governed more by diffusion and migration. 

In obtaining experimental information about the isomeric forms of ions, a variety of techniques have been used. These include ion cyclotron resonance (ICR),31 flow tube techniques, notably the selected ion flow tube (SIFT),32 and the selected ion flow drift tube (SIFDT)32 (and its simpler variant33), collision induced dissociation (CID),10,11 and the decomposition of metastable ions in mass spectrometers.13 All of these techniques are mentioned in the text of Section in whore they have provided data relevant to the present review. 

Using a selected ion flow tube (SIFT) technique, DePuy and coworkers studied such rates of deuterium-hydrogen exchange for a series of neutral carbon acids10. Table 1 contains some selected rates of exchange with DO- from DePuy s work these rates are approximate measures of relative acidity in the gas phase. 

During excitation, ion channels open and close and a few ions flow 98 Gating mechanisms for Na+ and K+ channels in the axolemma are voltage-dependent 98... 

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