Negative ions mobility

M. Tabrizchi and A. Abedi, A novel electron source for negative-ion mobility spectrometry. International Journal of Mass Spectrometry, 218 (2002) 75—85. 

Eiceman, G.A., Leasure, C.S., Vandiver, V.J. Negative ion mobility spectrometry for selected inorganic pollutant gases and gas mixtures in air. Anal. Chem. 58, 76-80, 1986. 

Tabrizchi, M. Abedi, A. A novel use of negative ion mobility spectrometry for measuring electron attachment rates. J. Phys. Chem. A 2004,108, 6319-6324. 

MoFarland M, Albritton D L, Fehsenfeld F C, Ferguson E E and Sohmeltekopf A L 1973 Flow-drift teohnique for ion mobility and ion-moleoule reaotion rate oonstant measurements. III. Negative ion reaotions of 0 + CO, NO, FI2, and D, J. Chem. Phys. 59 6629-35... 

Ion exchange, in which cation and/or anion resins are used to replace undesirable anionic species in liquid solutions with nonhazardous ions. For example, cation-exchange resins may contain nonhazardous, mobile, positive ions (e g., sodium, hydrogen) which are attached to immobile acid groups (e.g., sulfonic or carboxylic). Similarly, anion-exchange resins may include nonhazardous, mobile, negative ions (e.g., hydroxyl or chloride) attached to immobile basic ions (e.g., amine). These resins can be used to eliminate various species from wastewater, such as dissolved metals, sulfides, cyanides, amines, phenols, and halides. 

The discussion of molecules and molecular ions will be continued in Sec. 29. Here we shall begin the detailed examination of solutes that are completely dissociated into ions. The conductivity of aqueous solutions of such solutes has been accurately measured at concentrations as low as 0.00003 mole per liter. Even at these concentrations the motions of the positive and negative ions are not quite independent of each other. Owing to the electrostatic forces between the ions, the mobility of each ion is slightly less than it would be in a still more dilute solution. For example, an aqueous solution of KC1 at 25°, at a concentration of 3.2576 X 10 6 mole per liter, was found to have an equivalent con-... 

Further wc may notice that there is a striking resemblance to Fig. 28 in Chapter 4, where the temperature coefficient of the ionic mobility was plotted against the mobility itself. This resemblance is more interesting when it is recalled that the experimental values plotted in Fig. 28 are obtained for each species of positive and each species of negative ion separately and do not contain any arbitrary factor (like the assignment... 

The frequency-dependent spectroscopic capabilities of SPFM are ideally suited for studies of ion solvation and mobility on surfaces. This is because the characteristic time of processes involving ionic motion in liquids ranges from seconds (or more) to fractions of a millisecond. Ions at the surface of materials are natural nucleation sites for adsorbed water. Solvation increases ionic mobility, and this is reflected in their response to the electric field around the tip of the SPFM. The schematic drawing in Figure 29 illustrates the situation in which positive ions accumulate under a negatively biased tip. If the polarity is reversed, the positive ions will diffuse away while negative ions will accumulate under the tip. Mass transport of ions takes place over distances of a few tip radii or a few times the tip-surface distance. 

Figure 7.31 Negative-ion thermospray mass spectrum of the disulfonated azo dye Direct Red 81 (mobile phase contains 10mmolL ammonium acetate). After Niessen [568]. Reprinted from W. Niessen, in Encyclopedia of Spectroscopy and Spectrometry (J.C. Lindon, ed.), Academic Press, pp. 2353-2360, Copyright (2000), with permission from Elsevier...

If a voltage is applied across two platinum electrodes (usually platinum sheets coated with platinum black) placed in an electrolytic solution, an electric current will be transferred to an extent that is in accordance with the amounts and the mobilities of the free positive and negative ions present in the solution. Under the precautions required (see Section 2.1.1.2), the experiment obeys Ohm s law, which here can be described by... 

Methods of Measurement. The positive and negative small-ion concentrations, the electrical conductivity, and ion mobilities were measured with a Gerdien-type instrument. From analyses of current-versus-voltage curves obtained with the apparatus operated at constant volume flow, values for the ion density, the conductivity, and the mean mobility of the ions can be determined (Wilkening and Romero, 1981). 

An early theory of ionic recombination in liquids was developed by Jaffe (1913) for application at a relatively high LET. However, in Jaffe s theory, coulombic interactions are ignored and the positive and negative ions are assigned the same mobilities and distribution functions. Therefore, its use in a... 

As the electric current passes through this system, the cathode (negative electrode) grows in thickness while the anode (positive electrode) shrinks. At the cathode, M+ ions are converted to M atoms, which results in growth of the cathode. From this observation, it is clear that the cations are primarily responsible for conductivity, and this is the result of a vacancy type of mechanism. In this case, the positive ion vacancies have higher mobility than do the vacancies that involve negative ions. 

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