Compensation voltage

Thus the Volta potential may be operationally defined as the compensating voltage of the cell. Very often the terms Volta potential and compensation voltage are used interchangeably. It should be stressed that the compensating voltage of a voltaic cell is not always the direct measure of the Volta potential. 

In contradiction to the usual treatment, relation (5) is not general (see below). For this reason, as well as the lack of an exact thermodynamic relation with the changes in Gibbs energy, the term compensation voltage is also recommended instead of emf, which is commonly used for... 

The main difficulty in measuring the compensation voltage of voltaic cells is the very large resistance of the system caused by the presence of a dielectric gas phase. Therefore there are two possibilities for solving the problem reduce this resistance or measure the work of the charge transfer across the dielectric. The first possibihty is accomplished by the ionizing method and the second by condenser and jet methods. 

Applying the condenser or ionization methods (Section IV), the voltage E is determined as a difference in the compensating voltages of the following two cells ... 

Adsorption of a dipolar substance at the w/a and w/o interfaces changes surface tension and modifies the surface potential of water (Fig. 11). As seen in Fig. 11, the change in compensation voltage due to adsorption is the surface potential difference, usually called the surface potential or better the adsorption potential and often indicated unnecessarily by AV. ... 

Usually before adding a surfactant it is necessary to clean the surface of the water solution by siphoning off the top layers of water with a glass capillary until the constant compensation voltage is obtained. This is not done in the jet method. 

If both liquid junction potentials are eliminated and supporting electrolytes MX are not adsorbed at the free surfaces of solvents, the compensating voltage is... 

As seen in this sketch, the change of compensation voltage A.E, due to adsorption is the surface potential difference, usually called shortly surface potential, or better the adsorption potential... 

The condition at equilibrium is that tp(a ) = and fie(a) = jue()3) (the latter equation describes the condition for contact equilibrium between the electrons in phase oc and j3). The measured compensating voltage U,... 

Thus the compensating voltage U yields the difference between the outer electrical potentials of the metal and the solution with which it is in contact. 

Ioperating = measured current with compensating voltage OFF (milliamps)... 

The ionization chamber compensation curve, Figure 21, is a plot of the percent compensation versus compensating voltage. This compensation curve must be plotted prior to using a compensated ion chamber. 

Small changes in compensating voltage change the percent compensation. 

An ion that is displaced from the center of the analyzer can be restored to the center of the gap (i.e., compensated) when a DC potential from, for example, 20 to 10 V is superimposed on the separation field. This second potential is called the compensation voltage and will allow an ion to be passed through the DMS drift tube and to a detector. A scan of the compensation voltage provides a measure of all ions in the analyzer and is termed a differential mobiftty spectrum as shown in Figure 10. This method is now understood as a technique for separation of ions based on AK rather than K as seen with conventional drift tubes. 

Figure 12 Topographic plots of a DMS-IMS analyzer response to 2,4-DNT (left frame) and 2,4,6-trinitrotoluene (right frame). Positions ofions in plots are circled the reactant ion peak is seen at compensation voltage of 8V and drift time of 2 ms. Source (C.R. White et al., unpublished data. New Mexico State University, September 2005.)...

A new analyzer based on ion mobihty has been introduced in 2005 and combines DMS and IMS analyzers in tandem, hence ions are first separated in a DMS drift tube and then characterized by twin IMS drift tubes [62]. Because the DMS is comparatively slow (0.1—1 Hz) and the mobihty spectrometer operates at 30 Hz, mobility spectra can be obtained throughout a DMS sweep of compensation voltage, creating a three-dimensional plot as shown in Figure 12 for DNT and TNT (unpublished experimental results provided by C.R. White et al. at New Mexico State University, September 2005). As shown in the topographic plots of Figure 12, a benefit of ion characterization for K and AK is seen in the improved separation of peaks over DMS and IMS alone. The tandem DMS-IMS was described at the 2005 International Symposium on IMS and is under development requiring detailed evaluation as drift tube improvements are made. 

Wu, S. T., Xia, Y. Q., and Jemal, M. (2007). High-field asymmetric waveform ion mobility spectrometry coupled with liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-FAIMS-MS/MS) multicomponent bioanalytical method development, performance evaluation and demonstration of the constancy of the compensation voltage with change of mobile phase composition or flow rate. Rapid Commun. Mass Spectrom. 21 3667-3676. 

Thus, alpha is associated with a difference in mobility of the ion may be positive or negative in sign, which discloses the direction of change in the coefficient of mobility (and compensation voltage) with E at constant N. In practice, ions are characterized by... 

Without intervention, all ions apart from those with no dependence of mobility on field will strike a wall, be neutralized, and be swept as a neutral from the analyzer. However, a DC voltage (the compensation voltage) can be added to the bottom electrode and superimposed on the megahertz waveform (Fig. 6). As this potential is applied, ion... 

Fig. 7. Differential mobility spectra (intensity vs. compensation voltage plot). The relationship between AK and the compensation voltage is shown for ions with positive and negative alpha functions.

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