Mobility methods

A multitude of methods have been developed for the measurement of the mobility of charge carriers in liquids. Many methods employ pulsed sources of charge carriers, as radioactive isotopes, lasers, or accelerators. In other methods a continuous charge carrier injection is modulated by an electric field. Sometimes electric field impulses are applied. In a few cases liquid flow was superimposed on the action of the electric field. Liquids with low vapor pressure allow mobility measurements by monitoring the decay of a surface charge layer. 

The most important method for measuring electron or ion mobilities is the time-of-flight method (TOP). It consists of the measurement of the time, td,it takes a group of charge carriers to traverse a certain distance, d, in an electric field, E. The drift velocity v is given as 

In insulating liquids, TOP methods are very suitable since the drift of a small number of charge carriers in an electric field can be monitored very effectively by measuring the electric current induced in an external circuit. The intrinsic conductivity of the liquid has to be small enough so that the relaxation time, T i, of the liquid given as 

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J. T. Ransom, D. L. DiGiusto, and J. Cambier, Flow cytometric analysis of intracellular calcium mobilization, Methods Enzymol. 141, 53-63(1987). 

The first applications of ion mobility methods to obtain structural information of polyatomic ions were on cluster ions, that is carbon [1-5] and silicon [6, 7] cluster ions. In carbon clusters atoms are bound to each other by covalent bonds, leading to structures like chains for small clusters (<10 atoms), rings, polycyclic... 

Nearest Integer Hydration Number of Electrolytes from the Mobility Method and the Most Probable Value from Independent Experiments... 

The mobility method (Section 2.10.1) has the advantage of yielding individual solvation numbers directly (as long as the transport numbers are known). However, this positive point is offset by the fact that the viscosity term used should be the local viscosity near the ion, which will be less than the viscosity of the solvent, which is... 

It is apparent from the above discussion that many hemoglobins with different amino acid substitutions demonstrate identical electrophoretic mobilities. Methods that rely on differences other than net charge are needed to establish the identity of these hemoglobins. Definitive... 

FIGURE 1.1 A proliferation of mobility methods occurred during the past decade, ranging over dimensions, pressnres, and arrangements of electric field (constant or time dependent). Pressure of measurements is given in the fill pattern of boxes for individual methods. 

A surge of interest has occurred in the interest in and use of mobility methods to provide additional ion filtering between ESI sources and mass spectrometers and to explore gas phase ions of biomolecules for shape, size, and transformations. This was simulated by availability of commercial instruments, including the ThermoFisher FAIMS/MS, AB SCIEX SelexION, the Owlstone pFAIMS/MS, and... 

At the level of science, the concept of mobility in fundamentally disclosing properties of an ion and the relationship between the collision cross section and the ion shape/structure is under discussion. While this may have little effect on the applications of IMS as given in Section IV, there is value in clarifying with precision these meanings. At the moment, mobility methods particularly at ambient pressure and the meaning of a mobility coefficient are still disproportionally influenced by the experimental parameters or perhaps the control or knowledge of these parameters. How the community of researchers will develop this topic is unclear and is yet another opportunity to bring mobility methods to an improved level of practice and value. 

MOBILITY METHODS BEYOND MILITARY AND SECURITY VENUES (1990 TO 2000)... 

At the beginning of this century, nascent developments in ion mobility methods were recognizable with on-site instruments for use in clinical and laboratory settings. 

Company arose from Thermidics, then Thermo Electron Corporation http //www.tsi.com/scanning-mobility-particle-sizer-spectrometers Scanning mobility particles by differential mobility methods... 

MOBILITY METHODS WITH CONTINUOUS FLOW OF IONS INTO THE DRIFT REGION... 

Several mobility analyzers commercially available today are designed with a continuous flow or stream of ions from a reaction region into the mobility measurement region, and although resolving power has been considered low, these mobility methods have anerged for laboratory and field measurements. These methods are FAIMS, DMS, DMA, and alMS methods. 

FIGURE 6.1 A block diagram of the main components of a generic ion mobility spectrometer regardless of mobility method. Any ion mobility instrnment will be comprised of a drift tube, which includes an ion sonrce, region for mobility characterization, detector and the utilities needed to support the measurement. This usually involves flows of purified gases, power supplies, and temperature control. Options for ion sources were described in Chapter 4, and methods for ion injection were presented in Chapters. 

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