Single Ion Mobilities

Approximate single ion mobilities may be calculated by assuming that the cation and anion mobilities of a selected electrolyte are the same and equal to... 

Table 2 lists limiting equivalent conductance and association constant values for a number of 1 1 electrolytes in the solvents of Table 1, and Table 3 gives single ion mobility values. The data include results that appear to have sufficient precision to give meaningful values when treated by the Fuoss-On-sager conductance equation. In a few cases data of somewhat lower precision have been included to indicate the magnitude of the association constants, which can often be determined with fair accuracy from such data. 

Fig. 4. Limiting single ion mobilities vs. reciprocal of estimated crystallographic radii of alkali metal ions AN, acetonitrile NM, nitromethane DMF,dimethylformamide PY, pyridine NB, nitrobenzene DMSO, dimethylsulfoxide EC, ethylene carbonate...

Fig. 8. Limiting single ion mobility-viscosity product vs. reciprocal of estimated crystallographic radii for cations in methanol, ethanol, and acetonitrile (from Ref. 16 )...

Fig. 10. Limiting single ion mobility-viscosity product for alkali metal ions vr. solvent Lewis basicity (as measured by enthalpy of reaction with SbCl5)...

Other ions in the spectrum are the result of ion fragmentation at the IMS-MS interface. The ion fragments are easy to recognize in the spectrum because they produce a mass spectrum at a single mobility. Within the metabolite trend band, individual metabolite ions are positioned above or below the average trend line as a result of differences in their SCS (0/m). Thus, isomers and isobars are separated within the metabolite trend band. Hundreds of specific metabolites can be identified and quantified from a single ion mobility MS run in a matter of seconds. 

Table 9.1 Single ion mobilities at infinite dilution in aqueous solutions at 25 °C ...

Conductometric Analysis Solutions of elec trolytes in ionizing solvents (e.g., water) conduct current when an electrical potential is applied across electrodes immersed in the solution. Conductance is a function of ion concentration, ionic charge, and ion mobility. Conductance measurements are ideally suited tor measurement of the concentration of a single strong elec trolyte in dilute solutions. At higher concentrations, conduc tance becomes a complex, nonlinear func tion of concentration requiring suitable calibration for quantitative measurements. 

Selection of on-site analytical techniques involves evaluation of many factors including the specific objectives of this work. Numerous instrumental techniques, GC, GC-MS, GC-MS-TEA, HPLC, HPLC-MS-MS, IR, FTIR, Raman, GC-FTIR, NMR, IMS, HPLC-UV-IMS, TOF, IC, CE, etc., have been employed for their laboratory-based determination. Most, however, do not meet on-site analysis criteria, (i.e., are not transportable or truly field portable, are incapable of analyzing the entire suite of analytes, cannot detect multiple analytes compounded with environmental constituents, or have low selectivity and sensitivity). Therefore, there exists no single technique that can detect all the compounds and there are only a few techniques exist that can be fielded. The most favored, portable, hand-held instrumental technique is ion mobility spectrometry (IMS), but limitations in that only a small subset of compounds, the inherent difficulty with numerous false positives (e.g., diesel fumes, etc.), and the length of time it takes to clear the IMS back to background are just two of its many drawbacks. 

It has been pointed out above that electroosmotic and electrophoretic mobilities are converse manifestations of the same underlying phenomena therefore the Helmholtz-von Smoluchowski equation based on the Debye-Huckel theory developed for electroosmosis applies to electrophoresis as well. In the case of electrophoresis, is the potential at the plane of share between a single ion and its counterions and the surrounding solution. 

Values of ionic mobility for various ions in water are shown in Table 1.8. For the estimation of the diffusion coefficient of a single ion the second term in the right-hand part of the eq. (1.24) is replaced by k.Jnv... 

Tomlinson, Wang and Caruso [96] used an Alltech Adsorbosphere cation-exchange column for the speciation of vanadium (IV) and (V) with ICP-MS detection. Single ion monitoring at m/z 51 was used and the mobile phase consisted of 7 mM 2,6-pyridine... 

Rocuronium bromide Verapamil (i.s.) Column Symmetry Human plasma Shield RP18 cartridge (50 x 2.1 mm) Detector ESI-MS Mobile phase linear gradient from 10% to 90% of ACN in water containing 0.1% TFA/ applied in 15 min. Column was then washed for 3 min at final gradient condition and set back to initial condition in 1 min and equilibrated for 5 min Single ion recording Rocuronium bromide m/z 265 and m/z 529 Verapamil m/z 455... 

Recently, the ion drift tube mobility studies from Bowers group (von Helden et al. 1991) have provided a means for separating carbon cluster ions with different structures because the reciprocal of the ion mobility is proportional to the collision cross-section. Thus a single cluster mass often consists of clusters with several different chemical structures and thus different cross-sections. 

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