Modulated temperature theoretical considerations

The ability of a GC column to theoretically separate a multitude of components is normally defined by the capacity of the column. Component boiling point will be an initial property that determines relative component retention. Superimposed on this primary consideration is then the phase selectivity, which allows solutes of similar boiling point or volatility to be differentiated. In GC X GC, capacity is now defined in terms of the separation space available (11). As shown below, this space is an area determined by (a) the time of the modulation period (defined further below), which corresponds to an elution property on the second column, and (b) the elution time on the first column. In the normal experiment, the fast elution on the second column is conducted almost instantaneously, so will be essentially carried out under isothermal conditions, although the oven is temperature programmed. Thus, compounds will have an approximately constant peak width in the first dimension, but their widths in the second dimension will depend on how long they take to elute on the second column (isothermal conditions mean that later-eluting peaks on 2D are broader). In addition, peaks will have a variance (distribution) in each dimension depending on... 

Hyperfine coupling constants provide a direct experimental measure of the distribution of unpaired spin density in paramagnetic molecules and can serve as a critical benchmark for electronic wave functions [1,2], Conversely, given an accurate theoretical model, one can obtain considerable information on the equilibrium stmcture of a free radical from the computed hyperfine coupling constants and from their dependenee on temperature. In this scenario, proper account of vibrational modulation effects is not less important than the use of a high quality electronic wave function. 

In principle there is a possibility to stabilize bivalent metal cation with a ligand, which transforms bivalent cations to monovalent species, for example, (ZnOH)+. It is reasonable to expect appearance of such species as a result of dissociative adsorption of water and it will be discussed below. However, the most interesting catalytic processes proceed at high temperatures when the above-mentioned species became unstable. It should be noted that all the above considerations are applicable to zeolites with rather high zeolite module Si/Al >5. The theoretical treatment of traps of exchange metal cations in zeolites with lower module requires different approach. The stabilization of bivalent metal cations in zeolites is considered in the Sect. 20.2 of this review which discusses the example of Zn/ZSM-5 zeolites. These zeolites are active in the catalytic process of small alkane dehydrogenation. Thus, we will explore the influence of the stabilization forms of zinc cation on different stages of this catalytic reaction. 

---