PARAMETERS AFFECTING SELECTIVITY

Where possible, we will derive simple relationships between retention and the relevant parameters. For reasons of clarity, we will express all equations in terms of the capacity factor (k). Obviously, the simplest possible equations will be most useful for optimization purposes. Ideally, we will be looking for linear relationships, since straight lines allow straightforward interpolation. 

At the end of the chapter (section 3.5) we will summarize the relationships that are recommended for the various parameters in different kinds of chromatography. 

---

IMPREGNATION OF CONTROLLED-POROSITY SILICA Cu/Si02, Co/Si02 and Cu-Co/SiOg INVESTIGATION OF THE PARAMETERS AFFECTING SELECTIVITY IN CO HYDROGENATION... 

The major process parameters at selected periods in the four experiments are listed in Tables II, IV, VII, and VIII. Carbon recoveries ranged from 63 to 91%. Most of the losses occurred in connection with the recycle compressor system, and they decreased correspondingly the volume of product gas metered. Such losses, however, did not affect significantly the incoming gas to the main reactor or reactor performance. 

CA Dunbar, AJ Hickey. Selected parameters affecting characterization of nebulized aqueous solutions by inertial impaction and comparison with phase-doppler analysis. Eur J Pharm Biopharm 48 171-177, 1999. 

The selectivity of a number of organic modifiers was examined using the predicted log k values of the log P — 3 models from each group in different organic modifier-water mixtures. The composition of the eluent was adjusted so that either the solubility parameter,1 polarity (Po), proton acceptor (Xa), proton donor (Xd), or dipole moment (Xn) values were kept constant to determine which parameter affected the selectivity. The results are summarized in Table 4.3. 

It is assumed that the reader is familiar with such common chromatographic concepts as efficiency, selectivity, capacity factors, and theoretical plates, and how these parameters affect and effect chromatographic resolution. Excellent descriptions of these general chromatographic principles have been published. Other reviews on various aspects of carbohydrate separations will be cited in the appropriate Sections. 

More than likely you will need to describe a commercially available instrument or standard piece of instrumentation in your Methods section. Several common types of instrumentation (and their abbreviations) are listed in table 3.2 these instruments are so common and standardized that no instructions or diagrams are needed to explain how they work. It is necessary, however, to report the operational parameters under which an instrument was operated. Parameters are selected and optimized for each particular application of an instrument and can vary among users, even for the same instrument. Moreover, parameters affect the outcome and reproducibility of an experiment hence, they must be described. Characteristic ways to report parameters have been developed for many types of... 

Search for effective organic promoters. Selective and active catalysts for Reaction 4 should not only be effective carbonylation catalysts, but also be highly effective in hydrogenation-hydrogenolysis reactions in the presence of CO. The most obvious parameters affecting activity and selectivity include Rh/Ru ratio, partial CO and H2 pressures, temperature, solvent type, and type of iodide promoter. 

To a much greater extent than either metals or ceramics, the mechanical properties of polymers show a marked dependence on a nnmber of parameters, inclnding temper-atnre, strain rate, and morphology. In addition, factors snch as molecnlar weight and temperature relative to the glass transition play important roles that are not present in other types of materials. Needless to say, it is impossible to cover, even briefly, all of these effects. We concentrate here on the most important effects that can affect selection of polymers from a mechanical design point of view. 

Resolution is a measure of the relative separation achieved between two chromatographi-cally distinct materials, and maximum resolution is the primary goal of any purification step. This discussion covers the main theoretical parameters that affect ability to resolve components of a protein sample into chromatograph i-cally distinct forms, thereby providing a basis on which to judge chromatographic results. The main parameters affecting resolution are selectivity, efficiency, and capacity. More detailed... 

Although supercritical extraction (SFE) has been known for some time, it is still a relatively new technique to the analytical chemist. Before developing an SFE method, the chemist must understand the composition of the matrix and the analyte properties. The key instrumental parameters affecting the extraction of analytes from the matrix include fluid density, temperature, and fluid composition. Both the make-up of the matrix and the analytes must be considered when selecting the extraction conditions. Consideration of the extraction parameters must be given with respect to their affect on the analytes of interest and on the compounds present in the matrix that may either coextract with the analytes or inhibit their extraction by physical or chemical means. 

Cluster Growth. Would solvated atoms, allowed to slowly warm and nucleate to Au-Sn intermetallic alloy particles, show any selectivity toward growth of particular AuxSny species What properties of the solvent or other experimental parameters affect this selectivity These are the questions we attempted to answer with the following experiments. 

The previous chapter was devoted to the development of guidelines for the selection of a suitable propellant combination. It was assumed implicitly, for the purpose of predicting and comparing the performance of different propellant combinations, that other parameters affecting performance were fixed. The effects of system parameters, other than the propellant combination itself, are now considered. 

Primary parameters are those which have a large effect on retention. Usually, these parameters do not affect selectivity to the same extent. Therefore, these are the parameters that can be used to bring the capacity factors of the solute into the optimum range. 

Secondary parameters may affect retention, but always affect selectivity. In fact, ideally the parameters should be selected such that the retention (k) is kept roughly constant (i.e. in the optimum range) while the selectivity (a) can be varied. If the secondary parameters do affect retention, then sometimes this ideal situation can be approached by the simultaneous variation of two (or more) parameters at the same time. Examples of this may be found in chapter 5. 

Summary of parameters which affect retention (k), but do not affect selectivity (a). The proportionalities given assume all other parameters to be constant. 

---