Chromatographic separation factors

Fig. 4.6 Chromatographic separation factors for various uranium isotopes vs. 238U as a function of mass at 433 K. s = ln[(238U/1U)iv,aq/(238U/1U)vi,resin]- The field shift (FS) and vibrational (BM) contributions are of opposite sign. Triangles = calculated vibrational (Bigeleisen-Mayer) contribution, diamonds = calculated FS contribution, circles = measured effects, open squares = calculated effects. Note that agreement between calculation and experiment is quantitative. The correlation lines are drawn through even/even data points only (Data from Bigeleisen, J., J. Am. Chem. Soc., 118, 3676 (1996))...

For two peaks to be resolved chromatographically, the capacity ratios, Kj and K2, must be different. For analytical purposes, two interdependent chromatographic properties must be considered the chromatographic separability factor, a, and the resolution, Rs. The chromatographic separability factor is defined as... 

Figure 2.13 A hypothetical chromatogram, showing the retention time of an unretained compound (/<,), the retention times of two analytes, and and the relationship of these quantities to the capacity ratios, K/ and K2 , and the chromatographic separability factor, a.

The balanced final energy values between the complexes with (J )- and (S)-derivatized amino acids did not correlate well with their separation factors. The final energy values, however, indicated the chromatographic elution order, and van der Waals energy values are useful in the search for the best complex conformation. The precision of prediction of chromatographic separation factors may be improved by using a powerful computer that can handle both a brush-type chiral phase as a model surface for packing, and the solvent effects. 

Table 14 Elution Volumes (IQ and Chromatographic Separation Factors (a j) for Substrates on Polymer-coated Silica Prepared using 48 as a Template...

Table 15 Capacity Factors k ) and Chromatographic Separation Factors ( y) for Imidazole and Substrates 48,50,52, and 53 on Polymer-coated Silicas Prepared using 48,50,52, or 53 as Templates...

The Chirbase/GC and Chirbase/Flavor data banks document separations of enantiomers performed by gas chromatography. It contains bibliographical, structural, and chromatographic (separation factor a, retention factor k and resolution Rs) information based on standard database software. 

Gas chromatographic separation factors for for several different liquid phases on... 

A variable-size simplex optimization of a gas chromatographic separation using oven temperature and carrier gas flow rate as factors is described in this experiment. 

The separating power of a chromatographic process arises from the development of many theoretical plates to achieve adsorption equiUbrium within a column of moderate length. Even though the separation factor between two components may be small, any desired resolution may be achieved with sufficient theoretical plates. 

When the adsorption equihbrium is nonlinear, skewed peaks are obtained, even when N is large. For a constant separation-factor isotherm with R < 1 (favorable), the leading edge of the chromatographic peak is steeper than the trailing edge. Wmen R > 1 (unfavorable), the opposite is true. 

The distribution coefficient can be determined by batch experiments in which a small known quantity of resin is shaken with a solution containing a known concentration of the solute, followed by analysis of the two phases after equilibrium has been attained. The separation factor, a, is used as a measure of the chromatographic separation possible and is given by the equation,... 

Factors may be classified as quantitative when they take particular values, e.g. concentration or temperature, or qualitative when their presence or absence is of interest. As mentioned previously, for an LC-MS experiment the factors could include the composition of the mobile phase employed, its pH and flow rate [3], the nature and concentration of any mobile-phase additive, e.g. buffer or ion-pair reagent, the make-up of the solution in which the sample is injected [4], the ionization technique, spray voltage for electrospray, nebulizer temperature for APCI, nebulizing gas pressure, mass spectrometer source temperature, cone voltage in the mass spectrometer source, and the nature and pressure of gas in the collision cell if MS-MS is employed. For quantification, the assessment of results is likely to be on the basis of the selectivity and sensitivity of the analysis, i.e. the chromatographic separation and the maximum production of molecular species or product ions if MS-MS is employed. 

Funk et al. have used a low-pressure mercury lamp without filter to liberate inorganic tin ions from thin-layer chromatographically separated organotin compounds these were then reacted with 3-hydroxyflavone to yield blue fluorescent chromatogram zones on a yellow fluorescent background [22]. Quantitative analysis was also possible here (XoK = 405 nm, Xji = 436 nm, monochromatic filter). After treatment of the chromatogram with Triton X-100 (fluorescence amplification by a factor of 5) the detection limits for various organotin compoimds were between 200 and 500 pg (calculated as tin). 

Solvent selectivity is seen as the factor that distinguishes individual solvents that have solvent strengths suitable for separation. In reality, separations result from the competition between the mobile and stationary phases for solutes based on the differences of all intermolecular interactions with the solute in both phases. Solvents can be organized on selectivity scales that are useful for initial solvent selection, but in a chromatographic separation the properties of the stationary phase must be taken into consideration. Methods that attempt to model chromatographic separation need to consider simultaneously mobile and stationary phase properties [38]. 

For optimization of chromatographic separations the ratio of the time spent by the solute in the stationary phase to the time it spends in the mobile phase is more fundiwentally i tortant. This ratio is called the solute capacity factor and is given by equation (1.8)... 

The variables that control the extent of a chromatographic separation are conveniently divided into kinetic and thermodynamic factors. The thermodynamic variables control relative retention and are embodied in the selectivity factor in the resolution equation. For any optimization strategy the selectivity factor should be maximized (see section 1.6). Since this depends on an understandino of the appropriate retention mechanism further discussion. .Jll be deferred to the appropriate sections of Chapters 2 and 4. 

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