Capacity ratio, liquid chromatography

Jandera, P. and Churacek, J., Gradient elution in liquid chromatography. I. The influence of the composition of the mobile phase on the capacity ratio (retention volume, band width, and resolution) in isocratic elution — theoretical considerations, /. Chromatogr., 91, 207, 1974. 

The log Ofj term reflects the differences in capacity ratios of the two peptide solutes Sj and Sj which differ by a functional group and is analogous to the term used to predict selectivity differences for the classical liquid-liquid partition chromatography of peptides. The influence of functional group behavior on the retention of polar solutes in reversed-phase HPLC has been the subject of several recent articles and similar trends are apparent with peptide derivatives (29-31). 

The LFER-based retention parameter in high-performance liquid chromatography (HPLC) is the logarithm of the phase capacity ratio or retention factor k. The capacity... 

Capacity factor (k J. The fundamental dimensionless measure of retention in liquid chromatography is the capacity ratio (or capacity factor) (k ), which is defined as the ratio of the number of molecules of solute in the stationary phase, N, to the number of molecules in the mobile phase,... 

Retention in reversed-phase liquid chromatography decreases with decreasing concentration of water in the mobile phase. The logarithm of the capacity ratio for a given solute is linearly related to the volume fraction of the organic modifier in the mobile phase, O, according to equation (3.12) ... 

Retention time in gas chromatography is related to a combination of retention and volatility, similar to solubility in liquid chromatography. Predicting volatility is as difficult as predicting solubility. Volatility has been explained as the enthalpy of vaporization (Avap f), and a method for predicting volatility has been proposed." If the A apH values are available, it may be possible to predict retention time. Unknown A apH values have been calculated from the relationship between the van der Waals volume and reference AyapH values. The values are summarized with the corresponding reference values in Table 1 of the Appendix (p. 278). Values of A apH have also been related to capacity ratios. The correlation coefficients were 0.896 and 0.852 ( = 48) for DBl and CPSilS columns, respectively, which appear to be acceptable correlation coefficients, except that the relationship for allq l alcohols deviated from those of other compounds as seen Figure 4.4. 

The coefficient of correlation between the calculated individual molecular interaction (MI) energies and the logarithmic capacity ratio indicated the contribution of individual factors to the retention. MIVW was the main contributor to the interaction in reversed-phase liquid chromatography, and MIES was the main contributor to the retention in ion-exchange liquid chromatography. Steric hindrance affected the molecular interaction in enantiomeric separation. ... 

The retention time of phenolic compounds in reversed-phase liquid chromatography was predicted via molecular interaction energy values calculated using the MM2 program. The precision of the capacity ratios predicted by this new method was equivalent to a former method in which the retention time was predicted by log P calculated using the MOPAC program. Furthermore, the prediction of capacity ratios of phenolic compounds in reversed-phase... 

The capacity ratios of partially ionized compounds can be predicted using eqn (9). For evaluation by the above approach, k and iti were replaced with energy values calculated using eqns (4) and (5), respectively. The predicted p Ta values from the atom partial charge related to the measured p/fa values in liquid chromatography were used for the calculation. The results are summarized in Figure 6.22. 

The pH effect on the molecular interactions can be examined experimentally using liquid chromatography. The capacity ratio in an eluent of a given pH can be predicted from and the MI energy at a given pH can be calculated using eqn (4). 

The capacity ratios of molecular-form compounds measured in reversed-phase liquid chromatography can be related to their log P values, given by the following equation (2) ... 

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