Retention factor index

When a combination of CE and HPLC systems would be considered, the most dissimilar from the global set could be selected according to the above approach. For the CE methods, a response should be selected and applied with values in the same order of magnitude as the retention factors of the CSs, e.g., the migration times. Another possibility would be to use the so-called normalized migration indexes (see further Section III.C) for both the CE and the HPLC measurements. ... 

A great number of stationary phases are listed in catalogues and it is sometimes difficult to choose the best column for a particular analysis. The chemical nature of the phases and their polarities do not always allow one to predict which column will be optimal for a given separation. Therefore, a technique called the retention index system has been developed with the use of reference compounds whose retention factors differ with different stationary phases. Using retention indices obtained on columns of different stationary phases, it is possible to characterise a compound and facilitate its identification. 

Radioactive label, 330 Raman diffusion, 184 Raman scattering, 227 Ratio fluorimeter, 228 Rayleigh scattering, 226 Real mean, 385 Red-shift, 196 Reference electrode, 347 Reflectron, 298 Refractive index detector, 59 Relative response factor, 78 Relative standard deviation, 387 Reliability, 389 Resolving power, 282 Response factor, 77 Restrictor, 98 Retardation factor, 88 Retention factor, 14 Retention index, 41 Retention time, 7 Retention volume, 14 RP-18, 53 RSD, 387 Ruhemann, 112... 

The lipophilicity index q>0 was defined by Valko et al. (1993). cpo is the volume percent of organic modifier in the mobile phase by which the retention time is twice the dead time, which means the retention factor k is equal to 1. It was reported that using the cpo scale, the inter laboratory comparability was improved compared to using log kw. The correlation with traditionally determined log Pow values was shown to better (Valko 1993) using the cpo index. The analytical advantage of the cpo value is that it can be estimated from bracketing experimental results and not from extrapolation to 0 % organic modifier. 

However, there are obvious differences between the classically determined octanol-water partition data and the reversed phase chromatographic partition data due to the different nature of the partitioning solvents. The correlation between shake flask octanol water partition coefficients and chromatographic retention factor kw (0 % organic solvent) was described to be low (Valko 2004) when structurally diverse compound sets were analysed. Using the q>o or the CHI lipophilicity index an improvement in agreement to logPow was reported (Valko 1993,1997). 

The retention factor, Eq. (7.2), for each species / is calculated knowing the dead time, t(), and the retention time of species i at infinite dilution, /r,./- There are known methods in the literature for calculating the dead time or retention time for a non-retained peak in normal-phase, reversed-phase and ion-exchange chromatography [67]. For example, in normal-phase chromatography, pentane in 95 5 hexane-acetone is unretained. In reversed-phase chromatography, a common measure of void volume is from the refractive index response obtained when the sample solvent composition is different from the mobile-phase composition. 

From this retention factor, the Migration Index (MI) for a compound in microemulsion electrokinetic chromatography was defined as [Ishihama, Oda et al., 1996]... 

SP is some free energy related solute property such as a distribution constant, retention factor, specific retention volume, relative adjusted retention time, or retention index value. Although when retention index values are used the system constants (lowercase letters in italics) will be different from models obtained with the other dependent variables. Retention index values, therefore, should not be used to determine system properties but can be used to estimate descriptor values. The remainder of the equations is made up of product terms called system constants (r, s, a, b, I, m) and solute descriptors (R2,7t2, Stt2, Sp2 log Vx). Each product term represents a contribution from a defined intermolecular interaction to the solute property. The contribution from cavity formation and dispersion interactions are strongly correlated with solute size and cannot be separated if a volume term, such as the characteristic volume [Vx in Eq. (1.6) or V in Eq. (1.6a)] is used as a descriptor. The transfer of a solute between two condensed phases will occur with little change in the contribution from dispersion interactions and the absence of a specific term in Eq. (1.6) to represent dispersion interactions is not a serious problem. For transfer of a solute from the gas phase to a condensed phase this... 

Effect of Solvent Strength on Retention Factors. Solvents that interact strongly with. solutes are often termed strong" solvents. Strong solvents are often, but not always, polar solvents. Solvent strength depends on the nature of the analyte and stationary phase. Several indexes have been developed fur quantitatively describing the polarity of solvents. The most useful of these for partition chromatography is the polarity index P which was developed by Snyder." This parameter is based on. solubility measurements for the substance in question in three solvents dioxane (a low ... 

In the isocratic mode of RP-HPLC, the use of retention factor extrapolated to pure water (log kw) is very common in practice instead of retention factor itself, to obtain a more comparative hydrophobic index and avoiding the effect of changing the organic modifier. The extrapolation is based on the following Soczewinski-Snyder relationship 4 4 ... 

A dimensional analysis of the perfonnance index shows that it has the dimension of an inverse viscosity. With a little algebra, using the equations for permeability [Eq. (2.51)3, die definitions of the flow-resistance parameter [Eq. (154)3, linear velocity [l s. (110 and (111)3. retention factor [Eq. (161)3 and the reduced plate height [Eq. (113)3, we can lit the performance index into its components ... 

The performance index is a measure of the quality of the separation. Knox (19) was searching for a criterion that is a purer measure of column performance and criticized the performance index for its dependence on the retention factor and the viscosity. Therefore he defined a dimensionless group, the separation impedance ... 

As in other variants of chromatography, the retention values used most in GSC are not absolute but relative (retention factor, k, relative retention, r, and Kovats retention index, /), characterized by a higher reproducibility than that of absolute retention values. 

Lee et al. separated 18 L-amino acids by RP-HPLC. Binding energy ( b), hydrophobicity (log P), molecular refractivity (MR), polarizability (a), total energy (E ), water solubility (log S), connectivity index (%) of different orders and Wiener index (W) were also theoretically calculated. The retention factors with various physicochemical and structural properties of L-amino acids were represented. After investigating the effect of descriptors on the retention factors, the live major ones were found to be E y, MR, Et, V, and W. The correlation coefficient was more than 0.95. 

Retention index obtained in programmed-temperature analysis Compressibility correction factor McReynold s constant for iodobutane Retention factor (capacity factor)... 

Many factors can influence the Kovats index which can make it unreliable at times for the characterization of gas chromatographic behavior, although it generally varies less than the relative retention with temperature, flow, and column variation. However, for many it is the preferred method of reporting retention data. 

Table n. Physical Properties, SFC Capacity Factors, and GLC Retention Indexes for the PAHs Studied... 

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