Linear solvent strength

In 1996, Snyder and Dolan elaborated the linear solvent strength (LSS) approach allowing the evaluation of log few from a single gradient run and its precise determination from two gradient runs [48]. From a practical point of view, LSS is the most useful approach to describe theoretical aspects and LSS gradients are convenient for optimization studies. Several commercially available optimization software packages which are able to predict resolution or retention in RPLC are currently based on this approach. 

In this section a phenomenalogical approach to the description of solvent gradients will be adopted based largely on the linear solvent strength model prt osed by Snyder [552-555]. This is the least complicated of the models available and provides a reasonable approximation for typical experimental conditions. Mathematically more rigorous approaches have been developed by Jandera and Churacek [551,556], schoenmakers et al. [520,534,557] and Tomellini et al. [558]. 

Figure 4.36 Example of an optimum linear-solvent-strength gradient. Peak Identification 1 benzyl alcohol 2=2-pbenylethanol 3 = o-cresol 4 nitrobenzene 5 diethyl o-phthalate 6 - benzophenone 7 = naphthalene 8 = biphenyl and 9 = anthracene. (Reproduced with permission fr< ref. 557. Copyright Elsevier Scientific P d)lishlng Co.)...

SELECTION OF OPTIMAL LINEAR SOLVENT STRENGTH GRADIENTS IN LIQUID CHROHATOGRAPHy... 

The basis for linear solvent strength theory is the assertion that the logarithm of the capacity factor is linearly related to the solvent strength. This is expressed in the Equation 87 90... 

The practical consequence of linear solvent strength theory is that, in principle, it is possible to estimate the retention times of all peaks at any... 

The conceptual basis for understanding the connection between isocratic and gradient elution is well established and is called "linear solvent strength theory".22 27 Linear solvent strength theory proposes that, for a given solute, mobile phase, and column, if one measures the retention time of an analyte at two organic component concentrations, it will be possible to predict the retention time with any other mobile phase composition. The k value that would be observed in pure water, kw, is related to the actual k by the relationship... 

The regression coefficients of descriptors denote the system (combination of mobile and stationary phases) response to these interactions. These coefficients can be measured, however the procedure is time consuming and inappropriate for practical purposes. According to the linear solvent strength theory (LSST) the retention of the analyte depends on the volume fraction (cp) of the organic modifier in binary mobile phase systems ... 

The linear solvent strength (LSS) model combined with QSRR calculations has been applied for the prediction of retention in gradient RP-HPLC. It was established that total dipole moment (jd), electron excess charge of the most negatively charged atom (<5Mm) and water-accessible molecular surface area (Awas) exert the highest impact on the retention ... 

A. Wang and P.W. Carr, Comparative study of the linear solvation energy relationship, linear solvent strength theory, and typical conditions model for retention prediction in reversed-phase liquid chromatography. J. Chromatogr.A 965 (2002) 3-23. 

T. Baczek and R. Kaliszan, Combination of linear solvent strength model and quantitative structure-retention relationships as a comprehensive procedure of approximate prediction of retention in gradient liquid chromatography. J. Chromatogr.A 962 (2002) 41-55. 

The relationship between retention and solvent strength in reversed-phase chromatography is described by the linear solvent strength model 19,20... 

Moreover, in various experiments it was found that at a constant total counterion concentration in the eluent the dependence of the retention factors on the organic modifier content tp largely follows the linear solvent strength theory (LSS) (Equation 1.5)... 

L.R. Snyder, J.W. Dolan, High-Performance Gradient Elution. The Practical Application of the Linear-Solvent-Strength Model. Hoboken, NJ Wiley-Interscience, 2007. 

For components which are eluted under ideal gradient conditions (i.e. those components that appear neither at the very beginning nor after the end of the actual gradient in linear solvent strength gradients, it can be shown that the median capacity factor kg is inversely proportional to the gradient steepness parameter, defined as [428]... 

The suggestion given before that in an ideal programmed analysis the peak width should be the same for all solutes (see also figure 6.1c) corresponds to the assumption that kg is equal for all peaks. For a definition of linear solvent strength (LSS) gradients see section 5.4. 

A simple way to estimate the appropriate isocratic conditions from the result of a gradient elution chromatogram is provided by the theory of linear solvent strength (LSS) gradients of Snyder (for a review, see ref. [528] or [527]). By definition, an LSS gradient obeys the following relationship ... 

The concept of linear solvent strength (LSS) gradients developed by Snyder (see also sections 5.4.2 and 6.2.2) incorporates optimization of both the shape and the slope of gradient programs. The shape of an LSS gradient is determined by... 

Vd is the so-called gradient dwell volume [i.e., the volume of the mobile phase contained in the instrument parts (mixer, filter, and tubing) between the pump and the column]. In an ideal case, linear concentration gradients in RPLC correspond to linear solvent strength (LSS) gradients according to the model developed by Snyder and Dolan " hence, Eq. 4 describes the retention data in LSS gradient elution. 

Snyder, L.R. Dolan, J.W. The linear-solvent-strength model of gradient elution. Adv. Chromatogr. 1998, 38, 115-187. 

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