Capacity factor organic modifier

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

The reduction of the capacity factors with increasing organic modifier concentration in the eluent was weaker when methanol was used compared to acetonitrile, and this was attribnted to its lower polarity [5]. Even if methanol or acetonitrile are the most common organic modifiers, an unusual solvent, tetramethylene oxide [16], was recently tested in the IPC of sulfides and aromatic sulfonated compounds and proved to play an important role in adjusting retention. 

Linearly extrapolated capacity factors should be preferred because quadratic extrapolation may lead to erroneous overestimated values. The linearity range depends on the organic modifier as well as on the solutes. Methanol does not disrupt, substantially, the hydrogen bonding network of water and, usually, a wide linearity range is achieved relative to acetonitrile or tetrahydrofuran. 

However, extrapolated capacity factors may be affected by the nature of the organic modifier. In a study concerning the measurement of lipophilicity indices for monosubstituted benzenes by HPLC, the log values of the more polar derivatives appeared to be lower when methanol was used as an organic modifier, compared to the log values obtained with acetonitrile. In contrast, for nonpolar derivatives, acetonitrile led to lower log fcw values. An analogous decrease in the log fcw values for a series of lipophilic 9//-xanthene and 9//-thioxan-thene derivatives was observed when tetrahydrofuran was... 

The relationships between capacity factor, k , and organic modifier concentration in the mobile phase, and the effect of the column temperature on k for the antibiotics studied have been used to define k as a function of T and V (volume fraction) on the basis of a small number of experimental measurements for a given combination of column, organic solvent, and type of antibiotic. From calculated values of k, resolution values, Rs, may be estimated for adjacent band-pairs under all conditions. The method developed enables the optimization of RP-HPLC separations of the p-lactam antibiotics in the absence of difficult theoretical calculations, using a small number of experimental data, including the influence of the organic solvent in the mobile phase (isopropanol) and the column temperature. 

Often, the separation factor can be increased by changing the experimental conditions of the separation, such as by decreasing the organic modifier concentration, the buffer concentration, the type of buffer used, or the pH of the mobile phase. These methods must be used to optimize the separation factor. Provided the coliunn saturation capacity does not decrease when cc increases, which may happen with macromolecules, this means maximizing a. 

The co-adsorption of neutral and/or ionic species plays a dominant role in the retention characteristics of solutes in electrochemically modulated chromatographic columns. The electrochemically modulated liquid chromatography is a new and promising technique, which uses conductive stationary phases and the whole column is configured as an electrochemical cell. ° If the mobile phase consists of the polar solvent S, an inert electrolyte, the organic modifier B and the eluite A, the capacity factor, k, for eluite A is given by ° ° ... 

This equation means that, if X, the concentration of organic modifier in the mobile phase, and and P, descriptors ofa compound are given, the logarithm of the capacity factor, log k can be determined for any chromatographic conditions. This is the basic concept of the retention prediction system investigated in this study. 

Single Column. It Is well known that the capacity factor, k, for a compound often varies In a predictable manner with respect to the concentration of organic modifier for aqueous solutions under reverse phase conditions. It has been shown for a single organic modifier the relationship is ... 

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