We have studied the dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond acceptor basicity (β) of sodium dodecyl sulfate (SDS) micelles using the Kamlet−Taft solvatochromic comparison method. The micellar environments of solubilized indicator molecules are quite polar (π* = 1.06) and have strong hydrogen bond donating ability (α = 0.87) and moderate hydrogen bond accepting ability (β = 0.40). Both the high dipolarity and especially the strong hydrogen bond acidity support previous work that indicates water is present in the indicators' micellar microenvironments. In contrast to many previous UV−vis spectroscopic studies of the polarity of SDS micelles, we have resolved the recorded micellar spectra so as to obtain the micellar spectrum of the indicators free from contributions of the indicator in the accompanying aqueous phase. This study was conducted to rationalize and complement linear solvation energy relationship (LSER) studies of partitioning in SDS micellar systems which have recently appeared in the literature. To our knowledge this is the first study in which curve resolution is applied to micellar spectra for the purpose of characterizing both the polarity and hydrogen bond ability of SDS micelles.

A number of common mobile phase modifiers were characterized by chromatographing monofunctional probe solutes on a cyano-bonded stationary phase under subcritical and supercritical conditions. Solvatochromic analysis techniques were used to characterize the relative selectivity, efficiency, and eluotropic strengths of the various modified mobile phases. Analysis of the combined results suggests that modifier choice may be made in a rational manner to either enhance or mask a particular type of molecular interaction. This control is necessary for challenging applications such as chiral separations. The relative effects of each modifier property change depending on whether the chromatographic system is subcritical or supercritical, thus making knowledge of the phase equilibria associated with the mobile phase essential.

The effect of mobile phase additives is investigated for a variety of compounds under subcritical and supercritical conditions using packed columns. Retention of hydrogen bond donor/acceptor analytes was found to be more dependent on the presence of mobile phase additives than weak hydrogen bond acceptor analytes. The temperature and pressure of the mobile phase are major factors in the extent of this dependence. Consequently, selectivity between homologous compounds is dependent on both the additive used and the state of the mobile phase. Efficiency is nearly always improved by the presence of mobile phase additives, more so under supercritical conditions than under subcritical conditions. These observations suggest that surface molar excesses of mobile phase additives play a large part in the resulting character of the supercritical chromatographic system.

Gas-apolane partition coefficients (L(87)) of 157 nonpolar and polar organic solutes, spanning a wide range of functional groups, dipolarities, and hydrogen-bonding capabilities, are measured by open tubular capillary gas chromatography at 40 °C. The experimental values compare well (R(2) = 0.999) with literature values of log L(87) from packed-column gas chromatography. The log L(87) values are also compared with gas-hexadecane partition coefficients (log L(16)) at 25 °C. A strong linear relationship exists between log L(87) and log L(16) for all solutes (R(2) = 0.994), as well as for chemically relevant subsets of the data. Therefore, unknown L(16) values at 25 °C can be predicted from the corresponding L(87) values, which can be measured on open-tubular or packed columns at higher temperatures, due to the low volatility of apolane. Predicted values of L(16) would be extremely useful, since log L(16) is often the major explanatory parameter in many linear solvation energy relationships.