Combined use of temperature and solvent strength in reversed-phase gradient elution .4. Selectivity for neutral (non-ionized) samples as a function of sample type and other separation conditions

The separation of nine un-ionized samples was studied as a function of temperature (T) and gradient steepness (b). Selectivity values Delta log alpha* were obtained for 160 compounds, ranging from nonpolar hydrocarbons to very polar drugs. Selectivity varied markedly with sample type: nonpolar compounds such as aromatic hydrocarbons and fatty acid methyl esters generally showed only modest changes in band spacing as temperature or gradient steepness was varied. More polar samples exhibited larger changes in alpha (Delta log alpha*) when temperature and/or gradient steepness were changed, but the largest values of Delta log alpha* for these non-ionized samples are less than the average value of Delta log alpha* for the ionized samples of Part III [1]. Poly-functional silane (''polymeric'') columns exhibit slightly increased b- and/or T-selectivity for some samples.