23.10 What is chromatographic solvent "polarity"?
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
23.10 What is chromatographic solvent "polarity"?
There are four major intermolecular interactions between sample and solvent
molecules in liquid chromatography, dispersion, dipole, hydrogen-bonding,
and dielectric. Dispersion interactions are the attraction between each pair
of adjacent molecules, and are stronger for sample and solvent molecules
with large refractive indices. Strong dipole interactions occur when both
sample and solvent have permanent dipole moments that are aligned. Strong
hydrogen-bonding interactions occur between proton donors and proton
acceptors. Dielectric interactions favour the dissolution of ionic
molecules in polar solvents. The total interaction of the solvent and
sample is the sum of the four interactions. The total interaction for a
sample or solvent molecule in all four ways is known as the "polarity" of
the molecule. Polar solvents dissolve polar molecules and, for normal
phase partition chromatography, solvent strength increases with solvent
polarity, whereas solvent strength decreases with increasing polarity
in reverse-phase systems. The subject is discussed in detail in Snyder
and Kirkland [10].
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