Page 181 - Illustrated Pocket Dictionary of Chromatography

SOLVENT SELECTIVITY TRIANGLE 183

where DE v is the vaporization energy of the compound and V is its
3
volume. Therefore, the unit of measure for d is ÷cal/cm . The solubil-
ity parameter correlates strongly with polarity; the higher the polar-
ity, the higher the d value. A scale of d was developed by Hildebrand
(the solubility paramter scale).
Determined by the equilibrium concen-
solubility product, K sp
tration of ions in a saturated solution. Mathematically the solubility
product for a salt nXmY is:
a+ n
b- m
K sp = [ X ] [ Y ]
a+
+
where [X ] is the cation concentration with charge a appearing n
b-
times in the salt and [Y ] is the anion concentration with charge b -
appearing m times in the salt. For example, the solubility product for
3- 2
2+ 3
2
Ca 3PO 4 is K sp = [Ca ] [PO 4 ] .
soluble A compound that can be dissolved is called soluble. Note
that soluble indicates a level that is different from miscible, which
means soluble in all proportions. As an example, chloroform is soluble
in water to 0.8% at 20°C.
solute A minor component that is dissolved in a solvent.

solvent The major component of a liquid mixture that contains
solutes.

solvent polarity index, P’ Experimentally developed by Snyder
by comparing the ratio of the capacity factor for a given solute when
changing from one solvent to another:
1 -
k 2 ¢ k 1 ¢ = 10 ( PP 2 ) 2
See individual solvent entries for their P’ value.

solvent selectivity groups Developed to classify solvents with
respect to their primary intermolecular interactions with an analyte.
These interactions included pure proton acceptor, pure proton donor,
and large dipole moment.

solvent selectivity triangle Originally was developed from the
solvent selectivity groups with each apex of the triangle representing
one of the critical intermolecular interactions. Now a solvent selec-