Page 102 - Illustrated Pocket Dictionary of Chromatography

98 HYDRODYNAMIC VOLUME

hydrodynamic volume A critical parameter for size-exclusion
chromatography because it is defined as the total volume swept out
by a molecule when it is completely rotated around its central axis.
Therefore, the only case when the true molecular volume matches the
hydrodynamic volume is in the case of a perfect sphere.
hydrogel A direct product of post-polymerization sineresis. This
type of gel is further hardened by heating to form a xerogel.
hydrolytic stability Any bonded phase that comes in contact
with aqueous solutions is susceptible to having bonded phase groups
cleaved from the surface because of chemical reaction with water.
The degree to which the phase is susceptible to hydrolysis is a
measure of the hydrolytic stability.

hydrophilic In general, refers to samples and stationary phases
that are compatible with high-percentage aqueous solutions. Hydro-
philic literally means “water-loving.”
hydrophobic In general, refers to samples and stationary phases
that are incompatible with high-percentage aqueous solutions, that is,
are compatible with nonpolar solutions. Hydrophilic literally means
“water-fearing.”

hydrophobic effect In highly aqueous solvents, hydrogen bond-
ing between water molecules is a strong and energetically favored
state. When nonpolar molecules are added to these systems they are
“expelled” from the solvent so that the hydrogen bonds can be
reformed and the most energetically favored state can be realized.
hydrophobic interaction chromatography (HIC) An LC
technique that uses low-polarity support materials and varying ionic-
strength mobile phases to generate separation of macromolecules
(e.g., proteins) that are incompatible with organic solvents. Elution
is generated by decreasing the salt concentration. To increase the
hydrolytic stability a number of routes have been taken: Add bulky
groups to the derivatizing silane [i.e., Cl-Si(C(CH 3) 3) 2R vs. Cl-
Si(CH 3) 3) 2R]; endcap the support material; form multiple bonding sites
to the surface, produce a polymeric bonded phase.

hydrostatic injection The process used in capillary elec-
trophoresis that utilizes differential pressure, such as gravity, to
make an injection. In this case the sample vial is positioned above the