Page 67 - Illustrated Pocket Dictionary of Chromatography

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ELECTROPHORETIC VELOCITY, v ep
An EI source is not particularly effective at producing molecular
ions (i.e., the molecular weight of the parent compound or its proto-
nated form). Chemical ionization sources are used for molecular ion
formation.

The flow of mobile phase
electroosmotic flow (EOF) v eo
through a capillary that is the result of an applied potential at the cap-
illary wall (i.e., a zeta potential). EOF is mathematically defined as:
v eo =ez E h

where e is the dielectric constant, z is the zeta potential, E is the
applied voltage, and h is the viscosity.
The flow velocity for the analyte
electroosmotic mobility, m eo
generated at a set field strength, E:
m eo = v eo E

electrophoresis A technique that separates molecules based on
differing charge densities and molecular size/shape through the appli-
cation of an applied electric field (potential).

electrophoretic mobility, m The mobility of an ion, that is, the
velocity at which an ion travels across a support material, is deter-
mined by its charge/volume ratio, three-dimensional structure, degree
of solvation, and viscosity of the carrier solution. Mathematically this
is represented as:

m = v E = q 6 phr

where is the ionic velocity, E is the applied potential, q is the net
charge of the ion, h is the solution viscosity, and r is the radius of the
solvated ion.
The rate at which an ion migrates
electrophoretic velocity, v ep
through the support system at a fixed potential:
v ep = L t

where L is the length of the support (cm) and t is the migration time
(s).