Page 68 - Illustrated Pocket Dictionary of Chromatography

64 ELECTROSPRAY IONIZATION (ES)

electrospray ionization (ES) An electrospray ionization source
generates a fine aerosol that is charged by poising a potential across
the exit needle. No thermal input, other than that generated by the
applied potential, is used to produce ionization. The produced ions
are then accelerated into the mass analyzer for charge/mass separa-
tion. This technique is very gentle and in general produces parent
molecular weight data. Molecular ions often bear multiple charges,
and so the mass-to-charge ratio is affected accordingly.
eluate The entire effluent that flows from a column.

eluent The component in the separation system that moves the
sample along the column.
eluite The portion of the sample that is analyzed, that is, the
analyte.

elutriation A technique used to fractionate particles based on their
density/shape and resulting movement in a flowing stream (liquid or
gas).

eluotropic series Lists solvents according to their elution
strength (i.e., the shorter an analyte retention time, the higher the elu-
otropic strength). This scale was developed for liquid-solid supports
such as silica and alumina, with pentane the weakest and water the
strongest commonly used solvents.

eluotropic strength, e o An experimentally derived number that
represents the relative elution strength of a solvent on a defined
sorbent material. This scale was originally developed for alumina and
o
silica, with the weakest solvent, pentane, having an e ∫ 0. See indi-
vidual solvent listings for values. Note that nomograms have been
developed in order for analysts to readily find solvent mixtures with
equivalent, or isoeluotropic, strengths. It must be realized, however,
that this equivalency only predicts relative elution strength and cannot
be used to predict selectivity effects.