Page 17 - Illustrated Pocket Dictionary of Chromatography

10 AMPHOLYTE

and optimizing sensitivity through the proper choice of the applied
potential. Pulsed amperometry is a modified amperometric technique
that rapidly increases the applied potential for a very short period of
time (milliseconds). The sample signal is obtained over a portion of
the pulse in order to reduce system noise.

ampholyte A compound that contains one (or more) acidic
functional group and one (or more) basic functional group. Amino
acids are examples of ampholytes having a carboxylic acid group
(—COOH) and a basic amine functional group (—NH 2). Note that
molecules that have multiple acid/base functional groups are
referred to as polyampholytes. Examples include polypeptides and
proteins.

amphoteric support Typically a resin that has both positively
and negatively charged functional groups permanently on the
surface.

analysis time The time required for any separation for all compo-
nents of a sample that is injected (t = 0) to migrate through the system
and detector. Note that in a gradient system additional time is required
for the system to return to the original conditions (e.g., the tempera-
ture for GC and mobile-phase composition for LC) and completely
reequilibrate to the initial conditions.

analyte The component of interest contained in the sample. It is
the component that is recovered and analyzed subsequent to all
sample preparation steps.

analytical HPLC column Has an inner diameter of 3.0–5.0mm
and ranges from 5 to 30cm in length. Injection volumes from 1 to 50
mL are typical, with sample loads in the microgram range. Note that
as the inner diameter increases in general the resolution, analysis
time, operation ease and upkeep, and maximum sample load increase
whereas sensitivity decreases.

anion A molecule or atom that bears a negative charge is an
-
anion or anionic. Examples of anions are acetate (CH 3COO ), phos-
-2
-3
-
-
phate (H 2PO 4 , HPO 4 , or PO 4 ), hydroxide (OH ), and chloride
-
(Cl ).