Page 18 - Illustrated Pocket Dictionary of Chromatography

11
ASYMMETRY FACTOR, A X
anion exchange An anion exchange material has a permanent
positive charge on the surface and is used to separate anionic com-
pounds (negatively charged species). The type of positive charge (e.g.,
a primary, secondary, or tertiary amine) and its concentration on the
surface (given as meq/g), the anionic analyte to be eluted, and the type
and concentration of anionic mobile-phase component that is used to
displace the analyte determine the overall elution time and profile.
Anion exchange resins are classified as strong or weak depending on
their relative affinity to anions.

anode In techniques in which a voltage is applied (i.e., electrolytic,
not galvanic), an anode is a positive electrode toward which anions
migrate.

area percent A determination of the level of analyte, A s, compared
with the total area of all the sample-related peaks in the chro-
matogram, S(A s) i,

area % of A s = [ A s S ( A s i ] ¥ 100
)
Note that for this method to be effective, all related components in
the sample must elute and be detected and all analyte responses must
be the same (response/mass).

asymmetric Refers to a carbon atom that has four unique sub-
stituents. This asymmetric carbon generates a chiral center.

asymmetry Refers to any elution profile varying from a symmet-
ric Gaussian distribution. It is mathematically calculated as an asym-
metry factor and is determined from a defined height on the peak (see
asymmetry factor, A x).

asymmetry factor, A x Calculated as a ratio of the distance
between the perpendicular dropped from the peak maximum that
elutes after the perpendicular to that which elutes before the per-
pendicular.