Page 113 - Illustrated Pocket Dictionary of Chromatography

110 ION-PAIR REAGENT

ion-pair reagent Used in LC separations, often reversed phase,
to give charged analytes a longer retention time through the formation
of an ion-pair complex with a mobile-phase modifier. For example,
deprotonated carboxylic acids can form ion pairs with quaternary
amines:

O

N(CH 2 CH 2 CH 2 CH 3 ) 3
O
Tetrabutylammonium
Cl

4-Chlorobenzoate Ion pair amine

and protonated amines can form ion pairs with sulfonic acids: The
result is an overall uncharged ion pair that is now more retained than
the ion itself.

NH

CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 SO 3 H 3 NCNCH 2 COOH
Hexanesulfonate
CH 3 Ion pair acid
Creatine

ion suppression Used for peak shape enhancement of weakly ion-
izable analytes such as primary and secondary amines and carboxylic
acids. The pH of the mobile phase is adjusted to below the pK a of the
analyte to achieve suppression.

ion-trap mass analyzer The ion trap is a monopole mass ana-
lyzing unit that utilizes radio frequencies (rf) to create a stable volume
within the ring electrode. Selected mass-to-charge (m/z) ratios are
moved from the analyzer to the detector by changing the rf in a con-
trolled manner.
irregular packing material The term “irregular” refers to the
shape of the base support material used in the column. As the term
suggests, the particles do not have a uniform shape (as contrasted to
spherical support materials). These particles are often manufactured