Page 34 - Illustrated Pocket Dictionary of Chromatography

CHECK VALVE 29

the type/concentration of the cationic mobile-phase additive used to
displace the substance determine the overall retention time and
elution profile. Cation-exchange resins are classified as strong (e.g.,
sulfonate) or weak (e.g., carboxylate).

certificate of analysis (COA) A document that accompanies
a material that represents the test results for a specific lot or batch
of material with respect to the actual specifications developed for
that material. A COA is a guarantee that the delivered material is
consistent with past lots of material and will possess the same attrib-
utes/properties in the future. A COA is also sometimes referred to as
a certificate of compliance.

chain length A parameter used to define the number of carbons
in the bonded phase, for example, octyl (eight carbons), aminopropyl
(three carbons terminating an amine group), and butyl (four carbons).

channeling Denotes the presence of an empty volume (or void)
present within the body of a packed column that ultimately leads to
band broadening. In extreme cases peak splitting may also occur.
Channeling is often the result of poor packing, physical shock to the
column, and extended use. The result of channeling is a decrease in
column efficiency, especially as increased tailing.

char The solid residue left from a completed pyrolysis process.

check sample See control sample.

check valve A component in LC systems that “directs” solvent
flow from the reservoir, through the column, to the detector by pre-
venting backflow during pump reciprocation. Check valves are paired
and typically affixed to the pump head. The inlet check valve is posi-
tioned between the solvent reservoir and the pump head. It is open
and permits flow of solvent from the reservoir to the pump head when
the piston reciprocates (i.e., draws out from the pump head). The inlet
check valve then closes as the piston pushes into the pump head,
thereby preventing solvent from flowing back into the reservoir. The
outlet check valve is positioned between the pump head and the injec-
tor. It is open and permits flow of solvent from the pump head to the
injector when the piston pushes into the pump. The outlet check valve
then closes as the piston reciprocates, thereby preventing solvent
from being pulled back from the column.