Capacity Factor (k')
A way of expressing the retention of the sample components. It is determined
by subtracting the COLUMN DEAD TIME from the retention time of the peak
of interest, and dividing that by the column dead time.
--
Capillary Electrophoresis (CE)
A special type of chromatographic analysis which employs the use of electricity
to selectively separate charged species comprising a sample. It is a powerful
technique that produces sharp bands with minimal tailing, with the main
difficulty being the sensitivity threshold.
--
Capillary Electrochromatography (CEC)
A newer type of chromatographic analysis which combines the benefits of
CAPILLARY ELECTROPHORESIS and HPLC. Typically, with standard HPLC, there
is a pressure limitation with the equipment which limits the number of
theoretical plates which can be employed. Because flow is driven electro-osmotically
in CEC analyses, there is no theoretical plate threshold.
--
Carbon Load
Term usually used to describe the degree to which the available silanols
on the column packing's surface have reacted and been replaced with the
bonded phase; the higher the carbon load, the lower number of residual
silanols.
--
Cartridge Column
A guard or analytical column that comes pre-packed, and is placed in a
reusable holder for use. Because of their design, cartridge columns are
often easier to change, less expensive, and more convenient than conventional
columns. [see
graphic]
--
Channeling
A phenomenon occurring when voids are evidenced in the column's packing
material, often due to improper packing or mishandling of the column.
--
Check Valve
A device inserted into a moving liquid stream that allows flow of the
stream in only one direction; often built into the HPLC pump.
--
Chemical Garbage
The contaminants in a sample that can foul up the LC column by irreversibly
sticking to the bonded phase. A guard column is often used to filter the
chemical garbage out of the flow path.
--
Chiral Stationary Phases
Specialized stationary phases used in chromatography to separate ENANTIOMERIC
COMPOUNDS. These are generating much interest in today's chromatographic
arena.
--
Chromatogram
A plot stemming from a detector's signal output, typically versus time.
It is identified often by a BASELINE offset by a series of PEAKS or BANDS.
--
Chromatography
Literally "color movement," a term describing a separation technique
that occurs based upon the difference of interaction of sample components
with two phases - a "stationary" phase (or non-moving) and a
"mobile" phase (or moving).
--
Chromatographic Conditions
Those parameters that describe how an analysis was achieved, for the purpose
of potential future duplication for verification purposes.
--
Column
Typically a tube of sorts that contains the STATIONARY PHASE of a chromatographic
system. [see
graphic]
--
Column Dead Time
The time it takes for solvent molecules or unretained sample bands (for
which capacity factor =0) to pass through the column. Uracil is often
used to measure the column dead time for reversed-phase column.
--
Column Packing
The particulate material packed inside the column; also called the STATIONARY
PHASE. This usually consists of silica- or polymer-based particles, often
chemically bonded with a chemical function al group. For analytical work,
3µm or 5µm spherical particles are used; for semi-preparative, 10µm or
larger spherical or irregular particles are favored. The most common packings
are as follows:
* Octadecyl (ODS, C18) the most popular phase, used for reversed-phase
HPLC
* Octyl (C8) more polar than C18, also a popular reversed-phase
column
* TMS (methyl, C1) weakly retentive in reversed-phase
* Silica (Si) unbonded silica used in normal phase mode, popular
for preparative LC.
* Phenyl, Cyano, Amino specialty phases used for specific applications.
--
Column Performance
A column's efficiency, often expressed through a THEORETICAL PLATE value,
used to describe how well theoretically a column will resolve sample components.
--
Concentricity
In HPLC, the degree to which the thru-hole of a part has a common centerline
with the part. This is critical when aligning small-bore tubing with a
union's thru-hole. If the thru-hole is not concentric, the flow path may
be restricted.
--
Conductivity Detector
A specialized detector which measures the conductivity of fluid passing
through its flow cell. Useful in a variety of applications, these detectors
can often provide analytical data on sample components that other, more
standard detectors, cannot provide.
--
Cracking Pressure
Typically relates to a check valve or back pressure regulator; describes
the minimum amount of (positive) pressure required to open and maintain
a continuous pathway through a device.
--
Cross
An x-shaped union used to connect four pieces of tubing. [see
graphic]
--
Cyano Phase
A specialized STATIONARY PHASE that consists of "cyano" (cyanopropylsilyl)
groups bonded to the base silica.
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