Study Set Content:
The affinity of a substance towards the stationary phase can be described in chemical terms as an
equilibrium constant called the
distribution constant,
The affinity of a substance towards the stationary phase can be described in chemical terms as an
equilibrium constant called the distribution constant, also known as the
partition coefficient.
The affinity of a substance towards the stationary phase can be described in chemical terms as an
equilibrium constant called the distribution constant, also known as the partition coefficient. Thus,
differences in the partition coefficient allow for the
chromatographic separation.
The affinity of a substance towards the stationary phase can be described in chemical terms as an
equilibrium constant called the distribution constant, also known as the partition coefficient. Thus,
differences in the partition coefficient allow for the
chromatographic separation.
- involves mixing a small sample size of a volatile compound
with a gaseous mobile phase to be passed through a non-volatile liquid stationary phase.
Gas-Liquid Chromatography
is when the stationary phase is solid. This method separates the
compound using adsorption so has a much longer retention time than GLC.
Gas-Solid Chromatography
-it is particularly effective for analyzing organic compounds, such as hydrocarbons,
pesticides, and volatile organic compounds.
Gas-Liquid Chromatography
in which is the sample’s entrance to the chromatography. Besides its role as
an inlet for the sample, it must vaporize, mix with the carrier gas and bring about the sample at
the head of the column. The characteristics of the injectors, as well as the modes of injection,
differ according to the column type. The use of an automatic injection system can significantly
enhance measurement precision.
Sample Injection
For packed and megabore columns which typically use a flow
rate of about 10 mL/min, direct vaporization is a simple way to introduce the sample.
Direct vaporization injector
For capillary columns able to handle only a small capacity of sample,
even the smallest volume that it is possible to inject with a micro-syringe 01L, can saturate the
column. Special injectors are used which can operate in two modes, with or without flow splitting
(also called split or splitless).
Split/splitless injector -
A special micro-syringe, whose needle is of 0.15 mm diameter, is
necessary for penetrating the column which is cooled to 40°C before being allowed to return to its
normal operating temperature. This is useful for thermally labile compounds or high boiling
compounds, and is difficult to master without the aid of an autosampler.
Cold on-column injection
is conceptually similar to the split/splitless model. The temperature of the
injection chamber can be programmed to effect a gradient, e.g. from 20 up to 300°C, in a few tens
of seconds. It becomes possible to inject greater volumes with standard syringes avoiding needle-
induced discrimination. Furthermore, compounds having low boiling points (particularly
solvents) can be eliminated.
Programmed temperature vaporization injector
There are three principal modes of operation which are:
split cold injection, splitless cold
injection and injection with elimination of solvent.
injection: the sample is introduced into the vaporization chamber and immediately
the vent valve is opened and the injector is heated. As the sample is not instantaneously
vaporized, the solvent and the different compounds penetrate onto the column in the order of their
boiling points.
1. Split cold
This method allows for injecting up to 50 μL in a single
injection or up to 500 μL of sample solution over several injections, eliminating the step of the
preliminary concentration of sample prior to injection.
Injection with elimination of solvent:
this mode is employed for trace analysis. The vent valve is closed
during the injection. The injection chamber is then heated in order to transfer the sample to the
column, which is maintained cold.
2. Splitless cold injection:
the mobile phase that transports the analytes through the column.
flow, which is precisely controlled, enables reproducibility of the retention.
Carrier Gas
The mobile phase is a gas such as
helium, hydrogen or nitrogen
3. Column Oven: Two methods:
Packed and Capillary Column.
are most powerful of all gas chromatography
detectors.
1. Mass Spectrometry Detectors
