In gas chromatography, the sample is first converted to the vapor state or volatile compound is used which are injected into heated port along with a carrier gas. Analyte in the vapor state distributes between the stationary phase and the carrier gas. As the analyte elute from column signal is displayed in the form of chromatogram. Measurements of GC are rapid and convenient. Retention times are used for qualitative identification. Peak areas are used for quantitative measurements.

1. 1
Instrumentation of Gas Chromatography
Murtaza Sayed
a
, Zohaib Hussain
b*
a
Assistant Professor, CIIT Abbottabad
b
Student, CIIT Abbottabad
5/5 (2016):1-4
Abstract
In gas chromatography, the sample is first converted to the vapor state or volatile compound is
used which are injected into heated port along with a carrier gas. Analyte in the vapor state
distributes between the stationary phase and the carrier gas. As the analyte elute from column
signal is displayed in the form of chromatogram. Measurements of GC are rapid and convenient.
Retention times are used for qualitative identification. Peak areas are used for quantitative
measurements.
1. Introduction
Instrumentation of GC is required for its wide application. GC was designed by joint efforts
among chemists, engineers, and physicists to done much more rapid analyses on a small scale.
Improved and effiecnt model is readily adopted by petroleum with in a few short years. GC was
used for the analysis of complex mixtures and organic compounds. GC-MS detection system
increases its sensitivity to much higher levels.
2. Instrumentation
Followings are the components of the GC
 The analytes are rapidly injected by means of a syringe. The analyte first goes into the inlet
and then the carrier gas carries it to the column. Packed columns analyte range is 0.1 to 10
µL to be injected and 1 to 10mL of carrier gas is injected. The carrier gas is a chemically
inert gas available in pure form such as argon, helium, or nitrogen. Carrier gas should be
injected at a constant volume. A highly dense gas gives best efficiency since diffusivity is
lower, but a low-density gas gives faster speed.
 The stationary phase is generally a nonvolatile liquid or a liquid-like phase support bonded
to inert solid particles such silica. There are large options for stationary liquid phases

2. 2
available and by changing the liquid phase rather than the mobile phase different separations
are done.
 Selection of the proper column for the particular separation is an important step in GC. The
nature of the liquid or solid phase will determine the distribution equilibrium with the sample
components. Distribution depends on the absorbability of the analytes, the polarity of the
stationary phase and sample molecules, the degree of hydrogen bonding and other
interactions.
 Sample splitters are used with capillary columns to deliver a small fixed fraction of the
sample to the column and remaining to waste.
 Gas chromatography always uses flow through detectors that automatically detect the
analytes as they emerge from the column. The majority of GC detectors are destructive. A
variety of detectors are used, the characteristics response is shown by each analyte. Some
detectors contain a reference side and a sampling side.
 Signal representing the chromatographic peaks is displayed by a data system as a function of
time. By measuring the retention time (the minutes between the time the sample is injected
and the time the chromatographic peak appears) and comparing this time with that of a
standard of the pure substance, it may be possible to identify the peak. The area under the
peak is proportional to the concentration, and so the amount of substance can be
quantitatively determined. Chromatography data handling systems usually have automatic
detection of peaks, readout of the peak area and/or peak height, as well as the retention time.
Fig 1: Schematic diagram of the Gas chromatography

3. 3
3. References
Analytical chemistry by Gary D. Christian
4. Note
*sp13-bty-001 Assignment no 3 analytical chemistry