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1. Gas Chromatography
A.) Introduction:
Gas Chromatography (GC) - chromatographic technique where the mobile phase is a gas.
GC is currently one of the most popular methods for separating and analyzing
compounds. This is due to its high resolution, low limits of detection, speed, accuracy and
reproducibility.
GC can be applied to the separation of any compound that is either naturally volatile (i.e.,
readily goes into the gas phase) or can be converted to a volatile derivative. This makes
GC useful in the separation of a number of small organic and inorganic compounds.
B.) Equipment:
A simple GC system consists of:
1. Gas source (with pressure and flow regulators)
2. Injector or sample application system
3. Chromatographic column (with oven for temperature control)
4. Detector & computer or recorder

2. Gas Chromatography (GC)
*Gas chromatography is a chromatographic technique that
can be used to separate volatile organic compounds.
*It consists of
a flowing mobile phase
an injection port
a separation column (the stationary phase)
an oven
a detector.

3. PRINCIPLE - ELUTION

5. CHROMATOGRAM

8. The organic compounds are separated due to
differences in their partitioning behavior between
the mobile gas phase and the stationary phase in
the column.
Principle

9. Mobile phases are generally inert gases such as
helium, argon, or nitrogen.
The injection port consists of a rubber septum
through which a syringe needle is inserted to inject
the sample.
The injection port is maintained at a higher
temperature than the boiling point of the least
volatile component in the sample mixture.

10. Since the partitioning behavior is dependent on
temperature, the separation column is usually
contained in a thermostat-controlled oven.
Separating components with a wide range of boiling
points is accomplished by starting at a low oven
temperature and increasing the temperature over time
to elute the high-boiling point components.

11. A gas chromatography oven, open to show a
capillary column

12. GC Columns
Capillary columns
Packed columns
•Typically a glass or
stainless steel coil.
•1-5 total length and 5 mm
inner diameter.
• Filled with the st. ph. or a
packing coated with the
st.ph.
•Thin fused-silica.
•Typically 10-100 m in
length and 250 mm inner
diameter.
•St. ph. coated on the inner
surface.
•Provide much higher
separation eff.
•But more easily
overloaded by too much
sample.

13. Components of a Gas Chromatograph
Gas Supply: (usually N2 or He)
Sample Injector: (syringe / septum)
Column: 1/8” or 1/4” x 6-50’ tubing packed with
small uniform size, inert support coated with
thin film of nonvolatile liquid
Detector: TC - thermal conductivity
FID - flame ionization detector

14. A typical GC system used is shown below (a gas chromatograph)
Carrier gas: He (common), N2, H2
Pinlet 10-50 psig
Flow = 25-150 mL/min packed column
Flow = 1-25 mL/min open tubular column
Column: 2-50 m coiled stainless steel/glass/Teflon
Oven: 0-400 °C ~ average boiling point of sample
Accurate to <1 °C
Detectors: FID, TCD, ECD, (MS)

15. THERMAL CONDUCTIVITY DETECTOR

16. FLAME IONIZATION DETECTOR