This document summarizes gas chromatography (GC), a common type of chromatography used in analytical chemistry to separate and analyze compounds that can be vaporized without decomposition. It discusses the basic components of a GC system including the carrier gas, sample injection systems, separation columns, detectors, and applications. The key components are the stationary and mobile phases that interact to separate sample compounds based on properties like volatility and polarity. Common detectors discussed are the thermal conductivity detector, flame ionization detector, and mass spectrometer for identifying separated compounds. Applications include analyzing samples from pharmaceuticals, foods, environmental sources, and petrochemicals.

1. Gas Chromatography

2. 1941 Martin and Synge

3. a. Gas-liquid
chromatogra
phy (GLC)/
(GC)
Liquid adsorbed or
bonded to a solid
surface
Type of equilibrium:
Partition between gas
and liquid
b. Gas-solid
SP: Solid
Type of equilibrium:
Adsorption
Types of Gas chromatography (on the basis of
stationary phase used)
solid stationary phase physically adsorbs
analytes leading to retention of the
analyte on the column. Thus, applications
of GSC are limited because problems like
long retention of active or polar
molecules and tailing of elution peaks
✓ availability of wide
range of liquid coatings
✓ wide range of
concentrations.
✓ good resolution of
peaks in a shorter
analysis time.

4. BLOCK DIAGRAM OF GC

5. Carrier Gas System
• The mobile-phase gas in GC is called the carrier gas and must be
chemically inert.
• Helium , argon, nitrogen, and hydrogen (pressurized tanks).
• Pressure regulators, gauges, and flow meters are required to control
the flow rate of the gas.
• In addition, the carrier gas system often contains a molecular sieve
to remove impurities and water.
• Inlet pressures usually range from 10 to 50 psi (lb/in.2 ) above room
pressure, which lead to flow rates of 25 to 150 mL/min with packed
columns and 1 to 25 mL/min for open tubular capillary columns

6. Sample Injection Systems
✓ microsyringes are often used to inject
liquid samples through a rubber or
silicone diaphragm, or septum, into a
heated sample port located at the head
of the column.
✓ The sample port is ordinarily about 50°C
above the boiling point of the least
volatile component of the sample.
✓ sample splitter: deliver a small known
fraction (1:50 to 1:500) of the injected
sample, with the remainder going to waste.

7. Sample Injection Methods
target
samples
• Gas (gas tight syringe) vol.
0.2 -1 ml
• liquid (Microscyringe/
autoinjectors) vol. 1-
2microliter
Sample Pre-
treatment
Devices
•Static Headspace (SHS)
•Dynamic Headspace (DHS)
•Pyrolysis Analysis (Py)
•Thermal Desorption (TD)

8. ❑ The sample is first sealed and heated.
❑ The gas in the space (headspace) above the sample matrix, within sealed container is
introduced into the GC.
❑ Components with relatively high volatility can be detected with high sensitivity.
❑ Samples are comprised of liquids and solids, but often are liquid samples.

9. Purge-and-trap is a device used for high sensitivity measurement of low concentration volatile organic
compounds (VOC) in water.
1.Purge trap An inert gas such as He or N2 is passed through the water sample to purge the volatile
VOC, and the evacuated VOC is then trapped in the trap tube (trap).
2.Dry purge (water removal) At the time of the purge trap, moisture is also trapped in the trap tube.
3.Sample introduction Heat the trap tube to desorb the VOC and introduce the sample into GC and
GC/MS.
4.Conditioning While flowing inert gas, heat and purge any remaining organic matter in the trap
tube.

10. In order to measure low concentration volatile organic compounds (VOC) in the environment and indoor
atmospheric air, a certain amount of gas has to be passed through a collection tube flled with an adsorbent,
the VOC is to be concentrated and then heated.
1. Collection A pump is connected to the collecting pipe, and the sample gas is passed, so that the VOC in the
atmosphere is collected.
2. Cold trap The VOC desorbed from the collection tube needs to be re-concentrated before it is introduced
the GC and GCMS via the cold trap. The trap flled with adsorbent is cooled to below room temperature and the
collection time is heated with the VOC being desorbed as to be able to recapture it with the trap.

11. 3. Sample introduction The trap is heated to desorb the VOC and introduce it to GC and GC-
MS.
4. Conditioning By heating the collecting tube, it is possible to reuse it by expelling the
remaining organic matter. It is desirable to heat the tube just before collection as much as
possible. The collecting tube has to be capped and not exposed to the outside air as to
prevent contamination of organic matter.

12. ❑ When a polymer sample is heated to about
400 to 900 °C, the decomposed gas is
generated.
❑ It is a method used to obtain information on
macromolecular monomers, dimers,
trimers and compounds derived from
polymer structures by introducing
decomposition gas into GC and GC/MS for
analysis.
❑ Typical methods for instantaneous heating
❑ In addition, an inert material or surface
treatment that does not cause any catalytic
reaction is required for the container (cup)
with a minimum sample amount (about 100
to 500 μg)

13. Separation Columns
• packed columns
• Their inner diameters
range from 1.5 mm to 6
mm.
• A category of micro-
packed columns (inner
diameters ranging from
0.3-1 mm and at lengths
varying from 1 to 15 m,
packed with particles
0.007-0.3 mm in diameter.
packed
columns)
glass or metal (mostly
stainless steel but also
aluminium, copper,
polytetrafluorethylene
Packing
small spherical inert
supports (e.g.
diatomaceous earth)

14. Separation Columns
• capillary (0.1-
0.53 mm
internal
diameter and
10-100 m)
common 0.25
mm internal
diameter and
30 m length
Polarity and Liquid Phase of Capillary Columns

15. Features of GC Detectors.

16. Thermal Conductivity Detector (TCD)
❑ TCD detects using difference of thermal conductivity of between sample and carrier gas (He, H2 , N2 or Ar)
❑ When thermal conductivity of target compound is larger than the carrier gas, peak is detected as a negative value.
❑ TCD can detect most compounds except for carrier gas but has low sensitivity
❑ Can analyze the compounds that are undetectable using FID, such as water, formaldehyde, and formic acid.

17. ❑ In FID, the components are burned and ionized and it is used for almost all organic compounds, which have C-H or
C-N structure.
❑ There are several exceptions such as CO, CO2 and CS2 which are non-organic compounds that cannot be detected.
Carbonyl group and C=O carbon atom of carboxyl group are also not detectable.
❑ highly sensitive detector

18. ❑ Radioactive isotopes are equipped in ECD.
❑ It is highly selective for electrophilic compounds which become negative ions after
obtaining electrons such as organic halogens, organic metal compounds, and diketones.
❑ ECD’s main application is environmental analysis, such as residual pesticides, residual PCB
(Polychlorinated biphenyls), Chlorine VOC in drain water, organic mercury in the
environmental field, etc.

19. ❑ FPD is a highly selective and sensitive detector, especially for phosphorus (P), sulfur (S), and tin (Sn) compounds.
❑ FPD is stable and sensitive.
❑ It has been used in food analysis, — to detect phosphorus pesticides, sulfur odors, and food favors — and in
environmental analysis to detect organic tin compounds in sea products.

20. ❑ A fame thermionic detector is a highly selective and sensitive detector for organic nitrogen compounds, inorganic
and organic phosphorus compounds.
❑ It is also known as a nitrogen phosphorus detector (NPD) because it can detect nitrogen and phosphorus
compounds. Its principle and basic structure is the same as FPD.
❑ Inorganic nitrogen compounds cannot be detected using FTD, so it cannot be applied to ammonium analysis.
❑ Its selectivity to phosphorus compounds is lower than FPD.
❑ The main applications of FTD include the analysis of drugs, nitrogen pesticides, and phosphorus pesticides, etc.

21. ❑ The sulfur-containing compound (RS) is burned at about 800 °C in a hydrogen-flled atmosphere, to
generate sulfur monoxide (SO).
❑ SO then reacts with ozone from the ozone generator to obtain an excited state of sulfur dioxide (SO2 ),and
detects chemiluminescence when it returns to the ground state.
❑ SCD is widely used for analysis of petroleum products and foods

22. Applications of GC
Pharmaceutical: Residual solvent analysis
Food and beverages: Component analysis,
food safety analysis, halal analysis of alcohol
Environmental: Air, water, soil
Petrochemicals: Simulated distillation,
component analysis
Chemicals Material, polymer, additive, gas
purity analysis, gas emission in automotives
Energy and gas: Artifcial photosynthesis
research

25. Figure 2: Chromatogram output from a GC or GC-MS
❑ The x-axis is the retention time, taken
from the time the sample was injected
into the GC (t0) to the end of the GC run.
❑ Each analyte peak has a retention time
tR measured from the apex of the peak.
❑ The y-axis is the measured response of
the analyte peak in the detector.
❑ The baseline shows the signal from the
detector when no analyte is eluting
from the column, or it is below the
detection limit. If the baseline is
higher than it should be, it is an
indication chemical noise, such as
impurities in the carrier gas, column
stationary phase bleed and system
contamination.
❑ measurements can be taken from the
peak, such as width at the baseline,
width at half height, total height and
area. The latter two are proportional
to the concentration, however it is the
area that is used for quantitation

26. Column Oven
isothermal
programming
the temperature (middle
point of boiling range) of
the column is held constant
throughout the entire
separation
Narrow BP range
temperature
programming
column temperature
(Rates of 5-7 °C/minute) is
either increased
continuously or in steps as
the separation progresses
Broad BP range
high boiling fractions are slow to elute with extensive
band broadening
the higher boiling components elute as sharp peaks but the lower
boiling components elute quickly with no separation.

27. This Photo by Unknown Author is licensed under CC BY-SA