it is a lecture on GC

1. Presenter's Information
Md.Mostak Uddin Thakur
B.Sc (Hons) M.Sc, CU
Certificate IV , HUNTER TAFE, NSW, Australia
Working Experience:
 BOF
 BSTI
 UFFL
 At Present
Additional Chief Chemist & Head of ACESD
Training Institute for Chemical Industries
Training: Fertilizer Quality Control, Harayna, India

2. What to talk in this presentation
Learning Objective:
Principle of chromatography
Classification!
Essential parts of a gas chromatograph:
GC Sample & Injection System:
Columns, types , column temperature:
Detector:
Miscellaneous.

3. Contents Of Topic
 History
 Introduction
 Principle
 Theory
 Instrumentation
Carrier Gas Flow Regulator
Flow Meter Columns Injection
System Detectors
 Advantages and Disadvantages

4. Inventor of Chromatography
Mikhail Tswett (Russian
Botanist), Invented
Chromatography in 1906,
During his research on plant
pigments.
He used the technique to
separate, various plant pigments
such as:
Chlorophylls
Xanthophylls
Carotenoids. 1872-1919

5. Introduction
 It is an analytical technique, used for separation
of Thermal stable and volatile substances.
Mobile Phase
Stationary Phase
Gas
Solid or Liquid

6. Principles
Adsorption
or
Partition
Depends on the Stationary
Phase used.
If Stationary phase is:
Liquid -> Gas Liquid Chromatography-> Partition Principle
Involved.
Solid -> Gas Solid Chromatography-> Adsorption
In general, compounds with low boiling points (High Vapor
Pressures) spend more time in the Mobile Phase and
elute from the column in a shorter amount of time than
compounds with High Boiling Points.

7. Theory
 The component to be separated from Gas
Chromatography should be:
Volatile and
Thermo stability.

8. Gas chromatograph
An analysis technique in
which the sample mixture
is injected, vaporized into
a stream of carrier gas (as
nitrogen or helium)
moving through a column
containing a stationary
phase, separated into its
component according to
their affinity for the
stationary phase and
detected.

9. Separations
1.Boiling points is The number one factor to
consider in separation of compounds on the GCs.
2. Differences in polarity of the compounds is only
important if you are separating a mixture of
compounds which have widely different polarities
3.Column temperature, the polarity of the column,
flow rate, and length of a column are constant .

10. 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.

11. Components of a gas chromatographic system:
Separation is based on the differences in migration rates
among the sample components
Sample is injected & vaporized onto the
head of the chromatographic column

12. Carrier Gas
The mobile phase or moving phase is a carrier gas,
usually an inert gas. Such as Helium or an
unreactive gas such as Nitrogen.
Note: Probably more than 90% of the present GC
instruments run with Helium as a carrier gas. Some use
Hydrogen and Nitrogen as well.
Hydrogen-> Adv: Better thermal conductivity, Low
density. DisAdv: Reacts with unsaturated compounds, and it
is inflammable.
Helium-> Adv: Excellent thermal conductivity.
DisAdv: Expansive.
Nitrogen-> Adv: Inexpensive. DisAdv: Reduced sensitivity.

13.  Column
• Made of Glass or Metal, such as Stainless Steel.
• Stainless steel-> Long life, can be handled easily and
it reacts with some compounds.
• Glass-> Widely used, as they are inert but highly
fragile.
• Column can be used both for preparative and analytic
purpose
 Types
• Packed Column->GSC:Packed with graded adsorbnt or porous
polymer. GLC: Packed with liquid phase coated graded inert solid support.
• Open Tubular Column->Made of stainless steel with long
capillary tubing in length and have uniform, narrow internal diameter, know as
Capillary of Golay column.
• Support Coated Open Tubular Column-> Improve
version of OTC.

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

17. Sample capacity v. resolution
Sample capacity: the amount of sample that can be
injected onto a column without overloading. Often
expressed as grams of sample per gram of packing.
Overloading is defined as the point at which the
sample mass injected makes the column efficiency
N, decrease by 10% from its normal value;
sometimes called sample loading.

19. GC Column and Oven

20. Theory of Operation
• Velocity of a compound through the column
depends upon affinity for the stationary
phase Area under curve is
______ of compound
adsorbed to stationary
phase
Gas phase concentration
Carrier gas
mass

21. Component Separation with the Column
< The process of separation >
A series of partitions : Dynamic In-and Out (or Stop-and-Go)
All differential migration process.
The most volatile components usually pass through the column
first, the least volatile or highest boiling emerges last.
Mobile phase( Driving
force)
Stationary phase ( Resistive force)








Analyte
s

24. 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.

25. Activity

26. 1. Draw and describe the basic setup of a gas chromatograph
2. Which gas is mostly as mobile phase, mention its percent
3. Predict the retention order for a series of compounds
separated by gas chromatography
4. Factors that effect for the resolution for analyte

27. 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.

28. 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.

29. GC Sample & Injection System
• Liquid Sample:
• Liquid samples are injected with a micro-syringe (10
ml to 0.1 ml) through a silicon rubber septum in a
heated injection system.
• There are two common injection techniques when
using a split/splitless injection port; Another one is on
column injection system. All are discussed
below.

30. Gas Chromatography
Sample Injection
1.) Split Injection
 Delivers only 0.2-2% of sample to the column
- Split ratio of 50:1 to 600:1 (sample discarded)
 For samples where analytes of interest are >0.1% of sample
- Best resolution is obtained with smaller amount of sample
- ≤ 1 mL with ≤ 1 ng of each compound (0.5 mL of gas volume)
 Not quantitative, split not constant
After mixing, pressure regulator
controls the fraction of sample
discarded
Remainder of the sample is
flushed from injector port to
column

31. Gas Chromatography
Sample Injection
2.) Splitless Injection
 Delivers ~80% of sample to the column
 For trace analysis, where analytes of interest are < 0.01% of sample
- Large volume (~2 mL) injected slowly (2s)
 No mixing chamber or split vent
- Injection temperature is lower (220oC)
- 40oC below the boiling point of the solvent
Lower temperature “traps”
solvent in a narrow band at the
head of the column
Raise temperature to volatize
sample and start separation
Injecting larger volume, don’t
want broad peaks

32. Gas Chromatography
Sample Injection
2.) Splitless Injection
 “Solvent trapping” significantly improves the performance of splitless
injections
- Initial lower temperature of column during injection keeps larger volume into a
narrow band
- Chromatography is initiated by raising column temperature
- Cold trapping – condense solutes in narrow band at the beginning of column by
using an initial temperature 150oC below boiling points of solutes of interest
Without “Solvent trapping”
With “Solvent trapping”

35. Representative injection conditions for split, splitless, and on-column
injection into an open tubular column.

36. Gas Chromatography
Sample Injection
3.) On-column Injection
 Delivers ~100% of sample to the column
 For samples that decompose above their boiling points
 Solution injected directly on column
- Warming column initiates chromatography
Raise temperature to volatize
sample and start separation
Lower initial column temperature to
prevent sample decomposition

37. GC Detectors
After the components of a mixture are separated using
gas chromatography, they must be detected as they exit
the GC column.
Thermal-conduc. (TCD) and flame ionization (FID)
detectors are the two most common detectors on
commercial GCs.
The others are
1. Electron-capture detector (ECD)
2. Flame-photometric detector (FPD)
3. Mass spectrometer (MS)
4. Photoionization detector (PID)

38. Detector:
• Types of detector:
• A wide numbers of detector are used in gas chromatograph:
• Thermal conductivity detector(TCD)
• Flame ionization detector(FID)
• Phosphorus - nitrogen (PN) detector
• Thermionic detector (TID)
• Electron capture detector(ECD)
• Helium ionization detector
• Flame photometric detector(FPD)
• Mass spectrometric detector (MSD)
• TCD and FID are the most widely used detectors.

39. General application of different detectors:
• TCD: Type Concentration; For O2, N2, H2, He, Ar, NH3,
etc and all volatile organic components.
• FID: Type Mass flow; ,Sensitive to all organic
components; insensitive to He, Ar, Ne, Xe, H2, O2,N2,
H20, CO, CO2, SO2, SO3, CCl,, NH3, NO, NO2, N2O, etc.
• ECD : Type Concentration; Halogen, metal and oxygen
compounds, compounds containing Cl2 in the ppm and
ppb range.
• FPD: Type Mass flow; Selective determination of
compounds containing sulphur and phosphorus in the
ppm range. Identification of air pollution by SO2.
•

40. GC Detectors Cont’d
The requirements of a GC detector depend on the separation
application.
E.g.
An analysis may require a detector selective for chlorine
containing molecules.
Another analysis might require a detector that is non-
destructive so that the analyte can be recovered for
further spectroscopic analysis. You can not use FID in that
case because it destroys the sample totally. TCD on the other
hand is non-destructive.

41. 1.)Thermal Conductivity Detector
A TCD detector consists of an electrically-heated wire.The
temperature of the sensing element depends on the thermal
conductivity of the gas flowing around it. Changes in
thermal conductivity, such as when organic molecules displace
some of the carrier gas, cause a temperature rise in the element
which is sensed as a change in resistance. The TCD is not as
sensitive as other detectors but it is non-specific and non-
destructive.
•Thermal Conductivity Detector
– Difference in thermal conductivity between the carrier gas and sample
gas causes a voltage output
– Ideal carrier gas has a very Low thermal conductivity (He)

42. Gas Chromatography
Ohm’s Law: V =IR
Based on Ohm’s law, monitored
potential (V) or current (I) Changes as
resistance (R) of filament changes due
to presence of compound
Detectors
1.) Thermal Conductivity Detector

44. Detector
2.) Flame Ionization Detector
 Mobile phase leaving the column is mixed with H2 and air and burned in a
flame
- Carbon present in eluting solutes produces CH radicals
which produce CHO+ ions
- Electrons produced are collected at an electrode and
measured
 Responds to almost all organic compounds and
has good limits of detection
- 100 times better than thermal conductivity detector
- Stable to changes in flow rate and common mobile phase
impurities (O2, CO2,H2O,NH3)
Burn sample and measure
amount of produced electrons

46. Flame Ionization Detector
Hydrogen
Air
Capillary tube (column)
Platinum jet
Collector
Sintered disk
Teflon insulating ring
Flame
Gas outlet
Coaxial cable to
Analog to Digital
converter
Ions
Why do we need
hydrogen?

47. Detector
3.) Electron Capture Detector
 Sensitive to halogen-containing and other electronegative
compounds
 Based on the capture of electrons by electronegative atoms
- Compounds ionized by b-rays from radioactive 63Ni
 Extremely sensitive (~ 5 fg/s)
Steady current (flow of electrons)
disrupted by compounds with high
electron affinity

48. ECD Detector
When an org. mol. that contains
electornegative functional gr., such
as halojens, phosphorous and nitro
groups, pass by the detector, they
capture some of the electrons and
reduce the current.
Detector

49. Detector
4.) Mass Spectrometry
 Detector of Choice  But Expensive!
 Sensitive and provides an approach to identify analytes
 Selected ion monitoring – monitor a specific mass/charge (mz)
compared to scanning over the complete spectra
- Simplifies complex chromatogram
- Increases sensitivity by 102-103

50. Gas chromatograph
Mass Spectrometry
• Uses the difference in mass-to-charge ratio (m/e)
of ionized atoms or molecules to separate them
from each other.
• Molecules have distinctive fragmentation patterns
that provide structural information to identify
structural components.
• The general operation of a mass spectrometer is:
– create pure gas-phase ions Gas Chromatograph
– separate the ions in space or time based on their mass-
to-charge ratio
– measure the quantity of ions of each mass-to-charge
ratio

51. Mass Spec Output
• Each peak of a chromatogram becomes a
“fingerprint” of the compound
• The fingerprints are compared with a library
to identify the
compounds
mass-to-charge ratio

52. MS Detector Cont’d
The ion separation power of an MS is described by the
resolution:
R = m/Dm
Where m is the ion mass and Dm is the difference in mass
between two resolvable peaks in a mass spectrum.
E.g., an MS with a resolution of 1000 can resolve an ion with
a m/e of 100.0 from an ion with an m/e of 100.1.

53. Gas Chromatograph Output
time (s)
detector
output
• Peak ____ proportional to mass of compound
injected
• Peak time dependent on ______ through column
area
velocity

54. Techniques to Speed Analysis
• Problem: some components of a mixture
may have very high velocities and others
extremely low velocities.
• slow down fast components so they can be
separated
• speed up slow components so analysis
doesn’t take forever
• Solution…

55. Temperature Control Options
Column: Petrocol DH, 100m
x 0.25mm ID, 0.5µm film
Cat. No.: 24160-U
Oven: 35°C (15 min) to
200°C at 2°C/min, hold 5
min
Carrier: helium, 20cm/sec
(set at 35°C)
Det.: FID, 250°C
Inj.: 0.1µL premium
unleaded gasoline, split
(100:1), 250°C
Example Method

56. Headspace sampling
Headspace sampling
Headspace Vial
G = the gas phase - headspace and lies above
the condensed sample phase.
S = the sample phase - the sample phase contains
the analytes; liquid or solid in combination with a
diluent or a matrix modifier.
Sample phase is introduced into the vial and the
vial is sealed, volatile components diffuse into the
gas phase until the headspace has reached a state
of equilibrium. The sample is then taken from the
headspace with a gas sampling syringe.

57. gas
Applications
• Compound must exist as a gas at a temperature that can
be produced by the GC and withstood by the column
(up to 450°C)
• Alcohols in blood
• Aromatics (benzene, toluene, ethylbenzene, xylene)
• Flavors and Fragrances
• Permanent gases (H2, N2, O2, Ar, CO2, CO, CH4)
• Hydrocarbons
• Pesticides, Herbicides, PCBs, and Dioxins
• Solvents

58. 1.What are carrier gas with different properties & write their
function.
2.Compare of capillary & packed column.
3.Factor for the order of elution for analyte.
4.What are the two mode of separation by temperature control
system ( oven temp.)
5.Write comparative study of TCD, FID and ECD.
6.What do you mean by column bleeding?
7.Application of head space analysis.
8. Choice of column depends on which theory
9. Describe the difference between a split and splitless injection and
justify when and why you would want to use each
Learning Outcome