Detector used in gas chromatography

1. M.PHARM SEMINAR ON
Detectors Used in Gas Chromatography
SUB:- (MODERN PHARMACEUTICAL ANALYTICAL TECHNIQUES)
(MPA 101T)
Presented by:-
DEEPAK KUMAR SETHY
DATE:-31/01/2024
M.PHARM 1ST SEM.
INSTITUTE OF PHARMACY AND TECHNOLOGY, SALIPUR, CUTTACK

2. Introduction
Principle of Separation
Detector
Parts of GC
Reference
1
2
3
4
5

3. Introduction:
In early 1900s, Gas chromatography (GC) was discovered by Mikhail Semenovich
Tsvett as a separation technique to separate compounds.
The combination of gas chromatography and mass spectrometry is an invaluable
tool in the identification of molecules.
Gas chromatography consists of GSC & GLC.
The stationary phase is either a solid adsorbents, termed gas-solid
chromatography (GSC), or a liquid on an inert support, termed gas-liquid
chromatography (GLC).
In both the cases mobile phase is gas.
GSC is not widely used because of limited no of stationary phases.

4. Principle of Separation:
In GSC, the principle of separation is adsorption. In GLC, the principle of separation is partition.
Gas is used as mobile phase. Liquid which is coated on to a solid support is used as stationary
phase. The mixture of components to be separated is converted to vapor and mixed with
gaseous mobile phase. The component which is more soluble in the stationary phase travels
slower and eluted later. The component which is less soluble in the stationary phase, travels
faster and eluted out first. No two components has the same partition coefficient for a mixed
combination of stationary phase, mobile phase and other conditions. Hence the components
are separated accordingly to their partition coefficients. Partition coefficient is ratio of
solubility of a substance distributed between two immiscible liquids at a constant.

5. Carrier
Gas
Oven
Detector
Sample
Injector Port
Column
Gas Flow
Regulator
Waste
Fig. Gas Chromatography

6. Parts of GC: Gas chromatography is mainly composed of the following parts:
i. CarrierGas:
 Carrier gas in a high-pressure cylinder with pressure regulators and flow meters.
Helium, N2 , H, Argon are used as carrier gases.
Carrier gas from the tank passes through a toggle valve, a flow meter, (1-1000 ml/min),
capillary restrictors, and a pressure gauge (1-4 atm).
Flow rate is adjusted by means of a needle valve mounted on the base of the flow meter and
controlled by capillary restrictors.

7. ii. The Oven:
It keeps the column temperature constant.
It allows operation at elevated temperature (necessary to vaporize the sample).
It allows temperature programming. A controlled increase in column temperature during
an analysis. Due to this increase in column temperature slow-moving sample components
move faster.
It reduces the time needed for the analysis.
iii. Sample:
 Samples for introducing into the column can be of any type i.e. either gas, liquid or solid
in nature. Gases can be introduced into the column by valve devices. Liquids can be
injected through loop or septum devices.

8. iv. Column:
It is one of the imp part of GC which decides the separation of efficiencies.
Columns are made up of glass or stainless steel.
Glass columns are inert and do not react with any kind of materials.
The great disadvantage is fragile and are difficult to handle.
Columns can be classified on the basis its nature.
a. Open tubular column:
 which are also known as capillary columns, come in two basic forms.
1. wall-coated open tubular (WCOT) column
2. Support-coated open tubular (SCOT) column

9. b. Packed Column:
Columns are available in packed manner commercially and hence are called as packed columns.
Different columns ranging from low polar nature to high polar nature are available.
v. Detector:
1. Thermal conductivity detector (TCD or Katharometer)
2. Flame ionization detector (FID)
3. Electron capture detector (ECD)
4. Nitrogen phosphorous detector (NPD)
5. Mass spectrometer

10. 1. Thermal conductivity detector:
Construction and working-
TCD has a metal block with two cavities.
Four tightly coiled tungsten filaments are mounted in these cavities, two in each.(Wheatstone
bridge)
These filaments are heated electrically.
When through both these cavities pure carrier gas flows these filaments are cooled.
Next from one cavity pure carrier gas is flowing, while other cavity is connected to column
outlet.(vaporized solute + carrier gas is flowing)

12. Principle-
It works on difference in thermal conductivity of pure carrier gas and gaseous solute
molecules.
Thermal conductivity of hydrogen or helium is 6 to 10 times greater than most organic
compounds in gaseous form.

13. Advantages-
It is simple detector.
It give linear response.
It can detect both organic and inorganic solutes.
It is non destructive in nature.
Disadvantage-
It has low sensitivity.
Applications of TCD-
It is a universal detector and it can detect organic as well as
inorganic compounds.

14. 2. Flame ionization detector (FID):
Construction and working-
At the end of GC column a Platinum jet is placed which will carry the column effluent.
To this column effluent hydrogen gas and air is mixed.
Platinum jet will act as polarizing electrode (+) and other electrode (collector -ve electrode) is
placed at top of the flame.
Potential difference across them is of 400V.
Flame of column effluent, hydrogen and air mixture is burnt at the tip of jet.
FID is based on difference in electrical conductivity of gases.
At normal temperature and pressure gases act as insulators but will become conductive with
presence of electrons.

15. (-ve)
Platinum jet
(Polarizing electrode +ve)
Column Effluent
Fig. Flame Ionization Detector

16. Advantages-
It is a highly sensitive detector (detection limit up to pico gram).
It give liner response.
It is insensitive to presence of water or air in carrier gas.
It can not detect H2,02, CO, CO2, CS2, SO2, NO, NO2, H2O, etc.
Disadvantage-
It destroys the sample.
Application
Flame-ionization detection, or FID, is widely used because it senses carbon ions, allowing it to
detect virtually any organic compound.

17. 3. Electron capture detector (ECD):
Construction and working-
This detector has two electrodes. One of which is having radioisotope(Nikel63, 63Ni) coating
on it's surface.
Other electrode is a collector electrode.
Voltage difference is applied across these electrodes. The radioisotope emits electrons.
Gas eluted from column is passed over the radioisotope surface.
These electrons react with carrier gas molecules and ionize them and produce large no. of
secondary electrons.
Due to voltage difference these secondary electrons get attracted towards anode and current
will be flowing through these electrodes.
If only carrier gas is flowing then a steady current will flow.
But if some solute molecules which has tendency to capture electrons is flowing, the amount
of current will be reduced. This reductions proportional to amount of solute in sample.

18. Fig. Electroncapture detector

19. Advantages-
ECD is 1000 times more sensitive than Flame ionization detector for molecules containing
electronegative functional groups such as halogens, peroxides, nitro etc.
It can measure solute component at parts per billion and parts per trillion levels.
It is non destructive in nature.
Disadvantages-
It is insensitive to functional groups such as amines, alcohols, hydrocarbons.
Applications-
It is used in environmental testing for detecting PCB's.(Polychlorinated Biphenyls)
Used in environmental testing for organ-chlorine pesticides, herbicides and various
halogenated hydrocarbons.

20. 4. Nitrogen phosphorus detector (NPD):-
This detector is very sensitive to nitrogen and phosphorous containing compounds.
Construction of this detector is almost same to FID.
Difference is that a Rubidium silicate bead is placed 1.25cm above the flame tip.
It is heated electrically.
A fuel poor hydrogen plasma (low temperature flame) is used in this detector which
suppresses the normal flame ionization response and enhance the response to Nitrogen and
Phosphorous containing compounds.

21. Fig. Nitrogen Phosphorus Detector

22. Advantages-
It give 104 to 106 time more response to nitrogen and phosphorus atoms than carbon atom.
Response to phosphorous atom is 10 times greater than nitrogen atom.
It is more sensitive than FID.
Disadvantage-
It is not a universal detector.
It is destructive in nature.
Applications-
Used in analysis of food.
Used in forensic analysis.
Used in analysis of environmental sample.

23. 5. Mass spectrometer:-
GCMS is hyphenated technique.
Separation capabilities of chromatography are combined with qualitative and quantitative
detection capabilities of spectroscopy.
Mass spectrometer is powerful detector of GC. It measures mass to charge ratio of ions
produced form sample.

24. Fig. Mass Spectrometer

25. Advantages-
Speed of analysis is fast.
It gives total ion chromatogram.
One can select a single mass to charge value and monitor it through out the chromatographic
experiment, this is known as selected ion monitoring.
Disadvantage-
It is expensive technique.

26. Reference:
1. Gurdeep R. Chatwal, Sham K. Anand (2008). Instrumental methods of chemical analysis.
2. J Mendham, R C Denney, J D Barnes, M J K Thomas (sixth edition). VOGEL’S Quantitative
Chemical Analysis.
3. Harvey, David (2000). Modern analytical chemistry.
4. http://en.m.wikipedia.org/wiki/Gas_chromatography
5. https://youtube.be/BAqMoxYCrv8?si=sBtmCKTxcH8kkMCJ
6. All figures are collected from https://slideplayer.com