GAS CHROMATOGRAPHY

PRESENTED BYR.PRIYA

GAS CHROMATOGRAPHY (GC)

*Gas chromatography is a chromatographic technique that can be used

to separate volatile organic compounds.

*GLC( or) GC is a type of partition chromatography.

*It consists of

a flowing mobile phase (carrier gas)

an injection port

a separation column (the stationary phase)

an oven

a detector.

BASIC GC SYSTEM

One or more high purity gases are supplied to the GC. One of the

gases (called the carrier gas) flows into the injector, through the

column and then into the detector.

A sample is introduced into the injector usually with a syringe or

an exterior sampling device. The injector is usually heated to

150-250°C which causes the volatile sample solutes to vaporize.

The vaporized solutes are transported into the column by the

carrier gas. The column is maintained in a temperature controlled

oven.

The solutes travel through the column at a rate primarily

determined by their physical properties, and the temperature and

composition of the column.

The various solutes travel through the column at different

rates. The fastest moving solute exits (elutes) the column first

then is followed by the remaining solutes in corresponding

order.

As each solute elutes from the column, it enters the heated

detector. An electronic signal is generated upon interaction of

the solute with the detector.

The size of the signal is recorded by a data system and is

plotted against elapsed time to produce a chromatogram.

TYPES OF GC

Two types of gas chromatography

1. Gas-solid chromatography (GSC)

2. Gas-liquid chromatography(GLC)

Gas-solid chromatography

Is based upon a solid stationary phase

on which retention of analytes is the

consequence of physical adsorption.

Gas-liquid chromatography

Is useful for separating ions or

molecules that are dissolved in a solvent.

PRINCIPLE OF GC

The GC principle involves separation of components of the sample under

test due to partition in between gaseous mobile phase and stationary

liquid phase.

Gas chromatography runs on the principle of partition

chromatography for separation of components. In terms of stationary

and mobile phases it is categorized under gas-liquid type

of chromatography .

The organic compounds are separated due to differences in their

partitioning behavior between the mobile gas phase and the stationary

phase in the column.

WORKING PROCEDURE OF GC

Process Flow Schematic

Carrier gas (nitrogen or helium)

Sample injection

Long Column (30 m)

Detector (flame ionization detector or FID)

HydrogenAir

Gas Chromatograph Components

Flame Ionization Detector

Column

Oven

Injection Port

top view

front view

INSTRUMENTAL COMPONENTS

CARRIER GAS

The carrier gas must be chemically

inert. Commonly used gases include

nitrogen, helium, argon, and carbon dioxide.

SAMPLE INJECTION PORT

The most common injection method is

where a micro syringe is used to inject

sample through a rubber septum into a flash

vaporizer port at the head of the column. The

temperature of the sample port is usually

about 50°C higher than the boiling point of

the least volatile component of the sample.

The carrier gas enters the chamber and can

leave by three routes. The sample vaporizes

to form a mixture of carrier gas, vaporized

solvent and vaporized solutes.

COLUMNS

There are two types of column,

1.Packed column

2. capillary column (also known as open tubular).

PACKED COLUMNS

It contain a finely divided, inert, solid support material coated with liquid stationaryphase. Most packed columns are 1.5 - 10m in length and have an internal diameter of 2 -4mm.

CAPILLARY COLUMNS

1. wall-coated open tubular (WCOT)

2. support-coated open tubular (SCOT)

Both types of capillary column are more efficient than packed columns.

These have much thinner walls than the glass capillary columns, and are given strength bythe polyimide coating. They have the advantages of physical strength, flexibility and lowreactivity.

PREPARATION OF SAMPLE

Polar compounds are not directly applied. polar groups (-OH, -

COOH) into non-polar derivatives increases the volatility of these

compounds. Silanization, methylation and perfluoroacylation are common

conversion methods for CHO, fatty acids & amino acids. Non-polar organic

compounds need any such conversion and they can be directly applied.

APPLICATION OF SAMPLE

The sample for GLC is dissolved in a suitable solvent such as

acetone or methanol and is injected into the column using a micro syringe in

the injecting port.

SEPARATION PROCEDURE

The most commonly used carrier gases are nitrogen, helium

& argon. The gases are passed at a flow rate of 40 to 80 ml.

Two types of temperature control techniques:

1. Isothermal analysis

2. Temperature programming

DETECTORS

GC detectors detect the isolated components and helps in

identification and quantification of the sample.

TYPES OF GC DETECTORS

1.Thermal conductivity detector

2.Flame ionization detector

3.Electron capture detector

4.Flame photometric detector

5.Photo-ionization detector

6.Hall electrolytic conductivity detector

FLAME IONIZATION DETECTOR

The effluent from the column is mixed with hydrogen and air.

Organic compounds burning in the flame produce ions and

electrons which can conduct electricity through the flame.

A large electrical potential is applied at the burner tip, and a

collector electrode is located above the flame.

The current resulting from the pyrolysis of any organic compounds

is measured.

The FID is a useful general detector for the analysis of organic

compounds, it has high sensitivity, a large linear response range,

and low noise.

It is also easy to use, but unfortunately, it destroys the sample.

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

ELECTRON CAPTURE DETECTOR

The computer to record the analysed readings. This is

connected with the detector and hence records the detector

changes in reference to the flow of separated components from

the exit of the column. The record is called gas chromatograph.

The thermal chamber to fix or maintain fixed temperature.

Further improvement in GC apparatus is fixed with Mass

spectroscopy system (GC-MS) for better analysis of

components.

GAS CHROMATOGRAPH OUTPUT

time (s)

det

ecto

ro

utp

ut

•Peak area proportional to mass of

compound injected

•Peak time dependent on velocity through

column

USES OF GC

Widely used for the qualitative and quantitative

analysis of a large number of compounds

This technique provides a high speed and resolution

Very good reproducibility and high sensitivity

1000 of volatile organic compounds can be separated

by GC

Non-volatile substance can also separated if converted

in to volatile one by oxidation, acylation, alkylation,

etc.

Concentration of individual elements such as carbon

and hydrogen can be determined very accurately

Alcohols, esters, fatty acids and amines present in

biological samples are often separated by GC.

APPLICATION OF GC

Gas chromatography (GC) continues to play an important role in

the identification and quantification of ubiquitous pollutants in

the environment.

GC in the analysis of various classes of persistent organic

contaminants in air, water, soils, sediments. Special attention is

given to sample-preparation techniques.

The organic pollutant groups are: volatile organic compounds

(VOCs) , polycyclic aromatic hydrocarbons (PAHs) , pesticides

and halogenated compounds.

Trends and future perspectives of capillary GC in the field of

environmental analysis.

Refinery Solutions

Gas Chromatographs are uniquely designed to

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transfers

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chemical and petrochemical plants keep operating efficiently.

• Maintain proper chemical ratios

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• Measure impurities in product

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Chemical/Petroche

mical Solutions

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For gas processing plants, gas chromatograph product

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4) ENVIRONMENTAL MONITORING

SOLUTIONS

There are numerous gases found in industrial process

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Analytical process gas chromatographs provides

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humidity, and even samples will not deter accurate

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Environmental

Monitoring Solutions

Gas chromatograph with a headspace sampler

REFERENCES

Biomedical instrumentation- V.Arumugam

Palanivelu. P. Analytical biochemistry and separation

techniques.

Webster. J.G. Bioinstrumentation.

Bioinstrumentation- L.Veerakumari.

www.detectors of gas chromatography.com.au

www.science info world of gas chromatography.

www.gas cromatography.edu.au