GAS LIQUID CHROMOTOGRAPHY

8/7/2019 GAS LIQUID CHROMOTOGRAPHY

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SIR.M.V.GOVERNAMENT SCIENCE COLLEGE

-BHADRAVATHI

SEMINAR ON:GAS LIQUID CHROMOTOGRAPHY

AND

GAS SOLID CHROMATOGRAPHY

SUBMITTED BY:

VEERABHADRASWAMY.B.N,

I MSc (Chemistry),

Sir.M.V.Govt Science College,

Bhadravathi.

SUBMITTED TO:Dept. of Chemistry

Sir.M.V.Govt ScinceCollege,

Bhadravahti.


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CONTENTS:

INTRODUCTION GAS LIQUID CHROMATOGRAPHY

GAS SOLID CHROMATOGRAPHY

DETECTORS

APPLICATION


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INTRODUCTION:

Gas chromatography separates a mixture intoIts constituent by passing a moving gas phase over

a stationary sorbent. It is similar to liquid-liquid

chromatography except that the mobile liquid

phase is replaced by a moving gas phase. Only two

possibilities exit for the stationary phase; it can be

a solid or a liquid. This immediately limits the

separation mechanisms to adsorption or partition,

both of which are extensively employed in gas

chromatography


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TYPES OF GAS CHROMATOGRAPHYOriginally two types gas chromatography were described,

1. Gas liquid chromatography(GLC)

2. Gas solid chromatography(GSC)

This terminology has been superseded by the

simpler and more satisfactory term

Gas chromatography(GC)


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In gas liquid chromatography (GLC)mobile phase is gas and stationary is the

thin layer of non-volatile liquid bound to

solid support.In gas solid chromatography (GS)

mobile phase is gas and stationary phase is

solid adsorbent


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Gas liquid chromatography:

GLC consists of a mobile gas phase and a stationary

liquid phase that is coated on to either a solid matrix or the

wall of a capillary tube. Typically stationary phase has a

sufficient low Vapour pressure in column temperature so

that it can be considered as non-volatile. The sample

mixture in gaseous form is run through the column with a

carrier gas. Separation can be achieved by the difference

in the distribution ratio of the components of the sample

between the mobile and stationary phases causing them to

move through a column at different rate and with different

retention times. After elution the components of the

sample can detected be a suitable detector at the exist.


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Instrumentation:

Basically the GC consists of six basic components. They

are

A carrier gas which is maintained at a high pressure and is

delivered to the instrument at a rapid and reproducible rate,

A sample injection system,

The separation column,

One or more detectors,

Thermostat chambers for the temperature regulation of

the column and detectors,An amplification and recorder system.

Schematic diagram of a gas chromatographic instrument is

shown below


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BLANK DIAGRAM OF GC STRUCTURE


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Carrier gas supply:

Carrier gas must be chemically inert. It includes

Helium, Argon, Nitrogen, and Hydrogen and the type of

detector used often dictates choice of gases. In addition

the carrier gas system often contains a molecular sieve toremove water or other impurities.

Inlet pressure usually from 10 to 50 psi which lead to

flow rate of 29 to 150 mL/min with packed column and

1-25 mL/min for an open tubular capillary column.


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GAS CYLLINDERS


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Sample injection system:Column efficiency requires that the sample be of

suitable ug" of a Vapour, slow injection of over sized

samples causes band spreading and poor resolution.


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The most common method of sample

injection involves the use of a micro syringe to

inject a liquid or gaseous sample through a silicon

rubber diaphragm or septum in to a flashvaporizer, located at the head of the column above

50 0C which is above the boiling point of the least

volatile component in the sample

It is important to rapidly vaporize the sample.

Slow vaporization increases band broadening, by increasing

the sample plug.

Injection port temperature is usually held 50 0C higher than

the BP of the least volatile cpd.


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Column configuration and column oven:

The two general types of columns are encounteredin GC. Packed and open tubular or capillary

chromatographic column varies in length from less than

2m to 50m or more. They are constructed of stainless

steel, glass, fused silica or Teflon. The diameter is of 10 -30 cm. Column is ordinarily housed in a thermostated

oven and degree of separation required roughly a

temperature equal to or slightly above the average boiling

point of sample results in a reasonable elution time.


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PACKED COLUMN:

CAPILARY TUBE COLUMN:


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Gas solid chromatography:

In Gas solid chromatography stationary phase is solid,

GSC preceded GLC but never achieved the same

prominence. There are a number of reason for this

Adsorption isotherm are frequently nonlinear, leading to

several abnormal phenomena such as asymmetric peaks

and retention times that are dependent on sample size.

Retention times are excessively long because of the high

surface area of adsorption. Thus it is restricted to relatively

low molecular mass.


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Adsorbent are difficult to standardize and prepare

reproducibly and many active solids are efficientcatalysts. However, GSC enjoys some advantages over

GLC and it has some importance application areas such

as the separation of isomers, where it exhibits greater

selectivity and also in the separation of inorganic gasesand low molecular mass hydrocarbons for GLC shows

little selectivity.

Adsorbent are stable over a wide temperature range with

virtually nonexistent column temperature.Stationary phase which are commonly used in Gas Solid

chromatography is silica.


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Detector:

Characteristics of the ideal detector for GC are

Adequate sensitivity in the range 10 -8 to 10 -15 g/s,

Good stability and reproducibility,

A linear response to solutes that extends over several order of

magnitude,

A temperature range from room temperature to at least 4000C,

A quick response time that is independent of flow rate,

High reliability and ease of use,

Non destructive of samples.


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FID: Flame ionization detectors:

It is the most widely used and generally

applicable detector for gas chromatography

The FID exhibits a high sensitivity, a large linear response range and low

noise. It is generally rugged and easy to use. A disadvantage is that it destroys the

sample


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TCD: Thermal conductor detector:


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The TCD or catharometer was one of the earliest detectors

employed in GC studies and is based on the changes in the thermal

conductivity of the gas stream brought about by the presence of theanalyte molecule. The sensing element in the TCD is electrically

heated element whose temperature at constant electrical power

dependence upon the thermal conductivity of the surrounding gas.

The heated element may be a fine platinum, gold or tungsten wire or

semiconductor thermistar. The resistance of a wire is a measurement

of its temperature which depends in part upon the rate at which the

surrounding gas molecule conduct energy away from the detector and

the wall of the metal block in which it is housed.


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The advantage of a TCD is its simplicity, its large

linear dynamic range, and its general response to both

organic and inorganic species and its non-destructive

character that permits the collection of a solute.


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ECD: Electron capture detector:


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ECD operates in similar way as a proportional

counter for the measurement of X-radiation.Here the effluent from the column passes over

emitter.

The electron from the emitter causes theionization of the carrier gas and the production

of burst of electrons. In the absence of organic

species constant standing current between pair

of electrode results from this ionization process.


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The stationary liquid phases:

(a)polydimethyl siloxane ,

(b)5%phenyl poly siloxane ,

(c)50%phenyl poly siloxane,

(d)50% cyano propyl poly dimethyl siloxane ,(e)poly ethylene glycol.


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Desirable properties for the immobilized liquid phase inGLC include

A. Low volatility

B. Thermal stability

C. Chemical inertnessD. Solvent characteristics


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Chromatogram ofFermented Cabbage

Chromatogram ofOrange Juice Compounds


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Applications:

The principal applications of GC are the qualitative and

quantitative analysis of liquids, gases vapors particularly of

organic components.

Any stable compound that can be vaporized below 300 0C

can be determined by this method

It should be noted that the compounds must be stable with

respect to isomerization and decomposition at these

temperatures.Compounds that are unstable at these temperatures can be

analyzed by liquid chromatography.


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GAS LIQUID CHROMOTOGRAPHY

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