GAS LIQUID CHROMOTOGRAPHY
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Transcript of 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This terminology has been superseded by the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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