Aim: To study introduction of Gas chromatography.
References:
Gurdeep R.Chatwal and Sham K.Anand,Instrumental methods of chemical analysis Himalaya publishing house Page No: 2.673-2.703.
Principle:
The sample solution injected into the instrument enters a gas stream which transports the sample into a separation tube known as the "column." (Helium or nitrogen is used as the so-called carrier gas.) The various components are separated inside the column. The detector measures the quantity of the components that exit the column. To measure a sample with an unknown concentration, a standard sample with known concentration is injected into the instrument. The standard sample peak retention time (appearance time) and area are compared to the test sample to calculate the concentration.
Introduction:
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.
INSTRUMENTATION OF GAS CHROMATOGRAPHY:
1.CARRIER GAS
2.SAMPLE INLET
3.OVEN
4.DETECTORS
5.DATA SYSTEM
CARRIER GAS:
The carrier gas or mobile phase in GC is an essential, but limiting, facet in separations. Carrier gas is the means to move constituents of a sample through the column and yet the choice of possible gases is restricted.
The chromatographic process begins when sample is introduced into the column, ideally without disrupting flows in the column. The chromatographic results will be reproducible inasmuch as this is accomplished with a minimum of change in pressure or flow of the carrier gas or mobile phase.
Liquids or solids must be converted to vapour state and maintained as a vapour throughout the GC separation. Therefore, most gas chromatographs are equipped with ovens to keep the column at temperatures from 40 to 350 °C. Exceptions are those chromatographs that are used in separating simple gases such as light hydrocarbons or permanent gases. Early gas chromatographs.
Effluent from the column enters a detector where the composition of the carrier gas stream is characterized through one of several possible chemical or physical properties of molecules. The mainstays in GC have been the flame ionization detector (FID), the thermal conductivity detector (TCD) and the electron capture detector (ECD).
Other commercially available detectors include the photoionization detector (PID), the nitrogen–phosphorus detector and the atomic emission detector, though these have been less prevalent historically than the FID, TCD, and ECD were equipped with isothermal ovens. Other detectors have been introduced through the years but have never become widely used in GC methods. The FID relies upon the formation of gaseous ions from organic molecules combusted in a hydrogen–air flame; the TCD is based upon changes in the heat absorbing properties of the gas effluent when the carrier gas is altered with analyte. The ECD response is governed by the ability of some molecules to attract and remove thermalized electrons.
Importance of each detector
At a fundamental level, acquisition of chromatographic results has been little changed since the early days of GC, though the digital revolution has meant that strip chart recorders, once the mainstay of collecting chromatograms, cannot be found today and only electronic recording-integrators or microcomputers are used. Signal from the detector amplifier is digitized and stored to disk allowing enormous convenience in retrieving and replaying results.
Which Type Of Compounds Can Be Analysed On Gc
RESULT:
Remark:
Practical Performance
(2)
Conduct in Lab
(2)
Journal
(2)
Observations and Results
(2)
Viva-Voce
(2)
Total
(10)
Signature of Faculty In charge
EXPERIMENT NO: 7
