By, Blessy Babu

What is Gas Chromatography?  Gas spectroscopy is a technique used to separate volatile components in a mixture.  It is particularly useful for many organic compounds that have low boiling points.  The Stationary Phase :- Thin layer of a liquid or solid.  The Mobile Phase :- Gas  Gas chromatography is similar to Fractional Distillation, as both processes separate the components of a mixture primarily based on boiling point differences. However, fractional is used to separate components of a mixture on a large scale, whereas GC can be used on a much smaller scale.  One of the main use of GC is used to test the purity of a particular substance by separating the different components in a mixture  Although GC can separate components in a mixture, it cannot identify them. This is the reason why we combine gas chromatography with mass spectroscopy.

Gas Chromatography and Mass Spectroscopy Gas chromatography–mass spectrometry ( GC-MS ) is a method that combines the features of gas – liquid chromatography and mass spectroscopy to identify different substances within a test sample. GC and MS make an effective combination for chemicals analysis as GC separate the components in a mixture while. MS can provide detailed structural information on most compounds for exact identification. So by combining two of these techniques we can obtain a powerful and effective analytical tool than from each separate technique.

This is the mobile phase. Mixture is injected and vaporised. Mobile carrier Gas flushes the mixture through the column. This is the stationary phase(SP). Components slow down as they interact with the stationary phase. If SP is liquid components may dissolve, on the other hand if solid it is adsorbed. Different components are slowed down by different amounts, so the separate. Each components that leave the column at different time is detected. Computer processes the results to display a chromatogram 1):- Separation of components in a mixture using GC Separation can be improved by using different oven temperature and different flow of rates for the carrier gas

4) Mass Spectrum of 3 3) Mass Spectrometer 2) Gas chromatogram Components are first separated using GC Retention time may provide a preliminary identification When the Separated components are passed into the mass spectrometer, they are broken down into ionized fragments, and then each molecule is specifically identified based on mass and ionic charge. Generated mass spectrum can be compared with a spectral database by computer. A mass spectrum allows positive identification of each component in the original mixture.

Uses Of GC - MS Forensics :- GC/MS instrument helps separate and determine the individual elements and molecules in a sample from the crime scene. The GC/MS provides forensic investigators the ability to identify individual substances that may be found within a very small test sample. Forensic applications of GC/MS include:- Identification and detection of explosives Drug detection Environmental analysis Fire/ explosive investigation Identifying unknown compounds Airport security :- detecting dangerous substances in luggage, and on human beings. Because of its great sensitivity, gas chromatography/mass spectroscopy can be utilized to identify trace elements of substances that were believed to be contaminated or to regarded as beyond usability.

Other Uses