2 Gas-liquid chromatography

Gas-Liquid Chromatography Gas-liquid chromatography can be used to separate mixtures of volatile liquids In gas-liquid chromatography, the mobile phase is a gas such as helium and the stationary phase is a high boiling point The time taken for a particular compound to liquid absorbed onto a solid. travel from the injection of the sample to where it leaves the column to the detector is known as its retention time. This can be used to identify a substance Carrier gas detector display column oven Sample in Waste outlet Flow control Some compounds have similar retention times so will not be distinguished. Basic gas-liquid chromatography will tell us how many components there are in the mixture by the number of peaks. It will also tell us the abundance of each substance. The area under each peak will be proportional to the abundance of that component It is also possible for gas-liquid chromatography machine to be connected to a mass spectrometer, IR or NMR machine, enabling all the components to be identified in a mixture. Most commonly a mass spectrometer is combined with GC to generate a mass spectra which can be analysed or compared with a spectral database by computer for positive identification of each component in the mixture. GC-MS is used in analysis, in forensics, environmental analysis, airport security and space probes. Callibration To calculate the concentration of each component in the curve it is necessary to complete external calibration curves to confirm concentrations of components. Known amounts of a pure component can be passed through the GC machine. The calibration curve will give the retention time of the component and the area under the curve (the peak integration value) will be a measure of the pure concentration. This can then be compared with the retention times and integration values of the components in the mixture to work out the amounts and proportions of the components in a mixture.