Gas chromatography is auseful method in analytical chemistry used to isolate and evaluate a specificcompound that has the ability to vaporize without decomposing, contained withina matrix.
The gas chromatograph can be used in a variety of situations such asanalyzing the purity of the compound in question, or separating the individual componentsof a mixture and determining the amount of compound you have in relation to themixture. A gas chromatograph is comprised of several main components: a carriergas which is most often helium due to its inert nature, a flow valve thatcontrols the speed at which the gas moves, the column which is a long piece oftubing made of either steel or glass, and the detector which is comprised ofelectrodes near a hydrogen flame that measures differences in potentials as thehydrocarbons pass through it. In Gas chromatography, you have two distinctphases, mobile and stationary. The mobile phase occurs ingas state while the stationary phase is a liquid coating along the walls of thecolumn. Compounds of interest are separated due to the difference in theirchemical and physical properties.
As the various analytes travel through thecolumn, they are each impeded by the process of adsorption onto the columnwalls. How fast an analyte is able to travel through the column depends on the capacityof adsorption, which as mentioned before depends upon its chemical and physicalproperties. Due to this, each compound will therefore reach the detector atdifferent time periods. The time it takes for this to happen is referred to asthe retention time.
The main focus ofthis experiment is to obtain the retention times of C16, C18,and C20 individually, and to then figure out what operatingconditions are ideal to separate the 3 alkanes in a single solution of hexane byvariation of the mobile phase velocity through the adjustment of the columnhead pressure. It would be expected that as the CHP decreases the retentiontimes of the individual alkanes become more distinguishable (narrower peaks)but at a cost to the resolution of the peaks on the graph. To test theserationales, I will be using the following formula: