------------------------------------------------- 4 May 2012
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4 May 2012
Introduction:
In this experiment gas chromatography is applied to separate the water-ethanol mixture. This method is often used in the determination of alcohol in blood or urine. One obvious application is when law enforcement agencies need to determine whether or not someone is inebriated. In these cases, high sensitivity is required since 0.1% blood alcohol content is considered to be legally intoxicated in most states. Our own determination will deal with higher concentrations (up to 25% by volume) which are more typical of alcohol levels found in many alcoholic beverages.
Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of the phases constituting a stationary bed of large surface area, the other being a fluid that percolates through or along the stationary bed
Gas chromatography (GC) is a powerful and widely used tool for the separation, identification and quantitation of components in a mixture. In this technique, a sample is converted to the vapor state and a flowing stream of carrier gas (often helium or nitrogen) sweeps the sample into a thermally-controlled column. In the case of gas-liquid chromatography, the column is usually packed with solid particles that are coated with a non-volatile liquid, referred to as the stationary phase. As the sample mixture moves through the column, sample components that interact strongly with the stationary phase spend more time in the stationary phase vs. the moving gas phase and thus require more time to move through the column.
The goal of GC is to separate and detect components of a mixture as efficiently as possible and it is thus desirable to have a measure of the efficiency of a given chromatographic column. One common