Gas chromatography (GC) is a powerful instrumental technique used to separate and analyze mixtures. A gas chromatograph is a standard piece of equipment in forensics, medical, and environmental testing laboratories. 2.5A: Overview of GC Gas chromatography (GC) is a powerful instrumental technique used to separate and analyze mixtures. A gas chromatograph is a standard piece of equipment in forensics, medical, and environmental testing laboratories . 2.5B: Uses of Gas Chromatography A Gas Chromatography (GC) instrument is very good at verifying (or disproving) the purity of samples, and it can often spot trace quantities of impurity. Due to the precision of retention times, GC can be used to identify components of a mixture if pure samples are acquired and if the components separate on the column. 2.5C: Separation Theory Gas Chromatography is an excellent analytical tool for separating mixtures in a sample. In this section are discussed the details of the separation. 2.5D: Quantitating with GC Peak integrations are useful because it is possible to correlate the area under a peak to the quantity of material present in a sample. Note it is the area of a peak that is relevant, not the height. A tall, narrow peak may have a smaller area than a short, wide one. It would be very useful if peak areas would directly reflect mixture composition, but that is unfortunately not always the case. The reason for this has to do with how compounds are detected upon exit from a column. 2.5E: GC Parameters There are many factors that affect the separation (and/or retention times) in gas chromatography, including the type of column, sample concentration, oven temperature, and flow rate of carrier gas. The factors controllable by a student are described in this section, and are related to concentration and temperature. 2.5F: Sample Preparation for Gas Chromatography