Chromatography is a laboratory technique for the separation of compounds. In liquid chromatography, a solution is dissolved in a fluid called the mobile phase, which carries it through a column holding another material called the stationary phase. The point where a compound is eluted from the column is called the retention time, which is one of several factors taken into consideration when identifying compounds. If the retention time for an unknown compound matches that of a known standard, this indicates that the compound might be the same as the standard, though further qualification is needed.
Several methods of detecting the eluted compounds exist, but in common techniques, a chromatogram showing the response over time is produced. An increased response over a short time interval is called a peak. The area under such a peak is proportional to the concentration of the compound in the injected sample, and can be used for quantification.