Pytochemistry is a sub-field of both chemistry and botany. This field studies chemical compounds that are derived from plants. Typically these chemicals are secondary metabolites that are used to treat plants or to fend off insects but some of them are valuable chemical precursors. In example, many of the alkaloids, terpenes, saponins, flavonoids, anthraquinones and volatile oils are still extracted from plants. Analytical work mostly requires the use of liquid and gas chromatography systems.