Forensic drug test result. Graphs showing the pattern of ultraviolet light absorption (top) in a high-pressure liquid chromatography drug test at a forensic laboratory. This test is carried out to identify a sample of an unknown drug. The sample is separated into its different components in a high-pressure liquid chromatography column. The peaks on the bottom graph show emergence of the different fractions from the column over time (horizontal axis). Each fraction is identified by ultraviolet (UV) light absorption (top) as it emerges. Drugs present in the sample show distinctive UV absorption spectra.