what is a gcms test?
Gas Chromatography-Mass Spectrometry (GC/MS) As It Relates To Urine Drug Testing. Gas Chromatography-Mass Spectrometry (or GC/MS) is a two-step methodology used to identify different substances within a test sample. GC/MS is widely used due to its ability to perform a specific test, and is an extremely effective in identifying the presence of a specific substance within a given sample.