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. The GC-MS method uses two devices called a gas chromatograph and a mass spectrometer. Chromatography is used to separate mixtures of chemicals into individual components, or ‘aliquots.’ Once the mixtures are separated into individual components, the mass spectrometer then works to determine the elemental value of each aliquot and identifies and quantifies the chemicals within them.

Urine drug screen testing can utilize GC/MS methodology to confirm the presence of a specific substance within the urine sample. But the initial phase of the urine screen testing process begins with the use of a biochemical test known as immunoassay, where the urine sample is screened and analyzed for a specific drug. A urine drug screen is a simple yet effective way to test for drugs of abuse. Immunoassay is a test used to measure the amount of a specific substance present within a solution. These solutions are often comprised of a complex mixture of several substances, like that of urine. A good example of a urine drug screen test that utilizes the immunoassay procedure is the DrugCheck Urine Drug Test. This rapid test measures the presence of drugs such as cocaine and marijuana within the urine sample. This one-step test takes a total of 5 minutes, and the test results can then be interpreted as a presumptive positive or negative.

After the immunoassay test is complete and the urine screen tests positive for the specific drug(s) being tested, these findings can then be confirmed through the use of GC/MS. In some cases, positive test results from the urine drug screens must be verified before the findings can be used for legal purposes. While the initial drug screen test can be done at home or at an on-site testing location, GC/MS methodology is conducted in a lab.