Gas Chromatography and Mass Spectrometry

These are the most precise tests for identifying and quantifying drugs or their metabolites in the urine. They are usually used as a confirmation test following a positive result on an Immunoassay. It involves a two step process, whereby Gas Chromatography separates the sample into its constituent parts and Mass Spectrometry identifies the exact molecular structure of the compounds. The combination of Gas Chromatography and Mass Spectrometry is considered to be the definitive method of establishing the presence of drugs or their metabolites in the urine. However, the equipment necessary to perform it is extremely expensive and this is reflected in the price for testing each sample. Occasionally problems do arise with poor calibration of the equipment.