Gas Chromatography/Mass Spectrometry (GC/MS) is a combination of two techniques: Gas Chromatography and Mass Spectrometry. It uses internal standards and provides identification and quantification of drugs and serves as the gold standard in the confirming the abuse of prohibited drugs such as heroin.
Gas Chromatography is a technique used to separate the drugs that may be present in the patient's sample. The chromatography column is a long tubular column where the sample is injected and is swept through the column by means of a gas such as helium. Drugs present are separated from one another since some drugs take longer to pass as compared with others. The chemical characteristics of drugs the time it takes for the drug to travel through the chromatography column. This is referred to as the retention time which is an identifying characteristic of the drug.
Mass Spectrometry is the detector of Gas Chromatography. When the drug exits from the GC column, it is separated via ionization. The fragments are sorted by mass forming a fragmentation pattern which is also an identifying characteristic of a drug which is said to be as unique as a fingerprint.
This standard is a deuterated version of the drug being tested and has similar characteristics with the one that is being tested. A precise amount is added before preparation so that the IS is prepared and analyzed similarly with the drug assayed. Quantification of the drug and qualification of the assay is done by comparing the signals produced by the internal standard with the signals produced of the drug being tested. The deuterated drug is made by substituting one or more hydrogen atoms with a deuterium atom. It exhibits similar characteristics as the non-deuterated drug but can be differentiated by the detection of the fragment mass.
Drugs are identified by the combination of its retention time by means of gas chromatography, fragmentation by means of mass spectrometry and specific information due to the presence of the IS