Everything You Need To Know About Gas Chromatography-Mass Spectrometry

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5 September 2023

Everything You Need To Know About Gas Chromatography-Mass Spectrometry

Gas Chromatography-Mass Spectrometry (GC-MS) is a powerful tool that has been used to analyze the atmosphere of Venus, diagnose disease and even identify the compounds used to mummify ancient Egyptians.

GC-MS is often employed to detect volatile substances in chemical compounds in both industrial and commercial settings. For example, it can be used in airport screening to identify suspect substances on individuals or in luggage. Forensic investigators also employ it for their investigations of fires and explosions. The GC-MS process is capable of detecting even the tiniest amount of a specific chemical, which makes it extraordinarily useful in these investigations and in drug testing.

GC-MS is the most sophisticated drug test available, referred to as the “gold standard” in the industry. However, because it is a relatively complicated and expensive test, most laboratories prefer to use it only for confirmatory or definitive testing. Industries regulated by Department of Transportation (DOT) guidelines, for example, are required to use a GC-MS to confirm the presence of drugs identified in a positive urine test. It is also standard procedure to employ GC-MS confirmation in most laboratories.

How Gas Chromatography-Mass Spectrometry Works

Gas chromatography uses a gas carrier medium to separate a urine sample’s compounds by their molecular interactions with the carrier medium (mainly by different polarities). Essentially, the sample is vaporized in the gas, allowing only specific compounds to remain. These compounds are then blasted with an electron beam and ionized by the mass spectrometer before being sent into a magnetic tube.

Inside the magnetic tube, the mass spectrometer analyzes the fragments by their mass-to-charge ratios. Then, analysts measure molecular fingerprints against a predetermined standard to determine each distinct compound. Both their retention time relative to the gas chromatography and their mass spectrum identifies these substances. For example, concerning retention time, less volatile substances tend to move more slowly than more volatile chemicals. The mass spectrum is a graph used in chemistry to plot the number of ions versus the mass-to-charge ratio of a specific sample. Technicians can accurately identify the individual elements based on where they appear in the graph.

Although GC-MS is most often used to confirm the results of urine drug tests, it can also ensure the results of tests conducted using blood and other bodily fluids. It is often the only test used to detect performance-enhancing drugs in many athletic competitions, including the Olympics.

The Advantages of Gas Chromatography-Mass Spectrometry

GC-MS can screen for hundreds of different drugs. Unlike other types of urine tests, such as an immunoassay (IA), it can detect the presence of both specific drugs and their metabolites. In other words, it can detect drugs that are already in the process of being broken down in the bloodstream. This ensures a wider window of detection for drugs than many other tests.

The GC-MS is more accurate and is capable of identifying even the smallest quantities of specific drugs in urine samples. In fact, the GC-MS can detect trace chemicals as tiny as 0.000000000001 gram (1 picogram). To give you an idea of how small this is, one picogram is the average weight of the DNA in one cell of a hummingbird. The GC-MS is both incredibly sensitive and accurate.

With a GC-MS test properly designed to identify all potential compounds, the risk of a false positive is virtually zero. It is even more useful because it can detect both the presence and levels of each specific drug.

While there are still cut off limits for GC-MS, they tend to be much lower than those of IA and similar tests.

Limitations of the GC-MS

Given the complex nature of the GC-MS drug test, it tends to require a high amount of expertise to conduct and analyze. The equipment is intricate and must be appropriately maintained. Because it cannot detect polar, non-volatile and thermally labile compounds, these compounds must be pre-treated before undergoing testing via GC-MS. This is usually accomplished via derivatization, which increases the volatility and thermal stability of these compounds.

It can also take longer to complete and receive the results of the GC-MS test. Depending on the lab and the involvement of a Medical Review Officer (MRO), the general rule is between 24 and 72 hours after the initial 24-hour test result period for a confirmatory test.

These limitations mean that the GC-MS tends to be more expensive and often takes longer to complete than other tests, including the immunoassay test. It is also why it is the GC-MS is most often employed in drug testing when the results of other types of urine tests produce unexpected results.

The structure of a GC-MS test is also critical. If the GC-MS test is not designed to detect a specific drug analyte, it will not identify it. Most false negatives with the GC-MS test are the result of the test not being prepared to identify a potential compound specifically. However, this rarely happens in professional laboratories.

Human error is the cause of most of the limitations of the GC-MS drug test. When it’s employed correctly, it is one of the most sensitive and accurate drug tests available. It can detect even trace amounts of certain drugs and provides peace of mind that your drug testing program is working as it should.