Gas Chromatography Mass Spectrometry testing, or GC/MS testing, combines two different spectrometry techniques into a single process, making it one of the most broadly useful, accurate, and reliable methods of substance testing available today.
Here’s everything you need to know about GC/MS testing, with real-world use cases.
What is GC/MS testing?
GC/MS testing is one of the most broadly useful and commonly-applied analytical chemistry techniques used across industries today.
GC/MS testing is so effective because it combines the features of gas chromatography testing and mass spectrometry into a single analytical technique. This allows a wide variety of samples to be quickly and highly accurately analyzed, whether they’re in solid, liquid, or gaseous form. GC/MS can even be used to safely test volatile organic compounds (VOCs).
Despite its broad utility and ease of use, GC/MS testing is still considered a gold standard of substance analysis techniques. This is because, unlike many other forms of testing (such as FTIR oil testing), analysts use GC/MS testing to perform 100% specific tests, which identify not only the category of substances present in a sample, but what each of those specific substances are.
How does GC/MS testing work?
In GC/MS testing, the sample is initially injected into a port of the gas chromatograph, where it is heated to a temperature high enough to volatilize the components of the sample into a gaseous vapor.
At this point in the analysis, the instrument introduces an inert gas into the sample.
This introduction propels the vaporized sample into the GC column, which is a hollow tube that is typically many meters long, which is coiled and hung in the temperature-controlled oven of the GC.
The inside of the GC column is coated with a material called a stationary phase. The stationary phase separates the various chemical compounds in the vapor sample that travel through it based on their size and/or polarity. Smaller, more volatile compounds will travel through the column faster than others. The instrument measures how long it takes each component to make its way through the column. This is known as that component’s “retention time.”
These separated compounds flow from the column into a Mass Spectrometer, or MS. The MS subjects the sample to chemical ionization, further breaking it into positively-charged ions. These ions filter through an electromagnetic field programmed with an ion trap, which allows only a predetermined range of masses through.
As each molecular ion passes through the electromagnetic field, a detector counts them. The instrument generates a “mass spectrum” based on the distribution of ions of different sizes. This mass spectrum and the retention time of each component are both compared to a reference library of over 275,000 unique mass spectra in order to determine and quantify the compounds within the sample.
What is GC/MS testing used for?
GC/MS testing has an extremely broad range of practical uses, including:
- Identification and quantification of unknown samples
- Identification of unknown contaminants within a sample
- Environmental analysis (via testing of samples from the environment)
- Identification of trace elements in samples (via separation and quantification)
- Identification of gasses within a sealed environment
- Identification of residual solvents within a sample
As can be surmised from this extensive list of uses, GC/MS testing has applications in a similarly wide variety of industries, including:
- Food and drink
- Epoxies and other adhesives
- Plastics and plastics manufacturing
Use cases for GC/MS testing
Given how many different uses GC/MS testing has, it’s generally easier to understand the value of the testing via example. These are two real case studies that illustrate the various ways GC/MS testing can be so useful for substance testing:
Finding ethanol in a powdered drug
Our client was a pharmaceutical manufacturer who wanted to know whether the ethanol they were using during the manufacturing process was finding its way into their finished product.
To find out, our team used a variation of GC/MS testing called Headspace GC/MS analysis. In Headspace GC/MS analysis, the sample is placed in a vial, sealed and heated to a specific temperature so that certain volatile components within it escape into the headspace above the sample, where those components can then be introduced to the gas chromatograph.
Headspace GC/MS analysis was the right choice because it was able to successfully separate ethanol as a volatile compound from the main sample, then identify and quantify its presence very quickly and with a high degree of accuracy.
After running the test, the gas chromatogram of the drug showed a solvent peak at a retention time of approximately 1.67 minutes. By comparing that mass spectrum peak to the mass spectrum of ethanol, we were able to successfully identify the presence of ethanol within the sample, confirming the client’s suspicions.
Analysis of edible oil
Our client was a food service vendor who was considering switching to a new, cheaper vegetable oil for use in their product, but had to make sure that the new oil wouldn’t negatively impact quality. They wanted to know exactly how similar the new oil was to their previously used variety, and what impact any differences could have on the product.
In this case, GC/MS testing was the obvious choice for oil testing, because our experts could use it to separate, identify, and quantify each specific compound present in both oils, creating the most useful and specific information about their differences available.
The GC/MS analysis of the oils showed that the original oil contained four acids that the new oil did not:
- Palmitic acid (retention time of 19.00 minutes)
- Linoleic acid (retention time of 20.6 minutes)
- Oleic acid (retention time of 20.7 minutes)
- Stearic acid (retention time of 20.9 minutes)
This led our team of analysts to two conclusions:
- Making the switch could affect the flavor or preparation process: The fact that the new oil lacked these ingredients could make a difference, no matter how small, on either the food preparation process or the taste of the food itself.
- Making the switch could make the product healthier: Palmitic acid is a saturated fatty acid that tends to raise LDL-cholesterol. Oleic acid is also challenging for oxidative stability and nutritional quality. Removing these oils from the product by switching to the new vegetable oil could make the product healthier.
These are just a few examples of the many applications of GC/MS testing. If you think the analysis procedure may be right for your needs, get in touch with the experts at Innovatech. We can answer your questions and get started right away.