The GC is used to analyse volatile molecules with a high melting point, such as fatty acids in fish oil. In addition, samples submitted to the GC do not need solvents or a “liquid mobile phase”; instead, samples are carried by an inert gas through the system. Hence, if we are testing for solvents, the instrument of choice is the GC-FID/MS; no steps are needed to factor out any solvents used to prepare the sample.
GC-MS is precisely able to identify and determine the quantity of the molecules of interest, whereas GC-FID is only used to determine the quantity of molecules. Like LC-MS/MS, GC-MS is also able to create an electronic signature of a molecule. The complexity of running the test will dictate which instrument will be used.
In a GC system, the vaporized sample is moved with a carrier gas through a specially coated capillary column. The column separates the components before entry into the detector; in our case, either the FID or MS, depending on the application.
We also use the GC-FID system to determine the quantity of common fatty acids and essential oils present in oils such as tamanu, argan, and fish oil.
This is a typical fatty acids chromatogram of an argan oil sample.
PCBs and pesticides are tested for through the GC-MS. As the samples pass through the ionization chamber, they are bombarded with a very high voltage of electricity that results in complete fragmentation (separation) of the individual compounds. The fragments are reconstructed as they move through a vacuum tube as per their mass-to-charge ratio. The given signal is recorded by the computer for analysis.
The compounds are compared with a well-known library from the National Institute of Standards and Technology (NIST) or a certified reference standard material.
The total ion chromatogram below represents a pesticides mixture.
Samples being tested for solvents pass through our headspace GC-FID. The FID incinerates the sample, giving an electrical signal for analysis. We use this setup to detect if there are solvents, such as 1,2-dichloroethane and 1,1,1-trichloroethane—which are known human carcinogens. These contaminants can be present in low-quality herbal extracts.
The chromatogram below represents residual solvent.