In this article we discuss one of the two methods that we use to measure residues of solvents and pesticides with, GC-MS-MS. First we discuss which types of gas chromatography there are, what GC-MS-MS is, how it differs from GC-MS and what it brings us. Elsewhere on this website you will find an article in which we discuss the second method, LC-MS-MS.
What types of gas chromatography are there?
There are several variants of gas chromatography (GC) and each of them calls for a quite extensive explanation. Very briefly, these are the four best-known methods of gas chromatography:
The most simple form of gas chromatography without a mass spectrometer (MS)
Gas chromatography that uses a mass spectrometer (MS)
Also called triple quad GC, which uses a more extensive mass spectrometer (MS)
The time it takes the electrically charged particles to reach the detector is used to profile constituents. TOF stands for Time-of-flight.
At New Agro Research we are using GC-MS-MS. We can best explain how GC-MS-MS works by first explaning how GC-MS works. After that, we’ll tell you how GC-MS-MS differs from GC-MS and why this technique is best suited for the kind of research that we do.
How does GC-MS work?
GC is a method that is similar to HPLC in many respects, with the most important difference being that in GC a carrier gas is used instead of an eluent. In addition to this we of course need a sample of the product that we want to test for solvents and pesticides.
To start off the sample is vaporized and added to the carrier gas. Subsequently, this gas is led to a very thin column. This column has an inner coating that slows down the molecules. However, one molecule will get slowed down more than the other. As a result, the different molecules will not pass trough the column all at the same time, but apart from one another instead. The time it takes for a molecule to pass through the column is called the retention time (RT).
After the molecules have passed trough the column they enter a detector where they are bombarded with electrically charged particles (ions). As a result of this bombardment, the molecules will fall apart into fragments. The mass of these fragments is measured by the detector. Since the masses of the fragments in which a molecule falls apart are always the same, we can identify the molecule (and thus the component) by looking at the masses of its fragments. Finally, the detector sends its data to a computer which processes the data into a graph, called a chromatogram.
How does GC-MS-MS work?
For the biggest part, the principle of GC-MS-MS is the same as that of GC-MS, with the main difference being that a more extensive mass spectrometer (MS) is used in GC-MS-MS. As a result there is a big improvement in the accuracy of the measurements. The MS which is used in GC-MS-MS is called a triple quadrupole MS. This spectrometer consists of three parts. In the first part a selection of molecules is already made. By doing this a lot of molecules that we are not looking for can already be “filtered out” from the sample. In technical terms we call this an improvement in the signal/noise ratio. Subsequently, the molecules are bombarded with electrically-charged particles in the next part of the detector (exactly as we have already described in our explanation of GC-MS). Then finally, in the third part of the detector, the molecules are definitively measured. Because we already made a selection of molecules earlier in the process a much clearer picture of the different components is realized.
What does GC-MS-MS bring us?
With GC-MS-MS we can detect a large amount of pesticides and components of pesticides (several hundreds). In addition to the identification of these components, we can also determine in what quantity they are present, even if these numbers are very low. The same applies to residues of solvents.
For the profiling of some other pesticides LC-MS-MS works better. That’s why we use both methods.
After performing GC-MS-MS and LC-MS-MS you know which pesticides and solvents are present in your product. This allows you to check whether your product is clean and safe enough for consumption. Also read our article about LC-MS-MS.