The Importance of Mass Spectrometry in Cannabis Testing
In the more mature industries of food and drink or pharmaceuticals, mass spectrometry is a common workhorse in the analytical scene. The sensitivity of the technique has allowed scientists to conduct drug metabolism and pharmacokinetic studies during product development stages, and the method has become a mainstay of product safety and quality screening procedures.
With the cannabis industry’s increasing acceptance and regulation, mass spectrometry has also become a technique near-indispensable to the analytical scientists working within the cannabis testing sector.
How does mass spectrometry work?
Mass spectroscopy is a useful technique for both identifying unknown compounds and quantifying amounts of known compounds in a sample.
Imagine a bowling ball rolling past you. If you nudge it sideways with your foot, then the ball will deflect and begin to roll in a slightly different path. However, if you applied that same sideways force with your foot to a lighter object, such as a ping pong ball, the path of the rolling ping pong ball would be deflected by a much greater amount. Theoretically, if you knew the speed of the ball, the force applied with your foot, and the deflected path, it would be possible to calculate how heavy the ball was.
In simplest terms, this is very much like mass spectrometry. Mass spectrometry involves the use of magnetic fields to deflect the motion of ionized atoms or molecules through an analyzer – and as with the ping pong ball analogy, lighter molecular fragments will be deflected by a greater amount. This allows analytical scientists to separate out these molecules according to their mass-to-charge ratio, and from there it is possible to calculate the exact molecular mass of molecules and molecular fragments. Using this data, scientists can accurately identify the compounds in the original sample.
“Mass spectrometry is the world’s most powerful identification tool,” says Dr Lee Polite, president and co-founder of Axion Analytical Labs, Inc.
“It has the ability to identify unknown chemical compounds down to the sub-parts-per-billion levels. But it does not work on mixtures; it really only works on pure compounds. That’s where the HPLC [high-performance liquid chromatography] or GC [gas chromatography] comes in. Chromatography is the world’s best separation tool. So, combine the awesome separating power of HPLC with the positive identification ability of the MS, and you have the world’s most powerful analytical tool!”
Inside the mass spectrometer, the incoming sample from the chromatography apparatus is ionized. These ions are often unstable and can break down into smaller characteristic fragments of the starting molecule, which are also passed through the mass spectrometer. The ions and ion fragments are accelerated through the spectrometer so that they all have the same kinetic energy before they are deflected by an electromagnetic field and picked up by an electrical detector.
“The mass spec essentially accurately weighs the individual molecules as the elute from the HPLC or GC,” Polite continues.
“Not only does it weigh the individual molecules, it smashes them apart, and weighs the fragments. Then we ‘add’ all the fragments back together to see what it was before we smashed it apart – like putting a puzzle back together to see the picture. It turns out that molecules always smash apart the same way. This ‘fragmentation pattern’ becomes the fingerprint of the molecule.”
Mass spectrometry in the cannabis lab
There are several applications where mass spectrometry has already been proven useful in the cannabis lab, primarily in potency testing and pesticide analysis.
Within potency testing, HPLC with diode array detection (DAD) is normally the method of choice. However, for laboratories that already have HPLC-MS capacity, the mass spectrometer method is more than capable of performing potency analysis effectively.
“Potency testing is easy because we are looking for relatively high levels, so the simpler detectors work great,” says Polite. “We do potency by HPLC with diode array detection because it gives the best precision[…] and it’s about a fifth of the price! You can also do it on a single quadrupole LC/MS. Both of those detectors are good down to around 1 parts per million (0.0001 percent).”
“As impressive as that sounds, that is nowhere near sensitive enough to reach the outrageously low pesticide level requirements,” Polite adds. “You need another factor of 1000 to get down to the low parts-per-billion requirements. That’s when you need a triple quadrupole (AKA tandem MS, LC/MS/MS) and a lot of money – $250,000 may get you the floor model. The triple quad gets you the sensitivity you need to find the proverbial needle in the haystack. Without going into gory detail, the first quad gets rid of all the ‘hay,’ and the second quad can only see ‘needles.’”
Tandem mass spectrometry (MS/MS), as the name might suggest, uses two mass spectrometers in tandem to analyze the sample. The first spectrometer separates the ionized molecules according to their mass-to-charge ratio before these molecules are fragmented further and fed into a second mass spectrometer for additional analysis. Adding in this second spectrometer and extra fragmentation step allows this method to identify and separate ions that have very similar mass-to-charge ratios – ions that may be misidentified if using only a single spectrometer.
Future trends in mass spectrometry
Outside of pesticide testing and potency analysis, mass spectrometry could have many more applications in the cannabis lab.
Published in the Journal of The American Society for Mass Spectrometry, a recent paper authored by industry scientists outlines the current role that mass spectrometry plays within the cannabis industry. In addition to potency analysis and pesticide testing, the scientists draw attention to the use of GC/MS and LC/MS/MS techniques in the profiling of terpenes and the detection of heavy metals.
But the paper also notes a number of areas where the use of mass spectrometry could be introduced or expanded. For example, mass spectrometry is not currently used for detecting microbial growth on cannabis – quantitative polymerase chain reaction (qPCR) is currently the general industry standard – but the scientists say that matrix-assisted laser desorption/ionization (MALDI) MS would be well-suited for this sort of application. Additionally, isotope ratio mass spectrometry (IRMS) could be of interest to research and law enforcement groups who are looking to determine the geographical origin of a given sample, the paper authors say.
Other innovations, such as the development of a GC/MS-based method for analyzing the scent profile of wines, could also become relevant to the cannabis lab. Like with wine, aroma is also an important part of the use experience for many cannabis users. Similar research into the volatile compounds that contribute to the aroma of cannabis strains could then also become an interesting field of study for the cannabis industry becomes it increasingly commercialized.
This article originally appeared in Analytical Cannabis' Technologies and Techniques for Cannabis Testing eBook in September 2020.