New Method For Testing Heavy Metals in Cannabis Vapor Published
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Scientists at Medicine Creek Analytics have developed a new optimized method for collecting and analyzing heavy metal contaminants present in the aerosols produced by cannabis vape products.
As detailed in a paper published in ACS Omega, the scientists investigated several different methods for aerosol collection and evaluated how well each could detect ten different heavy metals.
The final method utilized a standard smoke machine, one impinger containing organic solvent, a second impinger containing aqueous solvent, and an additional collection step where the apparatus was rinsed down with nonpolar solvent to collect any cannabis oil residues. The resultant samples were prepared for analysis with inductively coupled plasma mass spectrometry (ICP-MS), with demonstrable measurable recoveries seen for nine of the ten metals considered in this study.
What makes cannabis vapor testing so difficult?
Cannabis vape products have been under increased scrutiny since the EVALI outbreak of 2019, which highlighted the potential risks posed by unregulated vape products. Recently, Colorado announced that it would be requiring labs to test the actual vapor emissions of cannabis vape products being sold in the state. The idea is that by testing the vapors instead of just the oils contained in vape cartridges, testing labs will get a more accurate picture of what consumers will actually be inhaling into their bodies.
“Ultimately, when you’re vaping it changes the chemistry of what is in your vape cartridge,” Kyle Boyar, vice-chair of the American Chemical Society’s Cannabis Chemistry Subdivision [CANN], previously told Analytical Cannabis in reaction to the Colorado rule changes.
“I think it is really important to do [vapor testing] because, yes, you can test the product and see what it is like pre-vaping, but without knowing what it looks like in that vapor stream you really don’t know what you’re getting.”
Unfortunately, vapor testing is a very challenging technique. There is no agreed standard method for vapor testing, which is a problem for an industry that wants easily replicable and reliable testing. Trying to develop a standard method is also difficult, as the nonpolar nature of the cannabis oil aerosol mixture is largely incompatible with the aqueous-based capture methods traditionally used for tobacco e-cigarette analysis. Moreover, these cannabis oils will readily condense out of the vapor and form oily deposits on the inside of the testing apparatus, which can be troublesome to deal with.
“You want everything to be exact every single time you are repeating it over. And you want [the apparatus] to emulate how a human actually smokes,” Brodie Thomson, a research associate at DELIC Labs who developed the lab’s own protocol for aerosol testing, told Analytical Cannabis earlier this year. “There could be so much research done on this, especially because there are so many parameters and so many variables between different vapes and vape oils, how the person is smoking them, there’s just so many different things to find in the long run.”
“We made a special holder so that we could have a filter that is immediately after the mouthpiece. We 3D printed this special mouthpiece that we could fit around all the different vapes we were testing, and even with that there is deposition,” Thomson added.
Strategies for effective nonpolar aerosol collection
The new study from Medicine Creek Analytics created a model matrix of flower and concentrate, which was spiked with ten different heavy metals – arsenic, cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, and tin. Three experimental set-ups and five different impinger solvent combinations were compared to see which was able to recover the heavy metals most effectively.
Each method utilized a smoke machine programmed to take one 3-second “puff” from the spiked vape cartridge or spiked combustible flower, then rest for 42 seconds. This resting period ensured that all visible aerosols had time to move through to the next stage of the apparatus and for the battery to establish a constant voltage before drawing another puff. The aerosol from the smoke machine was then fed through to either one or two impingers containing aqueous solvents, organic solvents, or one of each solvent type. After the aerosol is captured in the solvent, the resultant samples underwent a final microwave digestion step to prepare them for ICP-MS analysis.
From these experiments, the scientists determined that two impingers – one containing acetone as a nonpolar organic solvent and one with an acidic aqueous solvent – was the ideal experimental setup. The acetone effectively captured condensed cannabis oil droplets and was the only solvent to reliably capture cobalt, while the aqueous solvent was required to capture mercury. Rinsing the glassware and tubing with more organic solvent and including this in the analysis was also found to reduce non-aqueous condensation loss.
Overall, the recoveries of all ten metals were seen to be fairly low but had large standard deviations, a finding that is consistent with other e-cigarette studies and suggests that these metals do not aerosolize efficiently when vaped. However, the research authors suggest that future studies looking at heating coil temperature and different operational voltages could help scientists better understand what effects metal vaporization rates in cannabis vape products.
While such additional tests are needed to create a truly optimized method for testing cannabis aerosol mixtures, the Medicine Creek Analytics team believes that this study does demonstrate an improved and validated method for cannabis vapor analysis that could serve the industry well.