A schematic of the porous layer open tubular (PLOT) capillary used as a cryoadsorber trap. The PLOT capillary is coated with alumina, is approximately 1 meter long, can be as short as 0.1 meter, and is typically coiled at an 8 cm diameter to allow the capillary to be housed in the cryostat chamber (see Figure 1 ).
PLOT-cryo is an ultra-sensitive, quantitative, trace dynamic headspace (HS) analysis technique that was used to determine the mass of sample collected from the vapor phase at a given HS collection temperature. This method is used for trace vapor analysis (of polar and non-polar solutes of moderate to low volatility) with high reproducibility and thermodynamic consistency. In PLOT-cryo, a sweep gas is carried through a fused silica tube into a sealed vial containing the sample, with the entire assembly located in an oven ( Figure 1 ). The HS vapors are then carried by the sweep gas and trapped on a PLOT capillary ( Figure 2 ) contained in a temperature-controlled cryostat. PLOT-cryo has the inherent ability to stabilize labile solutes because collection is done at reduced temperature. The PLOT capillary column is robust, reusable, inexpensive and has a large temperature operability for less volatile solutes. While alumina is used in this research, the sorbent phase can be tailored for the chemistry of interest. Analytes are eluted from the PLOT capillary using a suitable solvent or thermal desorption and a gas flow. The collected analytes are then determined by use of any instrumental technique, but typically gas chromatography-mass spectrometry (GC-MS).
Vapor pressure is the very first thing needed to begin a rudimentary equation of state (EOS). An EOS is necessary to provide an avenue for predicting thermophysical properties that are important for designing and engineering a specialized device such as a cannabis breathalyzer. Vapor pressure measurements can be used to predict the normal boiling temperature (NBT, temperature that the fluid boils at 1 atm), which can then be used to predict the critical constants (critical temperature, critical pressure and critical volume). The uncertainty of calculations from these models is of course dependent on the uncertainty of the input data; more data and lower uncertainty is always desirable. For cannabinoids, there are no available data, thus these will be the first available measurements for the field. Well-developed models like standard reference equations are based on hundreds of measurements, whereas the models developed here are a rudimentary beginning but are far better than “chemical intuition” for predicting the important thermophysical properties for device optimization.
Since the invention of PLOT-cryo, it has been applied to sampling spoiled poultry, gravesoil, pyrolysis products, explosives, and characterizing natural gas and fire debris [23–28]. For the gravesoil experiment, the method was modified to sample the HS air above gravesoil with a motorized pipetter and a PLOT capillary at ambient temperatures. This modified approach provided us with the first generation of an in-the-field trace vapor collection device. Since the gravesoil work, a much more capable in-the-field trace vapor collection device has been built, which utilizes the air compressor from a typical fire truck to provide the suction and temperature control [29, 30]. No other energy inputs are necessary.
Most commercial methods for measuring vapor pressure are designed to measure volatile or moderately volatile compounds. These methods typically require day to weeks to collect sample and can require large sample sizes. A previously developed technique employing porous layer open tubular-cryoadsorption (PLOT-cryo) technology made vapor pressure measurements of cannabinoids possible [22, 23].
The quest for a reliable means to detect cannabis intoxication with a breathalyzer is ongoing. To design such a device, it is important to understand the fundamental thermodynamics of the compounds of interest. The vapor pressures of two important cannabinoids, cannabidiol (CBD) and Δ 9 -tetrahydrocannabinol (Δ 9 -THC), are presented, as well as the predicted normal boiling temperature (NBT) and the predicted critical constants (these predictions are dependent on the vapor pressure data). The critical constants are typically necessary to develop an equation of state (EOS). EOS-based models can provide estimations of thermophysical properties for compounds to aid in designing processes and devices. An ultra-sensitive, quantitative, trace dynamic headspace analysis sampling called porous layered open tubular-cryoadsorption (PLOT-cryo) was used to measure vapor pressures of these compounds. PLOT-cryo affords short experiment durations compared to more traditional techniques for vapor pressure determination (minutes versus days). Additionally, PLOT-cryo has the inherent ability to stabilize labile solutes because collection is done at reduced temperature. The measured vapor pressures are approximately 2 orders of magnitude lower than those measured for n-eicosane, which has a similar molecular mass. Thus, the difference in polarity of these molecules must be impacting the vapor pressure dramatically. The vapor pressure measurements are presented in the form of Clausius-Clapeyron (or van’t Hoff) equation plots. The predicted vapor pressures that would be expected at near ambient conditions (25 °C) are also presented.
1.2 PLOT-cryoadsorption (PLOT-cryo)
Cannabis is currently a Schedule 1 drug (illegal under federal law). In recent years, however, there has been a shift in some local or state policies towards the decriminalization of cannabis use. Decreased criminalization may lead to an increase in cannabis use and cannabis-related harm.[1, 2] Potentially negative impacts include: a rise in intoxicated drivers and workers, an increase in cannabis use among adolescents, and negative health effects from chronic cannabis use.[3–7] Unlike alcohol consumption, which can be detected by monitoring the concentration of ethanol in the blood or breath, determination of cannabis intoxication is not as straightforward.
The cannabis plant contains over 500 compounds, including more than 100 plant cannabinoids that have been isolated and identified.[8–10] Some of these plant cannabinoids impart therapeutic or psychoactive affects, e.g., cannabidiol (CBD) and Δ 9 -tetrahydrocannabinol (Δ 9 -THC), respectively. CBD is thought to effect pain sensation and mood but very little research substantiating these claims exist. Because of its psychoactive properties, Δ 9 -THC is a molecule of great interest in the research and law enforcement communities. However, there are several aspects of the compound Δ 9 -THC that make collecting and analyzing it in bodily fluids complex. For one, Δ 9 -THC is rapidly metabolized in the body into both a psychoactive (the hydroxylated metabolite) and a non-psychoactive (the carboxylated metabolite) compound. Δ 9 -THC is excreted in the urine as a glucuronic acid conjugate. Additionally, a small portion of Δ 9 -THC is stored in adipose tissue and is released slowly over long time periods (hours, days, weeks). Δ 9 -THC levels also depend on the mode of consumption (smoking versus eating), when the user consumed, whether or not they are a chronic, an occasional, or a first time user, and of course, what body fluid is sampled. In lieu of these complexities, some countries and states have set legal limits of Δ 9 -THC concentrations in the blood, including zero tolerance laws to established impairment.
To solve this problem and help cannabis consumers get the fullest experience of their flower & concentrates, the vaporizer specialists at Firefly have introduced a new technology to their latest product line—dynamic convection heating. Rather than heating to a specified temperature, dynamic convection heats the air around your cannabis across a gradually increasing range in temperatures. This process activates the whole spectrum of terpenes and cannabinoids because it allows them to boil into inhalable gas form at each of their individual boiling points.
As vaporization has grown in popularity, the field has gotten crowded with a variety of products. Vaporizers that let users set a temperature of their choice, and hit that temperature quickly and accurately, are fairly easy to find. But hitting one temperature reliably rarely reveals the whole story of any cannabis flower.
Why Boiling Points Matter
Moving to Vaporizers
All vaporizers aren’t created equal, though. If your vaporizer of choice isn’t hitting the boiling point of each terpene and cannabinoid in your cannabis, it’s still not delivering the best possible expression of the plant.
“What’s become clear in the last few years is that many of the effects we attribute to cannabis are not only from cannabinoids like THC and CBD, but from the way they work in concert with compounds like terpenes,” says Cameron Hattan, lead grower of the California cannabis company Fiddler’s Greens.
This new approach allows consumers to experience the full lineup of cannabinoids and terpenes present in every strain, revealing the true character of innovative new strains while uncovering unexpected sides of old favorites.
That’s part of why many modern cannabis consumers are bailing on combustion. While setting fire to cannabis activates some compounds in the plant, it scorches many others. This process is known as pyrolytic destruction, and it’s about as good for your cannabis as you’d expect for a phrase with the word “destruction” in it.