In my last column, I introduced Beer’s Law, which allows high performance liquid chromatography (HPLC) and infrared spectroscopy to be used to measure potency in cannabis samples. In this column, I establish the physical basis of Beer’s Law and derive it from first principles. I wrap up with a discussion of how the assumptions made in the derivation affect Beer’s Law experiments.

Beer’s Law allows spectroscopy to be quantitative because it relates the amount of light absorbed by a sample to the concentration of chemical species in that sample (1). From last time, Beer’s Law has the form of 

where A is the absorbance; ε is the absorptivity; L is the pathlength; and C is the concentration.

Spectroscopy is the study of the interaction of light with matter (2), so to understand Beer’s Law at a fundamental physical level, we need to think about light and how it interacts with molecules.

Light is properly called electromagnetic radiation because it consists of electric and magnetic waves undulating in mutually perpendicular planes (2). Although technically the term “light” is often used to refer to the electromagnetic radiation we can see with our eyes, I will be lazy and use it to refer to all electromagnetic radiation. Light is a mysterious devil since depending on what phenomenon of light is being measured it can be thought of as a wave or particle (3). For the purposes of this column, we will think of light as a particle. A particle of light is called a 

. A photon of light has energy but no mass, and its energy is given by 

 is the energy of a photon; h is Planck’s constant; c is the speed of light; and W is wavenumber.

Briefly, the wavenumber W of light is 1/wavelength, and if wavelength is measured in cm, then W has units of cm

-axis of spectra are often plotted in wavelength or wavenumber units. An example of the mid-infrared spectrum of a cannabis bud is seen in 

-axis of Figure 1 is in wavenumber units, and that the 

-axis is in absorbance. Note that when plotted in absorbance the peaks point up, and the tops of the peaks denote wavenumbers where a significant amount of light is absorbed. The absorbance here is the same as the A in Equation 1 above, and yes, the peak heights and areas in Figure 1 can be used to determine the potency of cannabis plant material (4-6).

When thinking of light as a photon, we can picture its interaction with molecules as that of a collision. 

 illustrates a photon about to collide with a methane molecule.

For simplicity’s sake, I have represented the methane molecule as a simple sphere. However, methane has a tetrahedral structure (7).

Physicists define different types of collisions based on what happens to the energy in the photon as a result of the collision (3). In Figure 2 before colliding with the methane molecule the photon has energy E

, and to make life simple we will assume the methane molecule is at rest and has no energy. In what is called an 

, no energy is exchanged between the methane molecule and the photon, and the photon leaves the collision with energy E

and the methane molecule is still at rest. Note in Figure 2 that the direction of the photon does change. Elastic collisions between photons and molecules give rise to a phenomenon called 

 (8). The intensity of Rayleigh scattering is proportional to the fourth power of the wavenumber, or W

, of the light being scattered. Rayleigh scattering is why the sky is blue; blue visible light is the highest wavenumber light we can see and is scattered with more intensity than all other visible light. Although Rayleigh scattering gives us a beautiful sky, it does not provide us with much chemical information.

During an inelastic collision the photon changes direction and loses some energy to the methane molecule, exciting it vibrationally. The amount of vibrational energy obtained by the methane molecule, E

, must be equal to the amount of energy lost by the photon to maintain conservation of energy. After the collision the total amount of energy in the system is the sum of the energies of the photon and molecule, E

And the amount of energy the photon now has is given by 

The collision of the photon and molecule exciting the molecule vibrationally is analogous to hitting a bell with a hammer, where the photon is the hammer, and the methane molecule is the bell. Some of the hammer’s energy is transferred to the methane molecule causing it to vibrate or “ring.”

The inelastic scattering of photons by molecules is called 

 (9). Analysis of Raman scattered photons provides chemical structural information about molecules, like how infrared spectroscopy provides this information. Raman spectroscopy is a well-developed field of chemical analysis (9) and has been used to analyze cannabis plant material (10-12).

 shows what happens when all the energy in a photon-molecule collision is transferred from the photon to the molecule. This is called a 

Again, since the Law of Conservation of Energy must be followed, and all the photon’s energy is deposited into the methane, the final energy of the methane molecule is then E

. As a result of a totally inelastic collision, the methane molecule can vibrate similar to the result of an inelastic collision. Since the methane molecule absorbs all the photon’s energy, inelastic collisions give rise to a phenomenon known as 

—yes, the A in Beer’s Law in Equation 1 above.

When a beam of photons travels through a sample of matter, let’s say a gas or liquid to make things simple, how many photon-molecule collisions occur? Intuitively, the more photons there are passing through a sample the more collisions there will be, and the number of photons a light beam contains is simply its intensity (I). Similarly, the more molecules there are in a sample the more photon-molecule collisions there will be. The number of molecules in a sample is determined by its concentration (C).

How do we quantify these ideas? Consider 

, which should look familiar as it was in the last column as well (1). This is an example of an experimental setup commonly used in Beer’s Law experiments.

In Figure 5, λ is the wavelength of light passing through the sample; I

is the measured light intensity before the light beam enters the sample; I is the measured light intensity after the light beam has exited the sample; L is the pathlength or sample thickness; and dL is an infinitesimally thin slab of the sample.

In Figure 5, the light beam of single wavelength l and intensity I

 impinges perpendicular to the face of a sample. The light beam leaves the sample at the same wavelength l but with intensity I. Light intensity has been lost by collisions between photons and molecules. L is the pathlength or sample thickness, and dL is an infinitesimally thin slab of the sample. As stated above, the number of collisions depends upon the number of photons, the number of molecules, and the pathlength—the thicker the sample, the higher the probability a photon will encounter a molecule. If we let -dI represent the light intensity lost by photon-molecule collisions, we can write proportionality 

where dI is the amount of light lost to all scattering; I is the light intensity in slab dL; C is the concentration; and dL is the infinitesimally thin slab of sample.

Proportionality, Equation 5 simply shows that the amount of light lost depends on the total number of photon-molecule collisions, which depends upon the number of photons I, the concentration of molecules C, and the thickness of our sample slab dL. Now, remember that Beer’s Law deals with absorbance, and that absorbance is due to totally inelastic collisions only. So, to measure the total absorbance we would need to know the number of totally inelastic collisions, or in other words what fraction of photon-molecule collisions are totally inelastic. This fraction is given by the absorptivity, e, yes, the same absorptivity that we discussed last time (1) and that appears in Equation 1 above. By inserting e into proportionality Equation 5, we obtain 

, which gives the amount of light intensity lost due to totally inelastic collisions, or absorbance, as such:

where dI is the amount of light lost in totally inelastic collisions; e is the absorptivity; I is the light intensity in slab dL; C is the concentration; and dL is the infinitesimally thin slab of sample.

At this point in the derivation, we need to get from Equation 6 to the final form of Beer’s Law. This necessitates using calculus to integrate both sides of Equation 6. I will not go into the math here—consult my book on quantitative spectroscopy for the details (3). Long story short we end up with 

where A is the absorbance; e is the absorptivity; L is the pathlength; and C is the concentration.

In the derivation of Beer’s Law several assumptions must be made, which effects how quantitative spectroscopy experiments are performed (3). These assumptions are:

The light beam contains only 1 wavelength, which is wavelength λ. We normally use a light beam containing many wavelengths in it to measure spectra. Fortunately, using light beams with many wavelengths in them generally presents no problems.

The sample is homogeneous. Remember we started with a slab dL, of the sample. The assumption in the derivation is that all such slabs dL are identical. This means we are assuming that all parts of the sample are the same, and that the concentration of the absorbing species is the same everywhere in the sample as well. We are also assuming that the physical condition, things such as temperature and pressure, is the same in all portions of the sample. Insuring sample homogeneity is normally not a problem for gases and liquids, which can be stirred and mixed easily. However, for a solid such as a cannabis bud, even one that has been ground, most certainly the sample is not homogeneous. That is why, for example, when using infrared spectroscopy to determine potency in dried, ground cannabis multiple portions of the sample are scanned, and the results are averaged to obtain representative data on the sample (5-6).

Our derivation of Beer’s Law assumes that all loss of photons in the sample is from totally inelastic collisions. Commercial spectrometers cannot distinguish between light lost by absorbance, Rayleigh scattering, or Raman scattering. Additionally, there are light losses because of reflections and absorbance by sample cell materials, contaminants on sample cell windows absorbing, suspended particles of dirt and dust that can scatter photons, and contaminant chemical species that can absorb. Since the spectrometer can’t tell the difference between all these sources of light loss, one needs to control or eliminate as many of these sources as possible. For sample cell contributions, one can scan a “background” scan of an empty cell, and if this contribution is the same from background to sample it is ok. Suspended crud should be filtered from gas and liquid samples, not so easy for solids. Lastly, make sure your sample does not contain impurities that can interfere with the measurement of the absorbance of your chemical species of interest.

Using the idea of photon-molecule collisions, we showed how totally inelastic collisions lead to light absorbance. Then, using the number of photons and molecules present, we wrote a proportionality which gave us the total number of photon-molecule collisions. Next, by inserting the absorptivity, which is the fraction of collisions that are totally inelastic we derived Beer’s Law. Lastly, the assumptions made in the derivation and how they affect real world experiments were discussed.

Fundamentals of Fourier Transform Infrared Spectroscopy

 2nd Ed. (CRC Press, Boca Raton, Florida, 2011).

Quantitative Spectroscopy: Theory and Practice

 (Elsevier, Boston, Massachusetts, 2002).

B.C. Smith, M. Lewis, and J. Mendez, “Optimization of Cannabis Grows Using Fourier Transform Mid-Infrared Spectroscopy,” PerkinElmer Application Note (2016).

https://en.wikipedia.org/wiki/Rayleigh_scattering

https://en.wikipedia.org/wiki/Raman_scattering

L. Sanchez, C. Filter, D. Baltensperger, and D. Kurouski, 

M. L’Heureux and M. Colli, (interview with D. Kurouski), 

, PhD, is Founder, CEO, and Chief Technical Officer of Big Sur Scientific. He is the inventor of the BSS series of patented mid-infrared based cannabis analyzers. Dr. Smith has done pioneering research and published numerous peer-reviewed papers on the application of mid-infrared spectroscopy to cannabis analysis, and sits on the editorial board of 

®. He has worked as a laboratory director for a cannabis extractor, as an analytical chemist for Waters Associates and PerkinElmer, and as an analytical instrument salesperson. He has more than 30 years of experience in chemical analysis and has written three books on the subject. Dr. Smith earned his PhD on physical chemistry from Dartmouth College.
Direct correspondence to: 

Articles

Cannabis Analysis 

In part II of this series, we establish the physical basis of Beer’s Law and derive it from first principles then wrap up with a discussion of how the assumptions made in the derivation affect Beer’s Law experiments.

Beer’s Law, Part II: Physical Basis and Derivation

Since 2019’s “vape crisis,” cannabis and nicotine vapes have been under a rollercoaster of scrutiny, and with good reason. In this two-part series, we will review the history of vape products and their obstacles, what to look for in vape cartridge hardware, and what operators should be aware of as producers of vape products.

Vaping is a choice made for many reasons such as health, discretion, flavor, and versatility. The first vaporizer was patented in 1930, but it wasn’t until 2003 that nicotine e-cigarette products became commercially available in China. In 2006, e-cigarettes made their way to Europe and the US when e-cigarette companies and the World Health Organization (WHO) both declared e-cigarettes a smoking cessation aid and marketed them as such. However, in 2008 the WHO rescinded their stance and marketing, no longer proclaiming e-cigarettes as a smoking cessation aid (1). The current concern is the potential toxins that can be found in e-cigarettes along with the flavors and marketing that is attracting youth to nicotine.

Herbal vaporizers have been popular for cannabis flower since the late 1990s, after the invention of the Volcano. However, cannabis extract vaporizer devices did not become readily available until sometime between 2010–2013. Manufacturers, consumers, and governing bodies believed the transition to vaping cannabis oil could be safer than combustion because of the ability to control the temperature at which the extract is vaped thereby limiting combustion. Research demonstrates that vaping pure cannabis extract is safer than smoking cannabis flowers (2). Vaporizing cannabis extract eliminates inhalation of combusted fibrous plant material, which is carcinogenic, and limits exposure to potentially toxic compounds. In addition, cannabis extract can be vaped at a lower temperature than smoking occurs. Extraction concentrates the desirable components of the plant matrix, mainly cannabinoids, terpenes, and terpenoids. Inhalable cannabis products, such as vapes, offer consumers immediate relief and predictable effects as opposed to the delayed and unpredictable effects of ingestible cannabis products. This promotes easy self-titrating, which benefits all types of consumers. For these reasons, it’s clear that vaping pure cannabis extract is safer than smoking and may be a better alternative for many users.

Given the history of nicotine vapes, the cannabis industry had an opportunity to limit the potential for toxic chemicals to be used in production. While the cannabis industry is strictly regulated, regulatory agencies are not sufficiently resourced and are unfamiliar with all that goes into producing an extract and a cannabis vapor product. While some regulations are in place to protect consumers, such as restricting pesticide use and testing to ensure heavy metal levels are below toxic limits, many states did not limit additives to cannabis extracts until after the “vape crisis” in 2019. It’s vital for consumers and industry members to advocate for safe vape products with minimal ingredients.

Responsible manufacturing is in the hands of the hardware suppliers and cannabis manufacturers producing vape cartridges and extracts. Margins are an important part of business success, especially in a time where cannabis is becoming more of a commodity. This incentivizes operators to source low cost vape hardware. However, there is now evidence to show that there is a wide range of vape cartridge quality and safety. This variety in quality results in a range of potential presence of harmful heavy metals in the vapor (3). While many states require heavy metal testing of the final extract, none require testing of product hardware or of the product after it has spent time in the hardware. Because of this, conscious vape companies are moving towards higher cost hardware and higher quality hardware to ensure their product is safe, thus providing a positive experience for the consumer. Because of their market growth, vape cartridges will continue to become better, safer, and more popular.

In part II of this series, we will review the methods for vape extract production and define the wide array of extract types.

https://casaa.org/education/vaping/historical-timeline-of-electronic-cigarettes/

J. Siklos-Whillans, A. Bacchus, and L.A. Manwell, 

https://doi.org/10.1007/s11469-020-00244-w

C. McDaniel, S.R. Mallampati, and A. Wise, “Metals in Cannabis Vaporizer Aerosols: Sources, Possible Mechanisms, and Exposure Profiles,” 

https://doi.org/10.1021/acs.chemrestox.1c00230

 is the founder, CEO, and Chief Extractor of Heylo. With a background in chemistry and clinical research, Lo was inspired to explore cannabis as a medicine and to enter the emerging industry. She joined Eden Labs, a leading CO

extraction equipment manufacturer to support and expand a Research and Development department. There she managed the development of their latest and greatest CO

 extraction system. In 2017, after working with Eden Labs and another cannabis processor, Lo launched Heylo with a mission to help people get more out of life with cannabis.

Extraction Science

In part one of this two-part series, we review the history of vape products and their obstacles.

What’s in a Vape, Part I

Gas chromatography (GC) resolution and analyses depend on the functionality of the chromatography phases. In the past columns, we looked at gases and the choices surrounding the gas phase. In this edition of “Navigating the Labyrinth,” we will seek to understand the functioning and chemistry of GC columns and how to change and manipulate the resolution equation and column chemistry to maximize our own analyses. We will take a deeper look into the chemistry, physics, and methodology of GC columns to see what changes can be made to increase resolution, efficiency, capacity, and change retention.

The first thing most analysts decide upon when developing a gas chromatography (GC) or gas chromatography–mass spectrometry (GC–MS) method is the chromatography column that will be used for analysis. There are two basic configurations for columns: packed or capillary columns (

). The earliest GC columns were packed columns composed of either glass or stainless-steel loops or coils between 1 m and more than 12 m in length with diameters in the mm range, which are filled with a stationary phase or packing material.

In the early days of GC, many analysts had to load or pack their columns with their selected solid phases. The packing or phase can be a solid, liquid, or mix of materials to facilitate chromatography. Packing materials are broken down into either coated or porous particles. Coated particles have an internal structural particle made of some type of inert compound or matrix such as diatomaceous earth and are coated with the active liquid stationary phase. Porous particles are materials like polymers or carbons (sieves, traps, and so on). Packed columns have shorter lengths than capillary columns and are very efficient at separating very volatile gases and other low-boiling compounds.

. The capillary column is composed of a very long tube of thin hollow silicate glass anywhere from 10–100 m long and diameters in the micron range. This small diameter and long length dramatically can increase pressure in a GC system, but produce more theoretical plates from the efficiency equations we looked at in previous columns where efficiency can be measured as a relationship between separation factor (α), column length (L), and particle size or film thickness (d

). So, more length or a thinner film equates to more theoretical plates.

The interior of the capillary column is coated with a stationary phase composed of either a solid or a liquid material. Capillary columns are able to achieve better separation, but can become overloaded by excess sample volumes. Several different physical configurations exist for capillary columns including some configurations that contain solid particle stationary phases instead of just liquid stationary phase.

The most common type of capillary column is the 

) columns. The WCOT column is usually composed of a silica tube coated with a liquid stationary phase. Most modern open tubular capillary columns are FSWC columns that are extremely thin-walled silica columns with open active site surfaces on the interior of the column where stationary phase not only coats the column but bonds to active, open sites.

Specialty open tube configurations such as the 

) are a blend of solid and liquid phases and supports, in some ways similar to both capillary and packed columns. The SCOT column has a solid framework or support upon which the liquid layer coats the support structures and the silica column. PLOT are a hybrid of an open tubular column and a packed column that contains a solid porous layer inside the column structure unlike packed columns which are completely filled or “packed” with a porous stationary phase (

There are two primary modes for chromatography: 

. Partition or gas-liquid (GLC) chromatography occurs in the transitioning of an analyte from the gas phase to liquid phase and back to gas phase along the column (that is, partitions). GLC is found in the capillary columns with a liquid stationary phase. Adsorption or gas-solid chromatography occurs (GSC) when targets in the gas phase are absorbed into a solid material stationary phase. GSC is found in both packed columns and in the PLOT columns. The materials of the solid support structures found in packed, PLOT, and SCOT columns can be made from a variety of inert materials like diatomaceous earth coated with a liquid stationary phase. Other stationary phase particles are created from porous materials such as carbon compounds and polymers.

For capillary columns, the most common stationary phase is composed of polysiloxanes with added phenyls and functional groups to the polarity and affinity of the column for a wide variety of compounds. The least polar stationary phases are polydimethyl siloxane (PDS). The most polar phase is composed of polyethylene glycols (PEG columns, carbowax or “wax” columns) (

Polarity increases with the number of phenyl groups or other functional groups used to create separation (Figure 3). The amount of these functional groups in some cases translates to the column name reflecting the percentage or composition of the siloxane groups. 

 lists the most commonly used capillary column phases and their naming convention, composition, and bonding characteristics. Most companies that produce columns use the same naming conventions in regard to common columns; with the first two or three letters being the company or brand with a dash followed by the composition. So, an RTX-5 is a Restek 5% DP, 95% PDS column and is equivalent in theory to another XX-5, like an Agilent StableBond SB-5.

Once a stationary phase or polymer is added to coat a column, a process of cross-linking may be used to stabilize the polymer over a wide range of temperature and reduce column bleeding. Manufacturers can also produce their own polymers and cross-linking agents, which can impact the column’s function. In all columns, there are potential active sites within the column material and open functional groups that are not deactivated fully even with crosslinking that could cause difference between different versions or brands of the same phase columns.

There are a number of factors that can affect resolution including: chemistries of solute, gas phase, and stationary phase plus a number of physical parameters such as flow rate, temperature, and column length, diameter, and film thickness.

If we think back to the resolution equation discussed in previous columns on chromatography, resolution is a product of retention, separation, and efficiency. Changing or influencing any of these parameters will change resolution (

One of the first changes a chromatographer can make to a system without changing the column is often temperature. Changes in temperature can influence the resolution equation by changing retention and selectivity. Increases in temperature change the amount of time the solute or target spends in the stationary phase, usually increasing retention times or by losing retention. Temperature increases can also influence or change the chemistry or physics of the interactions between the phases and thereby reduce selectivity. Another problem with raising temperature is that it will change flow rates of the system.

The next column variable to change is often the column length (L), which can then change resolution by altering the efficiency (N). While increasing length can change efficiency and resolution, large increases in length only fractionally change the resolution. Increasing a column length by four times only increases resolution about two times; but often comes with an exponential cost increase for that column (

A better way to increase retention is to decrease the column diameter (d) or alter both the film thickness and the diameter since they are interrelated. 

(df) is a measure of the amount of stationary phase that can interact with the target solutes. To understand this relationship, first we must look at the distribution constant (K

) which is the ratio of the concentration of the solute in the stationary phase versus the concentration of the solute in the mobile phase (

This distribution constant is also equal to the capacity factor (k) multiplied by the phase ratio (b), meaning it will affect the k retention variable. The true importance and influence of k occurs when the ratio between the phases is small (<5), increases to the film thickness will then increase resolution but, when k is greater than five, then resolution decreases as film thickness increases.

 is the relationship between the column inner diameter and the stationary phase film thickness, where the phase ratio is equal to the inner diameter divided by four times the film thickness (

The phase ratio can help narrow down the best choice of column ID and film thickness or can help change from one column dimension to another. Each phase ratio is best suited for particular classes of compounds. Very volatile compounds do best with a phase ratio less than 100, while most other compounds fall in a phase ratio between 100 and 400. The highest boiling or molecular weight compounds will do best at phase ratios greater than 400 (

Thicker films allow for more solute capacity on the column and decreases interaction with any open sites on the tubing, but thicker films increase column bleed and reduce the operating temperature for the column. Increasing film thickness can increase retention since peaks spend more time in the stationary phase, but they lose height and broaden. Increasing peak width and reducing peak height reduces efficiency as can be seen in the efficiency equations where large widths or shorter heights adversely affect efficiency (

A number of factors surrounding the GC column can influence your chromatographic resolution depending upon which component of the resolution equation is affected. Selectivity is mostly influenced by the type of stationary phase selected. The more substituted siloxanes of the phase are, the more polar the column, and the more polar the analytes it will detect. Selectivity can also be influenced by increases in temperature but often at a loss of other variables. Efficiency is most affected by column radius and film thickness, but can be increased with increasing column length, however, often at a monetary cost. Retention can be changed by manipulating the temperature of the system or changing the film thickness or column diameter. Decreases in column diameter can increase resolution but will also increase pressure and reduce sample sizes therefore reducing sensitivity. There is an old adage among chromatographers that you can want resolution, sensitivity, speed, and low cost but you cannot have them all at once. Often choosing one goal means sacrificing in another area. By understanding the function of each of the variables and how these variables can be manipulated in the chromatographic system, analysts can begin to make better choices to get the best response from their system.

https://www.cannabissciencetech.com/view/looking-with-light-breaking-down-liquid-chromatography-method-development

, 2nd ed., R.L. Grob, Ed. (Wiley: New York, New York, 1985).

W. Jennings, E. Mittlefehldt, and P.P. Stremple, 

, 2nd ed. (Academic Press: San Diego, California, 1997).

; The instant notes chemistry series; (BIOS: Oxford, 2002).

H.M. McNair, J.M. Miller, and N.H. Snow, 

, Third edition (Wiley: Hoboken, New Jersey, 2019).

Md. M. Rahman, A.m. Abd El-Aty, J.-H. Choi, H.-C. Shin, S.C. Shin, and J.-H. Shim, in 

 (John Wiley & Sons, Ltd, 2015; pp 823–834). 

https://doi.org/10.1002/9783527678129.assep024

Guide to GC Column Selection and Optimizing Separations, 

https://www.restek.com/en/technical-literature-library/articles/guide-to-GC-column-selection-and-optimizing-separations/

https://wwwqws.sigmaaldrich.com/US/en/technical-documents/technical-article/analytical-chemistry/gas-chromatography/column-selection

Introduction to GC - Introduction to GC - Chromedia, 

https://www.chromedia.org/chromedia?waxtrapp=xqegzCsHiemBpdmBlIEcCzB&subNav=tlpbfDsHiemBpdmBlIEcCzBsB (accessed 2022 -01 -11

 is a Senior Applications Scientist with Spex, an Antylia Scientific company and has been a member of many cannabis advisory committees and working groups for cannabis including NACRW, AOAC, and ASTM.

Navigating the Lab

Let’s try to understand the functioning and chemistry of GC columns and how to change and manipulate the resolution equation and column chemistry to maximize our own analyses.

Looking with Light: Understanding Gas Chromatography, Part III: Columns and Resolution

This article series explores some of the more technical aspects of cannabis cultivation that growers should understand to run their businesses more efficiently and more profitably. In this final article, we utilize concepts introduced throughout the series to address the pest problems created in commercial cannabis cultivation facilities when environmental control systems are improperly designed or implemented.

Too much moisture in the air, on plant leaves and buds, or around the roots is the most common culprit for the development of pathogenic infection of cannabis plants. Concurrent fluctuations in temperature can be detrimental to plant vitality as infectious organisms infiltrate deeper into plant tissues during those windows of time when optimal conditions are lost. 

 (root rot), and many more pathogens do not need optimal conditions to infect. They can lie dormant inside the plant (

), slowly growing their way into or across the plant until the perfect moment when conditions fall outside of a safe range for the plant.

Temperature, Relative Humidity, and Pathogens

When environmental control is lost, even if only for short periods of time, diseases can quickly grow deeper into the plant’s tissues. Cannabis has an optimum temperature range for highly productive growth and so do pathogens. The peak of productivity for both pathogens of cannabis and the plant itself overlap quite a bit. Typically, if the preferred temperature range for the plant is maintained, the pathogen is unable to grow at a rate that can keep up with the plant’s development and so its influence is never seen, even though the infection persists. However, if for a short period of time the temperature shifts out of the optimum range for the plant, but still lies in the optimum range for the pathogen, there will be a rapid growth response by the pathogen and symptoms may become visible as plant growth slows. This effect is often seen with fungal diseases such as

 as one day the plant looks healthy and vigorous and the next it is chlorotic with water-soaked and mushy tissue.

Damage from temperature swings is not limited to direct impacts on plant tissues and stress can occur even if humidity is in a sufficient range. Only certain organisms such as powdery mildew and 

 are directly dependent on the room air conditions, as opposed to water-borne diseases like 

 which would thrive in high humidity indirectly as water movement in the rootzone is suppressed by a high-humidity induced low vapor-pressure deficit (VPD).

Excessive moisture in the air (high humidity), even if only for moments at a time, greatly encourages the growth of diseases such as powdery mildew and bud rot. It is not enough to simply monitor your room humidity sensors that control your conditioning equipment, you must identify the microclimates within your cultivation facility. If the sensor for humidity is only a panel mounted on the wall, there could be a plethora of environmental conditions happening in the room. Perhaps your humidity sensor reads right at your setpoint most of the day, but if this is showing an average over a longer period of time it may not be informing you of the fluctuations in room air conditions. It could be that your sensor shows an average over a 10-minute period and during that time the humidity swings are ±10%, which could enter the pathogen favoring zone quite frequently. It’s not just about knowing what value is the optimum, you must ensure that you are providing those conditions uniformly and consistently.

The most sophisticated (and legal) pest management products will be unable to stop the proliferation of plant pathogens if the environmental conditions cannot be kept within an acceptable range. Exposure to the pathogen is extremely difficult to avoid and even harder to maintain for extended periods of operation, especially without fully clearing material from a grow room in between each production cycle.

Although air filtration and sterilization systems can greatly reduce the threat of pathogen propagation by eliminating airborne spores or organisms, the vitality of plants must be protected and favorable conditions for those pathogens must be eliminated by ensuring excess moisture is kept at bay and that excessive temperature swings are avoided.

Heating, ventilation, air conditioning, and dehumidification (HVACD) systems have advanced quickly as the needs of the commercial cannabis industry have evolved to support a much larger market. Legacy producers have primarily maintained environmental conditions using multiple pieces of equipment (that is, oscillating fans, standalone dehumidifiers, air conditioners, and heaters) to address individual environmental conditions. The upside to this approach is the ease of accessing retail equipment that can be added in a series to meet the changing needs of production and to provide redundancy in the case of equipment failure. The downside to this method is the variability of environmental conditions within a grow room is greatly increased as the plants are essentially located in an air mixing chamber. Pockets of high humidity form where the air is not mixed as frequently. This is most likely to happen in corners or near a source of moisture such as the grow tray, substrate, or leaves where water is evaporating continuously.

Very quickly, white fuzz can form in high humidity conditions as 

 colonize juicy leaves. Think of a newly sprouted seed—if it emerges and then conditions become dry, it is likely to die. If humid conditions remain, the roots have more time to establish a water column in the vascular tissue as the leaves acclimate to the air conditions. If it stays too wet, the root will likely rot as it is suffocated by oxygen-deficient water, leaving an opening for a pathogen to attack. You may have noticed some seedlings turn to white or gray mush when left in a tray that is too wet.

Some producers will keep humidity levels very low to avoid any chance of pathogens growing, but leaves need a certain amount of moisture in the air as well to remain healthy and this will change depending on the air temperature, light source, and maturity of the plant. If conditions are too dry while the lights are on, photosynthesis can be inhibited for several reasons. If they are too dry while the lights are off, xylem-based nutrient movement into the newly developing tissues can be inhibited, specifically calcium movement into the new growth is inhibited. Cell wall development requires a constant supply of calcium to form rigid structures that effectively prevent intrusion by pathogens. Calcium primarily enters plants through meristematic tissues (the foremost tip of a root or shoot) as the cell wall is still forming at this location exposing the vascular tissue where calcium can enter the plant and be transported into developing tissues through the unidirectional water stream called the xylem. If VPD is very high, calcium is likely to be shuttled into the tissues where transpiration is the highest, which is likely to be the large mature leaves with the most developed stomata. This shuttling of calcium away from newly developing tissues encourages poor cell wall development, leaving plants weak and susceptible to attack.

Ultimately, plant vitality will be strongest when plants are able to thrive without constantly adapting to shifting conditions. In nature, a plant must deal with an array of stressful circumstances, and it is loaded with mechanisms to ward off threats and protect itself from a shifting environment. However, these adaptations cost metabolic energy and will reduce plant productivity, yield, and end-product quality.

Many of these points are often overlooked as producers seek out short-term solutions to chronic issues caused by poor HVACD design and, subsequently, environmental control. Rather than pursue topical products to suppress pest issues, investigate what aspects of your environmental control systems might be providing an optimum habitat for pests to thrive rather than plants. Identify the microclimates and make attempts to de-stratify these pockets and you will see great improvements in the overall health of your facility.

https://www.cannabissciencetech.com/view/why-does-leaf-temperature-matter-in-a-commercial-grow-room

https://www.cannabissciencetech.com/view/a-deep-dive-into-vapor-pressure-deficit-for-commercial-cannabis-cultivation

https://www.cannabissciencetech.com/view/does-light-spectrum-alter-plant-transpiration-rates

https://www.cannabissciencetech.com/view/providing-sufficient-airflow-for-plant-growth-environments

https://www.cannabissciencetech.com/view/how-does-carbon-dioxide-enrichment-affect-environmental-control

 pursuing his PhD in cannabis cultivation. He is a solution-oriented, big picture researcher focused on finding the balance of production variables to optimize plant growth and facility operations without sacrificing quality. Sam holds a BSA and MS in horticulture and currently works as a crop science consultant. Direct correspondence to: 

Feature

How can we address the pest problems created in commercial cannabis cultivation facilities when environmental control systems are improperly designed or implemented?

How Poor Environmental Control Creates Pest Pressure

In honor of International Women’s Day and Women’s History Month, we’re featuring the amazingly talented female experts that will be presenting at our upcoming 2022 Cannabis Science Conference West May 18-20 in Long Beach, California. All these phenomenal women have played a part in the evolution of cannabis science and medicine and worked to end the stigma associated with cannabis. It is an honor to have the opportunity to work with such amazing presenters year after year. We are proud to play a part in lifting the voices of women and minorities in science, technology, engineering, and mathematics (STEM), cannabis, and psychedelics. I hope you enjoy reading about this wonderful group of individuals! 

peakers listed alphabetically by last name

Patricia Atkins, Senior Applications Scientist, Spex, an Antylia Scientific Company
Talk title

: Cannabis, Chemistry and Chromatography:Examining the Challenges of Cannabis Sample Processing, Analysis, and the Role of Reference Materials


: Patricia Atkins has been a Senior Applications Scientist at Spex for more than 13 years.She is a graduate of Rutgers University in NJ and was laboratory supervisor for Ciba Specialty Chemicals. Patricia conducted research and managed an air pollution research group within Rutgers University.

Moriah Barnhart, Executive Director & Co-Founder, Wise FL & CannaMoms
PANEL

: Moriah Barnhart’s introduction to cannabis as medicine came in 2013 when her daughter was diagnosed with aggressive brain cancer at the age of two. She has since cofounded two first-of-their kind federally approved non-profits, co-authorized Florida’s first CME approved program on cannabis for physicians, and currently sits on the State of Florida Department of Agriculture Hemp Advisory Committee.

Laura Barrett-Nutting, MBA, BSN, RN, Clinical Director, Nurse Laura
PANEL

: Expansion of the Clinical Directors Consortium


: Laura Barrett-Nutting, MBA, BSN, RN, is a plant-based and integrative medicine nurse who brings more than 20 years of experience helping patients cope with critical illness and chronic disease. Her enthusiasm for wellness and food as medicine led her to explore the multiple medical cannabinoid options available.

Gabriele Bertelli, Regional Sales Manager, Microfluidics International Corporation
Talk title

: Solubilizing Cannabis Ingredients for Improved Bio-Availability Through Nano-Emulsification Technology


 Gabi has more than 20 years of experience with the Microfluidizer® technology and it's applications across multiple industries. This knowledge enables her to better understand customers' needs and requirement and thus select best solutions which allow customers to successfully develop and manufacture their desired products.

AC Braddock, CEO, Eden Labs, LLC
Talk title

: AC Braddock is the visionary CEO of Eden Labs, an internationally recognized, 26-year-old botanical extraction technology company.AC is well known for her leadership in modern business practices, early recognition of growth sectors in scientifically-based health and wellness advancements and technically and ethically supporting market creation for sustainable, long-term success of the industry.

Lisa Buchanan, RN, Speakers Bureau Member, Cannabis Nurses Network
PANEL: 

Nurses Network: A Revolution in Healthcare


: Lisa Buchanan is a registered nurse and patient advocate who has cared for patients in Washington state for more than 25 years. Her specialty is oncology (cancer) care, and she has been an oncology certified nurse since 2013.

Marcie Cooper, RN, MSN, AHN-BC, Speakers Bureau Member, Cannabis Nurses Network
PANEL

: Nurses Network: A Revolution in Healthcare


 A Nurses Role in Spirit Medicine: Nurturing the Psychedelic Renaissance


 Marcie Cooper first became interested in cannabis medicine as she saw an increase in patients using cannabis and knew she needed a better understanding. The knowledge gained was so profound, she found herself emerged in the science of cannabis.

Nekeidra Cromwell, CEO, KeidyWeedy
Talk title

: Nekeidra is CEO of KeidyWeedy and the director of Community Outreach for the The National Cannabis Party. Cannabis saved her life after brain surgery. Nekeidra helps to decrease the stigma and increase the awareness on the benefits of medicinal cannabis. She assists the community on the education and resources that are available.

Heather Despres, PFC Program Coordinator, Americans for Safe Access
Talk title

: Analysis of State Cannabis Regulations


: Heather Despres is Director of PFC at Americans for Safe Access, a non-profit whose mission is to ensure safe, legal access to cannabis for therapeutic use and research, the first and only ISO 17065 accredited cannabis compliance program in the US.

Dr. Alison Draisin, PsyD, LMHC,Director of KAP Provider Training, Aims Institute
KEYNOTE

: Exploration of Protocols and Competencies in Cannabis and Psychedelic Assisted Psychotherapies


: Dr. Alison Draisin is the founder and CEO of Ettalew’s Edibles (established in 2009), past President of the Board of Directors for the Center for Cannabis and Social Policy (CASP), and an original member of Women of Weed. As an active member of the Washington state cannabis community, she speaks publicly on cannabis education locally and nationally. Alison seeks to support women by connecting them to cannabis community and to empower women to rise within the cannabis industry.

Tess Eidem, PhD, Director of Science, Willow Industries
Talk title

: From Microbes to Testing: Understanding and Preventing Contamination


: Tess earned her PhD in pathology and microbiology from the University of Nebraska Medical Center and University of Rochester. She strives to improve scientific standards within the industry by applying previously unused microbiological methods to production. Tess works with Willow’s partners to address source contamination with quality assurance programs.

Renee Engle-Goodner, MS, Principal Consultant, REG Science, LLC
Talk title

: Post-Harvest Loss Mitigation: Aspergillus Across the Supply Chain


: Renee worked in postharvest discovery science, focusing on volatile antimicrobial treatments of crops to increase shelf-life. As an analytical lab manager, she worked in the wine industry, ensuring quality from grape to wine. These experiences blend ideally for the cannabis industry where she works as a consultant.

Dr. Bonni Goldstein, Medical Director, Canna-Centers Wellness & Education
Talk title

: Cannabis and Children: A Pediatrician's Experience


: Bonni Goldstein, MD is the Medical Director of Canna-Centers Wellness & Education, a California-based medical practice devoted to educating patients about the use of cannabis for serious and chronic medical conditions.She has a special interest in treating children with intractable epilepsy, autism, cancer and other conditions.

Rhea Graham, Medicine Woman, Albany's Canna Kitchen & Research, LLC
Talk title: 

: Rhea and her daughter opened Albany's Canna Kitchen & Research on 11/11/11.Her ACKR Clinic provides doctors for cannabis card certifications. Currently, she has taken on the role as caregiver to over 100 OMMP patients and plans to open her Healing-Life Center in 2022. Smokeless cannabis remedies for the win!

Kaylene Gray, NP, Clinical Director, Grow West
PANEL

: Kaylene Gray, PMHNP-BC has spent more than 16 years working with patients in the hospital setting.Her experiences include ER, PACU, ICU, and nursing administration. Now going into her fourth year as a cannabis nurse, Kaylene is a Clinical Director and General Manager of a medical dispensary in Maryland.

Dr. Jacklyn Green, CEO, Agate Biosciences, LLC
Talk title

Dr. Jacklyn R. Green is the CEO of Agate Biosciences LLC, a science, research, and management innovation consultancy. She focuses on project management, systems engineering, and sustainability research in the cannabis business arena. She provides individualized problem-solving and help to companies in need of answers.

In honor of International Women’s Day and Women’s History Month, we’re highlighting the talented female experts that will be presenting at the upcoming 2022 Cannabis Science Conference West on May 18-20 in Long Beach, California. 

April 2022

Beer’s Law, Part II: Physical Basis and Derivation

What’s in a Vape, Part I

Looking with Light: Understanding Gas Chromatography, Part III: Columns and Resolution

How Poor Environmental Control Creates Pest Pressure

Cannabis Science Conference Honors the Wisdom of Women

Why All Legalized U.S. Jurisdictions Should (and Probably Will) Adopt the International Intoxicating Cannabis Product Symbol (IICPS)