In previous columns we established the importance of F

, the fraction of time an analyte spends on the stationary phase, in determining elution time. We can now move on and use the elution times in a separation to establish its quality. We will use the capacity factor of chromatographic peaks as discussed last time (1) to calculate separation factors, whose value tells us how well two peaks are or aren’t separated.

In my last column (1), we discussed how the capacity factor is used to normalize the peak positions in a chromatogram. For example, separations performed at different flow rates will have different elution times, but by calculating the capacity factors for the peaks in these chromatographs we can take the different flow rates into account and compare peak positions in different chromatograms to each other. To review, the capacity factor for a chromatographic peak is given by 

To see the impact of the capacity factor please look at 

Recall (1) that Figure 1 shows the retention times for two peaks we assumed were ethanol and tetrahydrocannabinol (THC). The problem here is that if the conditions of a separation are changed, such as the flow rate, the retention time will change. Figure 2 shows the chromatogram of Figure 1 with the peaks labeled with their capacity factors as calculated from Equation 1. Again, the k’s for these peaks should be the same even if variables like flow rate affected retention time.

 shows a chromatogram with three peaks labeled with their capacity factors.

We will assume the first peak with a capacity factor of zero is unretained ethanol molecules, the peak with k = 1 is THC, and for the sake of argument let’s assume the peak with k = 3 is from cannabidiol (CBD).

-axis unit that describes peak position in a similar fashion to retention time. Our goal in chromatography is to obtain a separation for all peaks that are baseline separated; that is, there is a region of flat baseline between all peaks. All the peaks in Figure 3 are baseline separated. Since k is a measure of peak position, the capacity factors of different peaks can tell us something about how well they are separated. For example, two peaks with k’s of 2 and 2.1 may overlap and not be baseline separated, whereas peaks with capacity factors of 1 and 3 are clearly baseline separated as seen in Figure 3. This means that the relative value of the capacity factors of two peaks tells us something about how far apart they are on the 

-axis and can give us a measure of separation quality. This quantity is called the 

As with all things chromatography, I refer you to publications (2,3) and references therein for a more detailed discussion of what is presented here.

The separation factor for a pair of chromatographic peaks is given by 

The restriction in Equation 2 is that the retention time of peak b must be greater than that of peak a is so that the separation factor is a number >=1.

Note in Equation 2 that the numerator, (t

), is the retention time for analyte b minus the void time t

, the time spent in the column by an unabsorbed molecule. Thus, (t

) measures the amount of time analyte b spends immobile and adsorbed to the stationary phase. Similarly, (t

) is a measure of how long analyte a spends immobile and adsorbed to the stationary phase. The separation factor then depends upon the ratio of the time two analytes spend adsorbed on the stationary phase. The greater the difference in these times, the further apart these analyte peaks will be and the better their separation will be. This is consistent with what we have said in the past about the importance of F

, the fraction of time an analyte spends on the stationary phase, in determining elution times and separation quality.

Using Equation 1 we can write the capacity factors for peaks a and b as such for 

 is the capacity factor for analyte b, and all other terms have been previously defined.

If we take Equations 3 and 4 and divide them into each other and rearrange, we find 

Note that the right-hand sides of Equations of 2 and 5 are the same, thus:

In other words, the separation factor depends upon the capacity factors for any pair of chromatographic peaks, in this case peaks a and b. Thus, the separation factor and hence the quality of the separation of two peaks can be calculated from knowledge of their capacity factors.

The purpose of this section will be to illustrate what the separation factor is for different qualities of separation. The worst possible scenario for a separation, of course, is when two analytes elute at the same time, otherwise known as 

. Substituting this into Equation 2 we find that in 

Note that the denominator and numerator are the same in Equation 7, so two co-eluted peaks have a separation factor of 1.

For a more realistic example, let’s imagine that two peaks both elute at 4 min, and that t

 is 2 min. The separation factor in this case is seen in 

In this case both the numerator and denominator are 2, and 2/2 equals 1. So, the worst possible separation factor a pair of peaks can have is 1, which is a lousy separation and something to be avoided.

What is the separation factor for the first two peaks in 

Using equation 6 we find that this is found in 

OOPS! We are trying to divide by zero here, which is an undefined mathematical operation. A sure way to crash most any computer is to tell it to divide by zero, and yes, I speak from personal experience here. What Equation 9 shows us is that we should not use void time peaks to calculate separation factors, only peaks with nonzero values of k will work.

What is the separation factor for peaks a and b in Figure 3? Again, using Equation 6 we find that in 

Note that these two peaks are far apart, are baseline separated, and have a separation factor of 3. What we know so far then is that a pair of peaks with α = 1 are poorly separated and a pair of peaks with α = 3 are well separated. Thus, the separation factor is a measure of the quality of the separation between
two peaks.

So far in our calculations of separation quality we have only used elution time, that is the value at the top of a chromatographic peak. However, chromatographic peaks clearly have widths in addition to heights as is clearly seen in Figures 1–3, and our equations so far have ignored this fact. This can be trouble in the case, for example, of the chromatogram seen in 

Using Equation 2 we find that the separation factor for peaks a and b, ignoring peak widths, as seen in 

Note that the chromatograms in Figures 3 and 4 both have the same separation factor of 3, but in Figure 3 the two peaks are baseline separated, whereas in Figure 4 the two peaks are clearly overlapped. This means that because the separation factor ignores peak widths in some cases it has limits in terms of how well it tells us the quality of a separation. We will see in the next column how to take account of peak widths to get around this problem.

We reviewed capacity factors and established that they are a measure of elution time. Then, we defined the separation factor and found that it depends upon the fraction time, F

, two analytes spend in the stationary phase. We also established that the separation factor is a function of the ratio of the capacity factors for a pair of chromatographic peaks, establishing that capacity factors can be used to determine separation quality. We found that for co-eluting peaks α = 1 whereas for a pair of well separated peaks α = 3. Lastly, we saw how that by ignoring peak width the separation factor has limitations and sometimes gives misleading information on the quality of a separation.

Smith, B., Chromatography Theory, Part III: Calculating Elution Times and Capacity Factors, 

Skoog, D.A.; West, D.M.; and Holler, E.J., Analytical Chemistry: An Introduction, Saunders College Publishing, 1994, 

Robinson, J.W., Undergraduate Instrumental Analysis, Marcel Dekker, 1995, 

, 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: 

Smith, B., Chromatographic Theory, Part IV: Measuring Separation Quality with Capacity and Separation Factors, 

Articles

Cannabis Analysis 

Part IV of this series discusses the capacity factor of chromatographic peaks to calculate separation factors, whose value tells us how well two peaks are or aren’t separated. We then introduce the reality of peak widths and how they impact separation quality.

Chromatographic Theory, Part IV:  Measuring Separation Quality with Capacity and Separation Factors

Most consumers are seeking tetrahydrocannabinol (THC) for its intoxicating effects. However, as medical research expands within the cannabis sector, manufacturers and consumers are finding value in the acidic forms of cannabinoids. It is only possible to experience acidic cannabinoids through ingestible or topical methods of administration because heat will convert the acidic cannabinoid into the neutral form. In this article, we explore how cannabis extraction technology can preserve the acidic cannabinoids in the process.

In the raw form of cannabis, the cannabis plant mainly produces acidic forms of cannabinoids. Cannabigerolic acid (CBGA) is the precursor to most of the cannabinoids produced by the cannabis plant (1). Tetrahydrocannabinolic acid (THCA) is another common and naturally abundant cannabinoid found in the cannabis plant. When cannabis is heated, acidic cannabinoids such as THCA undergo decarboxylation. For example, THCA converts to tetrahydrocannabinol (THC), the psychoactive compound that produces the well-known cannabis “high.” THCA, however, is non-psychoactive. There is limited research on the physiological differences between consuming acidic versus decarboxylated cannabinoids. However, there is growing evidence that acidic cannabinoids like THCA or cannabidiolic acid (CBDA) have unique medical benefits and bioavailability.

Smoking is the most common method of administration in cannabis, but acidic cannabinoids cannot be consumed by smoking due to triggering decarboxylation. Instead, the acidic cannabinoids can be extracted and infused in edibles, topicals, and can even be vaped at lower temperatures. With a variety of consumption methods, acidic cannabinoids are growing in availability and popularity. This is especially true of THCA, which shows promising medical benefits (1,2). Some potential medical benefits of THCA include:

: THCA has been shown to have anti-inflammatory properties, which could be beneficial for people with conditions such as arthritis, inflammatory bowel disease (IBD), and multiple sclerosis (MS).

: THCA has been shown to have anti-nausea properties, which could be helpful for people undergoing chemotherapy or experiencing nausea and vomiting from other causes.

: THCA has been shown to have neuroprotective properties, which means it may help protect the brain from damage or degeneration. This could be beneficial for people with conditions such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis.

: THCA has been shown to have anti-spasmodic properties, which means it may help reduce muscle spasms and cramps. This could be beneficial for people with conditions such as multiple sclerosis, spinal cord injuries, and cerebral palsy.

: THCA has been shown to have appetite-stimulating properties, which could be helpful for people with conditions that cause a loss of appetite, such as cancer or HIV and AIDS.

It’s important to note that more research is needed to fully understand the potential medical benefits of THCA and how it can be used to treat specific conditions. Until that research is available, consumers and medical patients are relying on manufacturers and leading cannabis scientists to offer insights into what products may support them on their cannabis journey.

Manufacturers are utilizing extraction technology to extract and purify THCA for the purpose of producing cannabis products for the medical market or for the novelty concentrate market. The novelty cannabis concentrate market has contributed to the growing popularity of THCA as products like “diamonds and sauce” take up market share. These products give consumers an opportunity to vaporize THCA before it converts to THC, however, most consumers are heating these extracts to temperatures at which point decarboxylation does occur. Other acidic cannabinoids do not seem to be of particular interest to recreational users.

How to Selectively Extract Acidic Cannabinoids?

 shows the differences between cannabinoids as well as acidic and neutral forms. Each of these compounds varies in molecular weight, polarity, size, and so on. Because of these differences, these compounds have different solubility and behavior during extraction. Most of the common solvents are non-polar. Carbon dioxide or hydrocarbons, for example, are non-polar solvents. Cannabinoids are also relatively non-polar, so polarity is not a lever that can be pulled to selectively extract acidic cannabinoids. Instead, manufacturers can start with plant material that is rich in THCA. The plant’s trichomes are most full of acidic cannabinoids late in the flowering stage and at peak harvest. If the plant is not dried or cured in the ideal conditions for preservation of the chemical profile, then degradation can occur of both the cannabinoids and terpenes. Some cultivators and extract manufacturers skip the drying and curing phase by freezing the cannabis flowers immediately upon harvest. In doing so, the acidic cannabinoids are preserved and undisturbed.

Acidic cannabinoids, especially from freshly frozen or freshly harvested cannabis flower, can be extracted from the plant using CO2, hydrocarbon, or ethanol. They can also be extracted using physical separation techniques such as the hash making process. In any of these processes, extraction technicians rely on optimal extraction parameters for these cannabinoids while minimizing the exposure of the extract to heat. Once extracted, the cannabinoids can be further purified using winterization or another filtration technique to remove any waxes and other undesirable fractions from the solution. Last, crystallization is encouraged by either gently heating or cooling the refined extract to initiate nucleation of the acidic cannabinoid crystals. Heating or cooling is based on the type of solvent that was used to extract the cannabinoids. Multiple nucleation and filtration steps can be used to increase the purity of the acidic cannabinoid fractions. Alternatively, chromatography can be used to separate the cannabinoids and other compounds from the extract mix. However, chromatography is much more expensive and more challenging to scale.

Products dominant in acidic cannabinoids may never achieve the same market share as the active compounds, like THC. However, consumer preferences and needs are becoming more diverse as cannabis becomes more accessible throughout the country. Acidic cannabinoids will continue to attract consumers seeking medical benefits or new experiences. As extraction technology develops, selectivity will improve, and unique chemistry will continue to find its way into the marketplace. Acidic cannabinoids are ripe for the picking.

Pellati, F.; Borgonetti,V.; Brighenti, V., Biagi, M.; Benvenuti, S.; Corsi, L.; 

L. and Nonpsychoactive Cannabinoids: Their Chemistry and Role against Oxidative Stress, Inflammation, and Cancer, 

, doi: 10.1155/2018/1691428. PMID: 30627539; PMCID: PMC6304621.

Ben-Cnaan, E.; Permyakova, A.; Azar, S.; Hirsch, S.; Baraghithy, S.; Hinden, L.; Tam, J.; The Metabolic Efficacy of a Cannabidiolic Acid (CBDA) Derivative in Treating Diet- and Genetic-Induced Obesity, 

, 23 (10). doi: 10.3390/ijms23105610. PMID: 35628417; PMCID: PMC9144717.

 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.

Friesen, L., Extraction of Acidic Cannabinoids, 

Extraction Science

In this article, we explore how cannabis extraction technology can preserve the acidic cannabinoids in the process.

Extraction of Acidic Cannabinoids

Retrocommissioning (RCx) can unlock your building’s energy potential by optimizing performance of environmental control systems. Achieve energy savings of 10-20% while reducing operational expenses with low- to no-cost improvements that may be incentivized by energy efficiency utilities. This column summarizes how cannabis facilities that invest in RCx projects can enhance equipment reliability and worker safety, improve conditions for plant growth and development, increase canopy yields, and reduce maintenance costs.

As stated above, retrocommissioning (RCx) can unlock your building’s energy potential by optimizing performance of environmental control systems. Achieve energy savings of up to 25% while reducing operational expenses with low- to no-cost improvements that may be incentivized by state and utility energy efficiency programs. Here, we summarize how cannabis facilities that invest in RCx projects can enhance equipment reliability and worker safety, improve conditions for plant growth and development, increase canopy yields, and reduce maintenance costs.

The value of a tune-up is apparent to anyone who has used a car. If driven without regular maintenance, components will wear and tear, filters will get clogged, fluids will run out, and wheels will get out of alignment. The check engine light will come on but may get ignored. Fuel mileage will decrease, mechanical issues will arise, and eventually the engine will not start. No one treats their car this way if they expect to go very far. Getting a regular tune-up is a practice to ensure long equipment life, a comfortable ride, and efficient operation.

Smart cannabis businesses tune up their cultivation and production systems for the same reasons. Tuning building systems can involve leveraging data from controls and automation systems to identify problems and optimize operations at low or no cost. When a building is constructed or renovated, a verification process called 

 (1) is performed to test equipment and check that the building is performing as designed. After commissioning, the building should be running to meeting the needs of the business for years to come. However, over time buildings functions can change, spaces may get redesigned, setpoints might shift, sensors get out of calibration, and equipment ages and performance degrades. This is where RCx is performed to re-examine equipment, recalibrate components to ensure proper operation, functionality, and maintenance of systems, and recommend component repair or replacement. Cannabis production facilities that implement tuning and retrocommissioning processes in their buildings can achieve both energy and non-energy benefits.

 describes the kinds of energy system deficiencies that can be uncovered from RCx studies. Energy benefits can include reduced energy use and lower energy costs. Non-energy benefits include improved operations and maintenance, safer conditions for staff, lower risk of equipment failure, and optimized environments for people, plants, and products.

Tuning and RCx will provide the best return on investment for businesses with multiple facilities like multi-state operators (MSOs), operators of larger buildings, buildings with high energy use, and buildings with higher utility costs. Tuning is especially important for operations that have been up and running for several years in buildings that have not been commissioned before or have not been evaluated in some time.

Control systems are in good working condition

Hardware includes digital controllers, actuators, and thermostats

Systems have been updated within the last 5-8 years

Automation system controls major air handling units and central plant equipment, such as chillers and boilers

Trend data for multiple harvests is available for analysis

If a building is older and systems have not been updated, it may prove challenging to leverage data from controls systems. In these cases, RCx engineers can use utility data, design drawings, equipment schedules, control sequences, history of occupant complaints, and conversations with maintenance staff to evaluate the performance of components and identify efficiency projects while also recommending repairs, replacements, and upgrades. Retrocommissioning can involve more capital investments, but after improving functionality and availability of data, low-cost tuning measures become much easier.

There are four main types of tuning measures applicable to any kind of building that when applied together, can result in annual energy savings of 5–25%:

Data collected by the Pacific Northwest National Laboratory (2) at federal General Services Administration (GSA) facilities from 2011–2021 showed total combined savings of 13.4% at more than 80 facilities. 

 shows estimated allocations of the savings from the four principle tuning categories.

Cannabis businesses can apply the four tuning principles in the following ways.

The start of any tuning journey is shutting things down more often. Turn systems off when not needed by scheduling equipment, programming horticultural lighting controls, and tweaking start and stop times for heating, ventilation, and air conditioning (HVAC) equipment based on occupancy schedules.

Turn systems down by adjusting setpoints for lighting and HVAC systems. Dimming horticultural lighting systems or increasing target grow room temperature reduces cooling load. Save energy with reset schedules for water temperature, fan static pressure, and pump differential pressure so motors modulate instead of running at constant speed.

Avoid simultaneous heating and cooling by limiting standalone dehumidification systems rejecting heat back into grow rooms, which cause cooling systems to kick on at the same time. Review sequences of operation to understand how HVAC systems work together to achieve target environmental conditions and minimize fighting, which wastes energy. Common RCx measures include supply air temperature reset and widening deadbands (the range of acceptable temperatures and relative humidity percent) so HVAC equipment runs less often.

Most cannabis facilities already limit the introduction of outdoor air, but this is the last place to look when tuning and retrocommissioning buildings. If operating in a leaky building, outdoor air enters the building via infiltration. Conditioning outdoor air requires energy. Some HVAC systems bring fresh air into the building for human-occupied spaces. Understand how HVAC systems move air through the building and exchange heat with production spaces. Tuning activities can include building pressure control, demand-controlled ventilation, exhaust fan control, and modifications to outside air damper operation.

Retrocommissioning cannabis facilities is crucial to keep mission-critical cannabis production systems performing efficiently and effectively. Work with engineers to perform tuning activities and identify energy-saving measures. Because RCx studies can uncover so many efficiency projects, some state and utility energy efficiency programs offer financial support or technical assistance. In some regions, businesses can have experts offer guidance while utilities cover 50% of the cost of the investigation and offer cost-sharing based on energy savings for implementation. States with legal commercial cannabis markets such as 

 (5) have programs for agricultural customers that can support tuning measures. Energy engineers can be trustworthy mechanics that help businesses navigate the landscape of government and utility programs by facility location, schedule regular tune-ups, and keep producers on the road and running efficiently. For those who need a tuning guide, 

reach out to experts at Energy Resources Integration, LLC (ERI

) (6) for a retrocommissioning study or other energy-related services.

Schimelpfenig, G. A Shipbuilding Concept That Can Save You Money 

https://www.cannabisbusinesstimes.com/article/commissioning-cannabis-cultivation-equipment-facility-design/

https://www.pnnl.gov/projects/best-practices/re-tuning-buildings#Retrocommissioning

Cannabis Resource Optimization Program (CROP) 

https://energyoffice.colorado.gov/clean-energy-programs/cannabis-resource-optimization-program-crop

https://www.masssave.com/en/business/programs-and-services/custom-incentives-and-technical-support/custom-incentives

ERI Offers A Suite of Energy-related Services to Cannabis Cultivators 

 is a Senior Energy Engineer at Energy Resources Integration, LLC where she implements energy efficiency programs and provides direct consulting services. She is the former Technical Director of the Resource Innovation Institute and manager of the organization’s Technical Advisory Council. She authored RII’s Lighting, HVAC, and Facility Design & Construction Best Practices Guides for Controlled Environment Agriculture and the Lighting, HVAC, and Controls Best Practices Guides for Cannabis Cultivation. She has worked with partners like the University of Vermont to optimize commercial and industrial buildings, including greenhouses and controls systems used for academic research on hemp and other cultivars. She has a B.S. in Architectural Engineering from the University of Wyoming and an M.S. in Civil Engineering from Stanford University. She is a licensed Civil Professional Engineer in California and Vermont.

The Cultivation Classroom

This column expresses how cannabis facilities that invest in RCx projects can enhance equipment reliability and worker safety, improve conditions for plant growth and development, increase canopy yields, and reduce maintenance costs.

Retrocommissioning Pays Dividends

In this issue, we will finish our discussion of energy and elements used in atomic spectroscopy by examining an important analytical technique: inductively coupled plasma-mass spectroscopy (ICP-MS). ICP-MS is an often-crucial technique in the detection of very low levels of potentially toxic elements. To use this technique to its fullest potential, it is important to understand its structure, operation, and functionality in order to optimize the analysis of toxic and trace elements that are important to the cannabis industry.

Analytical science has developed over the centuries as a method to identify and quantitate target compounds, elements, and organisms that impact life in both positive and negative fashions. Many analytical techniques have been streamlined and refined to respond to increasing smaller quantities of these targets as we discover the minute amounts that can be a detriment to life and health. One of the most powerful tools in the inorganic or elemental analysis arsenals is inductively coupled plasma-mass spectrometry (ICP-MS).

Mass spectrometry in its many forms continues to be the driving force of research and trace analysis for many components and elements due to its increasing sensitivity and accuracy. While other elemental techniques can be more selective or sometimes easier to use; ICP-MS continues to grow as the standard for minute trace level analytical instrument for a wide variety of disciplines and markets including cannabis.

The basis for an ICP-MS starts with similar interfaces we have discussed before with other elemental techniques such as ICP-OES with sampling, nebulization, and ionization by the plasma torch. The difference comes when the sample passes into the sample introduction area of the mass spectrometer where the sample is subjected to increasing vacuum pulled by first a rotary vacuum pump and then a turbo-molecular vacuum pump before introduction to the MS optics and hardware (see 

The pressure of the initial sample introduction and ionization starts at atmospheric pressure (760 Torr) and is decreased first to about 5 Torr (interface vacuum) by a rotary vacuum pump as it passes through the first sample introduction lens called a sampling cone that is usually composed of nickel and copper. This area is often referred to as the first vacuum stage. The second optic the sample reaches is the beginning of the high vacuum area or second stage (~1 x 10

 Torr) generated by a turbo pump. The skimmer is a nickel cone sometimes coated or tipped in platinum which directs the ion flow to the quadrupole. The platinum tipped cones are most commonly used in applications with high organic content or use highly corrosive acids such as HF which can damage the cone or contribute to interference.

In some instruments there may be some optics or mirrors that direct or divert ion flow from the skimmer cone before the flow enters the quadrupole to reduce interferences. The sampling cone and the second skimmer are also often slightly offset to reduce the flow of ions and interference from entering the MS (see 

). There are some ICP-MS configurations that offer additional skimmers and extraction lenses to further reduce the background flow that can cause interference in the system.

The nebulized sample that is ionized by the plasma moves through the sample interface (between the sample cone and skimmer), which allows the sample to cool as it passes through this water-cooled zone and transition to a higher vacuum area of the system before entering the second stage vacuum area.

Once the sample is pulled into the high vacuum area, it is directed and separated by a series of lenses and mirrors before being filtered by the quadrupole or magnetic sector. The quadrupole mass detectors are the most common type and are similar to the single quadrupole mass spectrometer for liquid chromatography we discussed in previous columns. The quadrupole consists of two pairs of parallel rods usually composed of a material such as molybdenum in which direct current (DC) and radiofrequency (RF) are applied to create a charged tunnel through which analyte ions and fragments are filtered by their mass-to-charge ratios.

One pair of the rods have a positively charged DC and RF applied while the second pair of rods have a negatively charged and 180 degree offset RF to the first pair RF setting creating horizontal and vertical fields of current. The ions that exit the plasma are positively charged and move towards the negatively charged rods and away from the positive rods. An alternating current is applied that moves the ions from the negatively charged rod down the tunnel in a spiral motion as the polarity shifts to be separated by their mass to charge ratio (see 

Lighter ions are affected more by the AC field and follow the RF fluctuations while heavier ions are less affected by the AC filed and follow the DC field. One m/z ratio travels down the path at a time and this can allow for the separation 
of isotopes.

Isotopes, Isobars, Abundances, and Interferences

The determination of any concentration of a particular element for ICP-MS will depend on the abundance and number of isotopes and isobars for that target element. Isotopes are atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons (different atomic mass). Some elements are polyatomic meaning they have multiple isomers with different masses, in natural abundance ratios (see 

For most elements, such as chromium there is one isotope that is the most abundant of the possible isomers, which is most commonly selected to analyze for that particular element. Other elements such as mercury have multiple isotopes with similar abundances that can be used depending on the method. The choice of which isotope to use can often be influenced by the other elements that could be present in the sample and interfere with monitoring of a particular isomer.

One type of interference for a target isotope is the occurrence of an isobar for the monitored mass. Isobars are atoms with the same mass number but different atomic numbers such as calcium, argon, and potassium (see 

In the example of Table II, both the argon and calcium have their major abundance at mass 40 which means that there is a built-in overlapping interference between 40Ca and 40Ar, which can be problematic in ICP-MS systems that rely on argon gas.

Interference for ICP-MS fall into similar categories as were found in the ICP-OES analyses in our previous column: physical, chemical, and spectral.

Physical interferences are the differences between the samples being tested on any standards, calibration curves, or blanks that can alter the sample introduction and nebulization. Most of the difference stems from the makeup of the matrices of the sample and standards.

Chemical interferences are differences in the way in which a sample, standard, or element reacts in the plasma. These interferences can result in ionization effects, formation of molecules, or changes to the plasma.

Spectral interferences are changes that can mask the detection of the target element through the detection of isobars or oxidation of an element in the plasma, or double charging of an ion. The conjunction of multiple ions in the plasma can create polyatomic interference complex that can alter the target mass detection (see 

Many common elements can contribute to polyatomic interferences, which can alter response at the most abundant masses. Gases such as oxygen and argon are large contributors along with common contaminants such as salts, and instrument components like the platinum from tipped cones. Most instrument manufacturers either have hardware filters or software corrections to reduce or eliminate polyatomic interferences such as the addition of collision gases, application of a collision cell, or multiple mass filters.

The physical filters such as collision or reaction cells or additional quadrupoles take advantage of the size and energy differentials between a single isotope atom versus a polyatomic complex. The size and the chemistry can make the polyatomic complex subject to either physical, chemical, or energy-based separation from the target analyte.

The benefit of ICP-MS is that the technique can be applied to a broad range of targets and samples with a high degree of accuracy and sensitivity, but this can also be its detractor when it lacks some degree of selectivity especially in the cases of interferences. Despite the challenges in cost, operation, and methodology, ICP-MS is the clear tool for trace elemental analysis and high-throughput laboratories. ICP-MS can monitor the greatest number of elements to the lowest concentrations while performing quantitative and isotopic analysis. The question is not whether a cannabis or hemp laboratory should be using ICP-MS; it is which type should be selected.

Cannabis testing laboratories have become the latest battleground for analytical instrumentation vendors. The entrepreneurial spirit in the cannabis industry has seen these laboratories springing up all over the US, trying to capture a slice of the lucrative testing market as new states begin the process of legalizing the use of medicinal and adult recreational cannabis consumer products. An investment of $1-2 million can get you all the required analytical instrumentation to start competing for business in one of the 38 states that currently allow for the use of these products. However, because of the competitive nature of this industry, the lowest bid typically gets the business. As a result, instrumentation vendors that have all the analytical instrumentation in their toolkit would normally beat out other manufacturers that offered only some of the equipment, which invariably meant that for any single technique like ICP-MS, the best instrument wasn’t always the one that was purchased.

Imagine you have just started a new job as a chemist at a start-up cannabis testing laboratory and you have been given the responsibility for buying a new ICP-MS instrument. You have previously used the technique in your last position at an environmental contract laboratory and knew the requirements for potable and wastewater samples, but you did not have a good understanding of the analytical demands of a cannabis testing laboratory. With that as background information, let’s first remind ourselves of the many benefits of ICP-MS for trace element analysis and specifically what’s important for carrying out the measurement of heavy metals in cannabis consumer products. There are several excellent commercial ICP-MS systems on the market—all with very similar specifications—so how do you choose the one that best fits your cannabis testing needs? How do you go about comparing the different designs, hardware components, and performance features, all of which are of critical importance in the decision-making process?

First, it’s very important to decide what your objectives are, particularly if you are part of your laboratory’s evaluation committee. You can have more than one objective, but they must be clearly defined. Every cannabis testing laboratory’s application demands are unique, even if they share some similarities, so it is important to prioritize them before you begin the evaluation process. Analytical capability, usability, and reliability are typically the areas that are considered the most important, so let’s take a closer look at them.

The major reason that the trace element community was attracted to ICP-MS more than 30 years ago was its extremely low multielement detection limits. Other multielement techniques, such as inductively coupled plasma-optical emission spectrometry (ICP-OES), offered very high throughput but could not achieve ultra-trace levels. Graphite furnace atomic absorption (GFAA) spectrometry offered much better detection capability than ICP-OES, it did not offer the sample throughput. In addition, GFAA was predominantly a single-element technique and was therefore impractical for carrying out rapid multielement analysis (see 

These limitations quickly led to the commercialization of ICP-MS as a tool for rapid ultra-trace element analysis. There are a number of performance metrics that are commonly used to measure the capability of an ICP-MS, including:

So, let’s take a closer look at each of these capabilities related to the demands of the cannabis industry, particularly how they might impact the evaluation process. It is not meant to be an exhaustive look but an overview of the most important criteria.

Most states that have approved the use of medical or recreational cannabis regulate four heavy metals: Pb, Cd, As and Hg, known as the “big 4.” Take for example the action limits for these four metals for orally consumed cannabis products for the state of California, which are shown in 

. Even when the concentrations in solution are calculated after sample preparation, it can be seen that ICP-MS detection limits comfortably meet these limits. Even if the inhalation action limits were used, which are typically 10x lower than the oral regulations, the technique would have no problem in meeting these limits as can be seen in the ICP-MS factor improvement.

So, it’s important to emphasize that all instruments on the market should offer similar detection capability. By all means, compare detection limits and real-world limits of quantitation of different instruments, but with cannabis-related samples it is unlikely you will be pushing the capabilities of the technique.

Accuracy is a very difficult aspect of instrument performance to evaluate because it often reflects the skill of the person developing the method and analyzing the samples, instead of the capabilities of the instrument itself. If evaluated correctly, it is a very useful exercise to go through, particularly if you can get hold of a cannabis reference material whose values are well defined. However, when attempting to compare the accuracy of different instruments, it is essential that you prepare every sample yourself, including the calibration standards, blanks, unknown samples, quality control (QC) standards, or certified reference material (CRM), if available. I suggest that you make up enough of each solution to give to each vendor for analysis. By doing this, you eliminate the uncertainty and errors associated with different people making up different solutions. It then becomes more of an assessment of the capability of the instrument, including its sample introduction system, interface region, ion optics, mass analyzer, detector, and measurement circuitry, to handle the unknown samples, minimize interferences, and get the correct results.

It is recognized that the major source of drift and imprecision in ICP-MS, particularly with real-world samples, is associated with either the sample introduction area, the interface cones, or the ion optics system. Some of the most common problems encountered with cannabis plant materials, and cannabinoid products include:

Pulsations and fluctuations in the peristaltic pump (if used) leading to increased signal noise

Blockage of the nebulizer over time, resulting in signal drift—especially if the nebulizer does not have a tolerance for high dissolved solids

Poor drainage, producing pressure changes in the spray chamber and resulting in spikes in the signal

Buildup of solids in the sample injector, producing signal drift

Blockage of the sampler and skimmer cone orifice with sample material, causing instability, particularly challenging when aspirating cannabis biomass samples

Erosion of the sampler and skimmer cone orifice with high-concentration acids

Coating of the ion optics with matrix components, resulting in slight changes in the electrical characteristics the of ion lens system

These can all be somewhat problematic depending on the types of cannabis samples being analyzed. However, the most common and potentially serious problem with real-world cannabis matrices is the deposition of sample material on the interface cones and the ion optics over time. It probably won’t significantly impact short-term precision because careful selection of internal standards matched to the analyte masses can compensate for slight instability problems. However, sample material, particularly matrix components found in cannabis matrices, can have a dramatic effect on long-term stability. The problem is exaggerated even more in a high throughput testing laboratory, because poor stability will necessitate more regular recalibration and might even require some samples to be rerun if QC standards fall outside certain limits. There is no question that if an instrument has poor drift characteristics, it will take much longer to run an autosampler tray full of samples, and in the long term, this will result in much higher argon consumption and more regular routine maintenance.

When ICP-MS was first commercialized, it was primarily used to determine very low analyte concentrations. As a result, detection systems were only asked to measure concentration levels up to approximately five orders of magnitude. However, as the demand for greater flexibility grew, such systems were being called upon to extend their dynamic range to determine higher and higher concentrations. Today, the majority of commercial systems come standard with detectors that can measure signals up to 10 orders of magnitude. This means they can measure concentrations from low parts per trillion levels up to hundreds of parts per million. This capability has definitely enhanced the flexibility and capability of the technique, but if you are going to be using the instrument primarily to measure low levels of heavy metals in cannabis related samples, it is unlikely you will need to evaluate the instrument’s extended dynamic range feature.

There are two major types of interferences that have to be compensated for in ICP-MS: spectral and matrix interferences Although most instruments approach the principles of interference reduction in a similar way, the practical aspect of compensating for them will be different, depending on the differences in hardware components and instrument design. If the sample is digested correctly and the cannabis material is completely dissolved, matrix interferences should not pose a significant problem, as long as the acid concentration is similar in blanks, standards, and samples. The only potential problem in a high throughput laboratory is that the interface cones should be cleaned on a regular basis, so the organic matrix components do not build up and block the cone orifice.

However, it is absolutely valid to evaluate the instrument’s spectral interference reduction techniques, especially if you are in a state that requires an expanded panel of heavy metals. Of the big four metals, Pb (208 amu), Cd (114 amu), and Hg (202 amu) are at a high enough mass that there are no obvious polyatomic spectral interferences to address. The only element that suffers from any serious spectral overlaps is As because of the polyatomic spectral interferences from the 

Cl polyatomic ion at mass 75 (produced by argon gas ions combining with chloride ions from the HCl used in the microwave digestion procedure), which interferes with the monoisotopic arsenic mass 75 amu. It is relatively straight forward to mitigate the 

Cl with a collision-reaction cell (CRC), which utilizes helium as a collision gas to reduce the kinetic energy of the interference and allows the 

As mass to be used for quantitation. However, if other elements such as Cr, Ni, Cu, and Zn are in the regulated panel, it could be more difficult to mitigate the spectral interferences that can potentially interfere with these analyte elements. For that reason, it’s essential if you are in one of the states that requires this panel of heavy metals, you could possibly need the capabilities of a CRC that utilizes reaction mechanisms to minimize these types of interferences. Furthermore, it has also been shown in the open literature that triple or multi-quadrupole ICP-MS technology is needed to resolve some of the more challenging polyatomic spectral interferences on the more difficult elemental analytes.

Most cannabis testing laboratories will experience high sample workloads at some point during their operation, even though it might not be on a regular basis. So, depending on your requirements, you have to decide if high sample throughput is a requirement of your evaluation. Therefore, if speed of analysis is important it is worth carrying out a sample throughput test. Choose a suite of elements that represents your analytical challenge. Assuming you are also interested in achieving good detection capability, let the manufacturer set the measurement protocol including integration time, dwell time, settling time, number of sweeps, points and peaks, sample introduction wash-in, stabilization, wash-out times, and so on to get their best detection limits. Then time how long it takes to achieve detection limit (DL) levels in duplicate from the time the sample probe goes into the sample to the time a result comes out on the screen or printer. If you have time, it might also be worth carrying out this test in an autosampler with a small number of your typical samples. It is important that the DL measurement protocol be used because factors such as integration times and wash-out times can be compromised to reduce the analysis time. However, it’s worth emphasizing if high sample throughput is truly important, there are automated productivity enhancement systems on the market that by maximizing sample delivery and optimizing wash-out of the sample they are realizing a two- to three-fold improvement in multielement analysis times.

Analytical performance is clearly a very important consideration when evaluating the capabilities of an ICP-MS. However, it’s important to assess what we call the intangibles including:

The vast majority of instruments in use today are being operated by technician-level chemists, who may have some experience in the use of AA or ICP-OES, but in no way could be considered ICP-MS experts. Therefore, ease of use including method development and routine operation is critically important to evaluate. Furthermore, good instrument reliability is often taken for granted nowadays, but it has not always been the case. When ICP-MS was first commercialized, the early instruments were a little unpredictable, and quite prone to breakdowns. However, as the technique became more mature, the quality of instrument parts—and hence the reliability—improved. You should therefore be aware of the instrumental components that are more problematic than others and might need to be maintained on a more regular basis. It’s also very important that you talk to other ICP-MS users in the cannabis testing field to get their perspective and, in particular, the quality of the technical support they get from theirinstrument manufacturer. Their experience, both positive and negative, can be very useful for you as you are going through the evaluation process.

Thomas, R. J., Measuring Heavy Metal Contaminants in Cannabis and Hemp, 

Atkins, P. Energy and Elements, Part I: Understanding Atomic Spectroscopy, 

Atkins, P. Energy and Elements, Part II: A Closer Look at ICP, 

Navigating the Lab

In this installment, we finish our discussion of energy and elements used in atomic spectroscopy by examining an important analytical technique: inductively coupled plasma-mass spectroscopy (ICP-MS).

Energy and Elements, Part III: Understanding and Choosing an ICP-MS

Editor's Note: This agenda was accurate at the time of publication in early April 2023. Speaker names and specific time slots are subject to change.

Low and Ultra-Low Doses of Cannabinoids: Are We Missing the Sweet Spot?

Fireside Chat Discussion, Analytical Focus

Integrating Risk Management Strategies and Data Analysis to Reduce Microbial Product Failure Rates


Speaker/Moderator: Patrick Bird, MS, Sr. Manager, Scientific Affairs, bioMerieux
Panelists: Heather Krug, Regulatory Programs Branch Chief, Colorado State Public Health Lab; Antionette Duncan, Sr. Director Quality Assurance, Curaleaf; Chris Hudalla, President and CEO, ProVerde Labs; Steve Jetter, Program Analyst for Cannabis and Psilocybin Policy, Oregon Health Authority’s Oregon Environmental Laboratory Accreditation Program (ORELAP); and Shane Flynn, Senior Director Laboratory Proficiency Testing, AOAC

Analytical Track: Electronic Cannabis Delivery System Aerosol Generation and Collection: Challenges, Best Practices


Speaker: Dr. Mark Crosswhite, Principal Scientist, ConsulticX Sciences Corp.

Medical Track: Chronic Exposure to Cannabis sativa Extracts Reduces Adiposity and Improves Metabolic Dysfunction Associated with Diet-Induced Obesity


Speaker: Bryant Avalos, Graduate Student Researcher, University of California, Riverside

Cultivation Track: Cannabis-Specific Plant Nutrition: Express Your Plant’s Full Potential with a Balanced Diet


Speaker: Christian West, Owner/Consultant, Big Earth Consulting, LLC

Analytical Track: Vaping Chemistry of Semi-Synthetic Cannabinoids


Speaker: Robert Strongin, Professor of Chemistry, Portland State University

Medical Track: Precision Cannabinoid Medicine is Here


Speaker: Len May, MCS, Endocanna Health, Inc.

Cultivation Track: Microbes are Multiplying: Finding the Source and A Solution to Your Cannabis Contamination


Speaker: Carly Bader, Manager of Science, Willow Industries

Analytical Track: Non-Targeted Analysis of Aerosol Delivery Systems – Challenges, Considerations, and Best Practices


Speaker: Dr. Mark Crosswhite, Principal Scientist, ConsulticX Sciences Corp

Analytical Track: Think Your Lab Testing Is Unbiased?.....You Might Be Surprised!


Speaker: Amber Wise, PhD, Science Director, Medicine Creek Analytics

Medical Track: Raising Awareness: The Implementation of Medical Cannabis and Psychedelics Used as an Adjunct to Standard Therapy in the Treatment of Advanced Metastatic Breast Cancer


Speaker: Jaime Brambila, Founder, Grace Health and Wellness

Psychedelics Track: Cardiovascular Disease Risk Among Cannabis + Psilocybin Co-Consumers


Speaker: Dr. Denise Vidot, University of Miami

Analytical Track: Cannabinoid Extraction Efficiency for Potency Analysis: An in Depth Look of Multiple Techniques


Speaker: Melinda Urich, Scientist, Restek

Medical Track: The Nose Knows: How Cannabis Aroma Is Transforming Medicine and Commerce


Speaker: Adie Rae, PhD, Assistant Scientist, Legacy Research Institute

Psychedelics Track: Quantification of Psilocybin and Psilocin Content Variety in Psilocybe cubensis Strains with LC-MS


Speaker: Sabrina Islam, Undergraduate Student, University of Texas at Arlington

Analytical Track: Hide and Seek: New Standards and Methods to Help Quantify Impurities Found in Cannabidiol Derived Phytocannabinoid Products

Check out the agenda for Cannabis Science Conference Spring 2023!

April 2023

Chromatographic Theory, Part IV: Measuring Separation Quality with Capacity and Separation Factors

Extraction of Acidic Cannabinoids

Retrocommissioning Pays Dividends

Energy and Elements, Part III: Understanding and Choosing an ICP-MS

2023 Cannabis Science Conference Spring Agenda

Areas of Growth: A Closer Look at Research on Cannabis Propagation