In this month’s “Cannabis Crossroads,” I would like to share inspiring stories of passion and persistence by highlighting the amazing efforts of some truly pioneering souls: Shannon Hoffman, the Regional Director of Operations and Certifying Chemist for Steep Hill Maryland, Pennsylvania, and Washington, D.C.; Dr. Jacklyn R. Green, Chief Executive Officer of Agate Biosciences; and Dr. Sue Sisley, M.D., President of Scottsdale Research Institute, on faculty at Colorado State University and Humboldt State University, and Senior Fellow at Thomas Jefferson University Lambert Center. These three women, each with a diverse background, are true leaders in cannabis science.

Please explain how long you have been working in the cannabis industry and what first got you interested in cannabis science.

I’ve been working in cannabis for close to a year. I started off doing some consulting last summer before joining Steep Hill in December 2017. I’ve been casually interested in cannabis science for some time. A merger at my previous employer led to my decision to resign at just the time when the industry was on the brink of opening in Maryland; it seemed fated for me to make the jump into cannabis.

 I was first introduced to cannabis science by my best friend, Dr. Claudia Jensen, in 1996, when the California laws changed. She was one of the very first cannabis doctors in California. I was supportive of cannabis, although I did not partake. Through my conversations with Claudia, I became much more attuned with the role of cannabis in helping people with a wide variety of conditions. At that time, I was working full time as a planetary scientist at The National Aeronautics and Space Administration’s (NASA) Jet Propulsion Laboratory. My husband, Dr. Roger Kern, a plant microbiologist, and I developed a concept for a small, autonomous greenhouse for the surface of Mars to test technologies that we would need for larger greenhouses for future astronauts exploring the Red Planet. This project gave us our first steps in developing controlled environment agriculture (CEA) systems. As the years flew by, we continued our work in CEA-and as cannabis laws changed across the country, we found ourselves in an environment that allowed us to bring our scientific knowledge, systems engineering approach, and project management experience from NASA to the cannabis industry to help solve some of the most challenging problems facing us to ensure safe and consistent products for people across the country.

 It’s been almost 10 years since I began studying cannabis as a medicine and fighting for public policy reform. Military veterans prompted my interest in studying cannabis. They claimed they were benefiting, but I was highly skeptical. I’m a lifelong Republican and had been brainwashed by big pharma and the medical profession to view cannabis as a dangerous addictive drug. I first began paying attention because of the social justice issues. We launched a charity called Doctors for Cannabis Regulation to try to create a safe harbor for physicians to speak openly about their views on ending cannabis prohibition. We’ve also created a veterans charity called the Battlefield Foundation, which recently received its 501(c)(3). We are busy trying to raise money for rigorous controlled trials as well as to create jobs in the cannabis industry for veterans. So we do a matchmaking service and it’s been very gratifying to create meaningful employment for veterans within the cannabis space.

What is one lesson that you had to learn the hard way, or a major obstacle that you had to overcome in cannabis science?

 Explaining the role of science, technology, engineering, and math (STEM) subjects to long-term cannabis industry participants is an ongoing challenge. Cannabis is coming out of the shadows into the bright light of scientific investigation, well-implemented systems engineering, and expert project management. The challenge is that people, in general, believe they know how to grow plants and specialists know how to grow cannabis in high-tech environments indoors. However, most cannabis insiders perform their work by the seat of their pants, by the look and feel of things. We must have rigorous procedures, exactness in standards, and intelligent planning for projects of all sizes that allow optimization, at the systems level, to create a safe and reliable supply chain and a consistent, regulated distribution chain for legal cannabis products.

 I learned that public universities are terrified of the word cannabis. Cannabis has become so politically radioactive that many universities are still convinced they will lose their federal funding if they do even U.S. Food and Drug Administration (FDA)-approved research.

Can you please share with me your biggest achievement or favorite memory from working in the cannabis industry?

My biggest achievement was leading our laboratories in Maryland and Pennsylvania through ISO 17025 accreditation. I’ve worked in the regulated industry with demanding quality systems, but ISO is quite rigorous. It required our entire team to come together and work tirelessly to meet tight timings. You really see what people are made of when you face challenges and I couldn’t ask for a more talented or dedicated team at Steep Hill.

 I am a competitive person, so I find it intensely gratifying to win licenses and permits for our clients. I love to start with them in our brainstorming workshops in which we use design thinking and creative problem-solving techniques to identify and tackle their most challenging problems. We go through an intense phase of concept development and then dig deep into the systems engineering for requirements and risk analysis. Finally, we go into the hard-core project management to get the full concept finalized and written up into a compliant, compelling, and beautiful application. I find that delivering a set of documents to our clients to be my favorite moment. I love to see their faces as they thumb through the documents. Then, of course, hearing that they have won through the official governing bodies is a moment of great satisfaction.

 The biggest achievement is perseverance in the face of constant government blockades. Over the course of the past 10 years we have managed to overcome some really onerous hurdles to get efficacy research started. The U.S. government has systematically impeded cannabis efficacy trials for so many decades. But we are slowly learning how to navigate these waters and teaching other young scientists how to pick up the baton!

What excites you most about the future of cannabis science?

There is so much yet to learn about how this amazing plant can benefit our health. Having more and more access to research is going to enable us to target therapy in ways we couldn’t imagine. I’m excited to be a part of Steep Hill because we can help to ensure that patients are getting safe, efficacious medicine now and in the future as we learn more about what this plant can do.

Cannabis science-it is a subject just waiting for exploration! As an astronomer, I love to explore and see what is new in the universe, or closer to home, in our own solar system. Who would imagine that there is a plant with special medicinal properties that any hobbyist could grow but that has been forbidden to us to explore and learn about? It defies logic that we would not explore and advance our knowledge for the good of humanity. There is a wide variety of potential studies, across the many disciplines of STEM, that would provide fundamental knowledge about cannabis. Unfortunately, we are not able to tackle those scientific studies at this time! We need federal funding for robust research programs, university research programs, and grants for private companies to conduct unbiased, zero conflict-of-interest studies. For that to happen, the laws will need to change at the federal level.

 I think it’s the opportunity to possibly work with other growers besides the University of Mississippi. Since 1968 the University of Mississippi has enjoyed a government-enforced monopoly on the only federally legal supply of cannabis for research. But thanks to relentless lobbying efforts from the Multidisciplinary Association for Psychedelic Studies (MAPS) and other good charities, we are finally seeing the U.S. Drug Enforcement Agency (DEA) entertain the idea of licensing other schedule one bulk manufacturers. 

Suddenly scientists will have access to unique phenotypes of cannabis in a timely manner. If this happens it will create a renaissance of cannabis research in the U.S.

What advice do you have for readers interested in starting a career in cannabis science?

You have to love it. I think anyone who feels a sense of purpose about cannabis can find a place for themselves in the industry, but you will have to work hard and should be prepared for challenges along the way. It is a volatile industry in the sense that it is varied and evolving and we are all learning together the best way to do this. There is a need for a diverse skill set in cannabis, so there are opportunities for anyone who feels that drive to be involved to work to their strengths and contribute to building something amazing.

 I am very clear in my advice to readers interested in starting a career in cannabis science-get as much education as you possibly can. Think of every degree you obtain as a ticket-a ticket to a journey that will take you far in life and in knowledge. As a scientist you have an element of wonder in your life. You see and experience nature in ways that most people don’t ever contemplate. You can become a world expert in cannabis across many scientific disciplines-from biology, chemistry, physics, engineering, math, computer science, numerical modeling, medicine, plant science, microbiology, and more. I am grateful beyond words that I became a scientist. Whether I am an astronomer or a cannabis consultant, my skills as a thinker and explorer serve me well every single day. I know that no problem is too difficult to tackle. We may make small steps in progress, but each small step opens up a new horizon. With a life in science, I always want to see the next horizon.

 The first step is volunteering with the team and your local area. Try to identify scientists who are already doing this work and see if they will mentor you or let you apprentice there. Even if you’re an unpaid intern for a few months, they will likely recognize your skill and enthusiasm and probably hire you on!

is the Regional Director of Operations and Certifying Chemist for Steep Hill Maryland, Pennsylvania, and Washington, D.C. Steep Hill, a leading cannabis science and technology company, was the first commercial cannabis lab in the U.S. and has expanded its best practices in cannabis testing to the mid-atlantic with physician-led laboratories in Maryland, Pennsylvania, and Washington, D.C. Hoffman is an analytical chemist with 18 years of experience in research and development and manufacturing of consumer products, cosmetics, and over the counter pharmaceuticals. She has a bachelor’s degree in chemistry from the University of Maryland, Baltimore County and a master’s degree in analytical chemistry from the Illinois Institute of Technology.

 is a project manager and systems engineer focused on commercial businesses in the cannabis industry. With her PhD from The University of Texas at Austin, she leads, manages, and delivers compliant, compelling, and selectable applications for city- and state-legal commercial cannabis businesses. She spent 27 years at NASA’s Jet Propulsion Laboratory as a scientist and project manager, leading advanced technology development projects and proposal development in the complex government-regulated environment. Now, as the Chief Executive Officer of Agate Biosciences, a consulting firm for project management, systems engineering, and science for controlled environment agriculture, she brings the best practices of management and systems engineering to cannabis businesses, allowing them to be successful in a complex, government-regulated environment.

, serves as President of Scottsdale Research Institute and Site Principal Investigator for the only FDA-approved randomized controlled trial in the world examining safety and efficacy of whole plant marijuana in combat veterans with treatment-resistant posttraumatic stress disorder (PTSD). Dr. Sisley is on the faculty at Colorado State University and Humboldt State University, and a Senior Fellow at Thomas Jefferson University Lambert Center, assisting their Institutes of Cannabis Research. Dr. Sisley has been a Member of Nevada ILAC Medical Cannabis Commission for the past three years, outlining regulations for laboratory testing including limits on pesticides, residual solvents, and other guidelines that are currently being used as a model for other states medical cannabis laws. Her other areas of current institutional review board (IRB)-approved research include supervising studies evaluating cannabis for pain management, cannabis as a substitution therapy for opioids, and also a safety study looking at cannabis. Dr. Sisley is also the Principal Investigator on a Colorado State University project to build a robust nationwide medical cannabis patient registry.

 is the columnist and editor of “Cannabis Crossroads” and a contributing editor to 

magazine. Crossney is also the president and CEO of CSC Events. Direct correspondence to: 

Articles

Pioneering Spirits: Three Women Leaders in Cannabis Science Share Their Trials, Tribulations, Successes, and Advice

Ultrasonic energy, broadly defined as sound above the range of human hearing (approximately 20,000 cycles/s or 20 kHz), can be used in several ways during the production of cannabis to ensure that the product is of the highest quality. In addition to providing a tutorial on how ultrasonic equipment works, this article describes how the equipment is applied in laboratory practices and manufacturing. Examples include extraction procedures, cleaning ion targets in mass spectrometers, preparing oil emulsions for edible or drinkable products, degassing oil (removing trapped air) to maintain stable oil volume during selling, degassing high performance liquid chromatography (HPLC) solvents, bubbling off ethanol before oil distillation, and removing gums and waxes from glassware used in production.

Ultrasonic energy is commonly associated with ultrasonic cleaning. As explained by Edward W. Lamm in his article “The Development of Ultrasonic Cleaning” (1), its history dates to the early 1930s and work done at Radio Corporation of America (RCA) laboratories in New Jersey. The first practical applications, according to Lamm’s article, were introduced in the 1950s, and were operated at 18–40 kHz. “Up until the late 1980s most of the commercially available systems operated at 25–40 kHz,” Lamm stated.

Today, ultrasonic cleaners are available in several frequencies, including 25, 45, 80, and 130 kHz. Units are also available offering dual-frequency options.

Ultrasonic energy is used in research, product development, and manufacturing operations. Typically, these involve homogenizing, emulsifying, dispersing, dissolving or mixing difficult samples, and degassing liquids to remove trapped air.

Ultrasonic energy is a proven technique to achieve fast, safe extraction. For example, it is a method often specified in United States Pharmacopeia (USP) monographs to extract active pharmaceutical ingredients from carriers for content uniformity and potency assay tests.

In cannabis production, most regulated markets require all cannabis products to be tested for efficacy (active ingredients, such as cannabinoids and terpenoids), as well as for contaminants (such as pesticides, mycotoxins, heavy metals, microbes, and residual solvents).

Cannabis products include plant material (mostly flowers and trimmed leaves), concentrated extracted essential oils (concentrates, waxes, and oils), and infused products (edibles such as candies, chocolates, baked goods, transdermal patches, suppositories, and beverages).

Clearly, accurate test results depend on efficient, reproducible extraction from these often complex matrices, and sonication is one way many cannabis laboratories seek to achieve those goals. Sonication is valuable because it deposits energy into the solvent–matrix system, effectively speeding the process of extraction and dissolution.

Mass spectrometers are typically the workhorse instruments in a cannabis laboratory. Many laboratories have inductively coupled plasma–mass spectrometry (ICP-MS), liquid chromatography–tandem mass spectrometry (LC–MS/MS) and gas chromatography (GC)–MS/MS instruments all in the same laboratory.

Since cannabis contains viscous oils and resinous compounds of moderate to high molecular weight, ion sources and associated components can get contaminated with organic residues that are difficult to remove. In particular, contamination of electrodes that steer the ions leads to defocusing and loss of signal.

Sonication is often the most efficient method to clean these parts. Likewise, the chromatography injectors and inlets can also become contaminated and clogged with the resins and residues and sonication in a nonpolar solvent is often the method of choice to clean these components as well.

For cleaning applications, ultrasonic energy is used to remove contaminants from the surfaces of virtually any product that can be safely immersed in a water-based biodegradable ultrasonic cleaning solution. Cleaning solution formulas, dilution recommendations, and operating procedures are available for specific cleaning tasks.

Components of Ultrasonic Cleaning Equipment

There are multiple manufacturers of ultrasonic cleaning and processing equipment. Regardless of the manufacturer, common components include
A tank, usually stainless steel, to hold the cleaning solution or water that is typically mixed with a surfactant

Ultrasonic transducers bonded to the bottom of the tank

A mesh-bottomed basket (standard or optional) to hold products being cleaned or processed without contacting the bottom of the tank

A lid (standard or optional) to reduce cleaning solution evaporation and noise

Cleaning tank size (length, width, and depth)

A control panel that can range from a simple on–off switch to highly sophisticated options including timers, thermostats, and features including sweep, normal, pulse, degassing, and adjustable ultrasonic power and frequency.

One might ask about the need for a more sophisticated unit. The answer is simple. It provides cannabis processors with the ability to develop and customize optimum processing steps to achieve consistent, high-quality product from a variety of sources.

When activated, the equipment’s generator powers the transducers to vibrate at their designed ultrasonic frequency. This vibration causes the tank bottom to vibrate as a membrane that produces countless microscopic vacuum bubbles.

In applications such as cleaning glassware, these bubbles implode with tremendous force in a process called 

. This cavitation quickly and safely blasts loose contaminants and carries away even the most tenacious residue. Products are cleaned with a solution formulation designed for the application.

In a processing application, products are contained in Erlenmeyer flasks, test tubes, or beakers. These containers are lowered, but not fully immersed, into a water or surfactant solution. Ultrasonic energy passes through the glass walls of the containers to act on the contents.

This approach achieves the homogenizing, emulsifying, degassing, and other cannabis processing steps in a fast, efficient, and environmentally friendly way.

Comparing Ultrasonic Cannabis Production and Quality Control to Alternative Methods

In 2015, the National Hemp Association published an article in 

 titled “Five Major Types of Cannabis Extraction” (2). In the article, Rien Havens, PhD, CTO, Really Helping, PBC, stated that in the winter of 2014 he began research to develop the optimal methods of hemp extraction. “It was quite a ride. I had in mind three main goals,” said Havens. “No use of fossil fuels, low energy footprint, and cost effectiveness.”

Here, we paraphrase Havens’ findings as published in the article (2). Readers may wish to access the full article for additional details.

Ethanol produced a relatively good quality extract, but the solvent and energy costs were high. It did not produce the desired results of volume and speed. Residual solvent in the final product was also a drawback.

A closed-loop hydrocarbon extractor is inexpensive to set up, but uses fossil fuels, almost always contains cancer-causing components like benzene, and often there are metal filings and welding debris in the solvent tanks.

A supercritical carbon dioxide extractor was able to produce a high quality extract with very high terpene retention, a great color, taste, speed, and selectivity. The downside of this approach includes high overhead and unruly energy consumption.

Critical water extraction is “green” with no added solvents but clean water. There is no solvent loss, or cost, and the volume and cost of the extractor makes it a good candidate for industrial hemp extraction.

A truly solventless method is sonic and ultrasonic waves in the plant matter that push the product out through vibration. This method can also be scaled up, like water extraction on a budget, and produces a very nice, high-quality extract.

A Closer Look at Ultrasonic Equipment for Cannabis Production

Ultrasonic cleaner tanks are available in multiple sizes in terms of length, width, and depth. When processing in flasks and beakers, a shallow-depth tank is a good choice with a length and width that allows the processing of several containers at once.

The following sections provide a more detailed illustration of how the process works. This example describes the use of a 37-kHz ultrasonic cleaner based on its tank configuration and operating features.

Remember that the transformation or extraction process avoids chemical degradation that can be caused by excessive heat or mechanically induced damage.

Product is placed in flasks along with a recommended solvent. Flasks are partially immersed in a sonicator bath containing a surfactant.

The tank configuration of the ultrasonic unit used in this process is especially designed to quickly and safely accomplish extraction and further processing. The inside dimensions of the shallow basket, 17.9 x 9.8 x 2.2 in. (LxWxH), facilitate positioning of multiple smaller containers or larger beakers. Flask clamps are used to affix flasks to the mesh-bottom basket; test tube holders are also available.

The equipment described was also selected because of its high ultrasonic power per unit volume. This feature permits the preparation process to be completed before heat buildup, a natural result of ultrasonic energy, which can degrade product. If heat is a concern, a useful accessory is a cooling coil to prevent temperature increase. The cooling coil must be attached to a source of recirculating cold liquid such as a laboratory chiller.

Another suggestion for producers is to look for an ultrasonic unit equipped with a microprocessor-controlled ultrasonic generator that adjusts to the load; a degas mode to remove trapped air, and a timer that displays set and remaining time.

Other useful features include the ability to operate in a fixed frequency (also called normal) mode that is ideal for breaking up product and a sweep mode that provides uniform distribution of ultrasonic energy when it is used to clean glassware and other processing equipment (see below). The sweep mode delivers a small positive and negative fluctuation in ultrasonic frequency throughout the bath.

Water and a surfactant are added to the fill line of the sonicator tank. The unit is turned on and the degas function is activated to both mix the solution and drive off trapped air. This step should take about 10 min.

The product is lowered into the bath and the unit is set to operate in the normal mode. The generator provides ultrasonic energy in the bath that passes through flask walls. This step mixes, disperses, emulsifies, homogenizes, and dissolves the samples. The unit will shut down at the end of the timed cycle.

Operators will soon develop their own “techniques” or “standard operating procedures” for their processing cycles.

Cleaning Processing Glassware and Other Equipment

Substantial investments may be made in cannabis processing glassware and other tools. Because of the nature of the process, difficult-to-remove deposits adhere to the inside of flasks, test tubes, and beakers. Overall, cleaning is also recommended to ensure a quality product.

Cleaning internal surfaces can be accomplished by filling the container with a suitable biodegradable cleaning solution and, as with the extraction and processing steps, placing the container in the water–surfactant solution and activating the degas mode and ultrasound. Cavitation passes through the glass walls to loosen and remove the strongly adhering residues. These residues are then discarded and the containers can be rinsed for further use.

Small instruments can be placed in the mesh tray.  In this case, the water–surfactant solution is removed and replaced with a degassed biodegradable formulation designed for glassware. In this instance, cleaning should be accomplished using the sweep mode to provide more-uniform cleaning.

To thoroughly clean internal and external surfaces of processing equipment, a larger ultrasonic cleaner is required with a suitable depth to enable full immersion of the equipment.

Biodegradable concentrates for labware are available in acidic, basic, and neutral formulations depending on the nature of the contaminants to be removed. All of the formulations come with material safety data sheets and use instructions including dilution recommendations and cleaning temperatures.

The authors acknowledge with thanks the contributions of Donald P. Land, PhD, to this article. He is Chief Scientific Consultant for Steep Hill, a leading cannabis testing and research and development (R&D) company with locations across the world.

www.cemag.us/article/2003/10/development-ultrasonic-cleaning

National Hemp Association, “Five Major Types of Cannabis Extraction,” 

http://nationalhempassociation.org/the-five-major-types-of-cannabis-extraction/

 is Director of Business Development and Global Sales at Emerald Scientific, a distributor of cannabis-related scientific supplies including reference materials, chemicals, reagents, and equipment. Direct correspondence to: 

Applying Ultrasonic Energy to Cannabis Production and Quality Control

Testing, manufacturing, and research laboratories face more challenges and regulations than ever before. Many accreditation bodies issue increasing numbers of guidelines. Regulatory agencies increase the number of compounds and elements that need to be reported while the levels of detection required are being decreased. There is often a lot of time, effort, and money invested in deciphering the data and determining its validity and accuracy. Here, we explore the accreditation, regulation, and guidelines around the manufacture and use of standards and certified reference materials (CRMs) and discuss the variables from accreditation to uncertainty involved in producing and using standards and reference materials. We also discuss the changing field of chemical analysis and the challenges that arise from the pursuit of increasingly smaller levels of detection and quantitation, including clean laboratory techniques to reduce analytical error and contamination in standards use and data collection.

The complex question of whether or not data or results are valid involves both the testing process and the actual calculated results. The question of whether or not the results reflect the true answer becomes a function of the accuracy of your standards.

Standards in the laboratory industry can be either procedural standards or metrological standards. A 

 or method standard is an authoritative quality system, procedure, or methodology considered by general consensus as the approved model or method. These types of standards are created by organizations such as the International Organization for Standardization (ISO), Association of Official Agricultural Chemists (AOAC), and American Section of the International Association for Testing Materials (ASTM), to name just a few. In some instances, laboratories seek accreditation to validate their procedures and methods to ensure some benchmark of accuracy and quality.

The second important type of standard used to determine data validity are metrological standards. A 

 is the fundamental example or reference for a unit of measure. Simply stated, a standard is the “known” to which an “unknown” can be measured. Metrological standards fall into different hierarchical levels. The highest levels of metrological standards are primary standards. A 

 is the definitive example of its measurement unit to which all other standards are compared and whose property value is accepted without reference to other standards of the same property or quantity (1,2). Primary standards of measure, such as weight, are created and maintained by metrological agencies and bureaus around the world.

Secondary standards are the next level down within the hierarchy of standards. 

 are close representations of primary standards that are measured against primary standards. Chemical standards companies often create secondary standards by comparing their material to a primary standard, making that standard traceable to a primary standard source. The third level of standards are 

, which are often used to calibrate equipment and are created by comparison to a secondary standard.

There are also many standards designated as reference materials, reference standards, or certified reference materials. These materials are manufactured or characterized for a set of properties and are traceable to a primary or secondary standard. If the material is a certified reference material (CRM), then it must be accompanied by a certificate that includes information on the material’s stability, homogeneity, traceability, and uncertainty (2,3). 

Stability, Homogeneity, Traceability, and Uncertainty

 is when a chemical substance is nonreactive in its environment during normal use. A stable material or standard will retain its chemical properties within the designated “shelf life” or within its expiration date if it is maintained under the expected and outlined stability conditions. A material is considered to be unstable if it can decompose, volatilize (burn or explode), or oxidize (corrode) under normal stated conditions.

is the state of being of uniform composition or character. Reference materials can have two types of homogeneity: within-unit homogeneity or between-unit (or lot) homogeneity. 

 means there is no precipitation or stratification of the material that cannot be rectified by following instructions for use. Some reference materials can settle out of solution, but are still considered homogeneous if they can be redissolved into the solution by following the instructions for use (that is, sonicate, heat, shake). 

 is found between separate packaging units.

 is the ability to trace a product or service from the point of origin through the manufacturing or service process through to final analysis, delivery, and receipt. Reference materials producers must ensure that the material can be traced back to a primary or secondary standard.

 is the estimate attached to a certified value that characterizes the range of values where the “true value” lies within a stated confidence level. Uncertainty can encompass random effects such as changes in temperature, humidity, drift accounted for by corrections, and variability in performance of an instrument or analyst. Uncertainty also includes the contributions from within-unit and between-unit homogeneity, changes because of storage and transportation conditions, and any uncertainties arising from the manufacture or testing of the reference material.

There are two basic classifications for types of uncertainty: Type A and Type B uncertainty. 

 is associated with repeated measurements and the statistical analysis of the series of observations. Type A uncertainty is calculated from the measurement’s standard deviation divided by the square root of the number of replicates.

 is based on scientific judgement made from previous experience and manufacturer’s specifications. Type B normal distribution is used when an estimate is made from repeated observations of a randomly varying process and an uncertainty is associated with a certain confidence interval. This type of uncertainty distribution is often found in a calibration certificate with a stated confidence level. Reference materials providers accredited by ISO 17025 and ISO 17034 provide certificates using combined and expanded uncertainties within a normal distribution. These certificates contain stated values and the uncertainty associated with that value as well as the contributions to those uncertainties.

Uncertainty is not error or mistakes. Error causes values to differ when a measurement is repeated and is the difference between the stated measurement and the true value of the measurand. True values are never absolute. The nature of a true value is that it contains uncertainty and error, which make it somewhat indeterminate. True values are obtained by perfect and error-free measurements, which do not exist in reality. Instead, the expected, specified, or theoretical value becomes the accepted true value. Analysts then compare the observed or measured values against that accepted true value to determine accuracy or “trueness” of the data set.

Often, accuracy and precision are used interchangeably when discussing data quality. In reality, they are very different assessments of data and the acquisition process. 

 is the measurement of individual or groups of data points in relationship to the “true” value. In essence, accuracy is how close your data gets to the target and is often expressed as either a numerical or percentile difference between the observed result and the target or “true” value.

, on the other hand, is the measurement of how closely the data points within a data set relate to each other. It is the measure of how well data points cluster within the target range and is often expressed as a standard deviation. Precision is an important tool for the evaluation of instrumentation and methodologies by determining how data is produced after varied replications (Figure 1). (See upper right for Figure 1, click to enlarge; Figure 1: Representations of accuracy and precision.)

Repeatability and reproducibility measure the quality of the data, method, or instrumentation by examining the precision under the same (minimal difference) or different (maximal difference) test conditions. 

 (or test–retest reliability) is the measurement of variation arising when all the measurement conditions are kept constant. These conditions typically include location, procedure, operator, and instrument run in repetition over a short period of time.

 is the measurement of variation arising in the same measurement process occurring across different conditions such as location, operator, instruments, and over long periods of time.

Another way of looking at accuracy and precision is in terms of measuring the different types of error. If accuracy is the measurement of the difference between a result and a “true” value, then error is the actual difference or the cause of the difference. The estimation of error can be calculated in two ways, either as an absolute or relative error. Absolute errors are expressed in the same units as the data set and relative errors are expressed as ratios, such as percent or fractions.

 is the true value subtracted from an observed value and is expressed in the same units as the data. Errors in precision data are most commonly calculated as some variation of the standard deviation of the data set. An absolute precision error calculation is based on either the standard deviation of a data set or values taken from a plotted curve. A relative precision error is most commonly expressed as relative standard deviation (RSD) or coefficient of variance (CV or %RSD) of the data set (Table I). (See upper right for Table I, click to enlarge; Table I: Accuracy and precision for absolute and relative errors.)

The most common error in regards to data are observational or measurement errors, which are the difference between a measured value and its true value. Most measured values contain an inherent aspect of variability as part of the measurement process, which can be classified as either random or systematic errors.

Random (or indeterminate) errors lead to measured values that are inconsistent with repeated measurements. Systematic (or determinate) errors are introduced inaccuracy from the measurement process or analytical system. There are some basic sources for systematic error in data such as operator or analyst, apparatus and environment, and method or procedure. Systematic errors can often be reduced or eliminated by observation, record-keeping, training, and maintenance.

Understanding and Compensating for Indeterminate Error

Random or indeterminate errors arise from random fluctuations and variances in the measured quantities and occur even in tightly controlled analysis systems or conditions. It is not possible to eliminate all sources of random error from a method or system. However, random errors can be minimized by experimental or method design. For instance, while it is impossible to keep an absolute temperature in a laboratory at all times, it is possible to limit the range of temperature changes. In instrumentation, small changes to the electrical systems from fluctuations in current, voltage, and resistance cause small continuing variations that can be seen as instrumental noise. The measurement of these random errors is often determined by the examination of the precision of the generated data set. Precision is a measure of statistical variability in the description of random errors. Precision analyzes the data set for the relationship and distance between each of the data points independent of the “true” or estimated value of the data to identify and quantify the variability of the data.

Accuracy is the description of systematic errors and is a measure of statistical bias that causes a difference between a result and the “true” value (trueness). A second definition, recognized by ISO, defines accuracy as a combination of random and systematic error that then requires high accuracy to also have high precision and high “trueness.” An ideal measurement method, procedure, experiment, or instrument is both accurate and precise with measurements that are all close to and clustered around the target or “true” value. The accuracy and precision of a measurement value is a process validated by the repeated measurements of a traceable reference standard or reference material.

Certified standards or CRMs are materials produced by standards providers that have one or more certified values with uncertainty established using validated methods and are accompanied by a certificate. The uncertainty characterizes the range of the dispersion of values that occurs through the determinate variation of all the components that are part of the process for creating the standard.

Each of the components in the creation of the standard have a calculated uncertainty, which then are all combined to create a combined uncertainty associated with the certified value. For example, in the creation of a chemical standard there could be separate uncertainties for all the volumetric glassware used in the production of the standard as well as uncertainty from the purity of the starting material, variations in the balance, temperature of the laboratory, and purity of the solvents. Each uncertainty for individual components is calculated and added together to form the combined uncertainty for the standard. To be clear, the uncertainty listed on a standard certificate is the measured uncertainty for that standard’s certified value and not the expected range of results for an instrument or test method. Each test method or instrument carries its own set of uncertainty calculations that determine the accuracy and precision of that analytical method, which is independent of the value on the certificate of the standard.

CRMs have a number of uses, including validation of methods, standardization or calibration of instruments or materials, and quality control and assurance procedures. A calibration procedure establishes the relationship between a concentration of an analyte and the instrumental or procedural response to that analyte. A calibration curve is the plotting of multiple points within a dynamic range to establish the analyte response within a system during the collection of data points. One element of the correct interpretation of data from instrumental systems is the effect of a sample matrix on an instrumental analytical response. The matrix effect can be responsible for either analyte suppression or enhancement. In an analysis where matrix can influence the response of an analyte, it is common to match the matrix of analytical standards or reference materials to the matrix of the target sample to compensate for matrix effects.

Different approaches to using calibration standards may need to be employed to compensate for the possible variability within a procedure or analytical system. Internal standards are reference standards that are either similar in character or analogs of the target analytes that have a similar analytical response are added to the sample before analysis. In some cases, deuterated forms of the target analytes are used as internal standards. This type of standard allows the variation of instrument response to be compensated for by the use of a relative response ratio established between the internal standard and the target analyte. A second type of internal standard is a standard addition or spiking standard. In some analyses, the matrix response, instrument response, and analyte response are indistinguishable from each other because the analyte concentration nears the lower limit of detection or quantitation. A target standard can then be added in known concentration to compensate for the matrix or instrument effects to bring the signal of the target analyte into a quantitative range.

External standards are multiple calibration points that contain standards or known concentrations of the target analytes and matrix components. Depending on the type of analytical techniques, linear calibration curves can be generated between response and concentration that can be calculated for the degree of linearity or the correlation coefficient (

 value approaching 1 reflects a higher degree of linearity, most analysts accept values of >0.999 as acceptable correlation.

Calibration curves are often affected by the limitations of the instrumentation. Data can become biased by calibration points influenced by instrument limits of detection, quantitation, and linearity. Limit of detection (LOD) is the lower limit of a method or system at which the target can be detected as different from a blank with a high confidence level (usually over three standard deviations from the blank response). The limit of quantitation (LOQ) is the lower limit of a method or system at which the target can be reasonably calculated where two distinct values between the target and blank can be observed (usually over 10 standard deviations from the blank response) (4) (Figure 2). (See upper right for Figure 2, click to enlarge; Figure 2: Limits of detection and quantitation.)

A second method of determining levels of detection and quantitation can be considered using the signal-to-noise ratio (S/N). The signal-to-noise ratio is the response of an analyte measure on an instrument as a ratio of that response to the baseline variation (noise) of the system. Limits of detection are often recognized as target responses that have three times the response of baseline noise or S/N ≥ 3. Limits of quantitation are recognized as target responses which have 10 times the response of baseline noise or S/N ≥ 10.

Limits of linearity (LOL) are the upper limits of a system or calibration curve where the linearity of the calibration curve starts to be skewed creating a loss of linearity (Figure 3). (See upper right for Figure 3, click to enlarge; Figure 3: Calibration curve limits and range.) This loss of linearity can be a sign that the instrumental detection source is approaching saturation. The array of data values between the LOQ and the LOL is considered to be the dynamic range of the system where the greatest potential for accurate measurements will occur.

The understanding of a system’s dynamic range and the accurate bracketing of calibration curves within the range and around the target analyte concentration increase the accuracy of the measurements. If a calibration curve is created that does not potentially bracket all the possible target data points, then the calibration curve can be biased to artificially increase or decrease the results and create error. 

The elimination of error from analytical methods is an ongoing process that forces the analytical laboratory to examine all their processes to eliminate sources of systematic error and mistakes. It is then a process of identifying the sources of random error in the analysis and sample preparation procedures to calculate the uncertainty associated with each source. Standards and certified reference materials give an analyst the known quantity, character, or identity to reference against their samples and instruments to further eliminate error and increase accuracy and precision to bring them closer to their goal of determining the true value.

âInternational Vocabulary of Metrology – Basic and General Concepts and Associated Terms (VIM)

, 3rd Edition (JCGM member organizations [BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP and OIML] 200, 2012). Available at: 

International Organization for Standardization (ISO) Guide 30, "Terms and Definitions Used in Connection with Reference Materials."

International Organization for Standardization (ISO) ISO Guide 17034, "General Requirements for the Competence of Reference Material Producers."

Standard Format and Guidance for AOAC Standard Method Performance Requirement (SMPR) Documents (Version 12.1; 31-Jan-11).

 is a Senior Applications Scientist with SPEX CertiPrep in Metuchen, New Jersey. Direct correspondence to: 

Holding Data to a Higher Standard,  Part I: A Guide to Standard Production, Use, and Data Validation

Medical marijuana generally possesses high levels of the psychotropic tetrahydrocannabinol (Δ9-THC) and lower levels of the nonpsychotropic cannabidiol (CBD). Pain mitigation and reduced severity of nausea and seizures are just a few of the therapeutic benefits reported by medical cannabis patients. Conversely, hemp contains high levels of CBD and lower levels (generally less than 0.3%) of THC. CBD has been reported to reduce or eliminate pain, stress, depression, inflammation, and headaches.

To complicate matters, there is evidence that a combination of CBD, a host of other minor cannabinoids, and a complex array of terpenoids may provide the most benefit—called the 

 (1). Both free and esterified sterols and triterpenes have been identified in cannabis and hemp, among which β-sitosterol and β-amyrin have been shown to have antibacterial properties (2). CBD-rich oil has become increasingly popular and is administered via sublingual drops, gel capsules, or as a topical ointment.

The main source of CBD-rich oil is industrial hemp. Hemp is considered a rustic plant because it is frost resistant, adapts to poor soil, reproduces easily, and does not require chemical fertilizers, pesticides, herbicides, or fungicides to thrive. A hemp crop tends to resist mildew and requires less water than cotton. Hemp textiles are considered softer than cotton.

CBD oil is derived as concentrate from carbon dioxide or butane extraction of hemp, sometimes followed by steam distillation or ethanol distillation for purification. The Farm Bill of 2014 distinguishes hemp from marijuana, yet interpreting the law is difficult in that “CBD oil” may be classified as marijuana. Various forms of hemp oil may be purchased online.

The U.S. Food and Drug Administration (FDA) has issued warning letters against unproven claims to some companies that market products containing CBD. As part of these actions, the FDA has determined the cannabinoid content of some hemp products and many were found to contain levels of CBD that are very different from the label claim. It is important to note that such products are not approved by the FDA for the diagnosis, cure, mitigation, treatment, or prevention of any disease (3).

The literature indicates more than 90 phytocannabinoids in cannabis and hemp (4). Only a handful are common targets of analysis for medical potency because they are the most abundant. Like cannabis, hemp oil may be analyzed easily and effectively for its cannabinoid content. This work presents the quantitative determination of 11 important cannabinoids, including the predominate CBD (Figure 1), in various hemp oils. (See upper right for Figure 1, click to enlarge; Figure 1: Cannabinoids found in hemp and marijuana.)

Using a comprehensive mixture of 11 cannabinoids (Shimadzu Part #220-91239-21; 250 µg/mL), standard curves were prepared for each target analyte with a minimum acceptable correlation coefficient (R2) of 0.999 over six standard levels. A linear dynamic range was established at 0.5–100 mg/L (ppm) in each analyte.

Instrument and Chromatographic Conditions

Instrument: Shimadzu LC-2030C UV (Cannabis Analyzer for Potency)

Column: Shimadzu NexLeaf CBX for Potency (150 mm x 4.6 mm, 2.7-μm 

Guard column: Shimadzu NexLeaf CBX Guard

Mobile-phase A: 0.09% phosphoric acid in water

Mobile-phase B: 0.09% phosphoric acid in acetonitrile

Gradient: B concentration 70% (initial) →95% (8 min)

Hemp oils are typically rich in CBD, with relatively minor concentrations of other cannabinoids. All cannabinoid targets have a linear dynamic range, above which the detector response ceases to be linear with concentration. Accurate quantitation relies on the detector response to the analyte lying within the calibration range. Therefore, two dilution factors were used, depending on the quantitative goal. One dilution factor yielded the appropriate detector sensitivity to the array of minor cannabinoids. A second, higher dilution factor was established for the most accurate quantitation of the major CBD component so that it’s response was within the established quantitative dynamic range established for that analyte. In practice, it was found that the two approaches yielded quantitative values for CBD that agreed within 0.2%.

Add 400 µL of isopropanol to a 2-mL glass vial

Add 10 µL of hemp oil sample and completely dissolve

Filter the mixture through a 0.2-µm PTFE syringe filter into a high performance liquid chromatography (HPLC) vial

Add 800 µL of methanol to a 2-mL glass vial

Five hemp oils were tested in this study; they were purchased from various mail-order vendors. The appearance and label information for three of the five appear in Figure 2, referenced as black, blue, and green. (See upper right for Figure 2, click to enlarge; Figure 2: Hemp oil 1, black label, label claim: 23 mg per serving; 100 servings per 100 mL; calculation of label claim: 23,000 µg/mL or 2.3%. Hemp oil 2, blue label, 500 mg per 30 mL, calculation of label claim: 16,666 µg/mL or 1.7%. Hemp oil 3, green label, 15 mg per 1 serving per 0.5 mL = 15 mg/0.5 mL, calculation of label claim: 30,000 µg/mL or 3.0%.) The two other samples tested but not pictured are referred to as red and yellow.

Chromatograms for hemp oils 1 (black), 2 (blue), and 3 (green) appear in Figure 3. (See upper right for Figure 3, click to enlarge; Figure 3: (a) Hemp oil 1 (black), total cannabinoids (81x dilution). (b) Hemp oil 1 (black), CBD only (405x dilution). (c) Hemp oil 2 (blue), total cannabinoids (81x dilution). (d) Hemp oil 2 (blue), CBD only (405x dilution). (e) Hemp oil 3 (green), total cannabinoids (81x dilution). (f) Hemp oil 3 (green), CBD only (405x dilution).) Peak labels appear for only those cannabinoids identified in the sample.

Quantitative Results Summary for Hemp Oils

The astute reader may correctly ask about the noncannabinoid constituents in the sample and how they may influence the chromatography. As the sample preparation presented here is essentially a simple dilution of the oil sample into injectable form, nothing is done to separate cannabinoids from terpenes, phenolics, or pigment compounds. Under the reversed-phase chromatography conditions used here, any pigment compounds emerge early in the chromatography.

The sum total terpene content of hemp and cannabis is 1–3% (2), comprising possibly hundreds of terpenoids. As for chemistry, many triterpenes and sesquiterpenes have similar polarities to the cannabinoids and are expected to retain on the analytical column to similar degrees as the cannabinoids. Within the detection limits of this work, any terpenoids are undetectable, essentially lost in the baseline.

Tables I and II summarize the quantitative findings for the samples studied. Table I reflects the accurate quantitation of CBD using the higher dilution factor (405X). (See upper right for Table I, click to enlarge; Table I: Summary of CBD quantitative determination for five hemp oils.) Table II reflects the quantitation of the comprehensive target list. (See upper right for Table II, click to enlarge; Table II: Summary of total cannabinoids quantitative determination.)

As a general sample observation, hemp oils 1 (black) and 2 (blue) exhibited a transparent, weak-yellow or green coloration. Our assumption was that each of these is a product of multistep purification after extraction; for example, carbon dioxide or butane extraction followed by steam distillation. Notably, hemp oil 3 (green) was opaque brown or green and gritty in appearance. It also had the most intense smell—a distinctly “earthy” odor. Accordingly, our assumption was that the sample was the result of crude extraction only, with no further refinement.

It is important to note that it has been reported in the literature that the whole plant can be more beneficial to the consumer because it contains not only the cannabinoids, but also an array of terpenes providing a synergistic whole plant benefit. The whole plant can also provide essential fatty acids, plant sterols for lowering cholesterol, and antioxidants chlorophyll and vitamin E.

Hemp oils 1 (black) and 2 (blue) showed high ratios of CBD to total cannabinoids, both at 92%, and the lowest quantity of other cannabinoids. This finding supported the assumption, along with transparency and color, that these oils were the more highly purified samples. Both samples also tested close to label claim at 95% and 92%, respectively.

Hemp oil 3 (green) revealed the highest content of CBD and total cannabinoids, yet exhibited the lowest ratio of CBD to total cannabinoids (59%). This observation is consistent with the assumption that its crude appearance reflected the least amount of post-extraction purification. Although its CBD percent of label claim tested the lowest (81%), this sample did contain the highest level of CBD compared to all other oils tested.

Hemp oils 4 (red) and 5 (yellow) tested higher than label claim at 122% and 200%, respectively. The observation is consistent with FDA findings for CBD products, perhaps calling into question the type and accuracy of testing used to justify label claims.

In summary, all samples contained less Δ9-THC than the amount allowed by law (0.3%). Also, all samples showed an array of other cannabinoids, but the minor component, THC-V, was not detected in any of the hemp oil samples. From a quality control point of view, two samples were within a reasonable range of the label claim at ±10%. One sample was well below label claim and two other samples were well above the label claims, one by as much as 200%. When purchasing CBD oils, one should consider

C.M. Andre, J.F. Hausman, and G. Guerriero, “Cannabis Sativa: the Plant of the Thousand and One Molecules,” 

US Food and Drug Administration, Warning Letters: 

https://www.fda.gov/newsevents/publichealthfocus/ucm484109.htm

, MS, is the HPLC product manager for Shimadzu Scientific Instruments in Columbia, Maryland. 

, PhD, is the general manager for Shimadzu Scientific Instruments. Direct correspondence to: 

The Quantitative Determination of Phytocannabinoids in Hemp Oils Using HPLC with UV Detection

The 2018 Cannabis Science Conference will be held August 27–29, in Portland, Oregon. With the conference quickly approaching, we sat down with Josh Crossney, president and CEO of CSC Events, for a preview of what this year’s show will offer attendees.

What are some of the key topics that this year’s Cannabis Science Conference will address?

 Some of the key topics include advances in academic research and quality control (QC) testing, genomics, efforts to improve standardization, improvements in analytical instrumentation and testing methods, as well as greater medicinal cannabis information sharing, including physician and patient presentations. In the medical track, I also see increasing focus on cannabis as a more effective alternative to opiates. Opiates kill nearly 100 Americans a day, whereas no one has ever died as a direct result from a cannabis overdose. What could be a more relevant and important discussion than advancing alternative medicines that put an end to the terrible opioid epidemic?

We have also added a cultivation track this year, which differs greatly from other conferences because the focus is more technical. This year we also have technical updates from several cannabis testing labs, with topics ranging from sample preparation and method development to microwave-assisted extractions and informatics.

Can you tell us more about the addition of a cultivation track? Why did you feel there was a need to add that track?

At last year’s Canna Boot Camp, there was great interest from all participants in a phenomenal cultivation session hosted by Autumn Karcey (Cultivo, Inc.) and Ken Kovash (GI Grow). Cultivation techniques greatly impact cannabis science, both in terms of therapeutic efficacy as well as potential introduction of contaminants.

Additionally, many QC and research scientists lack a fundamental understanding of cannabis cultivation, so we felt there was a strong need to help bridge this gap by introducing a cultivation track.

What do you hope for people to learn or gain from your conference this year?

 My hope is that attendees walk away from this year’s conference feeling educated, empowered, inspired, and connected. By empowered, I mean that the Cannabis Science Conference has become the annual pilgrimage for key opinion leaders like Tracy Ryan, Professor Jack Henion, Professor Dedi Meiri, Dr. Scott Kuzdzal, Dr. Uma Dhanabalan, Dr. Sue Sisley, Janie Maedler, Sharlene Mavor, and Dr. Jahan Marcu. These truly inspirational people have so much knowledge to share, and at the Cannabis Science Conference we work very hard to maximize networking with these experts; including opportunities ranging from discussions at poster sessions and exhibit booths to participation in interactive panel discussions. Attendees will walk away with new knowledge and collaborations that will help catalyze and advance cannabis science for years to come.

Can you give us any hints as to who your plenary speaker will be?

: Every year the Cannabis Science Conference works diligently to create relationships with celebrity influencers who are either in the cannabis space, or looking to get involved. We are thrilled to be able to introduce Fran Drescher to the cannabis science community. It has been such a pleasure getting to know Fran over the past few years through Cancer Schmancer and their wonderful events, such as the annual Cancer Schmancer Health Summit in Los Angeles and Cabaret Cruise in NYC. When I saw that Fran and Cancer Schmancer were beginning to include medical cannabis education into their events, I knew that she would be a perfect fit to address our esteemed guests at the 2018 Cannabis Science Conference.

I mentioned previously that I want this year’s attendees to walk away inspired: Fran Drescher will most certainly inspire people.

Is there anything else you’d like to add about this year’s conference?

 This year we received hundreds of scientific abstracts. In addition to adding a cultivation track, attendees will see expansion in our poster sessions as well as the number of vendors on our exhibition floor. We are anticipating more than 160 sponsors, exhibitors, and media partners this year!

I am excited to announce that our Canna Boot Camp full-day, hands-on workshop will return to Chalice Farms again this year. By the time this article goes to print there will likely be only a few tickets remaining, but I strongly encourage everyone interested in a more hands-on experience covering everything from cannabis cultivation and preprocessing to extractions, analytical testing, edibles manufacturing, and dispensary operation to attend a future Canna Boot Camp.

 for your continued support. Your sister publications, 

, have been our premier media partner now for years, and I look forward to working with your team for years to come. There are many exciting things ahead for us!

Editor's Note: At the time this article originally went to press, Fran Drescher had not been announced as the plenary speaker at the 2018 Cannabis Science Conference. This version has been updated to include that announcement. 

Preview of the 2018 Cannabis Science Conference

The cannabis industry has been struggling to keep pace with the changing attitudes toward the drug. With no standardized regulations for quality control between states or countries, there is a huge gap to fill in terms of rigorous testing. The industry is considerably different than the pharmaceutical industry, where drugs pass through extensive quality control to meet stringent safety standards. The challenge for global cannabis producers and processors is how to combat the lack of rigorous testing and oversee quality control to ensure reliable, safe, and consistent products. Gas chromatography (GC) is a successful analytical technique for cannabis testing that provides opportunities to advance the cannabis industry.

The lack of standardized regulations means that producers of cannabis and cannabis-derived products can supply goods unhindered, potentially carrying unsafe levels of pesticides, mold, fungi, and bacteria that can be hazardous to human health. But the cannabis industry is constrained by a legal framework that makes it very difficult to find cannabis with tested cannabinoid content.

This article highlights the work that is being done by Shamanics, a cannabis oil extraction company based in Amsterdam (1). The company works with cannabis, in particular the cannabinoid cannabidiol (CBD), to produce high quality CBD oil. Unlike many of its competitors in the Netherlands, Shamanics conducts key analyses on products before they’re taken to market to provide tested, quality products to meet consumer demand.

Cannabis consists of the dried flowers of the female 

 L. plant, also known as hemp or marijuana, and contains a number of active substances including Δ

June/July 2018

Pioneering Spirits: Three Women Leaders in Cannabis Science Share Their Trials, Tribulations, Successes, and Advice

Applying Ultrasonic Energy to Cannabis Production and Quality Control

Holding Data to a Higher Standard, Part I: A Guide to Standard Production, Use, and Data Validation

The Quantitative Determination of Phytocannabinoids in Hemp Oils Using HPLC with UV Detection

Preview of the 2018 Cannabis Science Conference

Cannabis Quality Control Testing Using Gas Chromatography

A Comprehensive Approach to Pesticide Residue Analysis in Cannabis

Determination of Multiple Metals in Cannabis Samples Using ICP-MS and ICP-OES

I Can’t Afford Good Science: The Battle Between Economics and Method Development in the Emerging Cannabis Market

Medical Cannabis: Back to the Future After a Brief Push to the Past