TFNR is now the first recreational cannabis-testing laboratory in Alaska accredited to ISO/IEC 17025 standard. According to Roger Brauninger, A2LA biosafety program manager, this accreditation is a sign of attention to thorough science. “Cannabis testing laboratories that have gained ISO/IEC 17025 accreditation have demonstrated their competence and commitment to rigorous science,” says Brauninger. “In the greatly scrutinized recreational cannabis industry, we are pleased to have granted the first accreditation of its kind in Alaska.”
Roger Brauninger, A2LA biosafety program manager
According to the press release, the ISO/IEC 17025 accreditation is the most significant third-party lab accreditation an organization can receive. The standard confirms labs have management, quality and technical systems designed for accurate and repeatable analyses, in addition to proper administrative processes for testing.
Jessica Alexander, technical director of the TNFR laboratory, says this is the first step in many to researching the medical properties of cannabis. “By achieving ISO/IEC 17025 accreditation, The New Frontier Research believes that it advances the cannabis industry as a whole so that we can conduct legitimate research to unlock the amazing potential that this plant has for development of more effective medicines to address problems like opioid dependence and pediatric seizures,” says Alexander.
Oregon cannabis regulators began enforcing new rules over the weekend when the October 1st compliance deadline passed. Compared to the relatively cut-and-dried new Colorado regulations, the Oregon cannabis market faces more complex and changing regulatory compliance issues.
The new rules in Oregon address changes to testing, packaging and labeling regulations along with concentration and serving size limits, according to a bulletin published by the Oregon Health Authority (OHA) and the Oregon Medical Marijuana Program (OMMP) earlier this week. Most of the new rules are meant to add safeguards for public health and consumer safety, while putting an emphasis on keeping cannabis away from children.
Around the same time, the Oregon Liquor Control Commission (OLCC) published a bulletin with a new temporary rule that is meant to prevent marketing to children. The OLCC’s temporary rule clarifies “restrictions on product wording commonly associated with products marketed by or to children.” The OLCC reviewed around 500 strain names and found roughly 20 of them that could appeal to children. The OLCC will not approve labels that include strain names like Girl Scout Cookies, Candyland and Charlotte’s Web, among others. This means that breeders and growers have to change strain names on labels like Death Star, Skywalker and Jedi Kush because they contain a reference to the Star Wars franchise, which is marketed to children.
Oregon Marijuana Universal Symbol for Printing
The new testing regulations establish requirements for testing cannabis products for THC and CBD concentrations, water activity, moisture content, pesticides and solvents in concentrates. They also stipulate that ORELAP-accredited laboratories must perform the testing. In the time leading up to the compliance deadline, many lacked confidence that ORELAP would accredit enough laboratories to meet the demand for testing. “We have heard from existing accredited labs that they can meet demand for cannabis product testing,” says Jonathan Modie, spokesman for the OHA. “We don’t yet know how much product requires testing, so we can’t speculate on whether labs will indeed be able to meet demand.” It is still unclear at this time if there are enough laboratories to perform all of the testing for cannabis products in the state.
The universal symbol on a label of a cannabis product purchased after Oct. 1
At this time, 16 laboratories have been accredited for some form of testing, but only four labs have been accredited for pesticide testing. A list of the labs that ORELAP has accredited can be found here. Notably, only one lab is accredited for testing microbiological contaminants, such as E. coli. Testing for microbiological contaminants is not required for all cannabis products sold, rather it is only required upon written request by the OHA or OLCC.
The new labeling and packaging requirements concern testing, consumer education, childproofing and preventing marketing to minors. All cannabis products must contain a label that has been pre-approved by the OLCC. “Cannabis products have to be clearly labeled, showing that is has been tested, or if it has not been tested then it must display ‘does not meet new testing requirements’,” says Modie. “It [the label] must be clear, legible and readable, so they [the consumer] know exactly what it contains, including what cannabis product is inside the package, how much of it, how much THC, and where the product came from.”
According to Modie, it is particularly important that the packaging is not attractive to minors. Cartoons, designs and names that resemble non-cannabis products intended for, or marketed to children, should not be on the packaging or label. “Part of our education to the public and recreational cannabis users focuses on keeping these products out of reach of children in the first place, like storing cannabis in a locked area or an area where a child cannot reach or see,” says Modie. “Our goal is always to protect public health.”
In previous articles, you may recall that Amanda Rigdon, one our contributing authors, stated that instrument calibration is the foundation of all data quality. In this article, I would like to expand on that salient point. A properly calibrated instrument will, in fact, produce reliable data. It is the foundation we build our data upon. All foundations are comprised of building blocks, and our laboratory is no exception. If we take this analogy further, the keystone to the laboratory foundation, the stone that all data relies upon, is the analytical reference material. Proper calibration means that it is based on a true, accurate value. That is what the reference material provides. In this article, I would like to expand on the use and types of reference materials in analytical testing.
To develop sound analytical data, it is important to understand the significance of reference materials and how they are properly used. The proper selection and use of reference materials ensures the analytical certainty, traceability and comparability necessary to produce scientifically sound data. First, let’s take a moment to define the types of commonly used reference materials. According to the International Vocabulary of Metrology (VIM), a Reference Standard (RS) is something that is reused to measure against, like a balance or a set of weights. A Reference Material (RM) is a generic term. It is described as something that is prepared using a RS that is homogeneous, stable and is consumed during its use for measurement. An example of an RM is the solutions used to construct a calibration curve, often referred to as calibration standards, on your GC or LC. Due to the current state of cannabis testing, reference materials can be hard to find and, even more critical, variable in their accuracy to a known reference standard. Sometimes this is not critical, but when quantifying an unknown, it is paramount.
RMs can be either quantitative or qualitative. Qualitative RMs verify the identity and purity of a compound. Quantitative RMs, on the other hand, provide a known concentration, or mass, telling us not only what is present, and its purity, but also how much. This is typically documented on the certificate that accompanies the reference material, which is provided by the producer or manufacturer. The certificate describes all of the properties of the starting materials and steps taken to prepare the RM. For testing requirements, like potency, pesticides, etc., where quantitation is expected, it is important to use properly certified quantitative RMs.
Now, the pinnacle of reference materials is the Certified Reference Material (CRM). VIM defines a Certified Reference Material (CRM) as an RM accompanied by documentation issued by an authoritative body and provides one or more specified property values, with associated uncertainties and traceability using valid procedures. A CRM is generally recognized as providing the highest level of traceability and accuracy to a measurement – the strongest keystone you can get for your foundation. It is also important to recognize that the existence of a certificate does not make a reference material a CRM. It is the process used in manufacturing that makes it a CRM, and these are typically accreditations earned by specific manufacturers who have invested on this level of detail.
Now that we understand the types of reference materials we can choose, in the next article of this series we will describe what a CRM provider must do to ensure the material and how we can use them to develop reliable data. Without properly formulated and prepared CRMs, instrument calibration and the use of internal standards are less effective at ensuring the quality of your data.
If you have any questions please contact me, Joe Konschnik at (800) 356-1688 ext. 2002 by phone, or email me at joe.konschnik@restek.com.
Emerald Scientific, a supplier of reagents, supplies, equipment and services to cannabis testing and extraction facilities, recently named Amanda Rigdon as the company’s chief technology officer. Rigdon previously worked at Restek Corporation, a manufacturer of chromatography supplies, as an applications chemist and a member of their gas chromatography columns product marketing team.
Amanda Rigdon, chief technology officer at Emerald Scientific
Before working in the cannabis space, Rigdon began her career in the pharmaceutical and clinical/forensics industries. She spent seven years in Restek’s applications lab where she was responsible for the development and application of chromatography products for the pharmaceutical and clinical/forensics arenas. In recent years, she has been an outspoken advocate in the science of cannabis while with Restek.
As a strong proponent for scientific progress in cannabis, she brings extensive technical expertise and marketing experience related to cannabis testing and research. Presenting at numerous cannabis science conferences and seminars, she regularly provides education on analytical methods and best practices in the lab.
As a contributing author to CannabisIndustryJournal.com and member of the editorial advisory board, she writes a column addressing challenges in the lab and providing technical advice. “I’m thrilled to be a part of the Emerald Scientific team and a member of the cannabis community as a whole,” says Rigdon. “I’ve known the folks at Emerald [Scientific] for years; they’re among the best in the business, and they’ve been supporting the cannabis community since the early days of cannabis analytics.” Rigdon’s mantra in the cannabis testing space has long been to support sound science in the interest of protecting patient and consumer health.
“I’m really looking forward to using my technical skills in conjunction with Emerald’s position and reach in the market to make work easier for cannabis labs through education, applications and new products,” adds Rigdon. Emerald Scientific is widely known in the cannabis testing community for The Emerald Test, an inter- laboratory comparison proficiency test, organized twice per year. It also hosts The Emerald Conference, an annual scientific meeting for scientists, policy makers, producers, and other key members of the cannabis industry. ˇThe Emerald Conference is the first scientifically focused conference for the cannabis industry, now coming up on its third annual conference in February 2017.
If your laboratory utilizes an HPLC system for cannabinoid and pesticide analysis, it can be a daunting task to select a stationary phase that is both practical and sufficient for the separation at hand. Typically, when developing a new method, an analyst will either evaluate a column they already have in house or seek out a referenced phase/dimension in the literature before exploring other available alternatives.
Chemical structure of Tetrahydrocannabinol (THC)
A C18 phase is an excellent first choice for non-polar or slightly polar compounds. If the analyte in question has a minimum ratio of three carbon atoms for every heteroatom, it will be sufficiently retained on this phase. THC and other relative cannabinoids are prime candidates for separation via C18 due to their non-polar nature and structural components.
In addition to a universal C18 phase, alternative selectivity options do exist for laboratories concerned with the analysis of cannabinoid content. Another prevalent column choice features an aromatic or poly-aromatic stationary phase. Compatible with highly aqueous mobile phases, aromatic and poly-aromatic columns primarily rely on hydrophobic and π-π interactions as their main analyte retention mechanisms. Poly-aromatic phases provide enhanced retention and are more hydrophobic when compared to a single phenyl ring structure. While C18 phases are not ideal for resolving structural isomers, poly-aromatic columns are capable of separating these ring-based compounds. Chromatographers with a background in forensic analysis may be very familiar with this type of HPLC column due to its extensive use in drug testing applications.
Chemical structure of chlormequat, a hazardous polar pesticide commonly banned for use in cannabis cultivation
Besides cannabinoid content, many cannabis scientists are equally concerned with accurate quantitation of pesticides within a given sample. Many pesticides that have found themselves on regulatory lists in states such as Massachusetts, Washington or Nevada are extremely polar. In order to increase retention of these compounds, and thus improve your overall chromatographic method, it can be extremely advantageous to select a column that allows you to start your gradient at 100% aqueous mobile phase. An aqueous or polar modified C18 column contains an embedded polar group, polar side chain or polar end-capping to allow for separation of polar compounds, while still retaining and resolving non-polar analytes. For laboratories that necessitate the use of only one analytical column, an aqueous C18 phase will allow for separation of monitored pesticides without compromising the quality of cannabinoid data produced.
One must also take into account column length, pore size and particle size when purchasing a column. For the purposes of any cannabis related analysis, a pore size of 100-120Å will suffice. Larger pore columns are typically reserved for large peptides, proteins and polymers. Depending on the sensitivity and resolution needed within your laboratory, particle size can range from 1.8-5um, with the highest sensitivity and resolution coming from the smaller particle size. Core shell technology is also a popular option for laboratories who want to keep the pressure of their HPLC system low, without sacrificing any quality of their resolution. Column lengths of 50 or 100 mm are common for chromatographers who want to achieve sufficient sample separation while keeping their run times relatively short.
Regardless of the HPLC phase selected, it is very important that a guard cartridge is also used. Guard cartridges are traditionally the same phase and particle size of the HPLC column choice and help to prolong analytical column life. They provide additional sample clean up and are widely recommended by the majority of chromatography experts. Upon reviewing one’s options for HPLC phases and acquiring the necessary guard column, your cannabis laboratory will be ready to get the most out of your HPLC system for your analysis needs.
Emerald Scientific recently announced results for their latest round of the semi-annual Inter-Laboratory Comparison and Proficiency Test (ILC/PT), and the outcomes may bode well for one of the most vital quality and safety aspects of the cannabis industry. According to Cynthia Ludwig, director of technical services at the American Oil Chemists’ Society (AOCS), there are no official methods for cannabis testing from an internationally recognized non-profit organization known to provide ‘official methods’ to various industries, so method validation needs to be done in-house, which is very costly and time-consuming. Cannabis testing labs are charged with the difficult task of providing honest, consistent and accurate results for potency, pesticide residue, residual solvents and contaminants. AOCS partnered with Emerald Scientific in this round of ILC/PT and preformed the statistical analysis and reports. For the first time in The Emerald Test’s history, participants were able to review all of the raw data and were given a consensus mean, z-scores and kernel density plots in order to compare themselves to other participants.
Emerald Scientific’s ILC/PT program measures how accurately a cannabis lab performs along with comparing it to other labs for an indicator of variability and ways to improve, according to a press release. 46 cannabis laboratories participated in The Emerald Test’s latest round of proficiency testing for potency and residual solvents. Cynthia Ludwig sits on the advisory panel to give direction and industry insights, addressing specific needs for cannabis laboratories. Kirsten Blake, director of sales at Emerald Scientific, believes that proficiency testing is the first step in bringing consistency to cannabis analytics. “The goal is to create some level of industry standards for testing,” says Blake. Participants in the program are given data sets, judged by a consensus mean, so labs can see their score compared to the rest of the cannabis testing industry.
Proficiency tests like The Emerald Test give labs the ability to view how consistent their results are compared to the industry’s results overall. According to Ludwig, the results were pleasantly surprising. “The results were better than expected across the board; the vast majority of labs were within the acceptable range,” says Ludwig. The test is anonymous so individual labs can participate freely. “The overall performance of the participating labs in the Potency and Solvent Residue Emerald Test were very encouraging,” says Ludwig. “All but a couple of labs had the majority of their results fall within two standard deviations of the consensus mean, which is generally accepted as being within the acceptable limits to most evaluators.” Although requirements for labs testing cannabis differ in each state, Ludwig says the results show the ability of these labs to competently perform the tests and generate reliable results. “Given the lack of harmonized regulations, this is a testament to the self-imposed quality standards the industry is trying to achieve.”
Reggie Gaudino, Ph.D., vice president of scientific operations and director of genetics at Steep Hill Laboratories. (photo credit: Preston Gannaway)
Among the laboratories that participated, Steep Hill Laboratories joined the test at two of their locations. Reggie Gaudino, Ph.D., vice president of scientific operations and director of genetics at Steep Hill Laboratories, believes that tests like the Emerald Test ensure that the cannabis labs are performing their function to the best of their ability, which is extraordinarily important. “We, and not just Steep Hill, but all testing labs, are the custodians of quality and safety for the cannabis industry,” says Gaudino. “If we are not doing our best to ensure the quality of our science is beyond reproach, then we are failing the consumer; if even one person gets sick or dies because a lab cut corners and tried to make extra money, that is one person too many.” Accurate testing comes from internal and external proficiency testing.
According to Gaudino, how cannabis labs perform in The Emerald Test can affect every aspect of cannabis consumption: “Correct dosing from potency analysis reports, identification of as many, if not all, active compounds known to enable the consumer to make a determination as to which strain, edible or concentrate would be most beneficial and assurance that there are no harmful chemicals or biological contaminants on cannabis or cannabis derivatives; all of it stems from being able to accurately test.” Gaudino is a major proponent of The Emerald Test because it provides some measure of consistency and accuracy in the cannabis industry. Until more consistent regulations for cannabis testing are formed on a national scale, self-imposed quality standards such as The Emerald Test helps labs, growers and consumers know they are getting reliable data.
As a result of the rapidly developing cannabis industry, many forensic toxicology labs are looking for fast, reliable and cost-effective methods to determine cannabis potency and pesticide residue in edibles. Although the pros and cons of legalization are still heavily debated throughout the country, all scientists agree that uniform testing policies and procedures need to be established as soon as possible.
Within environmental and food testing laboratories, the use of QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) has been practiced widely for the past 15 years. In 2003, Dr.’s Michelangelo Anastassiades and Steven Lehotay published the first QuEChERS application, which detailed the determination of pesticide residues in produce. Since then, QuEChERS has become the gold standard for the testing and analysis of a wide variety of edible matrices. United Chemical Technologies (UCT) was the first company to commercialize the product and it became apparent that the application of this technology to cannabis edibles was a natural solution to pesticide residue testing. All of the data from the QuEChERS cannabis edibles pesticide and potency analyses can be found here.
Sample preparation
Hard candy before freezer mill grinding
Preparation of a sample for QuEChERS analysis varies depending on the type of edible product being tested. Baked goods, chocolate bars and hard candies should be ground into a fine powder prior to analysis. Although this can be achieved using a product such as a SPEX 6770 freezer mill, a blender can suffice when analyzing typical plant-based samples. Liquid samples, such as sodas or teas, should be degassed prior to analysis, whereas any gummy-based candies should be cut into fine pieces. With the exception of the liquid samples, all other matrices should then be hydrated for one hour within a QuEChERS extraction tube.
Hard candy after freezer mill grinding
Following sample preparation, acetonitrile is added to all samples along with a proprietary blend of QuEChERS extraction salts. These salts remove water from the organic phase, help to facilitate solvent partitioning and protect base-sensitive analytes from degradation. After shaking and centrifuging the sample, three distinct layers are formed. The top layer, which is the organic phase, can then be aliquoted off for further sample clean-up or dilution.
A mint milk chocolate sample after QuEChERS extraction
For pesticide analysis, an aliquot of the organic layer was subjected to dispersive solid phase extraction (dSPE). This process utilizes an additional blend of proprietary sorbents that remove chlorophyll, sugars, organic acids and fatty compounds from the sample. The resulting extract is free of pigmentation and is ready for analysis on the LC-MS/MS. All samples that were analyzed for cannabinoids did not undergo dSPE; rather, a serial dilution was carried out due to the high concentration of cannabinoids in the original organic layer. The original QuEChERS extract required a dilution of 100-200x in order to have a sample that was ultimately suitable for analysis on LC-MS/MS. A UCT Selectra Aqueous C18 HPLC Column and Guard Column were used in a Thermo Scientific Dionex UltiMate 3000 LC System. An aqueous C18 column was selected due to the extreme polarity of the pesticides being analyzed.
Comparison of QuEChERS extracts before and after dSPE cleanup (gummy sample)
Summary
This application utilizes the advantages of UCT’s proprietary QuEChERS combination to extract 35 pesticides and 3 cannabinoids, including tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) in edibles, followed by either serial dilutions for cannabis potency analysis, or a dSPE cleanup for pesticide residue analysis. This hybrid method allows QuEChERs, which are extensively used in the food testing industry, to be utilized in a forensic setting.
The American Oil Chemists’ Society (AOCS) held its annual conference in Salt Lake City this week, with a track focused on cannabis testing and technology. Cynthia Ludwig, director of technical services at AOCS and member of the advisory panel to The Emerald Test, hosted the two-day event dedicated to all things extraction technology and analytical testing of cannabis.
Highlights in the discussion surrounding extraction technologies for the production of cannabis concentrates included the diversity of concentrate products, solvent selection for different extraction techniques and the need for cleaning validation in extraction equipment. Jerry King, Ph.D., research professor at the University of Arkansas, began the event with a brief history of cannabis processing, describing the physical morphologies in different types of extraction processes.
J. Michael McCutcheon presents a history of cannabis in medicine
Michael McCutcheon, research scientist at Eden Labs, laid out a broad comparison of different extraction techniques and solvents in use currently. “Butane is a great solvent; it’s extremely effective at extracting active compounds from cannabis, but it poses considerable health, safety and environmental concerns largely due to its flammability,” says McCutcheon. He noted it is also very difficult to get USP-grade butane solvents so the quality can be lacking. “As a solvent, supercritical carbon dioxide can be better because it is nontoxic, nonflammable, readily available, inexpensive and much safer.” The major benefit of using supercritical carbon dioxide, according to McCutcheon, is its ability for fine-tuning, allowing the extractor to be more selective and produce a wider range of product types. “By changing the temperature or pressure, we can change the density of the solvent and thus the solubility of the many different compounds in cannabis.” He also noted that, supercritical carbon dioxide exerts tremendous pressure, as compared to hydrocarbon solvents, so the extraction equipment needs to be rated to a higher working pressure and is generally more expensive.
John A. Mackay, Ph.D., left at the podium and Jerry King, Ph.D., on the right
John A. Mackay, Ph.D., senior director of strategic technologies at Waters Corporation, believes that cannabis processors using extraction equipment need to implement cleaning SOPs to prevent contamination. “There is currently nothing in the cannabis industry like the FDA CMC draft for the botanical industry,” says Mackay. “If you are giving a child a high-CBD extract and it was produced in equipment that was previously used for another strain that contains other compounds, such as CBG, CBD or even traces of THC extract, there is a high probability that it will still contain these compounds as well as possibly other contaminants unless it was properly cleaned.” Mackay’s discussion highlighted the importance of safety and health for workers throughout the workflow as well as the end consumer.
Jeffrey Raber, Ph.D., chief executive officer of The Werc Shop, examined different testing methodologies for different applications, including potency analyses with liquid chromatography. His presentation was markedly unique in proposing a solution to the currently inconsistent classification system for cannabis strains. “We really do not know what strains cause what physiological responses,” says Raber. “We need a better classification system based on chemical fingerprints, not on baseless names.” Raber suggests using a chemotaxonomic system to identify physiological responses in strains, noting that terpenes could be the key to these responses.
Cynthia Ludwig welcomes attendees to the event.
Dylan Wilks, chief scientific officer at Orange Photonics, discussed the various needs in sample preparation for a wide range of products. He focused on sample prep and variation for on-site potency analysis, which could give edibles manufacturers crucial quality assurance tools in process control. Susan Audino, Ph.D., chemist and A2LA assessor, echoed Wilks’ concerns over sample collection methods. “Sampling can be the most critical part of the analysis and the sample size needs to be representative of the batch, which is currently a major issue in the cannabis industry,” says Audino. “I believe that the consumer has a right to know that what they are ingesting is safe.” Many seemed to share her sentiment about the current state of the cannabis testing industry. “Inadequate testing is worse than no testing at all and we need to educate the legislators about the importance of consumer safety.”
46 cannabis laboratories participated in The Emerald Test’s latest round of proficiency testing for potency and residual solvents. Cynthia Ludwig sits on the advisory panel to give direction and industry insights, addressing specific needs for cannabis laboratories. Kirsten Blake, director of sales at Emerald Scientific, believes that proficiency testing is the first step in bringing consistency to cannabis analytics. “The goal is to create some level of industry standards for testing,” says Blake. Participants in the program will be given data sets, judged by a consensus mean, so labs can see their score compared to the rest of the cannabis testing industry. Proficiency tests like The Emerald Test give labs the ability to view how consistent their results are compared to the industry’s results overall. According to Ludwig, the results were pleasantly surprising. “The results were better than expected across the board; the vast majority of labs were within the acceptable range,” says Ludwig. The test is anonymous so individual labs can participate freely.
The AOCS cannabis working groups and expert panels are collaborating with Emerald Scientific to provide data analytics reports compliant with ISO 13528. “In the absence of a federal program, we are trying to provide consistency in cannabis testing to protect consumer safety,” says Ludwig. At the AOCS annual meeting, many echoed those concerns of consumer safety, proposing solutions to the current inconsistencies in testing standards.
This column is devoted to helping cannabis analytical labs generate valid data right now with a relatively small amount of additional work. The topic for this article is instrument calibration – truly the foundation of all quality data. Calibration is the basis for all measurement, and it is absolutely necessary for quantitative cannabis analyses including potency, residual solvents, terpenes, and pesticides.
Just like a simple alarm clock, all analytical instruments – no matter how high-tech – will not function properly unless they are calibrated. When we set our alarm clock to 6AM, that alarm clock will sound reproducibly every 24 hours when it reads 6AM, but unless we set the correct current time on the clock based on some known reference, we can’t be sure when exactly the alarm will sound. Analytical instruments are the same. Unless we calibrate the instrument’s signal (the response) from the detector to a known amount of reference material, the instrument will not generate an accurate or valid result.
Without calibration, our result may be reproducible – just like in our alarm clock example – but the result will have no meaning unless the result is calibrated against a known reference. Every instrument that makes a quantitative measurement must be calibrated in order for that measurement to be valid. Luckily, the principle for calibration of chromatographic instruments is the same regardless of detector or technique (GC or LC).
Before we get into the details, I would like to introduce one key concept:
Every calibration curve for chromatographic analyses is expressed in terms of response and concentration. For every detector the relationship between analyte (e.g. a compound we’re analyzing) concentration and response is expressible mathematically – often a linear relationship.
Now that we’ve introduced the key concept behind calibration, let’s talk about the two most common and applicable calibration options.
Single Point Calibration
This is the simplest calibration option. Essentially, we run one known reference concentration (the calibrator) and calculate our sample concentrations based on this single point. Using this method, our curve is defined by two points: our single reference point, and zero. That gives us a nice, straight line defining the relationship between our instrument response and our analyte concentration all the way from zero to infinity. If only things were this easy. There are two fatal flaws of single point calibrations:
We assume a linear detector response across all possible concentrations
We assume at any concentration greater than zero, our response will be greater than zero
Assumption #1 is never true, and assumption #2 is rarely true. Generally, single point calibration curves are used to conduct pass/fail tests where there is a maximum limit for analytes (i.e. residual solvents or pesticide screening). Usually, quantitative values are not reported based on single point calibrations. Instead, reports are generated in relation to our calibrator, which is prepared at a known concentration relating to a regulatory limit, or the instrument’s LOD. Using this calibration method, we can accurately report that the sample contains less than or greater than the regulatory limit of an analyte, but we cannot report exactly how much of the analyte is present. So how can we extend the accuracy range of a calibration curve in order to report quantitative values? The answer to this question brings us to the other common type of calibration curve.
Multi-Point Calibration:
A multi-point calibration curve is the most common type used for quantitative analyses (e.g. analyses where we report a number). This type of curve contains several calibrators (at least 3) prepared over a range of concentrations. This gives us a calibration curve (sometimes a line) defined by several known references, which more accurately expresses the response/concentration relationship of our detector for that analyte. When preparing a multi-point calibration curve, we must be sure to bracket the expected concentration range of our analytes of interest, because once our sample response values move outside the calibration range, the results calculated from the curve are not generally considered quantitative.
The figure below illustrates both kinds of calibration curves, as well as their usable accuracy range:
This article provides an overview of the two most commonly used types of calibration curves, and discusses how they can be appropriately used to report data. There are two other important topics that were not covered in this article concerning calibration curves: 1) how can we tell whether or not our calibration curve is ‘good’ and 2) calibrations aren’t permanent – instruments must be periodically re-calibrated. In my next article, I’ll cover these two topics to round out our general discussion of calibration – the basis for all measurement. If you have any questions about this article or would like further details on the topic presented here, please feel free to contact me at amanda.rigdon@restek.com.
I have been working with the chemical analysis side of the cannabis industry for about six years, and I have seen tremendous scientific growth on the part of cannabis labs over that time. Based on conversations with labs and the presentations and forums held at cannabis analytical conferences, I have seen the cannabis analytical industry move from asking, “how do we do this analysis?” to asking “how do we do this analysis right?” This change of focus represents a milestone in the cannabis industry; it means the industry is growing up. Growing up is not always easy, and that is being reflected now in a new focus on understanding and addressing key issues such as pesticides in cannabis products, and asking important questions about how regulation of cannabis labs will occur.
While sometimes painful, growth is always good. To support this evolution, we are now focusing on the contribution that laboratories make to the safety of the cannabis consumer through the generation of quality data. Much of this focus has been on ensuring scientifically sound data through regulation. But Restek is neither a regulatory nor an accrediting body. Restek is dedicated to helping analytical chemists in all industries and regulatory environments produce scientifically sound data through education, technical support and expert advice regarding instrumentation and supplies. I have the privilege of supporting the cannabis analytical testing industry with this goal in mind, which is why I decided to write a regular column detailing simple ways analytical laboratories can improve the quality of their chromatographic data right now, in ways that are easy to implement and are cost effective.
Anyone with an instrument can perform chromatographic analysis and generate data. Even though results are generated, these results may not be valid. At the cannabis industry’s current state, no burden of proof is placed on the analytical laboratory regarding the validity of its results, and there are few gatekeepers between those results and the consumer who is making decisions based on them. Even though some chromatographic instruments are super fancy and expensive, the fact is that every chromatographic instrument – regardless of whether it costs ten thousand or a million dollars – is designed to spit out a number. It is up to the chemist to ensure that number is valid.
In the first couple of paragraphs of this article, I used terms to describe ‘good’ data like ‘scientifically-sound’ or ‘quality’, but at the end of the day, the definition of ‘good’ data is valid data. If you take the literal meaning, valid data is justifiable, logically correct data. Many of the laboratories I have had the pleasure of working with over the years are genuinely dedicated to the production of valid results, but they also need to minimize costs in order to remain competitive. The good news is that laboratories can generate valid scientific results without breaking the bank.
In each of my future articles, I will focus on one aspect of valid data generation, such as calibration and internal standards, explore it in practical detail and go over how that aspect can be applied to common cannabis analyses. The techniques I will be writing about are applied in many other industries, both regulated and non-regulated, so regardless of where the regulations in your state end up, you can already have a head start on the analytical portion of compliance. That means you have more time to focus on the inevitable paperwork portion of regulatory compliance – lucky you! Stay tuned for my next column on instrument calibration, which is the foundation for producing quality data. I think it will be the start of a really good series and I am looking forward to writing it.
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