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The Practical Chemist

Instrumentation Used for Terpene Analysis

By Tim Herring
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Terpenes are a group of volatile, unsaturated hydrocarbons found in the essential oils of plants. They are responsible for the characteristic smells and flavors of most plants, such as conifers, citrus, as well as cannabis. Over 140 terpenes have been identified to date and these unique compounds may have medicinal properties. Caryophyllene, for example, emits a sweet, woody, clove taste and is believed to relieve inflammation and produce a neuroprotective effect through CB2 receptor activation. Limonene has a citrus scent and may possess anti-cancer, anti-bacterial, anti-fungal and anti-depression effects. Pinene is responsible for the pine aroma and acts as a bronchodilator. One theory involving terpenes is the Entourage Effect, a synergistic benefit from the combination of cannabinoids and terpenes.

Many customers ask technical service which instrumentation is best, GC or HPLC, for analysis of terpenes. Terpenes are most amenable to GC, due to their inherent volatility. HPLC is generally not recommended; since terpenes have very low UV or MS sensitivity; the cannabinoids (which are present in percent levels) will often interfere or coelute with many of the terpenes.

Figure 1: Terpene profile via headspace, courtesy of ProVerde Laboratories.

Headspace (HS), Solid Phase Microextraction of Headspace (HS-SPME) or Split/Splitless Injection (SSI) are viable techniques and have advantages and disadvantages. While SPME can be performed by either direct immersion with the sample or headspace sampling, HS-SPME is considered the most effective technique since this approach eliminates the complex oil matrix. Likewise, conventional HS also targets volatiles that include the terpenes, leaving the high molecular weight oils and cannabinoids behind (Figure 1). SSI eliminates the complexity of a HS or SPME concentrator/autosampler, however, sensitivity and column lifetime become limiting factors to high throughput, since the entire sample is introduced to the inlet and ultimately the column.

The GC capillary columns range from thicker film, mid-polarity (Rxi-624sil MS for instance) to thinner film, non-polar 100% polysiloxane-based phases, such as an Rxi-1ms. A thicker film provides the best resolution among the highly volatile, early eluting compounds, such as pinene. Heavier molecular weight compounds, such as the cannabinoids, are difficult to bake off of the mid-polarity phases. A thinner, non-polar film enables the heavier terpenes and cannabinoids to elute efficiently and produces sharp peaks. Conversely the early eluting terpenes will often coelute using a thin film column. Columns that do not contain cyano-functional groups (Rxi-624Sil MS), are more robust and have higher temperature limits and lower bleed.

For the GC detector, a Mass Spectrometer (MS) can be used, however, many of the terpenes are isobars, sharing the same ions used for identification and quantification. Selectivity is the best solution, regardless of the detector. The Flame Ionization Detector (FID) is less expensive to purchase and operate and has a greater dynamic range, though it is not as sensitive, nor selective for coeluting impurities.

By accurately and reproducibly quantifying terpenes, cannabis medicines can be better characterized and controlled. Strains, which may exhibit specific medical and psychological traits, can be identified and utilized to their potential. The lab objectives, customer expectations, state regulations, available instrumentation, and qualified lab personnel will ultimately determine how the terpenes will be analyzed.

Shimadzu Launches Cannabis Analyzer for Potency

By Aaron G. Biros
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On Monday, March 6th, Shimadzu Scientific Instruments, a leading laboratory analytical instrumentation manufacturer, announced the launch of a new product focused on cannabis, according to a press release. Their Cannabis Analyzer for Potency is essentially a high-performance liquid chromatograph (HPLC) packaged with integrated hardware, software, workflows and all the supplies. The supplies include an analytical column, guard columns, mobile phase and a CRM standard mixture.canAnalyzerImg1

The instrument is designed to test for 11 cannabinoids in less time and with greater ease than traditional HPLC instruments. In the press release, they claim “operators are now able to produce accurate results with ease, regardless of cannabis testing knowledge or chromatography experience.” One very unique aspect of the instrument is the lack of experience required to run it, according to Bob Clifford, general manager of marketing at Shimadzu. “We have our typical chromatography software [LabSolutions] with an overlay that allows the user to analyze a sample in three simple steps,” says Clifford. Those in the cannabis industry that have a background in plant science, but not analytical chemistry, could run potency analyses on the instrument with minimal training. “This overlay allows ease of use for those not familiar with chromatography software,” says Clifford.

An overlay of a flower sample with the standards supplied in the High-Sensitivity Method package.
An overlay of a flower sample with the standards supplied in the High-Sensitivity Method package.

The instrument can determine cannabinoid percentages per dry weight in flower concentrates and edibles. “Once you open the software, it will get the flow rate started, heat the column up and automatically begin to prep for analysis,” says Clifford. Before the analysis begins, information like the sample ID number, sample name, sample weight, extraction volume and dilution volume are entered. After the analysis is complete all the test results are reported for each sample.

Because laboratories wouldn’t have to develop quantitative testing methodology, they argue this instrument would save a lot of time in the lab. “After one day of installation and testing, users are equipped with everything they need to obtain cannabis potency results,” states the press release. According to Clifford, method development for potency analysis in-house can take some labs up to three months. “We can bring this instrument to the lab and have it ready for testing almost immediately,” says Clifford. “The methods for this instrument were developed by a team of twenty scientists working on different platforms at our Innovation Center and was tested for ruggedness, repeatability and quantitative accuracy.”

Screenshots from the software on the instrument
Screenshots from the software on the instrument

The instrument’s workflow is designed to meet three methods of analysis depending on testing needs. The High Throughput method package can determine quantities of ten cannabinoids with less than eight minutes per sample. The method was developed in collaboration with commercial testing laboratories. The High Sensitivity method package adds THCV to that target analyte list with ten minutes per analysis. The method provides the sharpest chromatographic peaks and best sensitivity. The High Resolution method package offers full baseline resolution for those 11 cannabinoids in less than 30 minutes per analysis and the ability to add cannabinoids to that target list if regulations change.

The press release states the interface should allow users to reduce the number of steps needed in the analysis and simplify the workflow. The instrument comes with a three-year warranty, preventative maintenance plan and lifetime technical support.

The Practical Chemist

Potency Analysis of Cannabis and Derivative Products: Part 2

By Rebecca Stevens

As mentioned in Part 1, the physiological effects of cannabis are mediated by a group of structurally related organic compounds known as cannabinoids. The cannabinoids are biosynthetically produced by a growing cannabis plant and Figure 1 details the biosynthetic pathways leading to some of the most important cannabinoids in plant material.

Potency figure 1
Figure 1: The biosynthetic pathway of phytocannabinoid production in cannabis has been deeply studied through isotopic labeling experiments

The analytical measurement of cannabinoids is important to ensure the safety and quality of cannabis as well as its extracts and edible formulations. Total cannabinoid levels can vary significantly between different cultivars and batches, from about 5% up to 20% or more by dry weight. Information on cannabinoid profiles can be used to tailor cultivars for specific effects and allows end users to select an appropriate dose.

Routine Analysis vs. Cannabinomics 

Several structurally analogous groups of cannabinoids exist. In total, structures have been assigned for more than 70 unique phytocannabinoids as of 2005 and the burgeoning field of cannabinomics seeks to comprehensively measure these compounds.¹

Considering practical potency analysis, the vast majority of cannabinoid content is accounted for by 10-12 compounds. These include Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), cannabigerol (CBG), Δ9-tetrahydrocannabivarian (THCV), cannabidivarin (CBDV) and their respective carboxylic acid forms. The cannabinoids occur primarily as carboxylic acids in plant material. Decarboxylation occurs when heat is applied through smoking, vaporization or cooking thereby producing neutral cannabinoids which are more physiologically active.

Potency Analysis by HPLC and GC

Currently, HPLC and GC are the two most commonly used techniques for potency analysis. In the case of GC, the heat used to vaporize the injected sample causes decarboxylation of the native cannabinoid acids. Derivatization of the acids may help reduce decarboxylation but overall this adds another layer of complexity to the analysis² ³. HPLC is the method of choice for direct analysis of cannabinoid profiles and this technique will be discussed further.

A sample preparation method consisting of grinding/homogenization and alcohol extraction is commonly used for cannabis flower and extracts. It has been shown to provide good recovery and precision² ³. An aliquot of the resulting extract can then be diluted with an HPLC compatible solvent such as 25% water / 75% acetonitrile with 0.1% formic acid. The cannabinoids are not particularly water soluble and can precipitate if the aqueous percentage is too high.

To avoid peak distortion and shifting retention times the diluent and initial mobile phase composition should be reasonably well matched. Another approach is to make a smaller injection (1-2 µL) of a more dissimilar solvent. The addition of formic acid or ammonium formate buffer acidifies the mobile phase and keeps the cannabinoid acids protonated.

The protonated acids are neutral and thus well retained on a C18 type column, even at higher (~50% or greater) concentrations of organic solvent² ³.

Detection is most often done using UV absorbance. Two main types of UV detectors are available for HPLC, single wavelength and diode array. A diode array detector (DAD) measures absorbance across a range of wavelengths producing a spectrum at each point in a chromatogram while single wavelength detectors only monitor absorbance at a single user selected wavelength. The DAD is more expensive, but very useful for detecting coelutions and interferences.


  1. Chemical Constituents of Marijuana: The Complex Mixture of Natural Cannabinoids. Life Sciences, 78, (2005), pp. 539
  2. Development and Validation of a Reliable and Robust Method for the Analysis of Cannabinoids and Terpenes in Cannabis. Journal of AOAC International, 98, (2015), pp. 1503
  3. Innovative Development and Validation of an HPLC/DAD Method for the Qualitative and Quantitative Determination of Major Cannabinoids in Cannabis Plant Material. Journal of Chromatography B, 877, (2009), pp. 4115

Rebecca is an Applications Scientist at Restek Corporation and is eager to field any questions or comments on cannabis analysis, she can be reached by e-mail, rebecca.stevens@restek.com or by phone at 814-353-1300 (ext. 2154)

The Practical Chemist

Appropriate Instrumentation for the Chemical Analysis of Cannabis and Derivative Products: Part 1

By Rebecca Stevens
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Election Day 2016 resulted in historic gains for state level cannabis prohibition reform. Voters in California, Maine, Massachusetts and Nevada chose to legalize adult use of Cannabis sp. and its extracts while even traditionally conservative states like Arkansas, Florida, Montana and North Dakota enacted policy allowing for medical use. More than half of the United States now allows for some form of legal cannabis use, highlighting the rapidly growing need for high quality analytical testing.

For the uninitiated, analytical instrumentation can be a confusing mix of abbreviations and hyphenation that provides little obvious information about an instrument’s capability, advantages and disadvantages. In this series of articles, my colleagues and I at Restek will break down and explain in practical terms what instruments are appropriate for a particular analysis and what to consider when choosing an instrumental technique.

Potency Analysis

Potency analysis refers to the quantitation of the major cannabinoids present in Cannabis sp. These compounds are known to provide the physiological effects of cannabis and their levels can vary dramatically based on cultivation practices, product storage conditions and extraction practices.

The primary technique is high performance liquid chromatography (HPLC) coupled to ultraviolet absorbance (UV) detection. Gas chromatography (GC) coupled to a flame ionization detector (FID) or mass spectrometry (MS) can provide potency information but suffers from issues that preclude its use for comprehensive analysis.

Pesticide Residue Analysis

Pesticide residue analysis is, by a wide margin, the most technically challenging testing that we will discuss here. Trace levels of pesticides incurred during cultivation can be transferred to the consumer both on dried plant material and in extracts prepared from the contaminated material. These compounds can be acutely toxic and are generally regulated at part per billion parts-per-billion levels (PPB).

Depending on the desired target pesticides and detection limits, HPLC and/or GC coupled with tandem mass spectrometry (MS/MS) or high resolution accurate mass spectrometry (HRAM) is strongly recommended. Tandem and HRAM mass spectrometry instrumentation is expensive, but in this case it is crucial and will save untold frustration during method development.

Residual Solvents Analysis

When extracts are produced from plant material using organic solvents such as butane, alcohols or supercritical carbon dioxide there is a potential for the solvent and any other contaminants present in it to become trapped in the extract. The goal of residual solvent analysis is to detect and quantify solvents that may remain in the finished extract.

Residual solvent analysis is best accomplished using GC coupled to a headspace sample introduction system (HS-GC) along with FID or MS detection. Solid phase microextraction (SPME) of the sample headspace with direct introduction to the GC is another option.

Terpene Profile Analysis

While terpene profiles are not a safety issue, they provide much of the smell and taste experience of cannabis and are postulated to synergize with the physiologically active components. Breeders of Cannabis sp. are often interested in producing strains with specific terpene profiles through selective breeding techniques.

Both GC and HPLC can be employed successfully for terpenes analysis. Mass spectrometry is suitable for detection as well as GC-FID and HPLC-UV.

Heavy Metals Analysis

Metals such as arsenic, lead, cadmium, chromium and mercury can be present in cannabis plant material due to uptake from the soil, fertilizers or hydroponic media by a growing plant. Rapidly growing plants like Cannabis sp. are particularly efficient at extracting and accumulating metals from their environment.

Several different types of instrumentation can be used for metals analysis, but the dominant technology is inductively coupled plasma mass spectrometry (ICP-MS). Other approaches can also be used including ICP coupled with optical emission spectroscopy (ICP-OES).

Rebecca is an Applications Scientist at Restek Corporation and is eager to field any questions or comments on cannabis analysis, she can be reached by e-mail, rebecca.stevens@restek.com or by phone at 814-353-1300 (ext. 2154)

An inductively coupled plasma torch used in MS reaches local temperatures rivaling the surface of the sun. Image by W. Blanchard, Wikimedia
An inductively coupled plasma torch used in Optical Emission Spectroscopy (OES) reaches local temperatures rivaling the surface of the sun. Image by W. Blanchard, Wikimedia
Quality From Canada

Near Infrared, GC and HPLC Applications in Cannabis Testing

By Tegan Adams, Michael Bertone

When a cannabis sample is submitted to a lab for testing there is a four-step process that occurs before it is tested in the instrumentation on site:

  1. It is ground at a low temperature into a fine powder;
  2. A solution is added to the ground powder;
  3. An extraction is repeated 6 times to ensure all cannabinoids are transferred into a common solution to be used in testing instrumentation.
  4. Once the cannabinoid solution is extracted from the plant matter, it is analyzed using High Pressure Liquid Chromatograph (HPLC). HPLC is the key piece of instrumentation in cannabis potency testing procedures.

While there are many ways to test cannabis potency, HPLC is the most widely accepted and recognized testing instrumentation. Other instrument techniques include gas chromatography (GC) and thin layer chromatography (TLC). HPLC is preferred over GC because it does not apply heat in the testing process and cannabinoids can then be measured in their naturally occurring forms. Using a GC, heat is applied as part of the testing process and cannabinoids such as THCA or CBDA can change form, depending on the level of heat applied. CBDA and THCA have been observed to change form at as low as 40-50C. GC uses anywhere between 150-200C for its processes, and if using a GC, a change of compound form can occur. Using HPLC free of any high-heat environments, acidic (CBDA & THCA) and neutral cannabinoids (CBD, THC, CBG, CBN and others) can be differentiated in a sample for quantification purposes.

Near Infrared

Near infrared (NIR) has been used with cannabis for rapid identification of active pharmaceutical ingredients by measuring how much light different substances reflect. Cannabis is typically composed of 5-30% cannabinoids (mainly THC and CBD) and 5-15% water. Cannabinoid content can vary by over 5% (e.g. 13-18%) on a single plant, and even more if grown indoors. Multiple NIR measurements can be cost effective for R&D purposes. NIR does not use solvents and has a speed advantage of at least 50 times over traditional methods.

The main downfall of NIR techniques is that they are generally less accurate than HPLC or GC for potency analyses. NIR can be programmed to detect different compounds. To obtain accuracy in its detection methods, samples must be tested by HPLC on ongoing basis. 100 samples or more will provide enough information to improve an NIR software’s accuracy if it is programmed by the manufacturer or user using chemometrics. Chemometrics sorts through the often complex and broad overlapping NIR absorption.

Bands from the chemical, physical, and structural properties of all species present in a sample that influences the measured spectra. Any variation however of a strain tested or water quantity observed can affect the received results. Consistency is the key to obtaining precision with NIR equipment programming. The downfall of the NIR technique is that it must constantly be compared to HPLC data to ensure accuracy.

At Eurofins Experchem , our company works with bothHPLC and NIR equipment simultaneously for different cannabis testing purposes. Running both equipment simultaneously means we are able to continually monitor the accuracy of our NIR equipment as compared to our HPLC. If a company is using NIR alone however, it can be more difficult to maintain the equipment’s accuracy without on-going monitoring.

What about Terpenes?

Terpenes are the primary aromatic constituents of cannabis resin and essential oils. Terpene compounds vary in type and concentration among different genetic lineages of cannabis and have been shown to modulate and modify the therapeutic and psychoactive effects of cannabinoids. Terpenes can be analyzed using different methods including separation by GC or HPLC and identification by Mass Spectrometry. The high-heat environment for GC analysis can again cause problems in accuracy and interpretation of results for terpenes; high-heat environments can degrade terpenes and make them difficult to find in accurate form. We find HPLC is the best instrument to test for terpenes and can now test for six of the key terpene profiles including a-Pinene, Caryophyllene, Limonene, Myrcene, B-Pinene and Terpineol.

Quality Systems

Quality systems between different labs are never one and the same. Some labs are testing cannabis under good manufacturing practices (GMP), others follow ISO accreditation and some labs have no accreditation at all.

From a quality systems’ perspective some labs have zero or only one quality system employee(s). In a GMP lab, to meet the requirements of Health Canada and the FDA, our operations are staffed in a 1:4 quality assurance to analyst ratio. GMP labs have stringent quality standards that set them apart from other labs testing cannabis. Quality standards we work with include, but are not limited to: monthly internal blind audits, extensive GMP training, yearly exams and ongoing tests demonstrating competencies.

Maintaining and adhering to strict quality standards necessary for a Drug Establishment License for pharmaceutical testing ensures accuracy of results in cannabis testing otherwise difficult to find in the testing marketplace.

Important things to know about testing

  1. HPLC is the most recommended instrument used for product release in a regulated environment.
  2. NIR is the best instrument to use for monitoring growth and curing processes for R&D purposes, only if validated with an HPLC on an ongoing basis.
  3. Quality Systems between labs are different. Regardless of instrumentation used, if quality systems are not in place and maintained, integrity of results may be compromised.
  4. GMPs comprise 25% of our labour costs to our quality department. Quality systems necessary for a GMP environment include internal audits, out of specification investigations, qualification and maintenance of instruments, systems controls and stringent data integrity standards.
The Practical Chemist

Building the Foundation of Medical Cannabis Testing – Understanding the Use of Standards and Reference Materials – Part 2

By Joe Konschnik
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In the last article I referred to the analogy of the analytical reference material being a keystone of the laboratory foundation, the stone upon which all data relies. I then described the types of reference materials and their use in analytical testing in general terms. This article will describe the steps required to properly manufacture and deliver a certified reference material (CRM) along with the necessary documentation.

A CRM is an exclusive reference material that meets strict criteria defined by ISO Guide 34 and ISO/IEC 17025.  ISO is the International Organization for Standardization and IEC is the International Electrotechnical Commission. These organizations work together to set globally recognized standards. In order for a reference material to be labeled as a CRM it must 1) be made with raw or starting materials which are characterized using qualified methods and instruments, 2) be produced in an ISO-accredited lab under documented procedures, and 3) fall under the manufacturer’s scopes of accreditation. Verifying a CRM supplier has these credentials is easily done by viewing their certificates which should include their scopes of accreditation. Restek_accredit

There are many steps required to produce a CRM that meets the above three criteria.  The first step requires a review of the customer’s, or end-user’s requirements to carefully define what is to be tested, at what levels and which analytical workflow will be used.  Such information enables the producer to identify the proper compounds and solvents required to properly formulate the requested CRM.

The next step requires sourcing and acquiring the raw, or starting materials, then verifying their compatibility and stability using stability and shipping studies in accordance with ISO requirements. Next the chemical identify and purity of the raw materials must be characterized using one or more analytical techniques such as: GC-FID, HPLC, GC-ECD, GC-MS, LC-MS, refractive index and melting point. In some cases, the percent purity is changed by the producer when their testing verifies it’s different from the supplier label. All steps are of course documented.

restek_CRMThe producer’s analytical balances must be verified using NIST traceable weights and calibrated annually by an accredited third party provider to guarantee accurate measurement. CRMs must be prepared using Class A volumetric glassware, and all ampules and vials used in preparation and final packaging must be chemically treated to prevent compound degradation during storage. Next, CRMs are packaged in an appropriate container, labeled then properly stored to maintain the quality and stability until it’s ready to be shipped. All labels must include critical storage, safety and shelf life information to meet federal requirements. The label information must be properly linked to documentation commonly referred to as a certificate of analysis (COA) which describes all of the above steps and verifies the traceability and uncertainty of all measurements for each compound contained in the CRM. Restek_CRM2

My company, RESTEK, offers a variety of documentation choices to accompany each CRM. Depending on the intended use and data quality objectives specified by the end-user, which were defined way back at the first step, three options are typically offered:  They include gravimetric only, qualitative which includes gravimetric, and fully quantitative which includes all three levels of documentation. The graphic to the right summarizes the three options and what they include. 

It’s important to understand which level you’re purchasing especially when ordering a custom CRM from a supplier. Most stock CRMs include all three levels of documentation, but it’s important to be sure.

Understanding what must be done to produce and deliver a CRM sets it apart from other reference material types, however it’s important to understand there are some instances where CRMs are either not available, nor required and in those situations other types of reference materials are perfectly acceptable.

If you have any questions or would like more details about reference materials please contact me, Joe Konschnik at (800) 356-1688 ext. 2002 by phone, or email me at joe.konschnik@restek.com.

The Nerd Perspective

‘Instant’ Cannabis Potency Testing: Different Approaches from Different Manufacturers

By Amanda Rigdon

This is the first piece of a regular column that CIJ has been so kind to allow me to write for their publication. Some readers might recognize my name from The Practical Chemist column in this publication. Since the inception of that column, I’ve finally taken the plunge into the cannabis industry as chief technical officer of Emerald Scientific. Unlike The Practical Chemist, I will not spend the entire first article introducing the column. The concept is simple: while I find the textbook-esque content of The Practical Chemist scintillating, I have a feeling that the content is a little too heavy to spring on someone who is looking for engaging articles over their precious coffee break. Instead, The Nerd Perspective will consist of less-technical writing focusing on my experience and insights for the cannabis industry as a whole. But don’t worry – I’m sure I will not be able to refrain from technical jargon altogether.

To kick off the column, I want to talk about instrumentation for ‘instant’ cannabis potency testing. At this point, it’s common knowledge in the cannabis analytics industry that the most accurate way to test cannabis potency is through extraction then analysis by HPLC-UV. I agree wholeheartedly with that sentiment, but HPLC analyses have one drawback: they can be either inexpensive or fast – not both. There are some instruments entering the market now that– while not as directly quantitative as HPLC-UV – promise to solve the inexpensive/fast conundrum. During my most recent trip to California, I was able to spend some quality time with two well-known instrument manufacturers: SRI Instruments and PerkinElmer, both of whom manufacture instruments that perform fast, inexpensive cannabis potency analyses. From my previous home at the heights of The Ivory Tower of Chromatography: Home of the Application Chemists, SRI and PE couldn’t be more different. But as seen through the eyes of a company who deals with a wide range of customers and analytical needs, it turns out that SRI and PE are much the same – not only in their open and honest support of the cannabis industry, but also in terms of their love of all things technical.

My first stop was SRI Instruments. They are a relatively small company located in an unassuming building in Torrance, CA. Only a few people work in that location, and I spent my time with Hugh Goldsmith (chief executive officer) and Greg Benedict (tech service guru). I have worked with these guys for a few years now, and since the beginning, I have lovingly referred to them as the MacGyvers of chromatography. Anyone familiar with SRI GCs knows that what they lack in aesthetics, they make up for in practicality – these instruments truly reflect Hugh and Greg’s character (that’s meant as a compliment).

SRI specializes in relatively inexpensive portable and semi-portable instruments that are easy to set up, easy to operate, and most importantly – engineered for a purpose. It’s actually really hard to manufacture an instrument that meets all three of these criteria, and the folks at SRI accomplish this with their passionate and unique approach to problem solving. What I love about these guys is that for them, nothing is impossible. Here’s an example: the price of the portable GC-FID instruments SRI builds is inflated because the instruments require separate – and pricey – hydrogen generators. That’s a big problem – hydrogen generators are all pretty much the same, and none of them are cheap. This didn’t faze SRI: they just decided to design their own super small on-board hydrogen generator capable of supplying hydrogen to a simple GC macgyversystem for six hours with just 20mL of distilled water from the grocery store! I’m not kidding – I saw it in action on their new Model 420 GC (more on that in some future pieces). Was the final product pretty? Not in the least. Did it work? Absolutely. This kind of MacGyver-esque problem solving can only be done successfully with a deep understanding of the core principles behind the problem. What’s more, in order to engineer instruments like these, SRI has to have mastery over the core principles of not only chromatographic separation, but also of software development, electrical engineering, and mechanical engineering – just to name a few. These quirky, unassuming guys are smart. SRI is a company that’s been unapologetically true to themselves for decades; they’ll never be a contender for beauty queen, but they get the job done.

On the surface, PerkinElmer (PE) contrasts with SRI in almost every way possible. With revenue measured in billions of dollars and employees numbering in the thousands, PE is a behemoth that plays not only in the analytical chemistry industry but also in clinical diagnostics and other large industries. Where SRI instruments have a characteristic look of familiar homeliness, PE instruments are sleek and sexy. However, PerkinElmer and SRI are more alike than it would seem; just like the no-frills SRI, the hyper-technical PE instruments are engineered for a purpose by teams of very smart, passionate people.

DoogieWith its modest price tag and manual sample introduction, the SRI Model 420 is engineered for lower throughput users to be a fast, simple, and inexpensive approach to semi-quantitative process control. The purpose of the instruments manufactured by PE is to produce the highest-quality quantitative results as quickly as possible for high-throughput labs. PE instruments are built using the best technology available in order to eke out every last ounce of quantitative accuracy and throughput possible. Fancy technology is rarely inexpensive, and neither is rigorous product development that can last years in some cases. In a way, PE is Doogie Howser to SRI’s MacGyver. Like MacGyver, Doogie is super smart, and his setting is a sterile hospital rather than a warzone.

I had a wonderful conversation with Tim Ruppel, PE’s headspace-GC specialist, on the sample introduction technology incorporated into the TurboMatrix Headspace Sampler, where I also learned that the basic technology for all PerkinElmer headspace-GC instruments was designed by the men who wrote The Book on headspace gas chromatography: Bruno Kolb and Leslie Ettre**. Later, I was able to get a much-needed lesson on FT-IR and the Spectrum Two IR Spectrometer from Brian Smith, PE’s spectroscopy expert, who actually wrote the book on quantitative spectroscopy***. Tim and Brian’s excitement over their technology mirrored that of Hugh and Greg. It turns out that SRI and PerkinElmer are more alike than I thought.

These two instrument manufacturers have addressed the fast/inexpensive conundrum of cannabis potency testing in two different ways: SRI’s instrument is extremely inexpensive, easy to operate, and will provide semi-quantitative values for THC, CBD, and CBN in just a few minutes; PE’s instrument is more expensive up front, but provides quantitative (though not directly quantitative) values for all of the major cannabinoids almost instantly, and requires almost no maintenance or consumables. These two instruments were designed for specific uses: one for inexpensive, easy use, and the other for more comprehensive results with a higher initial investment. The question consumers have to ask themselves is “Who do I need to solve my problem?” For some, the answer will be MacGyver, and for others, Doogie Howser will provide the solution – after all, both are heroes.

** B. Kolb, L. Ettre, Static Headspace-Gas Chromatography: Theory and Practice, John Wiley & Sons, Hoboken, NJ, 2006.

*** Brian C. Smith, Quantitative Spectroscopy: Theory and Practice, Elsevier, Boston, MA, 2002.

From The Lab

HPLC Column Selection for Cannabis Chromatographers

By Danielle Mackowsky
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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.

Tetrahydrocannabinol (THC)
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
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.UCTcolumns

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.

The Practical Chemist

Calibration Part II – Evaluating Your Curves

By Amanda Rigdon
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Despite the title, this article is not about weight loss – it is about generating valid analytical data for quantitative analyses. In the last installment of The Practical Chemist, I introduced instrument calibration and covered a few ways we can calibrate our instruments. Just because we have run several standards across a range of concentrations and plotted a curve using the resulting data, it does not mean our curve accurately represents our instrument’s response across that concentration range. In order to be able to claim that our calibration curve accurately represents our instrument response, we have to take a look at a couple of quality indicators for our curve data:

  1. correlation coefficient (r) or coefficient of determination (r2)
  2. back-calculated accuracy (reported as % error)

The r or r2 values that accompany our calibration curve are measurements of how closely our curve matches the data we have generated. The closer the values are to 1.00, the more accurately our curve represents our detector response. Generally, r values ≥0.995 and r2 values ≥ 0.990 are considered ‘good’. Figure 1 shows a few representative curves, their associated data, and r2 values (concentration and response units are arbitrary).

Figure 1: Representative Curves and r2 values
Figure 1: Representative Curves and r2 values

Let’s take a closer look at these curves:

Curve A: This represents a case where the curve perfectly matches the instrument data, meaning our calculated unknown values will be accurate across the entire calibration range.

Curve B: The r2 value is good and visually the curve matches most of the data points pretty well. However, if we look at our two highest calibration points, we can see that they do not match the trend for the rest of the data; the response values should be closer to 1250 and 2500. The fact that they are much lower than they should be could indicate that we are starting to overload our detector at higher calibration levels; we are putting more mass of analyte into the detector than it can reliably detect. This is a common problem when dealing with concentrated samples, so it can occur especially for potency analyses.

Curve C: We can see that although our r2 value is still okay, we are not detecting analytes as we should at the low end of our curve. In fact, at our lowest calibration level, the instrument is not detecting anything at all (0 response at the lowest point). This is a common problem with residual solvent and pesticide analyses where detection levels for some compounds like benzene are very low.

Curve D: It is a perfect example of our curve not representing our instrument response at all. A curve like this indicates a possible problem with the instrument or sample preparation.

So even if our curve looks good, we could be generating inaccurate results for some samples. This brings us to another measure of curve fitness: back-calculated accuracy (expressed as % error). This is an easy way to determine how accurate your results will be without performing a single additional run.

Back-calculated accuracy simply plugs the area values we obtained from our calibrators back into the calibration curve to see how well our curve will calculate these values in relation to the known value. We can do this by reprocessing our calibrators as unknowns or by hand. As an example, let’s back-calculate the concentration of our 500 level calibrator from Curve B. The formula for that curve is: y = 3.543x + 52.805. If we plug 1800 in for y and solve for x, we end up with a calculated concentration of 493. To calculate the error of our calculated value versus the true value, we can use the equation: % Error = [(calculated value – true value)/true value] * 100. This gives us a % error of -1.4%. Acceptable % error values are usually ±15 – 20% depending on analysis type. Let’s see what the % error values are for the curves shown in Figure 1.

practical chemist table 1
Table 1: % Error for Back-Calculated Values for Curves A – D

Our % error values have told us what our r2 values could not. We knew Curve D was unacceptable, but now we can see that Curves B and C will yield inaccurate results for all but the highest levels of analyte – even though the results were skewed at opposite ends of the curves.

There are many more details regarding generating calibration curves and measuring their quality that I did not have room to mention here. Hopefully, these two articles have given you some tools to use in your lab to quickly and easily improve the quality of your data. If you would like to learn more about this topic or have any questions, please don’t hesitate to contact me at amanda.rigdon@restek.com.

AOCS Highlights Cannabis Lab Standards, Extraction Technology

By Aaron G. Biros
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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
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., 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.
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.