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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.


Pesticide & Potency Analysis of Street-Grade versus Medicinal Cannabis

By Danielle Mackowsky

In states where cannabis is legalized, some analytical laboratories are tasked with identifying and quantifying pesticide content in plant material. This is a relatively new concept in the study of cannabis as most forensic laboratories that work with seized plant material are only concerned with positively identifying the sample as cannabis. Laboratories of this nature, often associated with police departments, the office of the chief medical examiner or the local department of public health are not required to identify the amount of THC and other cannabinoids in the plant. While data is abundant that compares the average THC content in today’s recreational cannabis to that commonly consumed in the 1960s and 1970s, limited scientific studies can be found that discuss the pesticide content in street-grade cannabis.

Street-grade cannabis that is ground into a fine powder

Using the QuEChERS approach, which is the industry gold-standard in food analysis for pesticides, a comparison study was carried out to analyze the pesticide and cannabinoid content in street-grade cannabis versus medicinal cannabis. For all samples, one gram of plant material was ground into a fine powder prior to hydration with methanol. The sample was then ready to be placed into an extraction tube, along with 10 mL of acetonitrile and one pouch of QuEChERS salts. After a quick vortex, all samples were then shaken for 1 minute using a SPEX Geno/Grinder prior to centrifugation.

Formation of layers following QuEChERS extraction

For pesticide analysis, a one mL aliquot of the top organic layer was then subjected to additional dispersive solid phase extraction (dSPE) clean-up. The blend of dSPE salts was selected to optimize the removal of chlorophyll and other interfering compounds from the plant material without compromising the recovery of any planar pesticides. Shaken and centrifuged under the same conditions as described above, an aliquot of the organic layer was then transferred to an auto-sampler vial and diluted with deionized water. Cannabinoid analysis required serial dilutions between 200 to 2000 times, depending on the individual sample. Both pesticide and cannabinoid separation was carried out on a UCT Selectra® Aqueous C18 HPLC column and guard column coupled to a Thermo Scientific Dionex UltiMate 3000 LC System/ TSQ VantageTM tandem MS.

Supernatant before and after additional dispersive SPE clean-up using UCT’s Chlorofiltr

Pesticide Results

Due to inconsistent regulations among states that have legalized medicinal or recreational cannabis, a wide panel of commonly encountered pesticides was selected for this application. DEET, recognized by the EPA as not evoking health concerns to the general public when applied topically, was found on all medical cannabis samples tested. An average of 28 ng/g of DEET was found on medicinal samples analyzed. Limited research as to possible side effects, if any, of having this pesticide present within volatilized medical-grade product is available. Street-grade cannabis was found to have a variety of pesticides at concentrations higher than what was observed in the medical-grade product.

Potency Results

Tetrahydrocannabinolic acid A (THCA-A) is the non-psychoactive precursor to THC. Within fresh plant material, up to 90% of available THC is found in this form. Under intense heating such as when cannabis is smoked, THCA-A is progressively decarboxylated to the psychoactive THC form. Due to possible therapeutic qualities of this compound, medical cannabis samples specifically were tested for this analyte in addition to other cannabinoids. On average, 17% of the total weight in each medical cannabis sample came from the presence of THCA-A. In both medical and recreational samples, the percentage of THC contribution ranged from 0.9-1.7.


A fast and effective method was developed for the determination of pesticide residues and cannabis potency in recreational and medical cannabis samples. Pesticide residues and cannabinoids were extracted using the UCT QuEChERS approach, followed by either additional cleanup using a blend of dSPE sorbents for pesticide analysis, or serial dilutions for cannabinoid potency testing.


How Potent is Your Product: Getting Educated on Edibles Analysis

By Danielle Mackowsky
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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)


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.