Tag Archives: concentrations

Pesticide Remediation by CPC

By Arpad Konczol, PhD
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Like any other natural product, the biomass of legal cannabis can be contaminated by several toxic agents such as heavy metals, organic solvents, microbes and pesticides, which significantly influence the safety of the end products.

Let’s just consider the toxicological effects. Since cannabis products are not only administered in edible forms but also smoked and inhaled, unlike most agricultural products, pesticide residue poses an unpredictable risk to consumers. One example is the potential role of myclobutanil in the vape crisis.

Unfortunately, federal and state laws are still conflicted on cannabis-related pesticides. Currently, only ten pesticide products have been registered specifically for hemp by the U.S. Environmental Protection Agency. So, the question arises what has to be done with all pf the high-value, but also contaminated cannabis, keeping in mind that during the extraction processes, not only the phytocannabinoids get concentrated but the pesticides as well, reaching concentrations up to tens or hundreds of parts per million!

Currently, there are three different sets of rules in place in the regulatory areas of Oregon, California and Canada. These regulations detail which pesticides need to be monitored and remediated if a certain limit for each is reached. Because the most extensive and strict regulations are found in Canada, RotaChrom used its regulations as reference in their case study.

Centrifugal Partition Chromatographic (CPC) system

To illustrate that reality sometimes goes beyond our imagination, we evaluated the testing results of a THC distillate sample of one of our clients. This sample contained 9 (!) pesticides, of which six levels exceeded the corresponding action limits. The most frightening, however, regarding this sample, is that it contained a huge amount of carbofuran, a category I substance. It is better not to think of the potential toxicological hazard of this material…

The CPC-based purification of CBD is a well-known and straightforward methodology. As the elution profile on the CPC chromatogram of a distillate shows, major and minor cannabinoids can be easily separated from CBD. At RotaChrom, this method has been implemented at industrial-scale in a cost effective and high throughput fashion. In any case, the question arises: where are the pesticides on this chromatogram? To answer this, we set ourselves the goal to fully characterize the pesticide removing capability of our methodologies.

Our results on this topic received an award at the prestigious PREP Conference in 2019. The ease of pesticides removal depends on the desired Compound of Interest.

Here is a quick recap on key functionalities of the partition chromatography.

  • Separation occurs between two immiscible liquid phases.
  • The stationary phase is immobilized inside the rotor by a strong centrifugal force.
  • The mobile phase containing the sample to be purified is fed under pressure into the rotor and pumped through the stationary phase in the form of tiny droplets (percolation).
  • The chromatographic column in CPC is the rotor: cells interconnected in a series of ducts attached to a large rotor
  • Simple mechanism: difference in partition

Let’s get into the chemistry a bit:

The partition coefficient is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solubilities of the solute in these two liquid phases.

The CPC chromatogram demonstrates the separation of Compounds of Interest based on their unique partition coefficients achieved through a centrifugal partition chromatography system.

CPC can be effectively used for pesticide removal. About 78% of the pesticides around CBD are very easy to remove, which you can see here:

In this illustration, pesticides are in ascending order of Kd from left to right. CBD, marked with blue, elutes in the middle of the chromatogram. The chart illustrates that most polar and most apolar pesticides were easily removed beside CBD. However, some compounds were in coelution with CBD (denoted as “problematic”), and some compounds showed irregular Kd-retention behavior (denoted as “outliers”).

If pesticides need to be removed as part of THC purification, then the pesticides that were problematic around CBD would be easier to remove and some of the easy ones would become problematic.

To simulate real-world production scenarios, an overloading study with CBD was performed, which you can see in the graph:

It is easy to see on the chromatogram that due to the increased concentration injected onto the rotor, the peak of CBD became fronting and the apparent retention shifted to the right. This means that pesticides with higher retention than CBD are more prone to coelution if extreme loading is applied.

To be able to eliminate problematic pesticides without changing the components of the solvent system, which is a typical industrial scenario, the so-called “sweet spot approach” was tested. The general rule of thumb for this approach is that the highest resolution of a given CPC system can be exploited if the Kd value of the target compounds fall in the range of 0.5-2.0. In our case, to get appropriate Kd values for problematic pesticides, the volume ratio of methanol and water was fine-tuned. Ascending mode was used instead of descending mode. For the polar subset of problematic pesticides, this simple modification resulted in an elution profile with significantly improved resolution, however, some coelution still remained.

In the case of apolar pesticides, the less polar solvent system with decreased water content in ascending mode provided satisfactory separation.

Moreover, if we focus on this subset in the three relevant regulatory areas, the outcome is even more favorable. For example, myclobutanil and bifenazate, dominant in all of the three regulatory regions, are fully removable in only one run of the CPC platform.

Based on these results, a generic strategy was created. The workflow starts with a reliable and precise pesticide contamination profile of the cannabis sample, then, if it does not appear to indicate problematic impurity, the material can be purified by the baseline method. However, if coeluting pesticides are present in the input sample, there are two options. First, adjusting the fraction collection of the critical pesticide can be eliminated, however the yield will be compromised in this case. Alternatively, by fine-tuning the solvent system, a second or even a third run of the CPC can solve the problem ultimately. Let me add here, that a third approach, i.e., switching to another solvent system to gain selectivity for problematic pesticides is also feasible in some cases.

In review, RotaChrom has conducted extensive research to analyze the list of pesticides according to the most stringent Canadian requirements. We have found that pesticides can be separated from CBD by utilizing our CPC platform. Most of these pesticides are relatively easy to remove, but RotaChrom has an efficient solution for the problematic pesticides. The methods used at RotaChrom can be easily extended to other input materials and target compounds (e.g., THC, CBG).

Dr. Ed Askew
Soapbox

Distillation Of Your Cannabis Extract: Ignorance Is Not Bliss

By Dr. Edward F. Askew
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Dr. Ed Askew

In a previous article I discussed the elephant in the room for clients of laboratory services- the possibility of errors, inaccurate testing and dishonesty.

Now, I will explain how the current “smoke and mirrors” of distillation claims are impacting the cannabis industry in the recreational and medical areas. We have all heard the saying, “ignorance is bliss.” But, the ignorance of how distillation really works is creating misinformation and misleading consumers.

That is, just because a cannabis extract has been distilled, doesn’t mean it is safer.There have been reports of people claiming that “Distilled cannabis productsthat are Category 2 distillate are pesticide free and phosphate free, while Category 1 has pesticides and phosphates, but within acceptable limits”

The problem is that these claims of Category 1 and Category 2 cannot be proven just by saying they are distilled. Ignorance of the physical chemistry rules of distillation will lead to increased concentrations of pesticides and other organic contaminants in the supposedly purified cannabis distillate. That is, just because a cannabis extract has been distilled, doesn’t mean it is safer.

So, let’s look at a basic physical chemistry explanation of the cannabis distillation process.

  • First off, you must have an extract to distill. This extract is produced by butane, carbon dioxide or ethanol extraction of cannabis botanical raw material. This extract is a tarry or waxy solid. It contains cannabinoids, terpenes and other botanical chemicals. It will also contain pesticides, organic chemicals and inorganic chemicals present in the raw material. The extraction process will concentrate all of these chemical compounds in the final extract.
  • Now you are ready to distill the extract. The extract is transferred to the vacuum distillation vessel. Vacuum distillation is typically used so as to prevent the decomposition of the cannabinoid products by thermal reactions or oxidation. Under a vacuum, the cannabinoids turn into a vapor at a lower temperature and oxygen is limited.
  • Part of the vacuum distillation apparatus is the distillation column. The dimensions of this column (length and width) along with the packing or design (theoretical plates) will determine the efficiency of distillation separation of each chemical compound. What this means is that the more theoretical plates in a column, the purer the chemical compound in the distillate. (e.g. Vigreux column = 2-5 theoretical plates, Oldershaw column = 10-15 plates, Sieve plate column = any number you can pay for).
  • The temperature and vacuum controls must be adjustable and accurate for all parts of the distillation apparatus. Failure to control the temperature and vacuum on any part to the apparatus will lead to:
    • Thermal destruction of the distillate
    • Oxidation of the distillate
    • Impure distillate

Now, you can see that a proper distillation apparatus is not something you throw together from a high school chemistry lab. But just having the proper equipment will not produce a pure cannabis product. The physical chemistry that takes place in any distillation is the percentage a chemical compound that occurs in the vapor phase compared to the percentage in liquid phase.So, how can you produce a cannabis distillate that is clean and pure?

For example, let’s look at whiskey distillation. In a simple pot still, alcohol is distilled over with some water to produce a mixture that is 25%-30% ethanol. Transferring this distillate to an additional series of pot stills concentrates this alcohol solution to a higher concentration of 85%-90% ethanol. So, each pot still is like a single theoretical plate in a distillation column.

But, if there are any chemical compounds that are soluble in the vapor produced, they will also be carried over with the vapor during distillation. This means that pesticides or other contaminants that are present in the cannabis extract can be carried over during distillation!

So, how can you produce a cannabis distillate that is clean and pure?

  • Produce a cannabis extract that has lower concentrations of bad chemicals. Since a lot of the cannabis extracts available for distillation are coming from grey-black market cannabis, the chances of contamination are high. So, the first thing to do is to set up an extraction cleanup procedure.
    • An example of this is to wash the raw extract to remove inorganic phosphates. Then recrystallize the washed extract to remove some of the pesticides.
  • Make sure that the distillation apparatus is set up to have proper temperature and vacuum controls. This will limit production of cannabis decomposition products in the final distillate.
  • Make sure your distillation apparatus has more than enough theoretical plates. This will make sure that your cannabis distillate has the purity needed.
  • Finally, make sure that the staff that operates the cannabis distillation processes are well trained and have the experience and knowledge to understand their work.

Inexperienced or under-trained individuals will produce inferior and contaminated product. Additional information of extract cleanup and effective vacuum distillation can be obtained by contacting the author.