Quantification of pesticides to analyze the safety of therapeutic cannabis and its derived products

Cannabis is a psychoactive drug that is obtained by processing different parts of two varieties of plants: Cannabis sativa and Cannabis indica. The most used parts are the leaves and the bud, which can be consumed directly or can be processed to give rise to a wide variety of products, such as oils, creams, foods, etc.

Both fresh plants and their derived products have been used throughout history for medicinal purposes, however currently, and due to the legalization of cannabis for its therapeutic and recreational use in many countries, its consumption has increased considerably, and with it the need to ensure the safety of their use.

The quality control of cannabis and its derivatives includes, among other things, the analysis of pesticides; Contaminants that can accumulate during the cultivation of cannabis or during its processing, and whose exposure has been linked to different pathologies.

The extraction of pesticides using the “QuEChERS” method

The first step in pesticide determination is to homogenize the cannabis sample, using a grinder and adding the appropriate amount of water, until a paste is formed. Next, the pesticides are extracted, for which there are different methods, the most common being the “QuEChERS” method.

This methodology requires working with tubes of 50 and 15 ml., And to centrifuge both at more than 3000 xg; the Digicen 21 centrifuge allows working with both types of tubes thanks to its wide range of accessories.

For this method, 2 g of the homogenate are resuspended in 10-15 ml. of water in a 50 ml tube. Then 10-15 ml of ACN (acetonitrile) are added, which is the organic solvent used for the extraction, and the stipulated amount of internal standard.

The tube is shaken vigorously so that all the components are mixed well, and then the QuEChERS salts are added, these salts will absorb the water, and will favor the separation of the compounds between the water and the ACN in the centrifugation.

The tube of 50 ml with the salts is stirred again, and centrifuged for 5 minutes at more than 3000 xg. As a result of this centrifugation, a density gradient is formed; that is, the components of the sample are separated into phases depending on their density and their affinity to the different solutions of the mixture. 

The pesticides are concentrated in the upper phase, made up of ACN.

The quantification of pesticides using spectrophotometric methods

The next step is to wash the sample, taking the ACN phase and transferring it to a 15 ml tube. containing dSPE (dispersive solid phase extraction). The tube is centrifuged for 5 minutes again at more than 3000 xg.

Proteins, lipids, and chlorophyll have affinity for dSPE, so that after centrifugation two phases form in the tube: a dSPE pellet containing the proteins, lipids, and chlorophyll; and an ACN supernatant containing the pesticides.

Thanks to the progressive braking system, PCBS, of the Digicen 21 centrifuge, which has up to 175 selectable braking ramps, homogenization of the sample after separation will be avoided.

Finally, the supernatant is transferred to an appropriate vial for GC-MS (gas chromatography – mass spectrometry) or LC-MS (liquid chromatography – mass spectrometry) analysis, which are the two methods of choice for quantifying pesticides in cannabis and its derivatives.

The determination of pesticides in cannabis and its derivatives is decisive to guarantee the safe use of these products, and when this determination is made through the QuEChERS method, centrifugation is a fundamental step as it allows the extraction of pesticides from cannabis so that they can be quantified by spectrophotometric methods.