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Residual Solvent Analysis: Ensuring the safety of cannabis extracts

by Kelly Tatera
Published: Jun 01, 2017   
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Put simply, cannabis extraction is the process of collecting the desirable compounds from the plant whilst leaving behind undesirable/unusable materials. For cannabis users who would prefer not to smoke marijuana, concentrated cannabis extracts are a popular alternative. These products come in the form of butane hash oil (BHO), carbon dioxide (CO2) oil, hemp oil, and tinctures, or liquid concentrates which can be administered via a few drops under the tongue. 

As Leafly explains, some marijuana concentrates test as high as 80% in tetrahydrocannabinol (THC), the compound responsible for marijuana’s euphoric high, while others contain larger amounts of cannabidiol (CBD), a non-psychoactive compound. Whatever cannabis extraction method is utilized, figuring out the exact components of concentrated extracts is essential to ensure the safety of these popular products. 

What are residual solvents?

Residual solvents are the byproducts of extraction processes such as vacuum, heat, and winterization. Even solventless extractions with CO2 or water can result in residual solvents lingering in the final product. In some cases, these impurities can be toxic, which is why residual solvent analysis is a critical element of cannabis testing.

Testers typically search for a variety of harmful residual solvents, including acetone, ethanol, butane, benzene, propane, and more. The solvents are classified in one of three classes

  • Class 1 - solvents to be avoided in the production of cannabis extracts – these include known and suspected carcinogens and environmental hazards.
  • Class 2 - solvents not to be used outside of a stringent Good Manufacturing Practice environment – these include animal carcinogens, teratogens, or reversible neurotoxins. 
  • Class 3 - solvents with low toxic potential and the only class recommended for use in cannabis extract production – none are known to pose a risk to human health at levels to be expected in a cannabis extract.  

Effectively testing for residual solvents 

As reported by Steep Hill Labs, a leader in the field of cannabis analysis, residual solvent analysis is best performed using a process called headspace sampling.

In headspace analysis, researchers use a gas-tight syringe to obtain a sample of the gases in the headspace of a sealed vial which contains the prepared sample. The vapors of any volatile components will thus be acquired in the headspace sample.

Coupling headspace analysis with gas chromatography (GC) lends the most reliable results, according to established testers. Analytical 360, Washington’s first I-502 certified marijuana testing lab, approaches residual solvent analysis by pairing GC with a headspace sampler and a Flame Ionization Detector (FID).

GC is used to separate and analyze compounds that can be vaporized without decomposition. An FID, an instrument commonly used in conjunction with GC, measures the concentration of organic species in a gas stream. Together, all of these analytical techniques and tools enable cannabis researchers to measure the existence of harmful solvents in concentrated cannabis products.

Without residual solvent analysis, marijuana users could be repeatedly exposed to chemical residues which could have a significant negative impact on health. With the growth of the cannabis industry, there will be a higher demand than ever before for standard testing methods. 


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