Archive for the ‘Medical Marijuana’ Category
« Older Entries
Analyzing Residual Solvents in Cannabis Concentrates: A Sticky Situation
Tuesday, May 13th, 2014 by
Amanda Rigdon
Along with the increasing demand for various forms of cannabis concentrates comes increased concern regarding residual
solvents in these products. In many cases, cannabis concentrates are prepared by extracting either the acidic or decarboxylated
forms of cannabinoids from plant material using organic solvents. Some of the solvents used for extraction can have
detrimental health effects, which nobody wants.
After extraction, the solvents can be purged from the final product, but the effectiveness of the purge needs to be verified by
analyzing the final product to determine if any solvent remains. The most common way to do this is through headspace-gas
chromatography (HS-GC), which is perfectly suited to this purpose. Instead of injecting a liquid sample like we do for
traditional GC analyses, the headspace instrument heats the sample in a closed vial, releasing the volatile solvents for
introduction into the GC, but leaving the less volatile material behind. This results in a very clean chromatogram with very little
sample preparation. It also helps keep our injection port and column free of non-volatile material, resulting in very little
maintenance for the GC system.
For traditional HS-GC analyses, the sample is dissolved in a less-volatile solvent (most commonly DMSO, DMF, or water),
then placed into the headspace instrument. The dissolved sample is heated, establishing an equilibrium between the liquid and
gas phases, then the gas phase in the vial (referred to as headspace) is injected onto the GC and analyzed. Sample preparation
involving dissolving the sample into a solvent is often referred to as the solution approach. Figure 1 shows the general setup of
a HS-GC instrument.
So how do we analyze our sample if it won’t dissolve? One way to do that is to do away with the sample solvent altogether.
This is called the Full Evaporation Technique (FET), and it is useful for difficult and varied sample matrices like cannabis
concentrates. FET depends on using a very small sample size (about 20mg) and establishing essentially a single-phase
equilibrium in the headspace vial. Not only does this make sample preparation very simple, it also cuts down on the sample
amount required to perform an analysis, and we no longer have to worry about partition coefficients at equilibrium in the
Medical Marijuana « ChromaBLOGraphy: Restek's Chromatography Blog
1 of 21
02/08/2014 5:05 P
