Analysis of Residual Solvents in Hemp Extract by Headspace SPME-GC/MS

Marijuana oil, produced by extraction of the flower buds of the cannabis sativa plant, has reputed therapeutic benefits.1,2 The extraction process typically involves solvents such as hexane or some alcohols that may remain in the final product.3 The residual solvents are typically measured using a headspace analyzer interfaced directly to a GC. Solid phase microextraction (SPME) is an alternative approach that is often faster and easier to use. The method outlined here uses SPME with a GC/MS finish to measure solvents in hemp extract. Hemp and marijuana are both varieties of cannabis sativa, however hemp is a variety that is very low in THC content.

Experimental

Analytical conditions appear in Figure 1. The sample comprised 99% pure hemp extract in a base of hempseed oil, unspiked and spiked at 10 μg/g with the solvents listed in Table 1. Quantitation was by external standard against a 6-point curve from 6 to 100 μg/g prepared in soybean oil. Blank soybean oil was analyzed along with SPME fiber blanks to verify cleanliness of the system prior to testing and that there was no carryover between standards and samples. A Carboxen^® (CAR)/PDMS SPME fiber was chosen for the extraction step due to its ability to retain low molecular weight compounds with differing polarities, such as hexane and methanol. The column for the GC/ MS analysis, Supel-Q™ PLOT, was chosen for its ability to retain very low molecular weight compounds, and for its selectivity toward a variety of compounds, including alcohols, aliphatics, and aromatics. Supel-Q™ PLOT also has the ability to retain lighter aliphatics, such as butane and pentane, and thus would be a suitable choice if these compounds are to be analyzed.