Published Jack Cochran on March 1, 2017
In a recent “In My View” article I wrote for The Cannabis Scientist, which is a “mini magazine” from The Analytical Scientist, I posed the question on whether it was more appropriate to analyze pesticides in cannabis samples using GC-MS/MS or LC-MS/MS. Given the expense of capital equipment and the skills needed to operate it, this is not a trivial question. However, the answer is made simple by considering one important thing, especially for medical marijuana: consumer safety. To cover the full range of pesticides that are either currently used or have already been detected on cannabis, you need both techniques. This doesn’t come as any surprise to analytical chemists analyzing residues on food, where GC-MS/MS and LC-MS/MS are routinely employed as complementary techniques to screen for hundreds of pesticides.
Pesticide residue determinations are not the only important analytical work for cannabis. Terpene profiling using gas chromatography with either flame ionization detection or mass spectrometry has traditionally been used by the cannabis science community. Terpenes not only provide much of the flavor experience for cannabis consumption, but may have a medical benefit through what has been termed the “entourage effect”. There are even cannabis branding possibilities through terpene profile. One of the problems encountered during terpene characterization is the number of terpenes possibly present in cannabis, which inevitably leads to coelutions even when using high resolution GC. For a non-specific detector like FID, accurate identification and quantification are impossible when this occurs. Compounding the analysis difficulty is that even MS can struggle, as terpenes have very similar mass spectra that often cannot be deconvolved when a coelution occurs.
Fortunately, I just joined VUV Analytics and we have a vacuum ultraviolet spectrometer that has demonstrated the ability to differentiate between terpene variants. The absorbance spectra are distinct for each of the terpenes, including isomers, and provide sufficient feature differences to allow for spectral deconvolution of the co-eluting species (Figure 1). This capability was described in the recent paper in Journal of Separation Science by Schug, et al. Watch this space in the future as we present additional experimental evidence on how GC-VUV can be applied to the analysis of terpenes in cannabis.