Spectral data

This is interesting to me. I know nothing about MS or GC but found this chart in a researchgate article. When I run a scan on first run distillate (low potency) I inevitably see the first peak absorbance at 299 nm identified by the machine. A screenshot of my spectrophotometer scan is shown. The MS-GC chart (which I have no expertise in) also shows a peak at 299 nm that is unique to D9 THC. Thoughts?

No that is some weird coincidence. GC-MS generates a different set of data than a UV-Vis. In GC-MS, the horizontal axis represents the molecular weight basically and the vertical axis represents the relative abundance where 100% represents the most common fragment. It is a really cool technique that can seem daunting at first but is mostly different patterns.


UV-Vis generates spectral data which has wavelength in nm on the x-axis and the y-axis is absorbance. Also a really cool technique that you can get a lot of information from with pretty simple math.

1 Like

Aromatic compounds absorb UV light (pi to pi* transition). Which is why you see a peak at 299. You would also probably get a peak using 280nm light. On the mass spec Slooty is correct about the axis and how they are defined. Technically the x-axis is the mass/charge ratio. The predominant peak in the first mass spec at 299 basically tells you the most abundant fragment. At a basic level one could draw out the molecule and determine the compound based on the possibility (chemical intuition) of which groups could fragment off. the fact that the major peak is 15g/mol less then the actual molecular mass would, on first guess, indicates the loss of a methyl group as the major fragment.

Coupling GC-MS basically does a separation (the GC part) before any compounds enter the MS and hit the detector.