Problems with the Identification of CBD by Thin Layer Chromatography

Thin layer chromatography (TLC) is a well-known qualitative laboratory technique to separate, detect and identify plant material extracts that have been processed so they longer possess botanical characteristics that can be observed through macro and microscopic analysis.  This includes cannabis products like gummies, truffles, bars and other edibles, but also substances like tar, ground plant material and oils.

In the FAQ section of the Iowa Division of Criminal Investigation Criminalistic Laboratory – Drug Identification website (, testing for controlled substances includes:

The net weight (weight of substance without packaging) of the substance is recorded prior to any sampling and then a portion of the sample is taken for analysis. If available, a color test (field test), which reacts to certain functional groups, is performed as a presumptive test.  Then, either a Gas Chromatography (GC) or Thin Layer Chromatography (TLC) analysis is done as another preliminary test. Finally, either Gas Chromatography/Mass Spectrometery (GC/MS) or Infrared Spectrophotometery (IR) is done as a confirmatory test.  All tests are compared with a known standard ran in the same time frame to confirm the identity.

Plant material extracts that test positive for both the Duquenois-Levine (D-L) color test and TLC will be reported as a marijuana preparation according to the lab (Iowa Code section 124.101(20) defines marijuana in part as “any preparation of [Cannabis]”).

Reread the FAQ paragraph above and reflect on this for a moment.  The DCI lab identifies cannabis extracts as a preparation of marijuana based on the results of presumptive testing only.  Even though the FAQ says GC/MS testing will be used to confirm the preliminary tests, this critical step is not being performed by the lab.

This is even more problematic for cannabis extracts like CBD.  Is the lab also identifying CBD as a preparation of marijuana through the use of presumptive tests only?  Even CBD containing no THC as we see in many broad spectrum CBD extracts, which are now legal in Iowa under S.F. 599 and H.F. 2581?

Yes, it is.

The drug defense attorneys at GRL are involved in cases where broad spectrum CBD, which has been independently tested and reported as containing NO THC, is nevertheless identified as a marijuana preparation by the lab after D-L and TLC testing.  We’ve blogged previously on the fact that D-L testing should not be used with CBD because it will test positive for marijuana.  And our research shows that the separation and identification of cannabinoids like THC and CBD by classical TLC is not easy because these derivatives possess chemical structures with very close substitutes.  Not only are the molecular weights of THC and CBD essentially identical, their chromatograms are virtually indistinguishable.  We’ll find out whether the lab maintains the actual chromatograms for review or only preserves the lab notes regarding the colors and whether there was a clean separation of the compounds without too much diffusion or stretching.

No confirmatory testing according to the lab?  That may very well set the stage for NFG.