The modern day prosecution for the unlawful possession of marijuana is based upon a three test regime involving microscopic morphological examination, modified Duquenois-Levine colorimetric testing, and Thin Layer Chromatography. Each of these three tests are non-specific for THC which is the pharmacodynamically active ingredient which makes marijuana illegal. The question becomes is this three test battery collectively conclusively specific to arrive at a valid conclusion that the unknown seized and tested is in fact marijuana (contains THC) and there is no possibility of a false positive?

In this series of posts we are going to examine this seemly simple question:

1. What is the goal and the purpose of testing of unknowns generally? How do we best design a test for marijuana?
2. How is most marijuana testing conducted in the United States?
3. What is microscopic morphological examination? Is it a “good” test?
4. What is the modified Duquenois-Levine test? Is it a “good” test?
5. What is Thin Layer Chromatography? Is it a “good” test?
6. Is the combination of all three tests create a “good” testing scheme?
7. Is there a better way to test for marijuana?

Part 6: Is the combination of all three tests create a “good” testing scheme?

The government would choose to argue that the combination of these three tests results in a valid conclusion that this tested unknown is marijuana (contains THC). All  three roads leads, so they say, lead to THC. The more sophisticated version of this argument is the Venn diagram. Perhaps something like the below:

This is simply not proven or supported by the published empirical research. Even if it were true there is no evidence how wide or big that “D” area is. It could be very wide and large containing many compounds such as this below example below where the result of this type of testing would be a positive for O, T, H, P, M, A, B, X, K, Y and not for B alone:

There is no evidence that these distinct tests ever intercept.

While in earlier posts, we have examined the propriety and suitability of these three separate and distinct tests in the identification of THC, we cannot properly judge them in isolation. We must remember and in fairness this is a 3 test process and technique.

There are no meaningful or robust studies published that truly validates this three test procedure as resulting in a specific qualitative measure for THC.

What compounds the issue of the possibility of error is that as the analyst is not using the same sample throughout each of these 3 tests. It is in fact, three different samples of the original unknown. The analyst presumes that the unknown is homogenous. Further assumed is that the sampling and the sample selection of the unknown conducted by the analyst result in identical homogeneous samples. These are not justified scientific assumptions (An assumption is not drawn from evidence; it is a hypothesis {my assumption can be tested by looking at the dictionary}. A presumption implies a basis in evidence {the legal presumption of innocence})

Each of these tests are wholly destructive in nature by their very process.

• Just because the sought after features of the microscopic morphological examination were present in the first sample doesn’t necessarily mean that that this sample will contain the sought after features in the modified Duquenois-Levine and the TLC examination because they are not examined for in this sample.
• Just because the sought after features of the modified Duquenois-Levine examination were present in the second sample doesn’t necessarily mean that the features sought after in the microscopic morphological examination are there (because it was not examined) and the sought after featured of the TLC examination are there (because it was not examined) in this second sample.
• Just because the sought after features of the TLC examination were present in the third sample doesn’t necessarily mean that the features sought after in the microscopic morphological examination are there (because it was not examined) and the sought after featured of the modified Duquenois-Levine examination are there (because it was not examined) in this third sample.