The mod­ern day pros­e­cu­tion for the unlaw­ful pos­ses­sion of mar­i­juana is based upon a three test régime 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.