It depends on what your definition of “positive” is? TLC in marijuana testing

Like Bill Clinton’s famous re-framing of the issue in this video:

It depends on what your definition of “positive” is? TLC in marijuana testing

We have posted here before about the Thorton-Nakumura protocol that is used throughout the United States for the prosecution of illegal possession of marijuana (in its solid drug dose pre-consumption form). A fair examination of the question reveals that there is no validity to the notion that the 3 test regimen produces a valid conclusion that the unknown examined in fact contains THC. Here are those posts:

Here are those series of posts:

  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?

We looked at great detail about Thin Layer Chromatography in Marijuana testing in the following post What is Thin Layer Chromatography? Is it a “good” test?

There are also may publications that describe known false positives such as coffee, tobacco and basil.

Beyond that, the test to a large degree is totally subjective in its interpretation. Case in point consider this TLC plate:


Is this a positive

Is the sample labelled B2 a positive?

Different people can answer this differently, I suppose.

But what makes it worse is that few if any laboratories preserve their plates or take pictures of the results. So what you are left with is an unverified subjective opinion of someone who is in an adversarial position from the accused with no data that will support the “positive” call by the analyst. Doesn’t seem very scientific to me.

It’s time for SWGDRUG and drug seizure laboratories to come out of the 1950s and the 1960s and get with modern objective and valid science. It’s time to stop the non-validated Thorton-Nakumura protocol and move to GC-MS (it’s not that hard just put it in a methanol suspension and shoot away) and another technique Category A or Category B to verify it. Is it really that hard to do?

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