Presumptive Testing for LSD

The presumptive tests for LSD involve a fluorescence test and a chemical test.

3.2.3.1 Fluorescence Testing for LSD

One of the properties of LSD that can be exploited during the identification process is its fluorescence. In such a test, the original dosage form, or a drop of the methanolic extract from the dose form, is placed on a filter paper and allowed to dry. The material is then observed under long-wavelength UV light (360 nm). If LSD is present, blue fluorescence will be observed.

If a methanol extract solution is used, what are the appropriate positive and negative controls and what do they show?

Answer

If methanol is used, the appropriate negative control is methanol alone (not exposed to sample or drug). The relevant positive control is a methanolic solution of LSD at approximately the same concentration as the sample provides.

The negative control demonstrates that the fluorescence, if observed, is due to the drug extracted into the methanol. The positive control provides a reference colour reaction and gives an idea of the intensity of the fluorescence that might be observed.

3.2.3.2 Chemical Testing for LSD

The classical presumptive test for LSD is the Ehrlich's reagent test. In this, 1 g of the reagent (^-dimethylaminobenzaldehyde) is dissolved in 10 ml of orthophos-phoric acid. A small amount of the reagent solution is then added either directly to the test substrate or to the extract to be tested and any colour change observed.

If a blue/purple colour develops, then the presence of LSD may be suspected and confirmatory tests should be carried out.

Why is a confirmatory test required?

Answer

Ehrlich's reagent reacts with a wide range of controlled substances and other indole alkaloids. A positive reaction does not therefore prove the presence of a 'specific' drug. This is why it is necessary to carry out an additional confirmatory test.

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Responses

  • Janice
    Is ehrlich reagent a presumptive test?
    2 months ago

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