Folin's reagent or sodium 1,2-naphthoquinone-4-sulfonate is a chemical reagent used as a derivatizing agent to measure levels of amines and amino acids.

[1] The reagent reacts with them in alkaline solution to produce a fluorescent material that can be easily detected.

This should not be confused with Folin-Ciocalteu reagent, that is used to detect phenolic compounds.

The Folin reagent can be used with an acidic secondary reagent to distinguish MDMA and related compounds from PMMA and related compounds.

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