Chromotropic acid

Chromotropic acid has the formula is (HO)₂C₁₀H₄(SO₃H)₂.

It can be used for as a reagent in the quantitative determination of the systemic herbicide, 2,4-Dichlorophenoxyacetic acid.

Chromotropic acid is also used for testing of presence of formaldehyde.

The usefulness of this reagent in quantitative determination is the formation of a red colouration (peaking at 580 nm wavelength) when chromotropic acid in 75% sulfuric acid reacts with formaldehyde. The colouration is specific to this aldehyde and is not produced from other organic species such as ketones and carboxylic acids.