Chromotropic acid

Chromotropic acid is a chemical compound with the formula (HO)2C10H4(SO3H)2. Chromotropic acid is a chemical compound with the formula (HO)2C10H4(SO3H)2. It can be used for as a reagent in the quantitative determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Chromotropic acid is also used for testing for the presence of formaldehyde. The usefulness of this reagent in quantitative determination is the formation of a red coloration (peaking at 580 nm wavelength) when chromotropic acid in 50% sulfuric acid reacts with formaldehyde. The coloration is specific to this aldehyde and is not produced from other organic species such as ketones and carboxylic acids. The NIOSH Formaldehyde method #3500 is the reference analytical standard that uses chromotropic acid.