Nitric acid concentrated acid and nitric oxide for dilute acid. or Concentrated nitric acid oxidizes I, P, and S into HIO, HPO, and HSO, respectively. Nitric acid reacts with proteins to form yellow nitrated products. This reaction is known as the xanthoproteic reaction. This test is carried out by adding concentrated nitric acid to the substance being tested, and then heating the mixture. If proteins that contain amino acids with aromatic rings are present, the mixture turns yellow. Upon adding a base such as ammonia, the color turns orange. These color changes are caused by nitrated aromatic rings in the protein. Xanthoproteic
Chromotropic acid uses chromotropic acid. Chromotropic acid Chromotropic acid has the formula is (HO)CH(SOH). 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 50% 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. The NIOSH Formaldehyde method #3500 is the reference