Chromotropic acid is a chemical compound with the formula (HO)₂C₁₀H₄(SO₃H)₂. Its name is derived from the two

ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words ''χρωμός'' (chromos, color) and ''τροπέιν'' or ''τρέπω'' (verb: tropein, trepo, changing, turning), meaning it changes of color when reacting with some other compounds. This property is put to use in

analytical chemistry Analytical skill, Analytical chemistry studies and uses instruments and methods to Separation process, separate, identify, and Quantification (science), quantify matter. In practice, separation, identification or quantification may constitute t ...

for the

colorimetric Colorimetry is "the science and technology used to quantify and describe physically the human color perception". It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color p ...

assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...

of various compounds such as

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

anions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

and even some

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s. Chromotropic acid is used for testing for the presence of

. The usefulness of this reagent in quantitative determination is the formation of a red coloration (peaking at 580 nm

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

) when chromotropic acid in 50%

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

reacts with

. The coloration is specific to this aldehyde and is not produced from other organic species such as other aldehydes, ketones and carboxylic acids. The NIOSH Formaldehyde method #3500 is the reference analytical standard that uses chromotropic acid. Chromotropic acid is also used for the direct

spectrophotometric Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spe ...

determination of

according to a method developed by West and Lyles in 1960. It can also be used as a reagent for the quantitative determination of the

2,4-dichlorophenoxyacetic acid 2,4-Dichlorophenoxyacetic acid is an organic compound with the chemical formula . It is usually referred to by its ISO common name 2,4-D. It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most gra ...

(2,4-D).

References

{{Reflist 1-Naphthols Naphthalenesulfonic acids Polyphenols