Berthelot's reagent is an alkaline solution of

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...

and hypochlorite, used in

analytical chemistry Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...

. It is named after its inventor,

Marcellin Berthelot Pierre Eugène Marcellin Berthelot (; 25 October 1827 – 18 March 1907) was a French chemist and Republican politician noted for the ThomsenBerthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substa ...

. Ammonia reacts with Berthelot's reagent to form a blue product which is used in a

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 ...

method for determining

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

. The reagent can also be used for determining

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

. In this case the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

urease Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous bacteria, fungi, algae, plants, and some invertebrates, as well as in soils, as a soil enzyme. They are nickel-contai ...

is used to

catalyze Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

of urea into

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

and ammonia. The ammonia is then determined with Berthelot's reagent.

Variations

Phenol in the Berthelot reagent can be replaced by a variety of phenolic reagents, the most common being

sodium salicylate Sodium salicylate is a sodium salt of salicylic acid. It can be prepared from sodium phenolate and carbon dioxide under higher temperature and pressure. Historically, it has been synthesized by refluxing methyl salicylate (wintergreen oil) with a ...

, which is significantly less toxic. This has been used for blood urea nitrogen (BUN) determinations and commonly is used to determine water and soil total and ammonia-N. Replacement of phenol by

2-phenylphenol 2-Phenylphenol, or ''o''-phenylphenol, is an organic compound. In terms of structure, it is one of the monohydroxylated isomers of biphenyl. It is a white solid. It is a biocide used as a preservative with E number E231 and under the trade nam ...

reduces interferences by a variety of soil and water constituents and improves color stability at slightly lower pH.

Uses

Berthelot's reagent has been used in a range of situations. It is often used in colorimetric methods, through an

AutoAnalyzer The AutoAnalyzer is an automated analyzer using a flow technique called continuous flow analysis (CFA), or more correctly segmented flow analysis (SFA) first made by the Technicon Corporation. The instrument was invented in 1957 by Leonard ...

, spectrophotometer, or multiwell plate spectrophotometer. The reagent lacks sensitivity in situations where there may be

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...

s as well as ammonia, however this can be overcome in part by the use of 2-phenylphenol to replace phenol. An

ion selective electrode An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage is theoretically dependent ...

, or distillation/titration method can often be used in cases where Berthelot chemistry is ineffective. Berthelot chemistry has also been adapted for the analysis of nitrite and nitrate in soil and water after conversion, typically by reduction with

Devarda's alloy Devarda's alloy (CAS # 8049-11-4), is an alloy of aluminium (44% – 46%), copper (49% – 51%) and zinc (4% – 6%). Devarda's alloy is used as reducing agent in analytical chemistry for the determination of nitrat ...

, of these species to ammonium.

Variations

Uses

References

Further reading