A methylene blue active substances assay, or MBAS assay, is a

colorimetric analysis Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent. It is applicable to both organic compounds and inorganic compounds and may be used with o ...

test method A test method is a method for a test in science or engineering, such as a physical test, chemical test, or statistical test. It is a definitive procedure that produces a test result. In order to ensure accurate and relevant test results, a test ...

that uses

methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglob ...

to detect the presence of

anionic 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 conve ...

surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, fo ...

s (such as a

detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...

foaming agent A foaming agent is a material such as a surfactant or a blowing agent that facilitates the formation of foam. A surfactant, when present in small amounts, reduces surface tension of a liquid (reduces the work needed to create the foam) or increas ...

) in a sample of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

. An anionic surfactant detected by the

color reaction In chemistry, a color reaction or colour reaction is a chemical reaction that is used to transform colorless chemical compounds into colored derivatives which can be detected visually or with the aid of a colorimeter. The concentration of a color ...

is called a ''methylene blue active substance'' (MBAS). After first acidifying a water sample (with

boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...

, for example), one adds to it

chloroform Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various re ...

and a

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solutio ...

of methylene blue et al. Methylene blue is a

cationic 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 conve ...

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

. The

biphasic Biphasic, meaning having two phases, may refer to: * Phase (matter), in the physical sciences, a biphasic system, e.g. one involving liquid water and steam * Biphasic sleep, a nap or siesta in addition to the usual sleep episode at night * Phase ...

solution is then agitated to distribute these reagents throughout the aqueous and organic phases. If an anionic surfactant is present, then the cationic methylene blue and the anionic surfactant forms an ion pair, which is extracted into the organic phase. The

color saturation Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromatic ...

of the chloroform increases with the concentration of anionic surfactants. MBAS assay is an

ASTM International ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, a ...

standard technique for detecting anionic surfactants.ASTM International, West Conshohocken, PA
ASTM D2330 - 02 Standard Test Method for Methylene Blue Active Substances
/ref> These include

carboxylate In organic chemistry, a carboxylate is the conjugate base of a carboxylic acid, (or ). It is an ion with negative charge. Carboxylate salts are salts that have the general formula , where M is a metal and ''n'' is 1, 2,...; ''carbox ...

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

sulfate The sulfate or sulphate ion is a polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...

s, and

sulfonate In organosulfur chemistry, a sulfonate is a salt or ester of a sulfonic acid. It contains the functional group , where R is an organic group. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non- ...

s. An MBAS assay alone does not, however, identify specific surfactants. ASTM withdrew the standard (ASTM D2330-02) in 2011 pending a review and update of the method, which was last approved in 2003. The publication ''Standard Methods for the Examination of Water and Wastewater'' lists the following methods used by certified laboratories testing wastewater in the United States. * Method 5540B describes surfactant separation by sublation. * Method 5540C discusses anionic surfactants as methylene blue active substances (MBAS). * Method 5540D discusses nonionic surfactants as cobalt thiocyanate active substances (CTAS).

Notes

References

* Nollet, Leo M. L. ''Handbook of Water Analysis''. 2nd ed. New York: Marcel Dekker, 2007. {{DEFAULTSORT:MBAS assay Analytical chemistry Anionic surfactants Water pollution

See also

Notes

References