Introduction to Phosphates

Phosphate, the salt of phosphoric acid, is one of the natural ingredients of almost all foods. As an important food ingredient and functional additive, it is widely used in food processing.
On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization was preliminarily compiled and referenced. Phosphorus-32, phosphate forms are included in the list of a category of carcinogens.

Phosphate is one of the natural ingredients of almost all foods and is widely used in food processing as an important food ingredient and functional additive.
The naturally occurring phosphate is phosphate rock (containing calcium phosphate). Sulfuric acid reacts with the phosphate rock to produce calcium dihydrogen phosphate and calcium sulfate that can be absorbed by plants to produce phosphate. Phosphates can be divided into orthophosphates and polycondensed phosphates: the phosphates used in food processing are usually sodium salt, calcium salt, potassium salt, and iron and zinc salts as nutrient fortifiers. Commonly used food-grade phosphates There are more than 30 varieties. Sodium phosphate is the main consumption type of domestic food phosphate. With the development of food processing technology, the consumption of potassium phosphate is also increasing year by year.

Phosphates can be divided into orthophosphates and polycondensed phosphates.
Orthophosphate
Orthophosphoric acid is a tribasic acid, and there are three kinds of orthophosphates:
1. Dihydrogen phosphate MH2PO4, also known as first-generation phosphate, is soluble in water;
2. Hydrogen phosphate M2HPO4, also known as secondary phosphate;
3. Orthophosphate M3PO4, also known as third-generation phosphate.
The latter two are generally insoluble in water except sodium, potassium and ammonium salts. In addition to being a monovalent metal, M can also be a metal in other valence states. Sodium dihydrogen phosphate is used to control the concentration of hydrogen ions in the solution; disodium hydrogen phosphate is used in water treatment as a precipitant for polyvalent metals; trisodium phosphate is used in the manufacture of soaps and detergents.
Pyrophosphate
Pyrophosphoric acid is a tetrabasic acid. There are four types of pyrophosphate, of which M2H2P2O7 and M4P2O7 are common.
Metaphosphate
Metaphosphate is usually a cyclic compound, the general formula is (MPO3)n, the common ones are dipolymetaphosphate (six-membered ring) and tetrapolymetaphosphate (eight-membered ring), polymetaphosphate It does not have a definite crystal structure, and is also called a phosphate glass body. Sodium hexametaphosphate is the most common phosphate glass body. It has no fixed melting point and variable solubility in water. The pH of the aqueous solution is between 5.5 and 6.4. It is actually a long-chain compound with 20-100 PO3 units. Chain-type phosphate can be used as boiler water treatment agent, pigment dispersant, mud dispersant and metal preservative.

Phosphate ion can generate characteristic yellow ammonium phosphomolybdate precipitate, which can be used for analysis and verification.