Sodium pyrophosphate, also called tetrasodium pyrophosphate or tetrasodium phosphate, is a slightly toxic and mildly irritating colorless transparent crystalline chemical compound with the formula 427 and CAS number 7722-88-5. It contains the pyrophosphate ion. Toxicity is approximately twice that of table salt when digested orally.. There is a hydrated form, Na4P2O7.10(H2O) which has the CAS number 13472-36-1.
Sodium pyrophosphate is used as a buffering agent, an emulsifier, and a thickening agent, and is often used as a food additive. Common foods containing sodium pyrophosphate include chicken nuggets, marshmallows, pudding, crab meat, imitation crab, canned tuna, and soy-based meat alternatives. It is the active ingredient in Bakewell, the substitute for baking powder's acid component marketed during shortages in World War II.
In toothpaste and dental floss, sodium pyrophosphate acts as a tartar control agent, serving to remove calcium and magnesium from saliva and thus preventing them from being deposited on teeth. Sodium pyrophosphate is sometimes used in household detergents to prevent similar deposition on clothing, but due to its phosphate content it causes eutrophication of water, promoting algae growth.
Calcium pyrophosphate is the crystal deposited in joints in the medical condition pseudogout.