Phosphotungstic acid (
PTA),
tungstophosphoric acid (
TPA), is a
heteropoly acid with the chemical formula H
3P
12O
40. It is normally present as a hydrate.
EPTA is the name of
ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 H
2O hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of different names and acronyms (see 'other names' section of infobox).