Metaphosphoric acid is used as a dehydrating agent. Its derivative, sodium hexametaphosphate is used as a sequestrant and a food additive. It is also used as a phosphorylating agent, analytical reagent and in dental cements.
Alkorta, I.; Azofra, L. M.; Elguero, J. Ab initio study in the hydration process of metaphosphoric acid: the importance of the pnictogen interactions. Theor. Chem. Acc. 2015, 134 (3), 1-8.
Feitosa, V. P.; Bazzocchi, M. G.; Putignano, A.; Orsini, G.; Luzi, A. L.; Sinhoreti, M. A. C.; Watson, T. F.; Sauro, S. Dicalcium phosphate(CaHPO4·2H2O) precipitation through ortho- or meta-phosphoric acid-etching: Effects on the durability and nanoleakage/ultra-morphology of resin-dentine interfaces. J. Dent. 2013, 41 (11), 1068-1080.
Hazard Statements: H314-H318-H335
Causes severe skin burns and eye damage. Causes serious eye damage. May cause respiratory irritation.
Precautionary Statements: P260u-P303+P361+P353-P305+P351+P338-P301+P330+P331-P405-P501a
Do not breathe dusts or mists. IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. IF SWALLOWED: Rinse mouth. Do NOT induce vomiting. Store locked up. Dispose of contents/container in accordance with local/regional/national/international regulations.