Phosphoric acid: Properties and applications

What is phosphoric acid and how is it produced?

Phosphoric acid (H₃PO₄) is a colourless, odourless, non-volatile, and weakly acidic compound. It is primarily produced via the wet-process, where phosphate rock is reacted with sulfuric acid, or the thermal process, involving the combustion of elemental phosphorus. The wet-process is more common due to lower cost and higher yield. The resulting acid is available in concentrations ranging from 50% to 85% and is used in food additives, detergents, fertilisers, and metal surface treatment.

How is phosphoric acid used in regulated industries?

In pharmaceuticals and food manufacturing, phosphoric acid is used as an acidulant and pH stabiliser. It is listed in the European Pharmacopoeia (EP), British Pharmacopoeia (BP), and USP, and is approved for use in soft drinks (e.g., cola beverages). Regulatory compliance is ensured through documentation such as Certificate of Analysis (CoA), Safety Data Sheet (SDS), and adherence to ISO, REACH, and GHS standards. High-purity grades are available for laboratory and biotech applications, including buffer preparation (e.g., in HEPES or Tris buffers) and nucleic acid purification.

What safety and handling considerations apply?

Although not highly toxic, phosphoric acid can cause skin and eye irritation. Handling requires protective equipment and proper ventilation. Storage should be in corrosion-resistant containers, away from incompatible materials such as strong bases or oxidising agents. The acid is classified under GHS as a skin and eye irritant (H315, H318), and its use is regulated under REACH and TSCA where applicable.

Related concepts

Phosphoric acid is often used alongside other inorganic acids such as citric acid, hydrochloric acid, and sulfuric acid. It is also relevant in the context of phosphate salts (e.g., sodium phosphate, potassium phosphate), chelating agents (e.g., EDTA), and buffer systems in biochemical research.