Phosphotungstic acid (12501-23-4)

Phosphotungstic Acid Chemical Structure

What is Phosphotungstic acid?

Phosphotungstic acid (PTA) or tungstophosphoric acid (TPA) is a compound that belongs to the family of heteropolyacids. Chemically, it is a type of polyoxometalate, containing metal oxide clusters. It forms hydrates as H3[PW12O40]┬ĚnH2O. PTA has many potential applications, such as a catalyst, histology stain component, as a negative stain in transmission electron microscopy, etc.

Macsen Laboratories is the leading manufacturer and supplier of Phosphotungstic acid with ISO certification.
Name of Product Phosphotungstic acid
IUPAC Name phosphoric acid;trioxotungsten;hydrate
Synonyms Tungstophosphoric acid;12-Phosphotungstic acid; 12-Tungstophosphoric acid; Dodecatungstophosphoric acid; Phosphotungstic acid (PTA)
CAS No 12501-23-4
Molecular Formula H5O41PW12
Molecular Weight 2880.2 g/mol
Pubchem CID 16212977


SR. No Criteria Limit/Specification
1 Appearance (Form) Solid Powder or Crystals
2 Appearance (Color) White to Off-white to Yellow to Beige to Grey
3 Odor Odorless
4 Solubility (In water) 200 g/100 ml
5 Insoluble Matter NMT 0.01%
6 Chloride (Cl) NMT 0.02%
7 Sulphate (SO4) NMT 0.01%
8 Loss on drying NMT 15%


  • Phosphotungstic acid (PTA) is used in histology for staining specimens. It helps enhance the contrast of biological samples, allowing for better visualization of cellular structures.
  • It is a component of Phosphotungstic acid hematoxylin (PTAH) stain and trichome stain reagents.
  • It is widely used as a negative stain in electron microscopy for highlighting specific cellular structures under a microscope.
  • Various dyes have been precipitated as “lakes” using phosphotungstic acid. Example – basic dyes and triphenylmethane dyes.
  • It is often used as a catalyst in organic synthesis reactions such as esterification, oxidations, and dehydration reactions.
  • PTA can also be used for protein precipitation and purification, serving as a “universal” precipitant for polar proteins.


Q. What is phosphomolybdic acid and phosphotungstic acid?

Phosphomolybdic acid and phosphotungstic acid both belongs to the group of heteropolyacids, which consists of molecules that include several metal atoms (molybdenum or tungsten) surrounded by oxygen atoms. These compounds have diverse uses in the fields of chemistry, catalysis, and analytical chemistry.

Q. What is the role of phoshphotungstic acid in trichome stain ?

Phosphotungstic acid (PTA) is commonly used in trichome staining for light microscopy to enhance the visibility of trichomes (hair-like structures on the surface of plant tissues). The staining process helps highlight the structure and morphology of trichomes, aiding researchers in studying the distribution, density, and types of trichomes on plant surfaces.

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