Phosphomolybdic acid is used as reagent for colorimetric determination of phenothiazine derivatives in various pharmaceutical products. The reagent oxidizes the derivative to a cationic free radical, with which it then forms a coloured salt.

Phosphomolybdic is used as a stain for developing thin-layer chromatography plates, staining phenolics, hydrocarbon waxes, alkaloids, and steroids. Conjugated unsaturated compounds reduce PMA to molybdenum blue.

Dissolve 5.0 g in 30 mL of water, make alkaline with ammonium hydroxide, and add 0.25 to 0.30 mL of bromine water. Boil for a few minutes, filter, wash the precipitate several times, and discard the filtrate and washings.

Phosphomolybdic acid catalysts can be prepared by forming a mixture of hydrated Phosphomolybdic acid in an anhydrous alkyl alcohol. This is followed by adding a base to the mixture and evaporating the mixture to form a catalyst powder, and subsequently calcining and dehydrating the powder to yield the active catalyst.