SOP: Determination of Phosphoric Acid in Vinegar

GIFSQ — Global Institute for Food Safety & Quality

Principle

The vinegar is evaporated and the residue ashed to bring the phosphorus into a form that can be extracted with hydrochloric acid. The phosphorus in an aliquot of the extract is determined by the phosphorus method, and the result is expressed as phosphoric acid using the equivalence of 31 parts of phosphorus to 98 parts of phosphoric acid.

Apparatus required

• Silica dish
• Muffle furnace
• Watch glass
• Ashless filter paper

Reagents

a. 10% HCl.

b. Reagents for the determination of phosphorus (see page 125).

c. Hot water for washing.

Procedure

Evaporate 25 ml of the vinegar in a silica dish and ash the residue at 650° C

↓

To the ash in the dish, add 25 ml of 10% HCl, cover with a watch glass, and boil gently over a low flame for 5 min

↓

Filter through an ashless filter paper, wash with hot water, and make up the volume to 100 ml

↓

Determine the phosphorus in an aliquot by the method given for phosphorus (see page 125) and express the result as phosphoric acid (H₃PO₄)

Calculation

Phosphoric acid (g) = Phosphorus (g) × (98 ÷ 31)

Where,

• 31 parts of phosphorus are equal to 98 parts of phosphoric acid

Precautions

• Ash the residue at 650° C as prescribed.
• Wash the filter paper thoroughly with hot water so that no phosphorus stays on the paper.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.