SOP: Determination of Sulphated Ash

GIFSQ — Global Institute for Food Safety & Quality

Principle

In samples where complete combustion is difficult to achieve, or where constituents may be lost by volatilization on ignition, the ash is moistened with concentrated sulphuric acid and ignited gently to constant weight. The residue obtained is the sulphated ash.

Apparatus required

• Silica dish containing the ash
• Desiccator

Reagents

a. Concentrated sulphuric acid (H₂SO₄).

Procedure

Moisten the ash in the dish with a few drops of concentrated sulphuric acid

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Ignite gently

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Cool in a desiccator and weigh

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Repeat the ignition until the weight is constant — the constant weight is the sulphated ash

Calculation

The sulphated ash is reported as the constant weight of the ignited residue obtained above.

Precautions

• Use only a few drops of concentrated sulphuric acid to moisten the ash.
• Ignite gently; avoid strong heating.
• Repeat the ignition until consecutive weighings show no further loss.

References

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