DETERMINATION OF TOTAL ASH

Principle

            When a sample of a food material is ashed around 525⁰C, the organic matter present is decomposed and expelled. The residue remaining is the mineral matter. The ash content is expressed as per cent weight by weight.

Requirements

Equipment and Apparatus

Silica dish (100ml cap.)

Chemical balance, 1mg sensitivity

Hot plate or burner

Muffle furnace

Desiccators (with an active desiccant)

 Procedure

1. Note the tare weight of three silica dishes
2. Accurately weigh 5 g of sample into each.
3. Char the material carefully on a burner or hot plate and transfer the dishes to a muffle furnace and ash at a temperature of around 525⁰C until a white ash is obtained.
4. Moisten the ash in dishes with water. Dry on steam bath and on hot plate and re-ash at 525⁰C.
5. Cool in a desiccator and weigh.
6. Reserve the ash in one dish for determination of water-soluble and water-insoluble ash, in second dish for acid-insoluble ash, and the ash in the third dish for determining alkalinity of ash.

Observations

Weight of silica dish = W1 = ------- g

Weight of the silica dish with sample = W2 = --- --- g

Weight of the silica dish with ash = W3 =------- g

Calculation

Total ash (%) in the sample = Weight of ash (W3 – W1)/ Weight of sample (W2 – W1) × 100 = -------------

If the ash content has to be calculated on dry weight basis:

Total ash content (%) on dry weight basis = (W3 – W1) × 100/(W2 – W1) × (100 – M)

Where, M is the moisture content (%) of the sample in percent by weight

Expression of Results

Ash Content = % by weight or % by dry weight

Precautions

Do not transfer the hot silica dish directly from the muffle furnace to the desiccator. Cool to 100oC and transfer to desiccator.