The acid-insoluble ash is a measure of the sandy matter and plant body parts including calyx, leaves, etc., which contain a higher content of non-combustible acid insoluble matter.
Acid insoluble ash is determined by dissolving ash in dilute hydrochloric acid (10% m/m), the liquid filtered through an ashless filter paper and thoroughly washed with hot water.
The filter paper is then ignited in the original dish, cooled, and weighed.
- Flat-Bottom Dish – of stainless steel, porcelain, silica, or platinum.
- Muffle Furnace – maintained at 550 ± 10°C.
- Dilute Hydrochloric Acid (5N)
- To the ash contained in the dish, add 25 ml of dilute hydrochloric acid, cover with a watch glass and heat in a water bath for 10 minutes.
- Allow to cool and filter the contents of the dish through a Whatman filter paper No. 42 or its equivalent.
- Wash the filter paper with water until the washings are free from the acid and return them to the dish.
- Keep it in an oven maintained at 100 ± 2°C for about 3 hours. Ignite in a muffle furnace at 550 ± 10°C for one hour.
- Cool the dish in a desiccator and weigh. Heat the dish again at 550±10°C for 30 minutes, cool in a desiccator, and weigh.
- Repeat this process of heating for 30 minutes, cooling, and weighing until the difference between two successive weighings is less than 1 mg.
- Record the lowest weight.
W1 = weight, in g, of the empty dish,
W2 = weight, in g, of the dish with acid insoluble ash, and
W = weight, in g, of the sample.
RESULTS AND INFERENCE
- The difference between the results of two concurrent determinations carried out simultaneously or in rapid succession by the same analyst (repeatability) shall not exceed 0.01 % by mass.
- Higher content of acid-insoluble ash in food products is not desirable.
- It should be as minimum as possible (0.1 % Maximum).
• Ashing should be proper.
• Ashless filter paper should be used for filtration.