SOP: Determination of Acid-Insoluble Ash
GIFSQ — Global Institute for Food Safety & Quality
Principle
The ash of the sample is boiled with dilute hydrochloric acid. The material that remains insoluble — mainly sand and other siliceous matter — is filtered off, washed free of acid, ignited, and weighed. The acid-insoluble ash is a measure of the sand and siliceous matter present in the sample.
Apparatus required
- One of the silica dishes containing the total ash (from the total ash determination)
- Watch glass
- Ashless filter paper
- Desiccator
Reagents
a. Dilute hydrochloric acid (10% w/w).
Procedure
Add 25 ml of dilute hydrochloric acid (10% w/w) to the ash in the dish
↓
Cover with a watch glass and boil gently over a low flame for 5 min
↓
Filter through an ashless filter paper
↓
Wash the filter paper thoroughly with hot water
↓
Return the paper to the original dish, ignite, cool and weigh the insoluble ash
Calculation
Acid-insoluble ash % = (Weight of insoluble ash × 100) ÷ Weight of sample taken
Where,
- Weight of insoluble ash = weight of the ignited residue after boiling with dilute hydrochloric acid (g)
- Weight of sample taken = weight of the sample taken for the total ash determination (g)
Precautions
- Boil gently over a low flame; avoid vigorous boiling.
- Keep the dish covered with the watch glass during the boiling.
- Wash the filter paper thoroughly with hot water so that all soluble matter passes through.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.