SOP: Determination of Water-Insoluble Matter in Salt
GIFSQ — Global Institute for Food Safety & Quality
Principle
The salt is dissolved in water and the insoluble residue is collected on a prepared Gooch crucible, washed, dried to constant weight and weighed gravimetrically. The increase in weight is the water-insoluble matter, reported on a moisture-free basis.
Apparatus required
- Gooch crucible with asbestos mat
- Oven (110°C)
Sample preparation
Grind the salt sample to pass a No. 20 sieve and be retained on a No. 80 sieve; quarter and mix.
Procedure
Dissolve 10 g of salt in 200 ml of water; allow to stand for 30 min with frequent stirring
↓
Prepare a Gooch crucible with an asbestos mat; dry at 110°C for 1 hr; cool
↓
Filter the salt solution through the crucible; transfer the residue to the crucible using not more than 50 ml of water
↓
Wash the residue in the Gooch crucible with water until 10 ml of the filtrate shows only faint opalescence when tested with a few drops of dilute (0.1 N) silver nitrate solution
↓
Dry the crucible and its contents to a constant weight at 110°C
↓
Report the increase in weight as water-insoluble matter, in per cent on a moisture-free basis; if the content is more than 0.1%, examine the nature of the residue under the microscope
↓
Make the filtrate up to 1000 ml — it may be used for the other determinations
Calculation
Increase in weight of crucible (g)
% Water-insoluble = ————————————— × 100
matter Weight of moisture-free sample (g)
Where,
- Increase in weight of crucible (g) = weight gained by the prepared crucible
- Weight of moisture-free sample (g) = weight of the sample taken, corrected for moisture
Precautions
- Wash the residue until the filtrate gives only faint opalescence with silver nitrate.
- Dry to a true constant weight at 110°C.
- If the water-insoluble content exceeds 0.1%, examine the residue under the microscope.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.