SOP: Determination of Moisture in Salt
GIFSQ — Global Institute for Food Safety & Quality
Principle
Moisture is determined gravimetrically: the salt sample is heated and the loss in weight, brought to constant weight by repeated heating and weighing, is reported as the moisture content.
Apparatus required
- Tared 250-ml conical flask
- Small funnel
- Oven (capable of 250°C)
- Analytical balance
Sample preparation
Grind the salt sample to pass a No. 20 sieve and be retained on a No. 80 sieve; quarter and mix.
Procedure
Weigh accurately 10 g of the sample into the tared 250-ml conical flask; spread the sample evenly at the bottom of the flask by gentle shaking; place a small funnel in the neck
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Heat at 250°C for 1 hr
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Cool, remove the funnel, and weigh
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Reheat, cool, and weigh again; repeat until two consecutive weighings do not differ by more than 5 mg
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Report the loss in weight as per cent moisture content
Alternative methods given in the book
- ISI method for edible common salt: grind the sample in an agate mortar to a sieve size of 2.8 mm (without actually sieving); dry 20 g at 140° to 150°C for at least 4 hr to a constant weight.
- Food Chemicals Codex method: dry at 105°C for 2 hr.
In each case the loss in weight is the moisture content, calculated as a percentage.
Calculation
Loss in weight (g)
% Moisture = ———————— × 100
Weight of sample (g)
Where,
- Loss in weight (g) = constant weight lost on drying
- Weight of sample (g) = weight of the sample taken
Precautions
- Spread the sample evenly at the bottom of the flask before heating.
- Bring the sample to a true constant weight — two consecutive weighings must not differ by more than 5 mg.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
Specification for Edible Common Salt (Second Revision) IS: 253-1970, Indian Standards Institution, New Delhi, 1971 — cited in the book.
Food Chemicals Codex, National Academy of Sciences, Washington, D.C., 2nd edn, 1972, p. 734 — cited in the book.