SOP: Determination of Water-Soluble Matter other than Sodium Chloride in Common Salt
GIFSQ — Global Institute for Food Safety & Quality
Principle
The water-soluble impurities other than sodium chloride are obtained by a stepwise accounting of the determined constituents: carbonates, calcium, sulphate, magnesium and potassium are combined with their radicals in a fixed order, and the water-soluble matter other than sodium chloride is then calculated from the sodium chloride content and the water-insoluble matter.
Reagents
Use the results of the other determinations carried out on the same sample:
a. Total chlorides determination
b. Sodium chloride content determination
c. Water-soluble calcium determination
d. Water-soluble magnesium determination
e. Sulphate determination
f. Potassium determination
g. Water-insoluble matter determination
Procedure
Carry out the determinations and combine the results in the following order:
a. Report the soluble carbonates as calcium carbonate or sodium carbonate
b. Where calcium exceeds what the carbonate accounts for, unite all the calcium with the sulphate radical and report it as percentage of calcium sulphate
c. Where sulphate exceeds what the calcium requires, unite the excess sulphate with magnesium and report it as percentage of magnesium sulphate
d. If magnesium chloride still remains in excess, calculate the balance as magnesium chloride, and subtract the chloride belonging to that balance of magnesium from the total chloride content
e. Determine the potassium content and find the chloride belonging to the potassium. Subtract the value found from the total chloride content, and report the potassium content as potassium chloride
f. Report the remaining chloride as percentage of sodium chloride
Notes, as printed:
- If the sulphate content exceeds the calcium and magnesium sulphates, report it as sodium sulphate. If calcium exceeds the calcium sulphate, report it as calcium chloride. This situation generally does not arise in common salt.
- If calcium and magnesium are absent, report carbonates as sodium carbonate and sulphates as sodium sulphate.
Calculation
From the above results, calculate:
% Matter soluble in water other than sodium chloride = 100 − % NaCl content − % Matter insoluble in water
Where,
- % NaCl content = sodium chloride content of the sample, in per cent
- % Matter insoluble in water = water-insoluble matter of the sample, in per cent
Notes: the book’s printed equation line is garbled in the extraction; the formula above follows the printed column labels. The value includes the water of hydration retained at the temperature used for the determination of moisture.
Precautions
- Apply the (a)–(f) combinations strictly in the printed order.
- Use results obtained on the same sample for every constituent.
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.