Question

Discuss in detail the suitable Ashing method for Fe analysis in food

Answer 1

Ash is the inorganic residue that remains after the water and organic matter have been removed by heating, in the presence of oxidizing agents, which provides a measure of the total amount of minerals within a food.

The calcium or iron content of foods can be determined by titration with a solution of potassium permanganate, the end point corresponding to the first change of the solution from pale pink to purple. The calcium or iron content is determined from the volume of permanganate solution of known molarity that is required to reach the end-point.

For Iron, the reaction is:

5Fe2+ 5Fe3+ + 5e- (Oxidation reaction)

MnO4- + 8H+ + 5e-    Mn2+ + 4H20 (Reduction reaction)

5Fe2+ + MnO4- + 8H+  5Fe3+ + Mn2+ + 4H20 (Coupled reaction)

Potassium permanganate is titrated into the aqueous solution of Ashed Food

  

MnO4 -  is converted to Mn2+ as Fe2+  still remains in the food

All Fe2+ converted to Fe3+ and the remaining MnO4 -  leads the formation of a purple colour.

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