manual of methods of analysis of foods - Ministry of Health and ...

METALS
Determination:
(1) Quantitatively transfer the cooled digest solution to 100 ml separating
funnel with 37.5 ml of water and mix by rotating the funnel by hand.
The test solution thus obtained is approximately 4.5M in sulphuric
acid. (If the sample taken for digestion contains more than 25 µg of
Sn, quantitatively transfer the cooled digest into a 100 ml volumetric
flask with 37.5 ml of water and dilute to volume with 4.5M sulphuric
acid solution. Take a suitable aliquot of this solution into 100 ml
separatory funnel and bring the volume of solution in separator to 50
ml with 4.5M sulphuric acid and proceed as follows.
(2) Add 5 ml KI solution (g) mix and add 10 ml of cyclohexane. Shake
the funnel vigorously for 2 min and let layers separate. Transfer the
aqueous layer into a second separator and retain the pink coloured
cyclohexane layer.
(3) Add 10 ml of cyclohexane to the contents of second separator, shake
vigorously for 1 min let layers separate and discard aqueous phase.
(4) Combine cyclohexane extracts and discard any aqueous phase present
after combining the extracts.
(5) To the combined extracts add successively, 5 ml of water and 1.5 ml
of 5M NaOH solution (h - i). Shake the contents vigorously for 2 min.
Let layers separate and transfer aqueous layer into a 50 ml beaker
containing 2.5 ml of HCl (e).
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