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

METALS
Stopper separator and shake vigorously for 1 min. All Hypochlorite should
be reduced. Extract solution with 2 to 3 ml of CHCl 3 , drain off organic layer
carefully and discard. Final aqueous solution should now be colourless.
Now, to the solution in the third separator, add 3 ml of 30% HOAC and
appropriate volume and concentration of dithizone solution as indicated in
Table 3. Shake vigorously for 1 min and let layers separate. Insert cotton
pledget into the stem of the separator and collect dithizone extract
(discarding first ml) in test tube. Read absorbance ‘A’ of the extract at 490
nm. Convert ‘A’ to µg of Hg from working standard curve.
Preparation of Standard Curve:
Table 3 shown above is useful in preparing standard curve and for
establishing approximate Hg range in sample.
Prepare working standard curve of required range, starting with blank and
extending to final standard of range with 4 intermediate increments.
Add appropriate amounts of Hg to 50 ml of 0.1N HCl in separator. Add 5 ml
H 2 NOH.HCl reagent (f) and 5 ml of CHCl 3 . Shake vigorously for 1 min let
layers separate; drain off CHCl 3 and discard, being careful to remove as
completely as possible all droplets of CHCl 3 . Add 3 ml of 30% HOAC and
appropriate volume of dithizone solution. Shake vigorously for 1 min and let
layers separate. Insert cotton pledged into stem of separator and collect
dithizone extract (discarding first ml) in test tube and read absorbance at 400
nm. Plot ‘A’ against µg of Hg.
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