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

METALS
Reagents:
(a)
Lead standard solution:
(i) Stock solution: (1 mg Pb/ml in 1% HNO 3 )
Dissolve 1.5985 g of pure Pb(NO 3 ) 2 crystal in 1% HNO3 and
dilute to 1000 ml.
(ii)
Working solution:
Prepare as needed by diluting stock solution suitably with 1%
HNO 3 solution.
(b) Nitric acid: (1%) Dilute 10 ml of fresh, colourless HNO 3 (sp. Gr.
1.40) to 1000 ml with redistilled water. If acid is redistilled, boil off nitrous
fumes before diluting.
(c)
“Acid-aid” solution:
Dissolve 40 g Al (NO 3 ) 3 .9H 2 O and 20 g Ca(NO 3 ) 2 .4H 2 O in 100 ml water.
(d)
Citric acid solution:
Concentrated lead free solution. Prepare the solution so that 1 ml of
solution contains about 0.5 g of citric acid.
(e) Dithizone solution: (1 mg/ml in CHCl 3 )
Dissolve 100 mg of purified dithizone in chloroform and dilute to 100
ml. Prepare dilute solutions as needed by diluting stock solution
suitably with chloroform.
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