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

METALS
(j)
(k)
Sea sand:
To clean sand (30 mesh) before use and between determinations,
mount piece of 3 mm inner diameter glass tubing through rubber
stopper in suction flask. Fit a piece of rubber tubing over top to take
bottom of sulphide absorption tube easily and to maintain it upright.
Add, in turn with suction aqua regia, water, nitric acid and water to
remove all traces of acid. Wet sand with lead acetate solution and
remove the excess with suction.
Arsenious oxide standard solution
(i) Stock solution: (1 mg/ml)
Dissolve 1.0 g of As 2 O 3 in 25 ml of 20% NaOH solution and
dilute to 1000 ml.
(ii)
(iii)
Intermediate solution: (10 µg/ml)
Dilute 10 ml of stock solution to 1000 ml.
Working solution: (2 µg/ml)
Dilute 20 ml of intermediate solution to 100 ml.
Preparation of Sample:
(a)
Fresh fruits:
Weigh and peel representative sample (0.5 to 2 kg). At blossom and
steam end cut out all flesh thought to be contaminated with as
compounds and include with peelings, if desired. Place peelings in
one of more 800 ml kjeldahl flasks. Add 25 to 50 ml HNO 3 and
cautiously add 40 ml of H 2 SO 4 . Place each flask on asbestos mat with
5 cm hole. Warm slightly and discontinue when foaming becomes
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