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

METALS
(b)
(c)
(d)
Chloroform
Dithizone solution:
Prepare stock solution in redistilled chloroform (100 mg/l is
convenient) and store in refrigerator. Prepare dilutions as needed.
Sodium thiosulphate solution:- 1.5 % in water. Prepare daily.
(e)
Dilute acetic acid: 30 % by volume
(f)
Hydroxylamine hydrochloride solution:
20 % w/v in water. Extract with dilute dithizone solution until
chloroform layer remains green, remove excess dithizone with
chloroform and filter.
(g) Hydrochloric acid: 0.1N
(h)
Sodium hypochlorite solution:
Preferably 5% available chlorine reagent. Determine strength of
reagent and store in refrigerator and determine strength monthly.
Reagents with more than 0.1 µg Hg/ml should not be used.
Determination of strength of Hyprochorite solution:
A. Reagents needed:
(i) Arseneous oxide standard solution (0.1N)
Accurately weigh about 2.473 g of pure As 2 O 3 (dried for 1 hour
at 105º before use), dissolve in 25 ml of 1N NaOH while
heating on steam bath. Add approximately the same quantity of
1N H 2 SO 4 . Cool and transfer quantitatively to 500 ml
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