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

METALS
with dil. HCl solution leaving Cu, Hg, Ni and Co in organic phase. Aqueous
layer is adjusted to 5% NaOH and is extracted with dithizone – CCl 4
solution. At this alkalinity Zn, Bi and Pb do not extract whereas cadmium
dithizonate is relatively stable. Cadmium is finally estimated
photometrically at 510 nm.
Reagents:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
Citrate – Diammonium salt or citric acid.
Chloroform
Carbon tetrachloride
Dithizone
Dithizone in carbon tetrachloride: 20 mg/ 1 CCl 4. Prepare daily
Dithizone in chloroform – 1000 mg / 1 CHCl 3 Prepare when needed
Sodium hydroxide solution: 28% w/v. Dissolve 28 g of NaOH in
water and dilute to 100 ml.
Thymol blue indicator: Triturate 0.1 g of indicator in agate mortar
with 4.3 ml of 0.05N NaOH. Dilute to 200 ml in glass stoppered flask
with water.
Adsorbent cotton
Cadmium standard solution:
(i)
Stock solution: (1000 µg Cd/ml)
Dissolve 1.000 g of pure cadmium in 20 to 25 ml HNO 3 (1+9),
evaporate to dryness, add 5 ml HCl (1+1), evaporate to dryness.
Dilute to 1.0 litre with water.
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