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

METALS
Convert Cd and Zn dithizonates in third separator to chlorides by adding 40
ml of 0.2N HCl and shaking vigorously for one minute. Carefully drain CCl 4
layer and discard. Remove droplets of dithizone from aqueous phase by
rinsing with 1 to 2 ml of CCl 4 and drain off CCl 4 as completely as possible
without allowing acid layer to pass bore of separator. Again adjust alkalinity
to 5% by adding 10 ml NaOH solution. Add exactly 25 ml of dithizone
solution and shake vigorously exactly for 1 min. Allow layers to separate
exactly for 3 min. Wipe separator stems dry with cotton. Filter organic layer
through pledget of cotton, discarding first 5 ml. Read the absorbance of the
cadmium dithizone complex solution at 510 nm. Calculate cadmium in µg
from standard curve or by substituting absorbance in linear equation.
Preparation of Standard Curve:
Prepare in duplicate 6 standards containing 0, 5, 10, 15, 20, 25 µg of
cadmium as follows:
Add appropriate volumes of standard solution to separator, adjust to 40 ml
with 0.2N HCl, and 10 ml of NaOH solution and 25 ml of dithizone
solution. Shake exactly for 1 min. let stand exactly for 3 min and filter
organic layer through a pledged of adsorbent cotton, discarding first 5 ml.
Determine absorbance ‘A’ at 510 nm and plot standard curve.
(Ref :- A.O.A.C 15 th edn Official Method 945.58 Cadmium in Food ,
Dithiozone Method / Manual Methods of Analysis for Adulterants and
Contaminants in Foods I.C.M.R,1990 Page 148)
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