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

METALS
(iii) Conc. HCl, HNO 3 , Bromine: Distill the reagents in an all glass
apparatus.
(iv) Carbon tetrachloride: Reflux the ordinary CCl 4 vigorously on steam
bath for 1 hour with 1/20 volumes of 20% KOH in methanol. Cool,
add water, drain off CCl 4 layer and wash with water until alkali free.
Dry over anhydrous calcium chloride, filter and distill on hot water
bath.
(v)
Chloroform: Distil ordinary reagent, from hot water bath, collecting
distillate in absolute alcohol in proportion of 10 ml alcohol to 1000 ml
of distillate.
(vi) Dithizone: Dissolve about 1 g of commercial reagent in 50 to 75 ml of
CHCl 3 and filter, if insoluble materiel remains. Extract in separator
with three 100 ml portions of NH 4 OH (1+99). Dithizone passes into
aqueous phase to give orange solution. Filter aqueous extracts into
large separator through cotton pledget inserted in stem of funnel.
Acidify slightly with dilute HCl and extract the precipitated dithizone
with three 20 ml portions of CHCl 3 . Combine extracts in a separator
and wash, 2 or 3 times with water. Repeat the above process again.
Drain the final water washed solution of dithizone in CHCl 3 into a
beaker and evaporate major portion of CHCl 3 spontaneously and
complete drying under vacuum.
Store dry reagent in dark, in tightly stoppered bottle. Prepare solutions
for extraction in pure CHCl 3 / CCl 4 .
(vii) Citric Acid, Sodium/Ammonium acetate, Aluminium nitrate, Calcium
nitrate, Sodium Sulphate, etc. (in assay of lead).
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