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

METALS
Adjust pH of their aqueous solution to 3.0 to 3.5 (using bromophenol
blue indicator) with NH 4 OH. Precipitate lead and some other metals
from the solution as sulphides, with H 2 S using 5 to 10 mg of CuSO 4 as
co-precipitant. Filter, boil filtrate to expel excess H 2 S completely and
refilter, if necessary to obtain clear solution.
(Ref:- Manual Methods of Analysis for Adulterants and Contaminants
in Foods I.C.M. R, 1990 Page137)
2.0 DETERMINATION OF LEAD, CADMIUM, COPPER, IRON AND
ZINC IN FOODS BY ATOMIC ABSORPTION
SPECTROPHOTOMETER
Principle:
Test portions are dried and then ashed at 450 0 C under a gradual increase
(about 50 0 C / hr) in temperature, 6 N HCl (1+1) is added and the solution is
evaporated to dryness. The residue is dissolved in 0.1N HNO 3 and the
analytes are determined by flame and graphite procedures.
Apparatus
(a) Atomic absorption Spectrophotometer – with an air – acetylene
burner or nitrous oxide- acetylene burner for flame and a graphite
furnace for electrothermal determinations with appropriate
background (non atomic correction). Instrument parameters are
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