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

METALS
Transfer 20 ml aliquots of sample and blank digest solutions to generator
bottles. Add, while swirling after each addition, 10 ml water, 5 ml dil. HCl
(g), 5 ml of KI solution (e) and 4 drops of SnCl 2 solution (f). Let stand for
more than 15 min.
Place 4 g of sea sand over small glass wool wad in sulphide absorption tube
and cap with glass wool. Place 3 mm diameter solid glass beads in trap over
small glass wool pad until ¼ full and add 3.0 ml of sodium hypobromite
solution (h). Assemble apparatus except for generator bottle. Add 4 g of zinc
(i) to generator bottle, attach immediately and let react for 30 min.
Disconnect trap and transfer contents of 25 ml volumetric flask with the help
of aspirator assembly. Rinse trap with six 2 ml portions of water and aspirate
into flask. Add, with swirling, 0.5 ml ammonium molybdate-sulphuric acid
solution (c) and 1.0 ml hydrazine sulphate solution (d), dilute to volume,
mix and let stand for 75 min and mix. Read absorbance at 845 nm against
blank prepared similarly.
Preparation of Standard Curve:
Place 0.1, 1.0, 2.0, 3.0, 5.0, 6.0 and 10.0 ml of standard solution containing
2 µg As 2 O 3 /ml, in 25 ml volumetric flask. Add 3.0 ml of sodium
hypobromite solution and water to 15 ml. Add with swirling 0.5 ml of
ammonium molybdate sulphuric acid solution and 1.0 ml of hydrazine
sulphate solution. Dilute to volume, mix and let stand 75 min. Mix and read
absorbance at 845 nm. Plot absorbance against µg of As 2 O 3 .
( Ref :-/ Manual Methods of Analysis for Adulterants and Contaminants in
Foods I.C.M.R 1990 Page 144 /A.O.A,C 15 th edn, Official Method 942.17
Arsenic in Food Molybdenum Blue Method)
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