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

METALS
Calculate the available chlorine as follows:
Aliquot of As 2 O 3
Total volume
Soln. taken for titration × (T 2 – T 1 ) × 3.545 ×
of solution ‘B’
Available chlorine = ---------------------------------------------------------------
-----------------------
(g of chlorine per Aliquot of solution ‘B’ × T 2 × Volume
of solution ‘A’
100 ml of hypochlorite taken for titration taken
for dilution
reagent solution)
(i)
Urea solution: (40% w/v in water)
Preparation of Sample:
In all determinations use sample equivalent to less than or equal to 10 gm on
dry weight basis.
(a).
Fresh fruits or vegetables and beverages:
Place weighed sample in digestion flask with 6 glass beads, connect
assembly and add, through dropping funnel, 20 ml of HNO 3 . Pass
rapid stream of water through condenser, adjust stopcock of Soxhlet
unit to reflux position and apply small flame to flask. Original
reaction must not proceed vigorously or violently. After initial
reaction is complete, apply heat so that digest just refluxes. If mixture
darkens, add HNO 3 dropwise through funnel (B) as needed. Continue
refluxing 0.5 hr or until digest does not change consistency, and cool.
54