2:- Reducible fraction-bound to Fe and Mn
oxides
To the residue (pellet) from step 1 was added
20 ml of 0.5 mol/L hydroxylamine hydrochloride pH
1.5 (adjusted with 2 mol/L HNO3), the tube cappedand shaken at 30 rpm for 16 hr at room temperature.
The extract was separated from the solid phase by
centrifugation and decantation as described for step 1
and stored at 4 oC. The solid residue was washed as
in step 1 ready for step 3.