Step

Reagent

Treatment

1

Ion exchangeable

20 mL 1 M NH₄Ac at pH 7 adjusted with NH₃, for 1 h at 25˚C.

2

Acid soluble

20 mL 1 M NH₄Ac at pH 5 adjusted with HAc, for 5 h at 90˚C.

3

Reducible

20 mL 0.043 M NH₂OH-HCl in 25% HAc for 5 h at 90˚C.

4

Oxidizable

20 mL 0.02 M HNO₃ and 30% H₂O₂ (3/5 v/v) at pH 2, adjusted with HNO₃, for 3 h at 85˚C.

5

Residual

Digestion in a closed micro wave oven using concentrated nitric acid.