Step | Fractions | Reagent | Shaking time and temperature |
1 | Exchangeable (EXC) | 8 ml of 1 M MgCl2 (pH 7) in 1 g soil | 2 h at 25˚C |
2 | Bound to carbonates (CAR) | 8 ml of NaOAc (pH 5.0 with HOAc) | 5 h at 25˚C |
3 | Amorphous iron-manganese oxides (OXI) | 20 ml of 0.04 M hydroxylamine hydrochloride in 25% acetic acid (pH 2 with HNO3) | 6 h at 96˚C |
4 | Organic-bound (ORG) | 5 ml of 30% H2O2 (pH 2), plus 3 ml of 0.02 M HNO3 and 3 ml of 30% H2O2 (pH 2) Cool, add 20 ml of a mixture of 3.2 M NH4Ac and 20% HNO3 | 2 h at 85˚C |
5 | Residual (RES) | The residual fraction was digested by 8 ml of a mixture of HCl and HNO3Volume ratio of 3 to 1, therefore they were reached by 0.5 M HNO3 | 30 min at 25˚C |