Table 1.
Selected sequential extraction procedure for As fractioning.
| Step | Extractant | Time/Temperature | As Fraction | Reference |
|---|---|---|---|---|
| 1 | (NH4)2SO4 0.05M | 4 h/25 °C | Easily exchangeable As | [57] |
| 2 | (NH4)H2PO4 0.05M | 16 h/20 °C | Specifically adsorbed As | [57] |
| 3 | Acetic buffer 1M (pH 5) | 12 h/25 °C | As bound with calcite | [61] |
| 4 | NH4-oxalate buffer 0.2M (pH 3.2) | 4 h/20 °C + 10 min (wash) | Low crystalline Fe(III)-oxyhydroxides | [57] |
| 5 | NH4-oxalate buffer 0.2M + ascorbic acid 0.1M (pH 3.2) | 30 min/96 °C + 10 min (wash) | Crystalline Fe(III)-oxides | [57] |
| 6 | HNO3 8M | 3 h/80 °C | Sulfides | [84] |
| 7 | Microwave digestion (HNO3 + H2O2) | 30 min/180 °C | Residual fraction | [57] |