Table 1.
Proposed microwave-assisted digestion methods.
| Method | Digestion Solution | Step | Power W | Ramp time | Temp (oC) | Max Pressure (bar) | Hold Time (min) |
|---|---|---|---|---|---|---|---|
| 1 |
2.5 mL HNO3 |
1 |
1200 |
20 |
200 |
16 |
20 |
| 2a |
2.5 mL HNO3 + 3 μL HF | 1 | 1200 | 15 | 200 | 16 | 20 |
| 2 | Cooling to < 50 °C (45 min) followed by the opening of the vessels | ||||||
| 24 μL 5% m/v H3BO3 |
3 |
1200 |
20 |
200 |
16 |
20 |
|
| 3b | 2.5 mL HNO3 + 30 μL HF | 1 | 1200 | 15 | 200 | 16 | 20 |
| 2 | Cooling to < 50 °C (45 min) followed by the opening of the vessels | ||||||
| 240 μL 5% m/v H3BO3 | 3 | 1200 | 15 | 200 | 16 | 20 | |
a
This method is similar to the procedure used by Ref. [10].
b
In this method higher quantities of HF and H3BO3 are used to test if higher extraction efficiencies are obtained with the 10-fold increase in HF quantity adopted.