Table 1.
Factors and responses of model conditions of circumscribed central composite experimental design.
| Condition | Factors | Responses | ||||
|---|---|---|---|---|---|---|
| Temperature | Time | Yield of the extraction (%) | Nitrate content (%) | |||
| Coded | Actual (°C) | Coded | Actual (min) | |||
| 1 | -1 | 48.8 | -1 | 17.3 | 8.4 | 0.315±0.008 |
| 2 | 1 | 91.2 | -1 | 17.3 | 10.4 | 0.368±0.000 |
| 3 | -1 | 48.8 | 1 | 52.7 | 10.0 | 0.372±0.000 |
| 4 | 1 | 91.2 | 1 | 52.7 | 15.2 | 0.486±0.000 |
| 5 | -√2 | 40.0 | 0 | 35.0 | 6.0 | 0.175±0.000 |
| 6 | √2 | 100.0 | 0 | 35.0 | 16.6 | 0.578±0.000 |
| 7 | 0 | 70.0 | -√2 | 10.0 | 7.4 | 0.258±0.001 |
| 8 | 0 | 70.0 | √2 | 60.0 | 13.6 | 0.536±0.001 |
| 9 | 0 | 70.0 | 0 | 35.0 | 11.4 | 0.467±0.000 |
| 10 | 0 | 70.0 | 0 | 35.0 | 11.4 | 0.402±0.000 |