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Assignment of the variables and levels of the experimental design
| Levels | |||
|---|---|---|---|
| Variables | − 1 (low) | 0 (intermediate) | + 1 (high) |
| X1-Temperature (°C) | 140 | 160 | 180 |
| X2-Heating time (min) | 5 | 15 | 30 |
| X3-Extracting solvent | Me70 | Me + Ac | Ac80 |
Me70: Aqueous Methanol (70%, v/v); Me + Ac: mixture of aqueous acetone (80%, v/v) and aqueous methanol (70%, v/v) in a ratio of 1:1 (v/v); Ac80: Aqueous Acetone (80%, v/v)
