Table 2. Box-Behnken design matrix for three independent variables with coded values (in parentheses) and recovery (%): Volumetric ratio of methyl tert-butyl ether to ethyl acetate in the extraction solvent (%, A), volume of the extraction solvent (μL, B), and extraction duration (minutes, C).
| Run | Independent variables | Response variable | ||
|---|---|---|---|---|
| A (%) | B (μL) | C (minutes) | Recovery (%) | |
| 1 | 0 (-1) | 100 (-1) | 25 (0) | 68.01 |
| 2 | 50 (0) | 900 (1) | 45 (1) | 65.11 |
| 3 | 50 (0) | 500 (0) | 25 (0) | 94.05 |
| 4 | 100 (1) | 500 (0) | 5 (-1) | 102.54 |
| 5 | 0 (-1) | 900 (1) | 25 (0) | 56.92 |
| 6 | 0 (-1) | 500 (0) | 5 (-1) | 59.77 |
| 7 | 50 (0) | 500 (0) | 25 (0) | 90.70 |
| 8 | 100 (1) | 500 (0) | 45 (1) | 96.57 |
| 9 | 50 (0) | 100 (-1) | 5 (-1) | 76.92 |
| 10 | 50 (0) | 900 (1) | 5 (-1) | 72.12 |
| 11 | 50 (0) | 500 (0) | 25 (0) | 91.29 |
| 12 | 100 (1) | 900 (1) | 25 (0) | 91.90 |
| 13 | 50 (0) | 100 (-1) | 45 (1) | 74.85 |
| 14 | 50 (0) | 500 (0) | 25 (0) | 93.32 |
| 15 | 0 (-1) | 500 (0) | 45 (1) | 65.54 |
| 16 | 100 (1) | 100 (-1) | 25 (0) | 103.20 |
| 17 | 50 (0) | 500 (0) | 25 (0) | 92.29 |