Table 2 The central composite design matrix for optimal sample preparation
Run | Independent variables | Peak area | |
|---|---|---|---|
X1 extraction time (min) | X2 solvent-to-material ratio (mL/g) | Y(*106) | |
1 | 45 (0) | 100 (0) | 16.3 |
2 | 45 (0) | 100 (0) | 16.4 |
3 | 45 (0) | 100 (0) | 16.3 |
4 | 45 (0) | 100 (0) | 16.3 |
5 | 30 (− 1) | 100 (0) | 15.5 |
6 | 60 (1) | 125 (1) | 14.4 |
7 | 30 (− 1) | 75 (− 1) | 12.8 |
8 | 45 (0) | 75 (− 1) | 14.0 |
9 | 60 (1) | 75 (− 1) | 13.7 |
10 | 45 (0) | 100 (0) | 16.3 |
11 | 60 (1) | 100 (0) | 15.8 |
12 | 45 (0) | 125 (1) | 14.8 |
13 | 45 (0) | 125 (1) | 15.3 |