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The experimental range and levels of the variables in the central composite design (CCD).
| variable | Parameter | Variable Levels | ||||
|---|---|---|---|---|---|---|
| −α(low) | −1 | 0 | 1 | +α(high) | ||
| A | pH | 4 | 4.4 | 5 | 5.6 | 6 |
| B | Volume of CHCI3 (μL) | 310 | 326 | 350 | 374 | 400 |
| C | Volume of ACN (μL) | 1500 | 1541 | 1600 | 1659 | 1700 |
