Table 1.

Range of coded and actual values for Box–Behnken design.

Factor	Level
	−1	0	+1
X 1	40	60	80
X 2	30	40	50
X 3	30	90	150
X 4	400	700	1000

Legend: X₁, acetone concentration (% v/v, solvent/water); X₂, ratio (mL/g); X₃, time (seconds); X₄, power (Watt).