Table 1.

Variables with their corresponding values in the experimental design.

Variables	Levels
	Low	Medium	High
Independent variables (factors)
X1; Flow rate: mL/min	0.6	0.8	1.0
X2; Injection volume: μL	10	15	20
X3; Detection wavelength: nm	265	270	275
X4; Initial gradient acetonitrile ratio: % v/v	60	70	80
X5; Acetonitrile ratio at four minutes of gradient run: % v/v	85	90	95
Coded levels of levels of X1, X2, X3, X4 and X5	−1	0	+1
Dependent variables (responses)
Y1; Peak area of STP: mAU.s
Y2; Peak area of HI443: mAU.s
Y3; USP Tailing of STP
Y4; USP Tailing of HI443