Application of Box-Behnken experimental design and response surface methodology for selecting the optimum RP-HPLC conditions for the simultaneous determination of methocarbamol, indomethacin and betamethasone in their pharmaceutical dosage form

Table 5 Validation parameters and results obtained by the proposed RP-HPLC method for the simultaneous determination of MTL, IND and BET

Item	MTL	IND	BET
Retention time (t_R) (min)	3.15 ± 0.05	4.62 ± 0.31	6.17 ± 0.13
Wavelength of detection (nm)	235	235	235
Range of linearity (µg mL^− 1)	5-600	5-300	5-300
Slope	11.549	35.756	20.242
Intercept	116.170	29.758	12.521
Regression coefficient (r²)	0.9994	0.9998	0.9998
LOD^a (µg mL^− 1)	0.0966	0.750	0.672
LOQ^a (µg mL^− 1)	0.293	2.273	2.037
Standard deviation of the slope S_b	0.116	0.192	0.109
Standard deviation of the intercept (S_a)	39.018	27.593	15.706
Confidence limit of the slope	11.549 ± 0.116	35.756 ± 0.192	20.242 ± 0.109
Confidence limit of the intercept	116.17 ± 39.018	29.758 ± 27.593	12.521 ± 15.706
Standard error of estimation	66.57	47.55	27.06
Intraday precision^b	0.85-0.96-0.96	0.94-0.41-0.42	0.81-0.22-1.01
Interday precision^b	1.54-1.67-1.17	1.21-1.20-1.86	1.77-1.53-1.83
Drug in laboratory prepared mixtures	100.41 ± 0.60	100.86 ± 0.86	100.99 ± 0.65
Drug in dosage form	99.90 ± 0.36	104.79 ± 0.29	104.89 ± 0.04
Drug added	99.70 ± 1.26	100.70 ± 1.21	100.81 ± 0.99

The interday (n = 3), average of three concentrations of (344, 430 and 516 µg mL⁻¹) for MTL, (40, 50, 60 µg mL⁻¹) for IND and (12, 15, 18 µg mL⁻¹) for BET repeated three times in three successive days
^a Limits of detection and quantitation are determined via calculations: LOD = 3.3*SD/slope, LOQ = 10*SD/slope.
^b The intraday (n = 3), average of three concentrations of (344,430 and 516 µg mL⁻¹) for MTL, (40, 50, 60 µg mL⁻¹) for IND and (12, 15, 18 µg mL⁻¹) for BET repeated three times within the day

ISSN: 2661-801X