A Simple and Improved HPLC-PDA Method for Simultaneous Estimation of Fexofenadine and Pseudoephedrine in Extended Release Tablets by Response Surface Methodology

Table 9

Result of robustness study.

Parameter	Changed value	Retention		Tailing factor		Peak purity
		PSU	FEX	PSU	FEX	PSU	FEX
pH ± 0.4	7.2	3.0	4.6	1.63	1.15	0.999	1.000
	6.4	2.5	4.6	1.62	1.14	0.999	1.000
Flow ± 0.5	1.5	1.8	3.2	1.48	1.10	1.000	1.000
	0.5	4.8	7.0	1.71	1.21	0.999	0.999
Buffer conc. ± 10 mM	30 mM	2.8	4.9	1.59	1.13	1.000	0.999
	10 mM	2.6	4.4	1.61	1.21	1.000	1.000
Zorbax Eclipse XDB (Double Encapped)	Nonpolar	2.8	4.8	1.68	1.10	1.000	0.999
ProntoSIL C18-EPS (with amide embedded group)	Polar	3.5	4.1	1.36	1.31	0.999	1.000