Table 9.

Results of robustness.

Variation	Specific condition	Potassium guaiacolsulfonate			Sodium benzoate
		RSD (%) for area of peak 1	RSD (%) for area of peak 2	RSD (%) for content in oral powder	RSD (%) for peak area	RSD (%) for content in oral powder
Flow rate (mL/min)	0.8	0.12	0.01	0.09	0.64	0.98
	1.0 (normal)	0.03	0.04	0.06	1.36	0.90
	1.2	0.13	0.23	0.05	0.72	0.88
Concentration of tetrabutyl-ammonium- sulfate solution	0.0019 M	0.03	0.04	0.06	1.36	0.90
	0.0020 M (normal)	0.07	0.18	0.05	0.46	0.84
	0.0021 M	0.02	0.15	0.11	0.60	0.56
Gradient program
Initial hold time (min)	6.5	0.04	0.21	0.02	0.47	0.45
	7.0 (normal)	0.02	0.15	0.01	0.35	0.64
	7.5	0.03	0.04	0.06	1.36	0.90
Gradient length (min)	5.0	0.03	0.11	0.02	0.40	0.56
	5.5 (normal)	0.03	0.17	0.05	0.86	0.77
	6.0	0.05	0.08	0.03	0.38	0.81
Final hold time (min)	2.0	0.03	0.04	0.06	1.36	0.90
	2.5 (normal)	0.03	0.12	0.04	1.26	0.65
	3.0	0.06	0.15	0.04	0.98	1.05
Initial percentage of methanol in gradient slope	18%	0.03	0.04	0.06	1.36	0.90
	20% (normal)	0.04	0.07	0.02	1.09	0.94
	22%	0.03	0.16	0.02	0.76	0.58
Final percentage of methanol in gradient slope	48%	0.03	0.04	0.06	1.36	0.90
	50% (normal)	0.04	0.08	0.02	0.61	0.61
	52%	0.12	0.01	0.09	0.64	0.98