Parameters	Drug	% S.D	% RSD
Mobile phase composition (±0.1 ml)	NAC	0.231	0.245
Mobile phase composition (±0.1 ml)	TAU	0.462	0.458
Amount of mobile phase (±5%)	NAC	0.836	0.824
Amount of mobile phase (±5%)	TAU	0.792	0.773
Time from spotting to chromatography (±10 min)	NAC	0.573	0.568
Time from spotting to chromatography (±10 min)	TAU	0.924	0.916
Time from chromatography to scanning (±10 min)	NAC	0.635	0.628
Time from chromatography to scanning (±10 min)	TAU	0.527	0.523