2.6. Preparation of sample solution
A water and acetonitrile mixture (80:20, v/v) was used as thediluent in the sample preparation. The concentration of the VTXTsample was 0.5 mg/mL, and the solutions used to investigate thesystem suitability were prepared by spiking the VTXT sample withseven impurities at 0.1% of the sample concentration.To prepare the forced degradation solution, VTXT was subjectedto the following forced conditions: acidic and basic hydrolyticdegradations were carried out in 1 N HCl (1 mL) and 1 N NaOH(1 mL) at 100◦C for 5 h. For oxidative degradation, VTXT was treatedwith 0.5 mL of 30% H2O2at room temperature for 24 h. VTXT wasalso subjected to thermolytic (105◦C, 24 h) and photolytic(UV light,4500 lx ± 00 lx, 24 h) stress in the solid state. Different stress con-ditions were employed to achieve significant degradation. Acid-and base-hydrolyzed samples were neutralized with a base and anacid, respectively, and all the degradation samples were diluted to0.5 mg/mL for assay determination.