Agilent 1260 quat pump

The saturation solubility test was performed in various media to investigate the pH-dependent solubility of TEL. Excess TEL powder was placed into microtubes (Eppendorf, Westbury, NY, USA) containing 1 mL of test media: enzyme-free simulated gastric fluid (pH 1.2), acetate buffer (pH 4.0), enzyme-free simulated intestinal fluid (pH 6.8), phosphate buffer (pH 10) adjusted by 1 N NaOH solution, or deionized water. The samples were vortexed and then placed under mechanical stirring at 25 ± 0.5 °C at 100 rpm for 5 days, followed by centrifugation at 10,000× g for 10 min. The supernatant was collected, filtered through a 0.45 µm PTFE syringe filter, and then diluted with mobile phase to quantify the TEL concentration using HPLC (Agilent 1260 Infinity, Agilent technologies, Santa Clara, CA, USA). The HPLC system had a pump (Agilent 1260 Quat pump), a Capcell Pak C18 column (Shiseido, 250 × 4.6 mm I.D., 5 μm) maintained at a 35 °C oven temperature. The mobile phase consisted of a 40:60 (v/v) mixture of potassium dihydrogen phosphate and acetonitrile (pH 3.7) eluted at 1 mL/min and 10 μL volume of injection. The signals were monitored with an Agilent 1260 VWD detector at λ = 296 nm.

For the selection of a suitable solid matrix former, various hydrophilic polymers and surfactants were screened using solubility testing published guidelines with slight modifications [34 ]. An excess of drug was added to 1 mL of distilled water containing 1% (w/v) polymer or surfactant and vortexed for a few seconds. The microtubes were shaken at 25 °C and 100 rpm for five days in an isothermal water bath shaker. The resulting suspensions were centrifuged at 10,000 g for 10 min and the supernatant was filtered through a 0.45 µm membrane filter. The filtrate was diluted with methanol as needed and then assayed using an Agilent 1260 Infinity LC system (Agilent Technologies; Santa Clara, CA, USA) equipped with Agilent ChemStation software (version B.04.02), an Agilent 1260 Quat pump, and an Capcell Pak C18 column (Shiseido, 250 mm × 4.6 mm I.D., 5 μm). The mobile phase consisted of methanol, acetonitrile, and distilled water (v/v/v: 40/40/20), at a flow rate of 1 mL/min. The mobile phase was monitored using an Agilent 1260 VWD detector (Agilent Technologies; Santa Clara, CA, USA) at a wavelength of 240 nm, and the injection volume was 10 μL. All the experiments were carried out in triplicate (n = 3), and the solubility data are represented as mean ± standard deviation.