Xselect lc 18 column

In a 5% dextrose solution, PLGA NPs with different initial squalene contents (100, 75, 50, 25 µL of 2.05 M of squalene) were formulated and then washed twice with water using an ultrafiltration device (Amicon, molecular weight cut-off, 100,000 Da). Squalene was extracted from the NPs using ethanol and quantified by high-performance liquid chromatography (HPLC). The HPLC Waters Alliance 1695 (Waters, Milford, MA, USA) was used, which was retrofitted with a Waters DAD 2996 photodiode array detector, a Hewlett-Packard computer running Waters Empower 3 software and a Waters autosampler with a 50 µL loop. Synchronous spectra detection wavelengths ranging from 200 to 600 nm were recorded for all peaks. A non-gradient mobile phase of acetonitrile and methanol (50:50, v/v) was adopted at a constant flow rate of 1 mL/min on a Waters XSelect LC-18 column (2.1 mm by 150 mm, 3.5 µm). The squalene peak was calculated quantitatively by comparing it to a standard curve at a wavelength of 216 nm. The absorbance of the organic solvents in the selected wavelength of 216 nm was subtracted by the autozero.