Analyses were carried out using an HPLC system (Agilent series 1100, Santa Clara, CA, USA) equipped with an online degasser, a quaternary pump and an automatic injector and that was coupled to a C18 Spherisorb ODS-2 column (150 × 4.6 mm i.d.;
3 μm particle size), adjusted at 25 °C. Data acquisition and processing were performed using the CHEMSTATION® software programme. Bixin was eluted isocratically at a flow rate of 1 mL/min using acetonitrile/2% v/v acetic acid/dichloromethane (63:35:2 v/v) INCB28060 ic50 as the mobile phase. The chromatograms were processed at the maximum absorption wavelength of bixin (470 nm). All of the solvents used in the HPLC separation were of chromatographic grade and previously filtered through a Millipore vacuum filtration system using a 0.22 μm membrane for organic solvents (Millipore, Barueri, SP, Brazil). The injections were performed in duplicate. Before being injected, the bixin standard was diluted in acetonitrile and the content of bixin in the nanosuspension (250 μL) was extracted with acetonitrile (4.75 mL), homogenised by ultrasonication (30 min) and centrifuged (15 min at 2820×g). The content of bixin present in the aqueous phase was separated from the bixin nanocapsule suspension after ultrafiltration-centrifugation (15 min at 1690×g). The aqueous phase was directly injected in the HPLC without dilution. All
samples were filtered before the injections (0.45 μm, Millex with modified PTFE membrane for aqueous and organic solvents, Millipore, Barueri, São Paulo, Brazil). For the quantification of bixin, a standard Kinase Inhibitor Library curve with a determination coefficient (R2) greater Liothyronine Sodium than 0.99 was used. This standard curve was obtained plotting the peak areas (from the HPLC) of five solutions containing different concentrations of bixin (from 1.37 to 80.16 μg/mL) quantified previously by a spectrophotometer (UV–Visible Agilent 8453, Santa Clara, CA, USA) at 470 nm with an absorptivity coefficient of 2,826 in chloroform. The limits of detection (LOD) and quantification (LOQ) were 0.231 and 0.235 μg/mL,
respectively, and were determined according to the method described by Long and Winefordner (1983). The pH of the bixin nanocapsule suspension was measured at 25 °C using a DM-22 potentiometer (Digimed, Brazil). The nanocapsules mean diameter (z-average) and polydispersity index (PDI) were measured at 25 °C by Dynamic Light Scattering (DLS) and the zeta potential was measured by electrophoretic mobility (Zetasizer® nano-ZS ZEN mod. 3600, Nanoseries, Malvern, UK). The samples were appropriately diluted with a pre-filtered (0.45 μm) 10 mM NaCl aqueous solution or with MilliQ® water to determine the zeta potential and mean diameter (z-average), respectively. Data analysis was performed using Dispersion Technology Software (version 4.0, 2002, Malvern Instruments ltd). The mean diameter of the bixin nanocapsules was also measured by laser diffraction (LD) (Mastersizer 2000® 5.54, Malvern Instruments, UK), using water as dispersant.