Asap 2420 surface area analyzer

The shape and surface aspect of particles were accessed using the scanning electron microscopy (SEM) images taken in TM 3000 Microscope Hitachi (Tokyo, Japan). The particles were dried and mounted on metal stubs using double-sided adhesive carbon tape and analyzed at the voltage of 20.0 kV. The mean diameter and the size distribution of the microparticles was determined using dynamic light scattering (DLS) in a Nanotrac NPA252 (Montgomeryville, PA, USA) with Flex software 10.4.3. The amount of 4.0 mg of powder was dispersed in 15.0 mL of aqueous solution of polysorbate 80 at 0.5% w/v. The cumulative diameter of 10, 50 and 90% in the particle size distribution were determined in triplicate. The index span was calculated by the equation: SPAN = D90 − D10/D50 [28 (link)].
The surface area, pore volume and pore size of the chitosan microparticles were determined following the method of Brunauer-Emmett-Teller (BET), using the liquid N2 adsorption and desorption isotherms, measured at 77 K temperature with an ASAP 2420 surface area analyzer (Micromeritics Instrument, Norcross, USA). All samples were degassed and stored at vacuum at room temperature overnight prior to measurements. The experiments were repeated at least three times using fresh powder.

The structural features of as-prepared materials were analyzed by powder X-ray diffraction (X-ray diffractometer model XRD-6100, Shimadzu, Kyoto, Japan) with CuKα X-ray radiation (λ = 0.15406 nm). The morphological features were examined by scanning electron microscopy (FESEM, Hitachi, S-4800 and HRTEM, Tecnai G2 F20 S-Twin at an accelerating voltage of 200 kV). The elements of active materials were recognized using energy-dispersive X-ray spectroscopy (EDS) attached to the SEM. Sample mappings were obtained using annular dark-field imaging in a scanning transmission electron microscope (STEM) equipped with a high-angle annular dark field (HAADF) detector. The chemical states of the materials were tested using a Thermo Scientific X-ray photoelectron spectroscopy (XPS) instrument utilizing Al Kα radiation (λ = 1486.6 eV). The Brunauer–Emmett–Teller (BET) specific surface area was examined by N₂ adsorption-desorption measurements in a Micromeritics ASAP 2420 surface area analyzer. The samples were evacuated at 150 °C before the N₂ adsorption test. The BET surface area was estimated by the multipoint BET method based on the adsorption data in the P/P₀ range of 0.0–1.0, where P and P₀ correspond to the equilibrium and saturation pressures of the adsorbates at the temperature of adsorption, respectively.