A comparative analysis of dialysis based separation methods for assessing copper oxide nanoparticle solubility

Dissolution of nanoparticles (rate of dissolution, equilibrium concentration) is dependent upon physicochemical properties of nanoparticles viz. size, shape, crystal structure, surface charge, and aggregation/ agglomeration. Such a complex interplay between the physicochemical factors and dissolution makes the assessment of nanoparticles a challenging factor. Assessment of dissolution becomes a critical step for determining the concentration of dissolved species in the exposure system. In our study, we used three different physical separation techniques (viz. dialysis, ultrafiltration, centrifugal ultrafiltration) to demonstrate the technical and scientific efficacy of each methodology in assessing dissolution of copper oxide nanoparticles. Dissolution of CuO nanoparticles (31 ± 4 nm) was assessed in a range of simulated media (artificial seawater, artificial lysosomal fluid, 1 mM NaNO<inf>3</inf>), across varied concentrations (25 mg/L, 50 mg/L, and 100 mg/L) and up to 48 h. CuO dissolution was maximum in artificial lysosomal fluid (up to 97 wt.%) and the least in artificial seawater (up to 5 wt.%), across all the separation techniques. Ionic copper recovery experiments demonstrated >99% recovery for all of the separation methods. This study demonstrates how the choice of separation method can be critical in conducting nanoparticle solubility studies. The separation methods captured the dissolution profile of CuO nanoparticles in all the selected media. However, the rate of dissolution and saturation concentration varied among the three separation methods.