Number-concentration of nanoparticles in liposomal and polymeric multiparticulate preparations: empirical and calculation methods.

Abstract The actual number of particles in formulations of nanoparticles (NP) is of importance for quality assurance, comprehensive physicochemical characterization, and pharmacodynamics. Some calculation methods that have been previously employed are limited because they rely on several assumptions and are not applicable for certain preparations. Currently there are no validated experimental methods for determining the particle number-concentration ( N c ) of liposomal and polymeric nanoparticulate preparations ( N c values represent the original particles. It is concluded that nano-formulations with concentrations of up to 10 7 particles per 1 cm 3 air, corresponding to approximately 10 12 particles per 1 ml solution, can be directly counted within the size range of 30–900 nm. The measured values are compared to newly developed theoretical calculations to assess the viability of these calculations.