However, in cases of very high MALLS signal intensity the light scattering data from MALLS can be used to retrieve information about the particle concentration, i.e., the number of particles N in the scattering volume (number density). For certain samples, the number density is often used as a measure for the infectiousness, effectiveness and quality of viruses/virus like particles, lipidbased nanoparticles and other biological nanocarriers. In the case of LNPs the number density might be also interesting for their applications in cosmetic, pharmaceutics and absorbents. N can be calculated from the light scattering equation (Equation ) when the specific refractive index of the sample (np) and the eluent (n0) is known. In this study, a specific refractive index of 1.53 for LNP was assumed based on literature 10 , while a specific refractive index of 1.33 for the eluent (50 mM NaNO3 ) was determined by Astra software. As shown in Figure it is possible to estimate the particle concentration of a certain radius (Rg) solely from AF4-MALLS measurements.