A Small Angle Scattering Method for Quantifying Interparticle Interaction Ranges in Monoclonal Antibody Solutions

We recently developed a method to obtain interparticle interaction information directly from small angle X-ray or neutron scattering data by analyzing the low-Q asymptotic behavior of the effective structure factor. In particular, we introduce the radius of interparticle interaction (R_i) as a new interaction metric, which quantifies the mean-squared displacement (MSD) of the total correlation function, in analogy to the radius of gyration (R_g). For dilute solutions, R_i is directly the MSD of the interparticle potential (C.E.R. Edwards, W. Leite, Y. Liu, ACS Measurement Science Au, 2025). In this work, we demonstrate the utility of this method by applying it to low-concentration solutions of NIST monoclonal antibody reference material 8671 (NISTmAb) in various excipient conditions. Specifically, we quantify the impact of the sucrose, salt (NaCl), and surfactant (polysorbate 80) on the R_i between NISTmAb in aqueous solutions. The NISTmAb results are relevant to studying a wide variety of mAbs in the pharmaceutical industry, and the approach we developed can also be broadly used to characterize interactions in other polymer, polyelectrolyte, protein, and colloidal solutions.