Recently, the homogeneity of salt distribution in solid biologics has been evaluated by proteinbuffer miscibility using ssNMR. Mutukuri et al. found the 13 C-detected 1 H T1ρ values were significantly different for BSA, trehalose, and succinic acid in lyophilized formulations by ssNMR, as shown in Figure . This finding offers compelling proof of variability within a domain scale smaller than tens of nanometers. Besides the relaxation measurement, the distribution of chemical shifts implies variations in microenvironments acidity. It has been demonstrated that alterations in acidity, such as in frozen solutions or lyophilized protein formulations, can detrimentally affect stability. The distribution of microenvironmental acidity, as evidenced by the observed protein and excipient immiscibility, strongly aligns with the physical stability of BSA formulations. This is evident by the highest degree of monomer loss detected through SEC analysis in lyophilized BSA with succinate buffer.