As discussed in Section 2, spray drying attracted many interests as an alternative drying technology for biologicals with the advantages of high throughput, and the ability to obtain desired flowability and aerosolization. However, there is a stability concern with spray-dried protein solids associated with drying stresses such as high temperature, atomization stresses, and air-liquid interfacial stress. Such effects on the stability of the formulation are dependent on the process parameter, protein type, and formulation. Costantino et al. discovered a direct correlation between the surface area of spray-dried BSA powder and the loss of monomers. Similarly, a recent study examining the heterogeneity and particle surface composition of spray-dried BSA has indicated that proteins exposed at the surface of particles exhibit a higher degree of variability. 206 A correlation of the percentage surface composition of protein to the peak area of the deconvoluted mass envelope relative to an experimentally fully-deuterated sample which as an indicator for protein population heterogeneity was established.