Treated colloidal silica particles represent a new, prominent class of toner formulation additives, which have recently become commercially available. Many of the performance aspects of these particles are determined principally by the particle surface chemistry. We have found that by careful control and manipulation of the surface treatments, we can control the magnitude of the tribo-charge and manufacture additives with either a negative or a positive tribo-charge.In this paper we present tribo-charge results for a class of silica powders manufactured from aqueous colloidal silica dispersions. Surface treatments are done using various mono- and tri-functional organosilane treating agents. Analysis of these silicas using magic angle spinning cross polarization NMR provides detailed information on the chemical moieties present on the surface and allows us to better understand how these moieties impact the performance properties of the additive.