Inverse Gas Chromatography (IGC) has been applied to study the surface properties of developer materials, measuring acid, base and dispersion interactions. Model carrier and toner particles were prepared, where the toner was blended with various nano-particulate metal oxide surface additives: silica, titania and alumina. Toner charging was determined with these surface additive formulations. IGC was used to characterize carrier and additive surface chemistry. Results from IGC were evaluated with respect to toner charge and to metal oxide work functions. A correlation was found between IGC-determined surface acidbase interaction parameters of the developer materials, and their work functions and triboelectric charge. Together, the IGC, work function and charging results strongly support a work function model for developer charging, where the work function is determined by the acid and base properties of the developer components. Thus, as the ratio of the acid to base interaction parameters of the metal oxide surface additive increased, toner charge became more negative. A charging model incorporating all these results has been proposed and integrated with the current understanding of triboelectric charging in xerographic developers.