Inverse Gas Chromatography (IGC) has been applied to study surface Lewis acid and base properties of xerographic developers. Model carrier and toners were prepared and the toners blended with metal oxide surface additives: silica, titania and alumina. The effect of additives on charging, work functions and surface chemistry, as measured by IGC, was studied. All properties were evaluated as a function of relative humidity, to improve understanding of the effect of water as relative humidity increases. Results under dry and wet conditions generally support a work function model for charging, where work functions are determined by surface acid-base properties. Adsorption of water onto surfaces can be followed by IGC, work functions and charging. All provide a consistent picture that water adsorption leads to surfaces that have essentially the properties of adsorbed water at sufficiently high RH.