We have developed a method to measure the adsorption of polymers on silica particles using in situ transmission infrared spectroscopy. An "in situ" mixing cell is used which allows for the simultaneous measurement of adsorbed amount and specific segment/surface interactions. The adsorbed amount is calculated from setting curves which provide additional information on the particle stability. Moreover, the surface quality is maintained because all materials and suspensions are handled in vacuo. In this paper, the adsorption of polystyrene on high area fumed silica particles is discussed with emphasis on the importance of surface quality.