Upcoming regulations regarding diesel engine emissions require substantial reductions in particulate matter and nitrogen oxides through aftertreatment methods. Because sulfur oxides in the exhaust greatly reduce the performance of the aftertreatment system, a dedicated trap for the removal of sulfur oxides has been considered. Most adsorbents are more effective in removing SO3 than SO2; hence, oxidation catalysts have been employed to maximize the concentration of SO3 in the effluent. Although SO2 concentrations are easily measured, SO3 is less easily quantified. As a result, the only figure of merit for SOx trap performance has been total capacity, provided by post-characterization. In this paper, we describe a chromatographic method for the measurement of SO2 and SO3 adsorption in real time that provides adsorbent performance data on breakthrough capacities and sulfur slip. We also provide experimental measurements of breakthrough capacities for SO2 and SO3 adsorption for some common metal oxide adsorbents using this analytical system.