A fast parallel method for determining the capacity of an automotive catalyst to trap and especially store NOx has been established. A three-step approach, including parallel adsorption of NO onto the catalyst samples, water extraction of trapped NOx in the form of NO2-and NO3- in an aqueous solution, and colorimetric assay based on the sensitive and dramatic color change from colorless to deep red of the organic dye through the Griess diazotation reaction has been performed sequentially to give a fast parallel and quantitative evaluation of the amount of NOx trapped over promising automotive catalysts. The results correlate well with those obtained by means of traditional, time-consuming techniques, such as temperature-programmed desorption. (c) 2006 Elsevier Inc. All rights reserved.