A sample preparation method for characterization of nanoparticles embedded in the supports of heterogeneous catalysts, with improved particle dispersion, is introduced. The supported catalyst is first ground or milled into fine powder. Then, the powder is mixed into an organic solvent, and an etchant is added to the solvent to digest the supports and release metallic nanoparticles. The resulting solution is then placed in an ultrasonic bath where ultrasonic waves are generated and applied to the solution. The ultrasonic waves suppress agglomeration of the particles and also break up those particle clusters resulting from agglomeration during the prior steps. Subsequently, a sample is extracted from the solution and prepared for analysis.