Abstract: A method for reducing heterogeneity of a virus preparation may include generating virus ions from the virus preparation, repeatedly increasing at least one of a temperature and an incubation period at the increased temperature of at least one of the virus preparation and the generated virus ions, measuring mass-to-charge ratios and charge magnitudes of at least some of the generated virus ions at each increase of the at least one of the temperature and the incubation period, determining a mass spectrum at each increase of the at least one of the temperature and the incubation period based on values of the respective mass-to-charge ratios and charge magnitudes, and determining, based on the mass spectrums, optimum ones of the temperature and the incubation period which together minimize, or at least reduce, a heterogeneity of the virus preparation without aggregation of virus capsids in the virus preparation.