A device for ionizing sample particles of a sample gas flow comprises a first flow tube for providing the sample gas flow, and an introducing means for providing H2SO4 molecules to an interaction region. In addition the device comprises a generator for producing reagent primary ions from particles of candidate reagent gas flow essentially in a primary ion production region. The device is configured to introduce said reagent primary ions with H2SO4 molecules in said interaction region in order to arrange interaction between the reagent primary ions and the H2SO4 molecules, thereby producing HSO4− ions and again to produce HSO4− ion clusters comprising HSO4− ions and at least two H2SO4 molecules via interactions of HSO4− with other H2SO4 molecules in said interaction region. Furthermore the device is configured to introduce said HSO4− ion clusters with the sample particles of the sample gas flow in order to provide reactions between said HSO4− ion clusters and the sample particles, and thereby provide a sample cluster comprising the HSO4− ion clusters and said base sample to be determined.