Ion-molecule-reaction - mass spectrometry (IMR-MS) device, comprising an ion source (11), an adjacent reaction chamber (15) and a mass spectrometer (14) subsequent to the reaction chamber (15), wherein the reaction chamber (15) comprises an RF device (13) for creating a temporally changing electromagnetic field and wherein an adjustable reduced electric field strength (E/N) can be applied to the reaction chamber (15), characterized by an input device for entering a desired reduced electric field strength (E/N) by an operator when operating said IMR-MS device for analysing a sample, and a controlling device that operates the IMR-MS device by adjusting the settings of the IMR-MS device relating to a defined data set of a pseudo reduced electric field strength (PE/N 1,2 ) for the entered reduced electric field strength (E/N), wherein the pseudo reduced electric field strength (PE/N 1,2 ) has been determined by analysing a first analyte (A 1 ) in the IMR-MS device, wherein intensity signals (RS 1 ) of at least tw
