Ion-molecule-reactionmass spectrometry (IMR-MS) device, comprising an ion source, an adjacent reaction chamber and a mass spectrometer subsequent to the reaction chamber, wherein the reaction chamber comprises an RF device for creating a temporally changing electromagnetic field and wherein an adjustable reduced electric field strength (E/N) can be applied to the reaction chamber, 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 analyzing 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.sub.1,2) for the entered reduced electric field strength (E/N), wherein the pseudo reduced electric field strength (PE/N.sub.1,2) has been determined by analyzing a first analyte (A.sub.1) in the IMR-MS device, wherein intensity signals (RS.sub.1) of at least two product ions of the analyte (A.sub.1) are recorded and wherein the settings of the IMR-MS device are changed until the measured intensity signal (IS.sub.1) ratios of the at least two product ions match reference intensity signal (RS.sub.1) ratios within a given tolerance level of the at least two product ions determined in an IMR-MS device comprising an ion source, an adjacent reaction chamber with a DC-drift tube and a mass spectrometer subsequent to the reaction chamber, wherein the reaction chamber is operated only with an activated DC-drift tube at a certain actual reduced electric field strength (E.sub.a1/N), wherein these settings of the IMR-MS device relating to the pseudo reduced electric field strength (PE/N.sub.1) are stored in the controlling device, wherein the controlling device controls said IMR-MS device by performing analysis of the sample with the settings corresponding to the pseudo reduced electric field strengths (PE/N.sub.1).

Ion-molecule-reaction-mass spectrometry (IMR-MS) device, comprising an ion source, an adjacent reaction chamber and a mass spectrometer subsequent to the reaction chamber, wherein the reaction chamber comprises an RF device for creating a temporally changing electromagnetic field and wherein an adjustable reduced electric field strength (E/N) can be applied to the reaction chamber, 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.sub.1,2) for the entered reduced electric field strength (E/N), wherein the pseudo reduced electric field strength (PE/N.sub.1,2) has been determined by analysing a first analyte (A.sub.1) in the IMR-MS device, wherein intensity signals (RS.sub.1) of at least two product ions of the analyte (A.sub.1) are recorded and wherein the settings of the IMR-MS device are changed until the measured intensity signal (IS.sub.1) ratios of the at least two product ions match reference intensity signal (RS.sub.1) ratios within a given tolerance level of the at least two product ions determined in an IMR-MS device comprising an ion source, an adjacent reaction chamber with a DC-drift tube and a mass spectrometer subsequent to the reaction chamber, wherein the reaction chamber is operated only with an activated DC-drift tube at a certain actual reduced electric field strength (E.sub.a1/N), wherein these settings of the IMR-MS device relating to the pseudo reduced electric field strength (PE/N.sub.1) are stored in the controlling device, wherein the controlling device controls said IMR-MS device by performing analysis of the sample with the settings corresponding to the pseudo reduced electric field strengths (PE/N.sub.1).

Among other things, we describe methods and apparatus for the ionization of target molecular analytes of interest, e.g., for use in mass spectrometry. In some implementations, a thin molecular stream is emitted in either single or a split mode and encounters both an electron-impact ion source and trochoidal electron monochromator placed sequentially or coincidently. The first ion source emits high-energy electrons (70 eV) to generate characteristic positively-charged mass fragment spectra while the second source emits low-energy electrons in a narrow bandwidth to generate negative molecular ions or other ions via electron capture ionization. The dual ion source may be coupled to analytical instruments such as a gas chromatograph and to any number of mass analyzers such as a polarity switching quadrupole mass analyzer or to multiple mass analyzers.