A virtual slit cycloidal mass spectrometer and spectrometry methods are disclosed. The spectrometer size-selects particles, which in turn serve as a virtual slit for a cycloidal mass analyzer. This virtual slit provides unprecedented resolution in a system that takes up a much smaller physical footprint than was previously achievable. This spectrometer may facilitate field sampling of isotopes, such as uranium isotopes.

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.

The invention provides a cycloidal mass spectrometer and a method for adjusting resolution thereof. The spectrometer comprises a set of magnets, providing a magnetic field; two sets of electrode arrays, opposing to each other parallelly, each set of the electrode array including a plurality of strip electrodes arranged parallelly; at least one DC power supply, providing DC voltages to each set of the electrode array to form a DC electric field, the direction of the electric field being perpendicular to the direction of the magnetic field, and the electric field and the magnetic field superimposed on each other to form an electric-magnetic cross-field; an ion injection unit, configured to inject ions into the electric-magnetic cross-field. Said ions travel along a cycloidal trajectory in the electric-magnetic cross-field, in which the magnetic field intensity and the electric field intensity decrease simultaneously within at least part of the region in said cycloidal trajectory.