A combination electrospray/microwave induced plasma (MIP) ionization source is used as the ionization source for a mass spectrometer. The electrospray can be operated in positive mode, negative mode, or it can be switched off. The microwave-induced plasma can also be switched on or off. This allows the instrument to be operated in multiple modes. With the electrospray off and the MIP on, the instrument will normally have its maximum elemental sensitivity. Mixed mode operation potentially allows the determination of additional information about the chemical constituents present in the analyte. In pure electrospray mode, it is possible to obtain molecular information and to analyze organic compounds.