High-speed polarity switching dual conversion dynode ion detector for mass spectrometer

A mass spectrometer sub-system comprising:

• a mass analyzer;
• and
• at least one dual polarity ion detector configured to receive ions from the mass analyzer, each of the at least one dual polarity ion detector comprising:
• an entrance electrode disposed to receive a stream of the ions received from a single ion outlet of the mass analyzer and maintained at a reference voltage, V0;
• a first dynode and a second dynode;
• a shielding electrode disposed between the first and second dynodes;
• a first power supply that is configured to maintain the first dynode at a voltage, V1, that is negative relative to V0, whereby substantially positive ions of the stream of ions are directed from the entrance electrode to the first dynode;
• a second power supply that is configured to, simultaneously with the maintaining of the first dynode at the voltage V1, maintain the second dynode at a voltage, V2, that is positive relative to V0, whereby substantially negative ions are directed from the entrance electrode to the second dynode;
• and
• an ion detector comprising an entrance aperture and configured to receive and detect substantially secondary electrons from the first dynode and to receive and detect substantially secondary positive ions from the second dynode;
• wherein either the first or second power supplies or one or more additional power supplies are configured to maintain the entrance aperture of the ion detector at a voltage, Vaperture, that is intermediate between the voltage, V1, and the voltage, V2.