An electron multiplier apparatus of the type used in ion detectors, and modifications thereto for extending the operational lifetime or otherwise improving performance. The electron multiplier includes a series of discrete electron emissive surfaces configured to provide an electron amplification chain, the electron multiplier being configured so as to inhibit or prevent a contaminant from entering into, or passing partially through, or passing completely through the electron multiplier. The electron multiplier may include one or more baffles configured so as to decrease vacuum conductance of the electron multiplier compared to the same or similar electron multiplier not having one or more baffles.