Similar to a reflectron, the ESA uses multiple electrostatic analysers to focus ions with a wide range of energies so they arrive at the detector simultaneously. As the ions travel through the electric field they are deflected through multiple electric fields, focusing the ions based on their kinetic energies. Due to the way they are deflected, ions that have kinetic energies that are too high or too low can be blocked from progressing fully around the analyser, thereby excluding them from the system. This only allows ions of specific kinetic energies to pass through, thereby eliminating any unwanted products of metastable ion decay. This technique provides high mass resolution with high transmission efficiency.

An animation showing how an electrostatic sector analyser uses a series of curved channels to bring ions of differing energies together so they arrive at the detector at the same time.