reflectron

A reflectron is an electrostatic mirror used in time-of-flight mass spectrometry to compensate for kinetic-energy spread among ions, thereby improving mass resolution.

In a reflectron-based TOF instrument, ions are accelerated into a field-free drift region toward an electrostatic reflector. The reflector consists of a series of electrodes with progressively changing potentials that create an electrostatic field. As ions enter the reflector, they are decelerated, brought to a turning point, and then reaccelerated toward the detector. Ions with higher initial kinetic energy penetrate deeper into the reflector before turning around, so their time of flight through the reflector is longer, whereas lower-energy ions penetrate less deeply. By selecting appropriate voltage gradients, the overall arrival time at the detector becomes less sensitive to initial energy spread, effectively focusing the signal in time and increasing resolving power.

Variants include single-stage and multi-stage reflectrons, the latter using multiple voltage steps to improve energy compensation over a wider mass range and to optimize time focusing for different flight lengths. Reflectrons are commonly used in matrix-assisted laser desorption/ionization (MALDI) and other TOF configurations to achieve high-resolution mass spectra; modern instruments can reach resolving powers on the order of tens of thousands under optimized conditions.

Limitations include sensitivity to precise alignment and voltage stability, potential loss of ion signal if fields are not properly tuned, and limitations in very high mass ranges due to residual energy dispersion. Calibration is typically required to translate measured times to mass-to-charge ratios.