In order to make it through the curved tunnel of the mass analyzer, the ions need to have just the right mass (and charge) with respect to the pull of the magnetic field, and the geometry and setup of the instrument. Generally speaking: If ions are too “light”, or too “heavy” in their mass-to-charge ratio, they will veer into the wall of the tunnel and never make it to the instrument’s ion Detector. If the ions have just the right mass and charge, the particles travel through the mass analyzer unscathed and reach the detector. The arrival of each ion creates a pulse of electrons and this pulse is recorded.
Depicted is a single sector mass spectrometer. (Scientists also use dual sector mass spectrometers). This technology is widely used in many scientific fields including environmental chemistry, pharmaceuticals, forensic analysis, and even cancer screenings.