Mass Analyzer · 2 / 3
A magnetic field bends the ion path by mass · the classic, earliest analyzer
A magnetic sector accelerates ions to the same energy, then sends them through a magnetic field perpendicular to their motion. The Lorentz force bends each ion into an arc, and the radius depends on m/z: heavy ions curve gently (wide radius), light ions curve tightly (small radius), so the beam fans apart inside the magnet.
Ions enter together from the lower left and fan into arcs of different radius inside the curved magnet. Scan the field strength B — only the ion whose arc lands on the exit slit reaches the detector, and its peak lights up in the spectrum below; the rest strike the magnet wall.
By scanning the field strength, the sector selects which m/z reaches the detector, building the spectrum one m/z at a time. It also uses a magnet — but note the difference from FT-ICR: a sector bends ions through a single pass, whereas FT-ICR traps them to orbit many times.