A mass analyzer is the part of a mass spectrometer that makes ions distinguishable or selectively transmits them according to mass-to-charge ratio. The measured coordinate can be position, arrival time or transmission under a specified field setting. A separate mass spectrometer detector records the resulting signal.
A quadrupole mass analyzer selects trajectories using combined static and time-varying electric fields: chosen mass-to-charge values remain on stable paths while others are lost from the transmitted beam.[ref] A time-of-flight mass spectrometer instead encodes the ratio in arrival time after acceleration. Different physical designs can therefore provide the same kind of ionic-mass information through different observables.
An original magnetic example exposes an important assumption. For speed perpendicular to a uniform magnetic field , balancing the Lorentz force and circular acceleration givesIf the incoming ions have the same selected speed and charge, mass values in the ratio give bending radii in that ratio, about . But if ions instead start negligibly slowly and gain energy from the same electric potential difference , substituting gives . Their radius ratio is then . The initial-condition choice changes the mapping.
Analysis requires this mapping and its assumptions, not just separated peaks. Mass resolving power describes the ability to distinguish nearby peak coordinates under a stated width criterion; accurate assignment of those coordinates additionally needs instrument calibration and the correct charge-state interpretation.
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