Which particles reach the detector in MS?
During mass spectrometry, molecules must be ionized to charged species for manipulation by electromagnetic fields. In routine positive-mode operation, electron removal generates cations, typically [M+H]+ or multiply protonated [M+nH]n+ species, which are accelerated toward the analyzer. Electrons are filtered away by electrostatic lenses, neutrons remain neutral and unaffected, and anions are detected only when negative-mode methods are specifically employed. Cations possess appropriate charge and kinetic energy to traverse quadrupole, time-of-flight, or Orbitrap analyzers and strike the electron multiplier detector, producing measurable current used for spectrum generation.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.