What is the primary quantity measured in mass spectrometry?
Mass spectrometry converts neutral analytes into gas-phase ions and separates them in electric or magnetic fields according to mass-to-charge ratio. The analyzer does not measure optical properties like absorbance, fluorescence, or bulk density. After ionization, ions are accelerated and their trajectories, flight times, or oscillation frequencies depend strictly on m/z value. The resulting spectrum plots ion intensity versus m/z, revealing molecular weight, isotopic pattern, and fragment ions. This principle enables precise identification of proteins, metabolites, and glycans across biochemical research and clinical diagnostics.
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.