Mass spectrometry identifies analytes based on:

• A. Mass to charge ratio
• B. Retention factor
• C. Density of the band
• D. Molecular weight

Answer: (A)

In mass spectrometry, the key measurement is the mass-to-charge ratio of ions, which is what allows both separation and identification of analytes. When a sample is ionized, charged fragments and intact ions are propelled through the mass analyzer, and their m/z values determine their paths or flight times, producing a spectrum that shows how abundant each m/z is. This spectrum provides characteristic peaks that correspond to the molecular ion and its fragments, enabling identification by matching to known patterns. Concepts like retention factor or density of a chromatographic band come from chromatography and track how a compound behaves on a column, not how it is identified in MS. The molecular weight is related to m/z, especially for singly charged ions, but the fundamental identifier in mass spectrometry is the measured mass-to-charge ratio, which directly reveals the ion’s identity through its unique m/z signatures.