In mass spectrometry identification, the key signature used is which?

• A. Retention time
• B. Mass and fragmentation pattern
• C. UV absorbance
• D. Color

Answer: (B)

Mass spectrometry identification hinges on the mass spectrum, the set of ion signals produced when a molecule is ionized and then fragmented. The exact m/z values of the molecular ion and the pattern of fragment ions, along with how strong each peak is, create a unique fingerprint for that substance. This fragmentation pattern lets you determine molecular weight and infer structural features, and when you compare it to spectral databases or use MS/MS to examine specific fragments, you can identify the compound with high confidence. Retention time can help when MS is combined with chromatography, but on its own it doesn’t provide a definitive identity. UV absorbance reflects how a molecule absorbs light but isn’t unique to specific structures, and color isn’t a diagnostic spectral signature in MS.