What is a mass spectrometer used for?

• A. A device that measures humidity and temperature
• B. A device that filters airborne particles
• C. A device used to identify chemical compounds (determines their atomic mass)
• D. A device that emits ozone to neutralize odors

Answer: (C)

Mass spectrometry is used to identify chemical compounds by measuring the masses of ionized particles. In practice, a sample is ionized, and the resulting ions are separated inside the instrument according to their mass-to-charge ratio. A detector then records a mass spectrum, where peaks correspond to the molecular ion and fragments. From this pattern you can determine the molecular weight and often the molecular formula, and you may gain structural clues from how the molecule fragments. This makes mass spectrometry a powerful method for identifying compounds in mixtures and for confirming composition and isotopic information.

That’s why the correct choice describes identifying chemical compounds (and determining their masses). The other options describe devices for humidity/temperature measurement, airborne-particle filtration, or ozone emission for odors—functions unrelated to identifying chemical species by mass.