mass spectrograph

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An instrument used to determine the masses of atoms or molecules, in which a beam of charged particles is passed through an electromagnetic field that separates particles of different masses. The resulting distribution or spectrum of masses is recorded on a photographic plate.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics, analytical chemistry A mass spectrometer

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a mass spectrometer that produces a graphical representation of the mass spectrum