A mass spectrometer breaks a molecule into fragments and imparts them with a small amount of charge which then travel through the machine at a rate related to their mass. Some small fraction of the molecules will typically make it through the spectrometer whole but having been imparted a charge. Thus, we learn what the molecular weight of the molecule is. Seeing how it is broken apart also gives some insight as to the molecule's overall structure.
Page last modified May 11, 2011