Mass Spectrometer
Katie Petrie
A mass spectrometer is a device that is used to sort molecules based on their mass-tocharge ratio and concentration. This ability makes mass spectrometry useful in many fields for
identifying unknown substances and measuring the concentrations of known substances.
Mass spectrometers can be used in carbon dating, pharmokinetics, and protein
characterization. They can be used to analyze substances from other planets as well, while
aiding in space exploration (Hoffman et al., 2010). They are also used in forensic science for
toxicology analysis, arson investigations, and identifying unknown substances found at crime
scenes (Westchester). The important role mass spectrometers play in forensic analysis has even
been depicted in television crime shows like “Bones”.
Mass spectrometers are often used in conjunction with other devices, specifically gas
chromatographs. There are also different types and sizes of mass spectrometers. Some have
different methods for accomplishing the same steps, but the following describes the general or
most common steps in mass spectrometry (MSU Department of Chemistry). A small sample of a
substance is placed in the mass spectrometer via an air lock in order to maintain the vacuum in
the system. The vacuum prevents the ions from colliding with air molecules later in the process
(YouTube, 2008). The sample is vaporized and a heated metal coil produces electrons which are
shot at the vaporized molecules. The electrons can knock an electron or two off of the
molecules to create positive ions. Positively charged plates attract and trap the lose electrons
while forcing the newly formed cations through a tube as a beam. Electromagnets produce a
magnetic field through which the ion stream eventually travels. This causes the ions to deflect
around a curve, however the angle of deflection depends on the mass-to-charge ratio of the
molecules. This is represented by m/z, the relative atomic mass of the molecule over the
charge. Since most only lose one electron during the ionization process, the mass-to-charge
ratio would simply be equivalent to the mass. Lighter ions deflect at greater angles than heavier
ones. Ions traveling at a certain angle of deflection will enter the metal detector chamber.
Inside the chamber the ions hit the wall and are neutralized by the electrons in the metal. As an
electron leaves the metal, electrons from a wire flow to replace it, and this current is analyzed
by a computer. By gradually increasing the strength of the electromagnet, each type of ion can
eventually be deflected on a path that enters the detector chamber. Based on the strength of
the electromagnet and the amount of ions hitting the detector chamber, the mass-to-charge
ratio and the concentration can be determined. A computer produces a bar graph for the
sample. The different bars indicate different mass-to-charge ratios and the height of the bars
represents the concentration. This information can be used to identify the molecules in the
sample (Clark, J., 2011).
Works Cited
Clark, Jim, “The Mass Spectrometer”, Chem Guide, November 2011,
http://www.chemguide.co.uk/analysis/masspec/howitworks.html <March 7, 2013>
“Mass Spectrometry MS”, YouTube, September 27, 2008, http://www.youtube.com/watch?v=Jwao0O0_qM <March 8, 2013>
“Mass Spectrometry”, Michigan State University (MSU) Department of Chemistry,
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/MassSpec/masspe
c1.htm <March 10, 2013>
“Forensic Chemistry”, Westchester gov.com,
http://www.westchestergov.com/labsresearch/forensicandtox/forensic/chemistry/forc
hemframeset.htm <March 10, 2013>
Hoffman, John H., Griffin, Timothy P., Limero, Thomas, & Arkin, C. Richard, “Space Applications
of Mass Spectrometry”, NASA, February 2010,
http://ntrs.nasa.gov/search.jsp?R=20100039433 <March 11, 2013>