This video from NASA describes and animates the process by which mass spectrometry can identify chemical composition of matter. One example -- a specific inquiry about Mars -- is described, with reference to many other applications.
When we observe a sample of material – from the bottom of the ocean, from the Moon, from a forest floor, or even from another planet – it’s natural to want to know what’s in it, what it’s made of. A mass spectrometer can help answer that question. Most material samples we might collect for observation contain a wide mix of substances. Figuring out whether a sample contains a particular molecule or substance requires a way to break it apart into its molecular building blocks. A mass spectrometer works by deconstructing a sample and analyzing its component parts.
After the sample has been heated to the point it turns into a gas, it’s hit with a stream of electrons, which charge the gas particles, turning them into ions. The charged ions enter an area of strong electromagnetic field. The interaction of the electric and magnetic fields with the charged particles creates a way to “select” for specific elements. Since charged particles of different masses will behave differently to the same field, the paths of the particles create a way to physically distinguish them. Since an ion’s path will depend on both its charge and its mass, where it “lands” in the analyzer can be used to figure out what it is. In most cases, scientists will “tune” the mass spectrometer to select for a specific substance and then analyze how much of it is present. Running this process several times for different materials builds a picture of what the original material is made of and how much of it there is.
How can you take a substance that isn’t charged and give it a charge?
Have you ever seen tracks in a cloud chamber? If so, what do you think accounts for the different shapes you can see in the particles’ trajectories?
What if you had some unknown substance and you wanted to know what it’s made of? How could you find out?
What do you predict would happen when a charged particle passes through or near an electromagnetic field?
What’s the first step in the process for analyzing a sample with a mass spectrometer? Why does the process start this way?
In your own words, describe what happens in the analyzer segment of the mass spectrometry process.
How does the “quadrupole” structure of the mass spectrometer improve analysis of a sample?
Name a few things you think would be interesting to find out using a mass spectrometer.
Do you think there would be some materials that would be more difficult than others to analyze using a mass spectrometer? If so, what characteristics do you think would make that the case?
Can you think of times when you might have seen charged particles interacting with an EM field? Are there any natural phenomena that demonstrate this type of interaction?
Bonus Question: The quadrupole mass spectrometer works by passing the stream of charged particles through an area of changing electric field. Do you think you’d get the same result if it were a changing magnetic field instead? Why or why not?
Instructor provides students with actual mass spectrometer data read-outs (mass-to-charge ratios), and students work in groups to interpret and analyze the sample.
More About Mass Spectrometers
Students explore the Spectrometry Explained Interactive and the NASA / JPL web site Mass Spectrometry - A Closer Look and then create their own interpretation of how a mass spectrometer works, presenting that to the class through a drawing, verbal description, or other means.