Spectrometry Explained
(Interactive)
National K -12 Subject:
Download and ShareWhen 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.
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Classroom Activities
Mass Spectrometer Data Read-out
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.
Narrator: What happens if you have something like this, and you want to find out if something like this is inside? Obviously, you can like this is inside? Obviously, you can't tell just by looking at it, but if you separate things out, the answer becomes clear. Scientists have the same problem. How do you know if there was once water on Mars...or, for that matter, life? Obviously you can't tell just by looking at pictures of Mars, but scientists think the answer may lie hidden in tiny molecules in Martian soil. So, how do you take apart a molecule to see what's inside?
Luckily, scientists have a tool to do just that. It's called a mass spectrometer, and it lets us take an extremely close look at whatever we're studying. And even though Mars immediately comes to mind, mass spectrometers are used in multiple NASA missions. They're also used in labs for hundreds of scientific purposes. But the important question is: How does it work? Today, we'll be looking at a special kind of spectrometer called the quadrupole mass spectrometer. It's called this because of the four long poles that make up the center of the instrument.
So say you have a sample that's been turned into a gas, and you want to find out if it contains certain things. The gas is sent into the mass spectrometer first hitting a piece called the ion source. Here, a stream of electrons hits the molecule, breaking it into fragments and giving each fragment a charge. Next, the fragments enter what's called the analyzer. Here, they're separated based on their mass, and the analyzer is tuned so that only the fragments we want to see make it through. Everything else flies off in a different direction. After this, the fragments hit what's called the detector, and scientists record the data.
If you're looking for more than one kind, the analyzer can scan across a range of fragments, building up a record of not only what kind, but how many. Once you have these results, called a mass spectrum, you can verify that your sample in fact contains what you're looking for. And here, the real work begins. The mass spectrometer is a powerful tool, and by taking many samples, looking at the results, and studying what we find, scientists can work to discover not only the secrets of water and life on Mars, but also answers to bigger questions about the universe. And all by studying something as tiny as a molecule.
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