Sidebar: Mass Spectrometry

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molecule-imageDid you ever wonder how chemists figure out the atomic mass units for the periodic table? The answer comes from a piece of equipment that has been central to chemical exploration:  the mass spectrometer. We will be seeing a mass spectrometer on our field trip, so let’s take a few minutes to find out more about them.

Mass spectrometers are used find out what atoms are present in a sample based on size. They are so sensitive that they can even detect differences between isotopes of the same element.

How do they work? That depends on the type of mass spectrometer, but in general they:

1. Pull apart molecules and convert all the atoms into a gas.

2. Knock off electrons and turns the atoms into ions.

3. Line up the ions and shoot them through a magnetic field. The magnetic field deflects lighter ions more than heavier ones, separating them by mass.

4. The separated ions hit a detector, which counts them.

5. The results are compared to known samples.

If you’d like to read more, there is a detailed explanation at Chem Guide.

Bozeman Science has a good discussion of Mass Spectrometry in this video. (Note: He starts with a discussion of Dalton, but hang in there. He will tie it into mass spectrometry fairly quickly).

Simple Explanation of the Mass Spectrometer has a cool animation of how it works. (A snooker ball is pool or billiard ball.)

Now you know where atomic mass units come from, how scientists do radiocarbon dating, how chemists figure out the chemical formula of unknown molecules, etc. A mass spectrometer is a handy and versatile machine.

Have you ever seen one? Have you ever used one? Where?


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