Mass spectrometry is the study of the mass of molecules within any collected sample of gas, liquid, or semi-solid. The latter two substances have to be converted to a gas, but ultimately the mass spectrometer will be able to detect and measure the masses of various molecules in these substances as well. If you want to build a really cool science fair demo project for your students, you can build your own mass spectrometer. Obviously, you will be building a very basic model, one that measures the molecules' mass within an air sample, since this is the easiest to construct and will not require additional parts for sample conversions. The following components may be purchased through a mass spectrometry supplies company, or you can rig your own if you can figure it out.
The ionization chamber is critical to how a mass spectrometer works. Whatever type of sample you use, the gas form of the sample has to pass through the ionization chamber to become ionized molecules. If the molecules are not ionized, there is no way they can be deflected and measured in the areas of the spectrometer that come after the ionization chamber. This a part you may have to purchase, since building an ionization chamber from scratch takes more than just a perfectly welded metal box and ionizing filters.
A big, fat electromagnet is also necessary to spectrometry. It changes the electrical charge of the molecules so that they can be detected properly at the opposite end of the spectrometer (where the detection chamber sits).You could buy this part to make sure you have the exact electromagnetic charge you need to make your spectrometer work, or you could build your own using a giant magnet, some heated wire coils, and a car battery with jumper cables. You may also be able to use a portable car jump starter, especially since the tinier cable clamps will be easier to attach to the wires near the magnet.
After your ionized molecules have gone through the electromagnet stage, they enter a perfect vacuum. A solid piece of tubing or PVC pipe can be used for this stretch of the spectrometer, but you will need an attachment that creates a perfect vacuum for the molecules. Most medical grade spectrometers utilize a vacuum pump, which you can purchase from the medical supply company. However, you can jerry-rig your own vacuum pump using the motor and some parts from a very high quality vacuum too.