Ode to a Mass Spectrometer

For my dissertation, I am focusing on two techniques that rely heavily on (read: could not happen without) an incredible scientific instrument called a mass spectrometer.  These amazing machines don't often get much love from the common person (even many of the scientifically minded ones) because, I believe, they are intimidating.  The name alone is too esoteric for many people to approach, thus they don't even want to think about the inner workings and the functions of the machine.  So, this post is an effort to make these fascinating instruments a little more accessible and maybe even earn them a little more love and respect from the public.

*DISCLAIMER* - I am not an expert in the design, construction, maintenance, or even operation of these machines.  I will likely make an error somewhere in here, so be gentle if you are one of the aforementioned experts.

Now that we've gotten that out of the way, let's get to the nitty gritty.  I'm going to take you all the way back to your elementary chemistry class.  Don't worry, we're going to stay very basic here.  Remember atoms?  I hope so.  Atoms consist of a nucleus (containing protons and neutrons) and a very complicated "probability cloud" of electrons which we aren't even going to touch with a ten foot pole so don't worry.  Of these three particles, only protons and neutrons have mass.  A typical carbon atom has 6 protons and 6 neutrons, thus it's atomic weight is 12, whereas a typical nitrogen atom has 7 protons and 7 neutrons and it's atomic weight is 14.  Each element has a different number of protons and neutrons in its nucleus (which is what makes it a different element in the first place) and, because of this, a different atomic weight.

So, if we want to look at an object or some material (oh, let's say walrus bone collagen), and determine how many of each different type of atom make it up, how would we even go about doing that?

The ingenious answer developed by a long line of ingenious people too long to list here is known as the mass spectrometer. Behold:

It actually looks pretty simple, right?  The basic principle is this.  You take whatever material you are interested in studying and you set it on fire.  We're off to a good start, right?  After combustion, the resulting ionized particles (the atoms that made up your material, pre-combustion) are whisked away down a tube under vacuum.  The tube makes a bend and, at that point, an electromagnet subjects the particles to a strong magnetic field.  Lighter particles have less inertia and their paths are curved more sharply than heavier particles, which have greater inertia (due to their greater mass).  After making the turn, the particles continue traveling, now separated by mass, and smash into a detector.  This detector registers how many particles hit it in different locations and is programmed to know which location correlates with which atom.  Voila!  You now know what your material was composed of.

Excited yet?

Now, to make it just a tiny bit more complicated, we can also use this technology (as I do) to study stable isotopes.  I said before that a "typical" carbon atom has 6 protons and 6 neutrons.  Well, not all atoms are typical.  Some have more neutrons than they are "supposed to" and these different variations are called isotopes.  Some are stable and some are not.  The ones that aren't undergo radioactive decay (e.g. all the scary radioactive materials you have heard of like uranium-235 and plutonium-239, though the vast majority of them aren't dangerous in that sense and haven't been used to make weapons).  As an example, here are the two stable isotopes of hydrogen:

Mass spectrometers are so good at what they do, that they can separate out and distinguish between not just different elements, but also the different isotopes of the same element!  This, by the way, is the technology that makes possible not only my work but a huge field of study spanning a wide variety of disciplines.

Well, that's it.  Thanks for reading!  Hopefully you learned something.