Friday, April 13, 2007

Know your Germaniums!

I'm having a hard time thinking today so let's stick with a subject that I know backwards and forwards: Germanium Isotopes.

Joke’s on you! There’s hardly anything to know about germanium isotopes.


In addition to working on my Master’s Project with the silica and germanium in the North Pacific, I’m also partly working on a project to measure germanium isotopes. If you mention germanium isotopes to an Isotope Geochemist, take special note of the worried look in their eyes and congratulate yourself on stumping a very smart person. My advisor and I are pretty much developing the technique for measuring these little guys in seawater. Why, you ask? Why give a shit about an element with such a ridiculous name? Well, I’ll tell you.

Germanium is #32 on the periodic table of elements. It’s a metalloid meaning that its behavior exists somewhere between a metal and non-metal. The most abundant isotope of germanium is Ge74 with 32 protons, 32 neutrons. Other isotopes of interest are Ge70, Ge72, Ge73, and Ge74. There are also some weird radioactive species of germanium floating around, but I don’t worry much about those guys. These are the four isotopes that I measure when I use a mass spectrometer (which I don’t like using very much [see “Mass Spectrometry Blows”]).

We’ve talked a little bit before about fractionation. Isotopic fractionation means that something (evaporation, precipitation, biology, whatever) has fucked with the natural abundance of isotopes in your sample. In the case of oxygen, fractionation happens during evaporation and precipitation. The fatty Fatterton isotopes get left behind in the seawater during evaporation and they are the first to drop out of the clouds when it rains.

Biology does an amazing amount of fractionation. It’s a lot easier to move around light isotopes than it is to move around heavy isotopes. This might not seem like a big deal to you and me, I mean come on! What’s a few atomic mass units? But when you are a single celled critter, that shit adds up. Carbon, oxygen, sulfur, and iron are all things that biology needs, and since life is inherently lazy it will to the least amount of work to get what it wants.

Problems that arise when one attempts to measure germanium isotopes:

1.) The mass difference between the lightest (70) and heaviest (74) species of germanium is not much compared to the overall weight of germanium: 4 mass units out of 74, which is only about 5%.

2.) There isn’t much germanium in seawater. My advisor and I have developed a way to concentrate ~ 99% of the germanium in a 20L seawater sample into about 40 mL. If I told you how we do it, I’d have to kill you.

3.) You have to have a top of the line Mass Spectrometer. Expensive and fussy.

4.) You have to be able to convert your germanium concentrate to a gas and input the gas into the Bitchy Mass Spectrometer at a perfectly constant rate. Sounds easy, but this shit is sensitive. We’re talkin’ isotopes, people.

So that’s where we’re at. We’ve got our germanium concentrate. We’ve got friends with mass specs, we just need to fine tune the procedure a little bit and voila! Germanium Isotopes! The Big Butt here is “But will this information be useful?” I don’t know, probably not. Useful or not though, it's still uncharted isotope territory that should be explored by someone and that someone is me!

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