What’s an IRMS, and why do I care?

Mike Sullivan writes:

I have spent some time over the past two weeks trying to get my arms around some new equipment we are installing. An Isotope Ratio Mass Spectrometer is an impressive name, and Jay Brandesjay-brandes-a.jpg is having two of them installed in his new lab. But what does it do and why should anyone care? It turns out that it is a highly sophisticated piece of analytical equipment, with all sorts of “add-ons” to give it a great deal of flexibility. It’s easy to be dazzled and confused (as I was) by the technical jargon. Jay finally sat me down and explained it to me in a way that even I could understand. Here is the story of what the IRMSs do and why they are a great addition to Skidaway Institute.

There are lots of different kinds of equipment that can analyze samples of chemicals, water, soil, gasses, etc. They can tell you what is in the sample in terms of elements and compounds. The IRMS does similar analysis, but it’s main purpose is to tell you the source of the an element in a sample. For example, if you are looking at water samples from a coastal estuary, you may see a lot of nitrogen and wonder where it came from. Is it naturally occurring, or is it getting into the water from fertlizer run off from a golf course, a sewage plant or animal waste from a farm? The IRMS can help answer that question.

It uses a tool called “stable isotopes.” Let me explain that. (If you already know about stable isotopes, please forgive me for the explantion. You can skip this paragraph.) Most elements come in different forms called isotopes. The different isotopes are distinguished by the number of neutrons in their nucleus’. For example the nucleus of a carbon atom has six protons and most also have six neutrons giving an atomic number of 12. (6 + 6) The carbon atom also has six electons, but they aren’t relevant to this explanation. Less than 1% of carbon atoms also have an extra neutron in their nucleus giving them an atomic number of 13 (6 protons and 7 neutrons). An even smaller percentage of carbon atoms have two extra neutrons (atomic number 14). Carbon 14 is unstable and decays into another element. That is why it is used to date things like ancient bones, but that’s a story for another time. Carbon 13, on the other hand is very stable, hence the term “stable isotope.”

It seems that the ratio of carbon 12 and carbon 13 in a sample will vary according to the source of the sample. That ratio gives the source a signature. Carbon from various plants or animals will have different isotopic signatures that live on after they die, are eaten, decay, etc.

Another example — if you are analyzing the biomass in the sediment a salt marsh, you may want to know what is contributing to the organic material there. The carbon that is contributed from decaying marsh grass like spartina will have a different isotopic signature than carbon coming from phytoplanton, decaying marine animals, run off from the adjacent forest and so on. By analyzing the carbon with an IRMS, you can paint a picture of the sources of organic material that is in the salt marsh.

I just used carbon in salt marsh sediment as an example. The possiblities are endless.

One IRMS is on-line right now and a second is still being built and will be installed early in 2008. At that point, Skidaway Institute will be one of just a handful of labs in the country with this capability. We expect our lab will be used by our scientists, but also that researchers from throughout the Southeast may make use of this lab in their own research.

There is more information on the Skidaway Web site.

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