Go Team Molybdenum!

Last night we arrived at Argonne National Laboratory in preparation to use one of the beamlines at the Advanced Photon Source (APS—have you noticed yet that we scientists are fond of acronyms and abbreviations??) to analyze some samples. The APS is a synchrotron facility operated by the U.S. Department of Energy Office of Science. A synchrotron produces very bright x-rays by accelerating electrons. The electrons travel around a ring, and as they change direction, they emit radiation which is then harnessed by sophisticated optics and directed to the user’s sample. Some basics about synchrotron radiation and synchrotron sources around the world are available at lightsources.org. An intense and highly tunable source of x-rays is required for the experiments that we are going to conduct, and that is only available from a synchrotron.

We will be using x-ray absorption spectroscopy, known as XAFS (X-ray Absorption Fine Structure). XAFS is broken into two parts: XANES (X-ray Absorption Near Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure). At this stage I will confess that this is all new to me. Anthony has been teaching me about XAFS, and I am here at the beamline to learn as much as I can. This is actually my second trip to the APS, although the first time I was conducting a completely different experiment. Before my first trip, one of the beamline scientists remarked to me that, “It is OK to not know what you are doing; as scientists we do things that we don’t know how to do all the time.” In other words, we learn. So all of you can watch me learn about XAFS. It is difficult to discuss XAFS in depth without getting technical. For those of you who are interested, our beamline host Matt Newville has some excellent tutorials at http://xafs.org/Tutorials. I’m reading them too. Let me know if you want to discuss them at the next book club meeting.

The XAFS spectrum that is acquired contains information about the oxidation state of an element of interest (in our case, molybdenum) and its local coordination environment. Oxidation state is the formal charge on an atom (4+? 2-? 0?). Local coordination environment refers to the identity of the atoms that surround molybdenum, how many there are, and their arrangement in space. Our objective with molybdenum is to discover the geochemical mechanisms by which it is enriched in sediments. Knowing the compound(s) of molybdenum that exist in different environments would provide vital clues for answering our questions. On this trip we have some experimental samples that were prepared in the lab along with some sediment samples. Combining experimental work with observations of the real world is a great way to test ideas in a controlled setting, and then to see if they hold up in nature. Next Friday I will be in Riverside, California, (summer is travel season) visiting Professor Tim Lyons and his group, and this will be a good time to tell you more about why we are interested in molybdenum. It’s a good story, I promise, and it has to do with the origins of life.

For now I am running the risk of this post getting too dry and boring, so here is what all of you really want: pictures!

Our beamline

Anthony and Jacob working hard

Samples all loaded on the sample holder

Air-sensitive sample in position

Anthony working not so hard riding the big kid tricycle

Welcome!

Welcome to the first edition of Rock, Metal, and Water: Le GEM Blog! I am excited to begin this new endeavor as a blogger chronicling the exploits of the GEM lab at Central Michigan University. My name is Dr. Meghan Wagner, and currently I am a postdoctoral researcher working with Professor Anthony Chappaz. I earned my bachelor’s and master’s degrees in chemistry, and last year I completed my Ph.D. in earth and environmental sciences. Having a background in both chemistry and earth science allows me to act as a bridge between the two sciences, and—I think—to look at earth science problems in nontraditional ways. My personal research interests involve trace metal geochemical cycling, climate, and the relationship between ocean circulation and oxygen concentrations in the deep ocean.

The purpose of this blog is to give all of my readers an insider’s view of what happens in an academic research laboratory, and what the life of one postdoc is like. Each Friday, I will share our successes and failures, bring my readers along for fieldwork and conferences, and try to bring some clarity to scientific concepts and instrumentation that we will run across. Above all I want this blog to be widely accessible and fun to read! I am sure that my writing style and skill will improve with more practice, and so I ask that you, my readers, please contact me with questions, comments, and suggestions for things that you would like me to blog about.

I hope that you will take a few minutes to explore the GEM lab website to learn more about the people, our research interests, and facilities. Briefly, we are aquatic geochemists interested in trace metal chemistry. In other words, what are the trace metal concentrations in aquatic waters and sediments? What can trace metals tell us about nutrient cycling, primary productivity, oxygenation, and pollution? How and why are trace metals preserved? How are trace metals transported through aquatic and terrestrial systems?

And what are trace metals? Trace metals are metals present in small quantities—around the part per million (ppm) or part per billion (ppb) level. Usually this means transition metals, also known as d-block elements. There is a wonderful website www.webelements.com that has a wealth of information about all of the known elements. The transition metals are the ones colored in pink. Some of these elements are probably known to you, such as zinc (Zn) and copper (Cu), while others may be unfamiliar, such as scandium (Sc) and ruthenium (Ru). In human physiology, elements like zinc and copper are essential micronutrients. The same is true for other organisms—more on this later.

In our laboratory, we are especially interested in the interaction of the metal molybdenum (Mo) with dissolved organic matter (DOM). DOM is a complex mixture of naturally occurring organic molecules. The size that constitutes “dissolved” is not universally agreed on, but one common definition is anything that will pass through a 0.45 micrometer filter. For comparison, human hair is approximately 80-100 micrometers wide. So we are interested in very small things! Last Friday Anthony and I went out to the field to collect some DOM for our experiments. Here in central Michigan, we have recently had a lot of rain, which has washed organic matter produced by trees and other plants into the Chippewa River. So that day “the field” was a local park. Here I am collecting river water into a carboy.

Yes, that’s right: For my job, sometimes I get to play in the river. Neener neener, desk denizens! Afterward we brought the river water back to the lab and filtered it to remove the large particles. Here you can see the filtration in progress and what we collected on the filters.

The carboys are sitting in black plastic trash bags to protect the DOM from light. This is because some DOM is broken down by light (photodegradation), and we want to preserve our sample. The next step was to concentrate the DOM using a reverse osmosis system built in-house by one of our lab volunteers, Jacob Spreitzer. Here is the reverse osmosis system and the concentrated DOM sample (on the right, clean water on the left for comparison).

After a resin treatment to remove metals bound to the river DOM, we have a DOM sample ready to use!

So long for now! Next Friday will be very exciting because I will be writing from the Advanced Photon Source at Argonne National Laboratory where Anthony has been awarded beam time.