26 Mar 2014

Soil science group publishes CLS's 1000th peer-reviewed paper

The Canadian Light Source Synchrotron in Saskatoon, Saskatchewan, has just hit a major milestone. University of Saskatchewan researchers Courtney Phillips and Derek Peak, along with the CLS Spherical Grating Monochromator (SGM) beamline scientist, Tom Regier, recently published the 1,000th peer-reviewed paper to come out of data collected at the research facility.

Peak and his team have been pushing synchrotron soil science forward since the facility’s earliest days.

“As long as there have been CLS beam lines, our group has been over there working,” said Peak.

Peak and Regier have worked together on several soil science projects, unearthing the chemical changes that ultimately determine metal toxicity in soil, groundwater, and eventually plants. For the 1,000th paper, they took a look at liquid-copper solutions.

“At the end of the day what we want to understand how copper actually behaves in natural systems” said Peak.

That copper comes from all kinds of human applications, from mining to agriculture.

The team wanted to understand how aqueous copper bonded with various organics, which would help researchers understand copper’s potential toxicity in natural systems. If copper bonds with organic matter in soil, it is unlikely it will move around too much in natural systems. That’s a good thing, because too much copper can be toxic to aquatic organisms.

The team used soft X-rays, which are easily absorbed by even the lightest elements, including oxygen and nitrogen, to look at how aqueous copper interacts with dissolved organic matter.

At first glance, this seems like a straightforward task. But in fact, measuring liquid samples presents a special challenge on the SGM. Since soft X-rays are so easily absorbed by light elements, samples need to be kept in a vacuum chamber in order to be analyzed. For solid samples this is fairly simple to achieve, and is done regularly on SGM. However, liquids are trickier than solids, because the water in them evaporates in the vacuum chamber.

Though not the first research team to study aqueous samples in a soft X-ray beamline, the group developed a novel technique to address the evaporation issue.

The liquid samples lived in 3D-printed cells, which the researchers could continuously pump their solutions through, in order to do real-time copper chemistry. The liquid samples were separated from the vacuum by a silicon nitride window thousands of times thinner than a human hair, about 100 nm thick.  The soft X-rays are able to penetrate through the window and reach the solution, allowing them to be measured.

“We’re doing chemistry in the beamline. Everything happens right there, in place and in real time.”

Regier’s were also one of the first teams in the world to use silicon drift detectors on a soft X-Ray beamline, a technique that enables researchers to get separate fluorescence signals from each element, instead of as one lump. This made it possible to measure realistic systems as never before.

“The combination of techniques that we were using didn’t exist anywhere in the world,” said Peak, “but now we can do it, and other scientists can take advantage of it.”

Phillips joined the team as an undergraduate funded by an NSERC-USRA student in her undergrad scholarship, and the paper became the core of her Master’s of science project funded by an NSERC PGS-M fellowship. More funding came from Peak’s NSERC Discovery grant, and the CLS funding agencies.


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