New Developments in Hard X-ray Fluorescence Microscopy for In-situ Investigations of Trace Element Distributions in Aqueous Systems of Soil Colloids

• Published in: Journal of physics. Conference series Vol. 463; no. 1; pp. 12005 - 4
• Main Authors: Gleber, Sophie-Charlotte, Weinhausen, Britta, Köster, Sarah, Ward, Jesse, Vine, David, Finney, Lydia, Vogt, Stefan
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.01.2013
• Subjects: Aqueous environments; Binding; Colloiding; Colloids; Imaging; Microfluidics; Micrometers; Microscopy; Physics; Soil (material); Soil investigations; Spatial resolution; Three dimensional; Trace elements; X-ray fluorescence
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/463/1/012005

The distribution, binding and release of trace elements on soil colloids determine matter transport through the soil matrix, and necessitates an aqueous environment and short length and time scales for their study. However, not many microscopy techniques allow for that. We previously showed hard x-ray fluorescence microscopy capabilities to image aqueous colloidal soil samples [1]. As this technique provides attogram sensitivity for transition elements like Cu, Zn, and other geochemically relevant trace elements at sub micrometer spatial resolution (currently down to 150 nm at 2-ID-E [2]; below 50nm at Bionanoprobe, cf. G.Woloschak et al, this volume) combined with the capability to penetrate tens of micrometer of water, it is ideally suited for imaging the elemental content of soil colloids. To address the question of binding and release processes of trace elements on the surface of soil colloids, we developed a microfluidics based XRF flow cytometer, and expanded the applied methods of hard x-ray fluorescence microscopy towards three dimensional imaging. Here, we show (a) the 2-D imaged distributions of Si, K and Fe on soil colloids of Pseudogley samples; (b) how the trace element distribution is a dynamic, pH-dependent process; and (c) x-ray tomographic applications to render the trace elemental distributions in 3-D. We conclude that the approach presented here shows the remarkable potential to image and quantitate elemental distributions from samles within their natural aqueous microenvironment, particularly important in the environmental, medical, and biological sciences.