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Environmental Science & Technology
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A novel sample preparation technique to
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improve spectromicroscopic analyses of
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micrometer-sized particles
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Carmen Höschen*†, Till Höschen‡, Carsten W. Mueller†, Johann Lugmeier†, Stefan
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Elgeti‡, Thilo Rennert†§ and Ingrid Kögel-Knabner†║
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†
Lehrstuhl für Bodenkunde, Department Ecology and Ecosystem Management, Center of
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Life and Food Sciences Weihenstephan, Technische Universität München, Freising-
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Weihenstephan, Germany ‡
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Max-Planck-Institut für Plasmaphysik, Garching, Germany
Institute for Advanced Study, Technische Universität München, Germany
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ABSTRACT: Microscale processes occurring at biogeochemical interfaces in soils and
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sediments have fundamental impacts on phenomena at larger scales. In order to obtain the
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organo-mineral-associations necessary for the study of biogeochemical interfaces, bulk
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samples are usually fractionated into micro-aggregates or micrometer-sized single
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particles. Such fine-grained mineral particles are often prepared for nanoscale secondary
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ion mass spectroscopy (NanoSIMS) investigations by depositing them on a carrier. This
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introduces topographic differences, which can strongly affect local sputtering
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efficiencies. Embedding in resin causes undesired C impurities. We present a novel
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method for preparing polished cross sections of micrometer-sized primary soil particles
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that overcomes the problems of topography and C contamination. The particles are coated
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with a marker layer, embedded and well polished. The interpretation of NanoSIMS data
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is assisted by energy dispersive X-ray spectroscopy on cross sections prepared by a
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focused ion beam. In the cross sections, organic assemblages on the primary soil particles
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become visible. This novel method significantly improves the quality of NanoSIMS
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measurements on grainy mineral samples, enabling better characterization of soil
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biogeochemical interfaces. In addition, this sample preparation technique may also
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improve results from other (spectro-) microscopic techniques.
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Environmental Science & Technology
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■INTRODUCTION
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The spatial distribution of elements characteristic of organic matter (e.g., C or N) and
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minerals (e.g., Fe, Al, or Si) in soils and sediments at the sub-micron scale is of special
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interest for the identification of key biogeochemical processes such as C sequestration, or
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the sorption of pollutants.1-5 Making the sub-micron spatial distribution of soil and
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sediment particles accessible improves the understanding of these processes.
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Furthermore, information about the soil and sediment architecture would also extend the
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understanding of phenomena occurring at larger scales. However, to be able to study both
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structure and its effects on biogeochemical processes, it is essential to explore soil and
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sediment structures in intact conditions. Therefore, there is a need for sample preparation
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techniques that allow for the reproducible exploration of intact structures, ranging from
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single micrometer sized particles and micro-aggregates (particle cluster
