XANES-SiVM data processing for redox microsite detection

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Method synopsis

Combined XANES fitting and Simplex Volume Maximization analysis to identify and quantify redox microsites while eliminating false positives.

Synthesized from method descriptions across 1 paper using this protocol.

Procedure as described in the canonical source

Steps below were extracted from the paper that introduces this protocol — X-ray chemical imaging for assessing redox microsites within soils and sediments (2024), Frontiers in Environmental Chemistry. Implementations in other papers (listed below) may differ.

1. Process X-ray data using XANES fitting
   Data processing of Fe K-edge multiple energy μ-XRF maps involved fitting the six-point XANES spectrum of each pixel with a set of selected full XANES spectra across the Fe K-edge using XANES fitting. Reference compounds included FeII-(hydroxy)oxide, FeII-S, and FeIII CO3 microsites in FeIII-free sand core.
   Quantities: Six-point XANES spectrum per pixelDuration: Post-collection analysisConditions: Computational analysis
   Equipment: XANES fitting software, reference compound spectra
2. Apply Simplex Volume Maximization fitting
   The SiVM method is a non-negative matrix factorization algorithm which geometrically selects data points that are furthest away from each other in multi-dimensional space, within a user-defined noise threshold. This process effectively selects a set of endmembers, where all of the data points can be calculated as a linear-combination of these endmembers.
   Quantities: User-defined noise threshold appliedDuration: Post-collection analysisConditions: Computational analysis with noise threshold
   Equipment: SiVM analysis software

Typical Equipment

• XANES fitting software
• SiVM analysis software

Output Measurements

• redox microsite maps
• Fe speciation quantification

Papers Using This Protocol (1)

Species Studied With This Protocol

Places Where Used