Portable X-ray fluorescence trace metal measurement in organic rich soils: pXRF response as a function of organic matter fraction

• Published in: Geoderma Vol. 319; pp. 175 - 184
• Main Authors: Ravansari, Roozbeh, Lemke, Lawrence D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-06-2018
• Subjects: Calibration method; Geochemistry; Portable X-Ray fluorescence spectrometry; pXRF, trace metals; Soil organic matter; Soil organic matter; Geochemistry; Calibration method; Portable X-Ray fluorescence spectrometry; pXRF, trace metals
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2018.01.011

The influence of organic matter fraction on portable X-Ray fluorescence (pXRF) trace metal measurements was investigated through the incremental addition of three organic matter surrogates (cellulose, graphite powder, and confectioner's sugar) to a soil matrix. Each surrogate was independently added to and homogenized with samples of Natural Resources Canada Till-1 standard reference material that was initially expunged of organic matter through combustion. Incremental addition was performed 20 times for each surrogate, and concentrations of thirteen elements were measured as a function of varying organic matter fractions using a Thermo Scientific Niton XL3t GOLDD+ 950 XRF analyzer.
Results demonstrate attenuation of the pXRF signal with increasing sample organic matter fraction; however, elementally dependent deviations from expected concentrations were also observed. An empirical organic matter fraction-dependent calibration method was developed and its performance was evaluated using four unmodified soil standards with known organic matter content. Estimates incorporating soil organic matter differed from conventional calibration estimates neglecting organic matter content, yet were able to reproduce standard reference material values with similar success.
•pXRF concentration measurements vary as a function of soil organic matter fraction.•Deviations from theoretical dilution curves are elementally dependent.•Organic matter corrections compare favorably to conventional empirical calibration.