Characterization of phosphorus compounds in soils by deep ultraviolet (DUV) Raman microspectroscopy

Abstract

Deep ultraviolet Raman microspectroscopy was successfully investigated as a new approach to analyze the chemical state of phosphorus compounds directly in soil. We demonstrate that ultraviolet excitation has the advantage to avoid the interference with the strong fluorescence, which occurs in the visible spectral range caused by organic matter in soils. Furthermore, the spatial resolution of <1 μm2 enables the detection of very small phosphorus particles. For some organic phosphorus compounds (β‐glycerophosphate, aminomethylphosphonic acid), sample cooling to −100 °C is found to strongly reduce the rate of degradation induced by the illumination with the ultraviolet excitation light. However, phytic acid and adenosine monophosphate degraded even with cooling. Our results reveal the capability of deep ultraviolet Raman microspectroscopy as a high‐resolution benchtop imaging technique for the analysis of local interactions between soil compounds with the potential to become an analytical key to improve the understanding of transformation mechanisms of phosphates as well as other mineral phases in soils. Copyright © 2017 John Wiley & Sons, Ltd.

Determination of Soil Constituents Using Shifted Excitation Raman Difference Spectroscopy

“…This observation is in accordance with the literature where a coincidence between organic matter and calcite has been reported for certain soil types. 22 In the next step, using multivariate analysis, the SERDS spectra will be correlated with the SOM and nitrogen contents as determined by laboratory reference analyses to assess whether the spectroscopic data can be used to determine these key soil parameters.…”

“…A serious drawback of this excitation with high-energetic laser photons is the radiation-induced damage of specimens that has been reported, particularly for organic compounds. 22 Shifted excitation Raman difference spectroscopy (SERDS) 23,24 is a powerful physical approach to separate the characteristic molecular fingerprint from interfering contributions. The basic principle behind SERDS is that the sample is consecutively excited at two slightly different excitation wavelengths.…”

“…A serious drawback of this excitation with high-energetic laser photons is the radiation-induced damage of specimens that has been reported, particularly for organic compounds. 22 …”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…Vogel et al have characterized phosphorus compounds in soils by deep ultraviolet Raman microspectroscopy. They demonstrated that UV excitation has the advantage of avoiding strong fluorescence, which occurs in the visible range caused by organic matter in soils . Xia et al described a SERS optical fiber probe with plasmonic end‐facet.…”

“…They demonstrated that UV excitation has the advantage of avoiding strong fluorescence, which occurs in the visible range caused by organic matter in soils. [229] Xia et al described a SERS optical fiber probe with plasmonic end-facet. To further enhance the SERS enhancement factor, a hybrid graphene/Au nanotriangle structure is transferred onto the end-facet of the fiber probe to enable SERS.…”