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Christian Vogel, Manfred Ramsteiner and Christian Adam

Deep Ultraviolet Raman Microspectroscopy – Novel Technique

for the Characterization of Phosphorus in Soil

BAM Federal Institute for Materials Research and Testing, Berlin, Germany

Paul-Drude-Institut, Berlin, Germany

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Introduction

• Deep ultraviolet (DUV) Raman microspectroscopy

• Detection of P-Phases in soil

• Advantages and Disadvantages of DUV Raman microspectroscopy

• Outlook

• Conclusions

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Deep Ultraviolet (DUV) Raman Microspectroscopy - Theory

The electronic resonance enhancement effect can increase the intensity of the scattered light by a factor of 106.

from Asher, Analytical Chemistry, 1993, 65(2), 59A-66A

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UV/VIS

Guanosine-5´-monophosphate

from Dietzek et al., Chapter 2 in Confocal Raman Microscopy (Springer 2010)

Deep Ultraviolet (DUV) Raman Microspectroscopy – Enhancement Effect

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Deep Ultraviolet (DUV) Raman Microspectroscopy - Fluorescence

from www.semrock.com/uv-raman-spectroscopy.aspx

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DUV Raman Microspectroscopy of an Alluvial Soil

Alluvial Soil: pH(H2O) = 7.4; P = 0.36 wt.%

Instrument: HORIBA LabRam HR Evolution; Laser: 244 nm (Ar-Ion); Lateral Resolution: 1 µm; Spectral Resolution: 8 cm-1; Time: approx. 1h; Imaged Area: 15 x 15 µm2

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DUV Raman Spectra of Different Phosphates

AlPO4 (Berlinite)

Hydroxyapatite

Ca-Phytate

Fe-Phytate

Na-Phytate

500 1000 1500 2000Wavenumber (cm-1)

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Advantages and Disadvantages of DUV Raman Microspectroscopy

Advantages:

• Detection of organic and inorganic

phosphates

• High lateral resolution

(theoretical down to 150 nm)

• Almost no samples preparation required

• No fluorescence appears

Disadvantage:

• Localization of P-phases

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Outlook

Problem of P Localization Combination with laboratory micro X-ray

fluorescence (µ-XRF)

µ-XRF Mapping of the Alluvial soil

Instrument: HORIBA XGT 7200; Area: 512 x 512 µm2; Lateral Resolution: 10 µm; Time: 5 min

P Kα1 Ca Kα1 Si Kα1

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Conclusions

• Chemical state of inorganic and organic phosphates is detectable

by DUV Raman Microspectroscopy

• Almost no sample pre-treatment is required

• Combination with µ-XRF make it easier to localize P-phases