Deep Ultraviolet Raman Microspectroscopy –
Novel Technique for the Characterization of
Phosphorus in Soil
Christian Vogel, Manfred Ramsteiner and Christian Adam
BAM Federal Institute for Materials Research and Testing, Berlin, Germany
Paul-Drude-Institut, Berlin, Germany
1
Introduction
• Deep ultraviolet (DUV) Raman microspectroscopy
• Detection of P-Phases in soil
• Advantages and Disadvantages of DUV Raman microspectroscopy
• Outlook
• Conclusions
2
Deep Ultraviolet (DUV) Raman Microspectroscopy - Theory
from Asher, Analytical Chemistry, 1993, 65(2), 59A-66A
The electronic resonance enhancement effect can increase the intensity of the scattered light by a factor of 106.
3
Deep Ultraviolet (DUV) Raman Microspectroscopy – Enhancement Effect
UV/VIS
Guanosine-5´-monophosphate
from Dietzek et al., Chapter 2 in Confocal Raman Microscopy (Springer 2010)
4
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
6
DUV Raman Spectra of Different Phosphates
AlPO4 (Berlinite)
Hydroxyapatite
Ca-Phytate
Fe-Phytate
Na-Phytate
500
1000
1500
Wavenumber (cm-1)
2000
7
Advantages and Disadvantages of DUV Raman Microspectroscopy
Advantages:
Disadvantage:
• Detection of organic and inorganic
• Localization of P-phases
phosphates
• High lateral resolution
(theoretical down to 150 nm)
• Almost no samples preparation required
• No fluorescence appears
8
Outlook
Problem of P Localization
Combination with laboratory micro X-ray
fluorescence (µ-XRF)
µ-XRF Mapping of the Alluvial soil
P Kα1
Ca Kα1
Si Kα1
Instrument: HORIBA XGT 7200; Area: 512 x 512 µm2; Lateral Resolution: 10 µm; Time: 5 min
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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
10