『Abstract
Phosphorus Near Edge X-ray Fluorescence Spectroscopy (P-NEXFS)
data were collected on phosphorus containing phases including
organic and inorganic compounds and minerals. Although phases
containing P in the plus five oxidation state P(V) in a tetrahedral
PO4 structure have similar primary fluorescence
peak positions, the size, shape, and positions of secondary spectral
features are diagnostic for different compounds and minerals.
In particular, calcium phosphates exhibited a notable post-peak
shoulder at 2154.5 eV, while oxidized iron phosphates had a distinctive
pre-peak feature at 2148 eV. Polyphosphates have a broad secondary
peak located approximately 2 eV higher in energy than a similar
feature in phosphate esters and diesters. Compounds containing
P(V) in structures other than PO4 tetrahedral
such as phosphonates have a primary peak shifted about 1 eV lower
than corresponding organo-phosphates. Organo-phosphates with P
in the plus three oxidation state P(III) such as phosphines had
primary fluorescence peaks shifted still further down in energy
(2-3 eV). The substitution of aromatic carbon groups in close
proximity to P structures in organic compounds generated both
pre- and post-peak features as well as a number of secondary peaks.
In addition, X-ray fluorescence mapping of P, Si, Al,Mg, and Na
was conducted on a marine sediment sample with sub-micron spatial
resolution. Phosphorus was heterogeneously distributed in the
sample and not correlated on a broad scale with any other element
examined. Much of the P present in the sample was located in small,
0.6-8μm size, P-rich domains. Several P-rich regions were examined
with P-NEXFS using a focused beam with 60 nm resolution and were
found to consist of either calcium phosphate or polyphosphate
phases. The presence of significant polyphosphate-dominated regions
in a marine sediment sample supports the present observations
that such phases can play an important role in marine P cycling.
The combination of fluorescence mapping and P-NEXFS data collection
on fine particles provides a powerful new tool for environmental
phosphorus studies.
Keywords: Phosphorus; X-ray microscopy; Spectroscopy; Apatite;
Polyphosphate; Phosphonate; Marine sediments』
1. Introduction
2. Methods
3. Results
3.1. Minerals
3.2. Inorganic compounds
3.3. Organic compounds
3.4. Effingham Inlet surface sediment
4. Discussion
5. Conclusions
Acknowledgements
Appendix A. Supplementary data
References