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| Titel |
Technical Note: An X-ray absorption method for the identification of calcium phosphate species using peak-height ratios |
| VerfasserIn |
J. F. Oxmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 8 ; Nr. 11, no. 8 (2014-04-17), S.2169-2183 |
| Datensatznummer |
250117367
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| Publikation (Nr.) |
 copernicus.org/bg-11-2169-2014.pdf |
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| Zusammenfassung |
| X-ray absorption near edge structure (XANES) studies on calcium phosphate
species (Ca-P) deal with marginal differences among subtle spectral features
despite a hitherto missing systematic breakdown of these differences.
Related fingerprinting approaches depend, therefore, on spectral libraries
that are not validated against each other, incomplete and scattered among
publications. This study compiled a comprehensive spectral library from
published reference compound libraries in order to establish more clear-cut
criteria for Ca-P determination by distinctive phosphorus K-edge XANES
features. A specifically developed normalization method identified
diagnostic spectral features in the compiled library, e.g. by uniform
calculation of ratios between white-line and secondary peak heights.
Post-processing of the spectra (n = 81) verified distinguishability among
most but not all phases, which included hydroxylapatite (HAP), poorly
crystalline HAP, amorphous HAP, fluorapatite, carbonate fluorapatite (CFAP),
carbonate hydroxylapatite, β-tricalcium phosphate, octacalcium
phosphate (OCP), brushite, monetite, monocalcium phosphate, amorphous
calcium phosphate (ACP), anapaite, herderite, scholzite, messelite, whiteite
and P on CaCO3. Particularly, peak-height ratios significantly improved
analyte specificity, e.g. by supplementary breakdown into OCP and ACP. The
spectral analysis also revealed Ca-P standards that were rarely investigated
or inappropriately synthesized, and thus provides a basis for standard
selection and synthesis. The method developed and resulting breakdown by
species were subsequently tested on Ca-P spectra from studies on bone and
sediment. The test indicated that bone material likely comprises only poorly
crystalline apatite, which confirms direct nucleation of apatite in bone.
This biological apatite formation is likely opposed to that of sedimentary
apatite, which apparently forms by both direct nucleation and successive
crystallization. Application of the method to μXANES spectra of
sediment particles indicated authigenic apatite formation by an OCP
precursor. |
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