Phosphorus speciation in calcite speleothems determined from solid-state NMR spectroscopy

Details Phosphorus speciation in calcite speleothems determined from solid-state NMR spectroscopy Phosphorus speciation in calcite speleothems determined from solid-state NMR spectroscopy

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007e%26psl.254..313m&link_type=abstract

Earth and Planetary Science Letters, Volume 254, Issue 3-4, p. 313-322.

Physics

3

Scientific paper

Variations in speleothem P concentration show cyclic patterns that have important implications for high resolution palaeoclimate and palaeoenvironmental reconstructions. However, little is known about the speciation of P in calcite speleothems. Here we employ solid-state 31P and 1H magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopic techniques as a non-destructive method for analyzing the distribution of P in speleothems. The 31P MAS NMR results show three peaks indicating the presence of three primary types of phosphate species in samples from the Grotta di Ernesto (northeastern Italy): a broad peak at a chemical shift δP-31 = 3.1 to 3.7 ppm from individual phosphate ions incorporated within calcite, a narrow set of peaks near δP-31 = - 0.9 ppm from crystalline monetite and a narrow peak at δP-31 = 2.9 ppm from an unidentified crystalline phosphate phase. Essentially identical results were obtained for a synthetic calcite/phosphate coprecipitate. Spectra collected for a sample from Grotte de Clamouse (southern France) show only a broad peak near 3.5 ppm suggesting a possible limit for phosphate incorporation into the calcite structure. These data suggest that P in this system can interact to form calcium phosphate surface precipitates during infiltration events and are subsequently enclosed during calcite growth.

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