Detection of calcium phosphate species in soil by confocal μ‐Raman spectroscopy ^#

Background Raman spectroscopy is a promising but largely underexplored tool for the detection of phosphates (P) in soil. Although it requires minimal sample preparation, has been demonstrated mainly test matrices or substrates to circumvent typical signal interference caused by fluorescence organic matter actual agricultural soils. Aims The aim this study was highlight spectroscopic and identification distinct calcium phosphate species amended contrasting soil matrices—including real arable Methods Pure dihydrogen [Ca(H2PO4)2·H2O], hydrogen (CaHPO4), β-tricalcium [β-Ca3(PO4)2] were each Luvos® healing earth, loess from C-horizon, loam an Ap-horizon at dose 1 mmol (10 g soil)–1. unique signature pure determined confocal μ-Raman used subsequently as reference spectrum identify compound matrix. Controls without added P also analyzed. Results Ca(H2PO4)2·H2O, CaHPO4, β-Ca3(PO4)2 unambiguously detected treated Native hydroxyapatite [Ca5(PO4)3(OH)], quartz (SiO2), feldspar (NaAlSi3O8), calcite (CaCO3), dolomite [CaMg(CO3)2] identified, example, microscopic image control earth sample. Intrinsic Ca5(PO4)3(OH) present distinguished other Lorentzian fitting, which deconvoluted individual signals unresolved peak. Conclusions usefulness detect could be shown proof concept.