『Summary
　Common sequential phosphorus (P) extraction methods are not specific to particular chemical chemical species and have several limitations. This work presents the first chemical method for quantification of individual mineral and sorbed P species. It was developed by combining a conversion technique with a sequential extraction procedure. Mangrove sediments with different characteristics were incubated in pH-adjusted 0.01 M CaCl2 with and without reference material additions of octacalcium phosphate (Ca8H2(PO4)6・5H2O; OCP), hydroxyapatite (Ca5(PO4)3OH), strengite (FePO4・2H2O) or variscite (AlPO4・2H2O). The changes in soluble phosphate concentration were measured in the supernatant solution, while pH-induced variations in P composition were determined by subsequent sequential extraction of the sediments. Dissolved phosphate concentration was controlled by adsorption below pH 7.8. Above this pH, soluble phosphate concentration was governed by OCP, which was qualitatively determined by plotting the experimental values of pH + pH2PO4 and pH - 0.5 pCa on a solubility diagram including the isotherms of known crystalline phosphate compounds. In contrast to the often-predicted slow dissolution rate of crystalline phosphates in soils or sediments, drastic changes in P composition by dissolution, precipitation and adsorption processes are detected after 7 days. These were mainly not observed indirectly by changes in dissolved phosphate through adsorption effects, but were determined quantitatively by subsequent sequential extraction, thus enabling the quantification of individual species. Evaluation of the method was performed by standard addition experiments. Besides P species quantification, the method provides the means for other applications, such as the determination of P mineral dissolution kinetics in solids and sediments, the prediction of P composition in changing environmental settings and the refinement of theoretical models of phosphate solubility in soil and sedimentary environments.』

Introduction
Materials and methods
　Sediment sampling and preparation
　Reference materials for standard addition experiments
　Development of the CONVEX method
　Method evaluation by standard addition experiments
　Analytical methods and procedures
Results
　CONVEX method: soluble phosphate data
　CONVEX method: fractionation data
　Calculation of the data for P species quantification
Discussion
Acknowledgements
References