Phosphorus speciation using ion chromatography coupled with ICP-MS elucidates transformations of phosphorus compounds on reactive surfaces

Phosphorus (P) is an important and often limiting element in terrestrial and aquatic ecosystems. Insufficient understanding of the characteristics and environmental reactivities of organic and inorganic P compounds impedes developing efficient mitigation and recovery strategies. We developed a robust P speciation method utilizing ion chromatography (IC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). The method was sensitive (detection limits: 1.2–4.2 μg P L⁻¹), repeatable, and compatible with both inorganic (phosphite, phosphate, pyrophosphate, and triphosphate) and organic compounds (adenosine phosphates (mono-, di-, and tri-) and phytic acid). The IC-ICP-MS method effectively demonstrated the presence of distinct P compounds in several environmental water matrices: 1) anaerobic digestate supernatant was 99 % phosphate, 2) Pony Lake fulvic acid exhibited two distinct peaks related to organic P compounds having different sizes or polarities. The IC-ICP-MS method efficiently and comprehensively tracked both inorganic and organic hydrolysis products of model P compounds in water containing reactive CeO₂ surfaces, on which triphosphate and adenosine triphosphate were quickly dephosphorylated. The hydrolysis pathways were elucidated, in which a single phosphate group rather than bigger groups was rapidly lost. The benefits of the IC-ICP-MS method were highlighted in tracking by-products and addressing key challenges associated with the stability and transformations of P compounds, providing a foundation for continued bulk-property characterization of a critical environment nutrient.