The biogeochemistry and human use of phosphorus (P) resources relies on understanding P chemical speciation. Phosphorus molecules in environmental samples are diverse, with a wide range in molecule size, charge, hydrophobicity, and local bonding of the phosphorus. Given this array of characteristics, separation and detection of P molecules in complex matrices is inherently difficult. Targeting the small-molecule fraction (&lt;1000 Da), we apply liquid (LC) and ion chromatographies (IC) with inductively-coupled plasma mass-spectrometry (ICP-MS) detection to model compounds, wastewater samples, and environmental water samples to characterize P speciation. Mass-based detection of 31P is advantageous over conductivity or UV-visible absorption detection due to increased selectivity and sensitivity, with detection limits typically &lt;10 ppb P. Isobaric polyatomic interferences (e.g., NO+ and CH3O+) were alleviated with a dynamic reaction cell and oxygen gas to mass shift P, particularly with organic solvents. We find that ion chromatography excels at resolving deprotonated phosphate monoesters, phosphate diesters, organic or inorganic polyphosphates, and phosphite, whereas liquid chromatography excels at resolving phosphate triesters, phosphonates, phospholipids, and P bound to larger hydrophobic moieties (e.g., aromatics). More broadly, IC separation is characterized as suitable for molecules in which phosphate/phosphite charge and acid-base chemistry is a dominant chemical characteristic, whereas LC separation is more suitable for molecules in which other, often hydrophobic organic, functional groups dictate intermolecular interactions. By applying both methods, LC and IC, P peaks can be correlated to yield a P species distribution in complex unknowns.

Analyzing complex mixtures of small phosphorus molecules using liquid (LC) and ion chromatographies (IC) with ICP-MS detection: A two-dimensional approach to characterizing environmental phosphorus

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