Fragmentation Pathway of Organophosphorus Flame Retardants by Liquid Chromatography-Orbitrap-Based High-Resolution...

Organophosphorus flame retardants (OPFRs) have been widely used in polymeric materials owing to their flame retardant and plasticizing effects. Investigating the fragmentation pathway of OPFRs is of great necessity for further discovering and identifying novel pollutants using orbitrap-based high-resolution mass spectrometry (HRMS). A total of 25 OPFRs, including alkyl, halogenated, and aromatic types, were analyzed in this study. The fragmentation pathways of the OPFRs were investigated using orbitrap-based HRMS with high-energy collision dissociation (HCD) in positive mode. The major fragmentation pathways for the three types of OPFRs are greatly affected by the substituents. In detail, the alkyl and halogenated OPFRs underwent three McLafferty hydrogen rearrangements, wherein the substituents were gradually cleaved to form the structurally stable [H₄PO₄]⁺ (m/z = 98.9845) ions. In contrast, the aromatic OPFRs would cleave not only the C-O bond but also the P-O bond, depending on the substituents, to form fragment ions such as [C₆H₇O]⁺ (m/z = 95.0495) or [C₇H₇]⁺ (m/z = 91.0530), among others. Using HRMS improved the accuracy of fragment ion identification, and the pathway became more evident. These fragmentation laws can provide identification information in pollutant screening work and theoretical references for the structural characterization of compounds with diverse substituent structures.