Fragmentation Pathways and Enhanced Detection Sensitivity of OH-PBDEs via LC-ESI-MS²: A Comprehensive Analytical...

The fragmentation behavior of isomeric hydroxylated polybrominated diphenyl ethers (OH-PBDEs) remains poorly elucidated, although LC-MS/MS is essential for their analysis. This study systematically characterizes their fragmentation behavior by LC-ESI-MS², elucidating relationships between product ions, structural features, and instrument detection limits. Results demonstrated congener-specific variability in the signal intensity of [M-H]^-, particularly among isomers. Fragmentation behavior is highly dependent on the hydroxyl location on the diphenyl ether scaffold, as well as the bromine substituent pattern. Three distinct mechanisms are identified: (1) Br abstraction via free radical-mediated rearrangement cleavage in meta-hydroxylated PBDEs, (2) preferential formation of the [Br]^- ion via γ-elimination in ortho-hydroxylated PBDEs, and (3) characteristic formation of bromobenzoquinone anions via multistep fragmentation mechanisms in para-hydroxylated PBDEs. Furthermore, the ortho-effect, particularly pronounced in 2'-OH substituted congeners, significantly alters the fragmentation pathways. While the elucidated fragmentation pathways provided structural insights, the inherent weak signals challenged detection. A sensitivity-enhancing precolumn derivatization protocol with dansulfonyl chloride was introduced to solve the problem. The MS² fragmentation of these derivatives was conveniently dominated by the cleavage of the C-S bond within the dansyl group, yielding abundant diagnostic ions that greatly aided in structural confirmation. As predicted, the derivatization strategy achieved a remarkable up to 15-fold improvement in the sensitivity. This investigation advances the understanding of OH-PBDE fragmentation, establishes an identification framework using specific patterns and diagnostic ions, and demonstrates a practical derivatization approach for enhanced sensitivity, elucidating structure-fragmentation relationships in brominated aromatics and providing methodological guidance for future analysis.