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

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.