Chromatographic and Ionization Properties of Polybrominated Diphenyl Ethers Using GC/High-Resolution MS with Metastable Atom Bombardment and Electron Impact Ionization

The chromatographic and ionization properties of 35 polybrominated diphenyl ether (PBDE) congeners were investigated using GC/HRMS with metastable atom bombardment (MAB) and electron impact (EI) ionization. A multiple linear regression model based on bromine substitution patterns and MOPAC calculated physical properties was developed to predict relative GC retention times of individual PBDE congeners. Although five different sources of metastable rare gas atoms (He, N₂, Ar, Xe, and Kr) were investigated with MAB ionization, only MAB-N₂ provided adequate ionization efficiency and predictability. Because of reduced background noise to the MS detector, MAB-N₂ had a lower limit of detection for tetra- and penta-BDEs than EI, despite having a lower sensitivity. Using MAB-N₂, the molecular ion was always the base peak, with little fragmentation taking place. Conversely, using EI ionization, the [M − nBr]⁺ peak (where n = 1−4, depending on the number of Br substituents) was the dominant ion for all PBDE congeners. Multiple linear regression models representing the molecular ion response of PBDE congeners analyzed by GC/HRMS with MAB-N₂ and EI ionization were also developed using the number and type of Br substituents and ionization potentials. A significantly higher level of predictability was obtained for the MAB-N₂ response model than for EI.