Study of polybrominated diphenyl ethers using both positive and negative atmospheric pressure photoionization and tandem mass spectrometry

Atmospheric pressure photoionization (APPI) was assessed for the mass spectrometric analysis of polybromodiphenyl ethers (PBDEs) on the basis of a set of 17 standard compounds. Positive and negative ionization modes were both investigated. M(+.) ions were formed under positive ion conditions whereas the negative ion mode yielded M-Br+O](-) ions. The behavior of these APPI-produced ions towards collisional activation was studied using an ion trap mass spectrometer. In positive ion mode, the loss of Br(2) was one of the major fragmentation pathways, and was favored for ortho-substituted PBDEs. Conversely, the loss of COBr(.) occurred only for non-ortho-substituted congeners. The collisional excitation of M-Br+O](-) ions in the ion trap also led to the loss of Br(2), to the elimination of HBr, and to the formation of product ions by cleavage of the ether bond. The formation of para-quinone radical anions was observed for PBDEs ranging from penta- to hepta-congeners, whereas brominated aromatic carbanions were formed preferentially for the most brominated PBDEs studied in this work (hepta- or deca-BDEs). M(+.) ions did not undergo this fragmentation process.