High sensitivity of ortho-substituted polychlorobiphenyls in negative ion mass spectrometry (NCI - MS): A comparison with El - MS and ECD for the determination of regulatory PCBs in soils

Selected ortho-substituted PCBs (IUPAC no. 28, 52, 101, 118, 153, 138, 180) were quantified at trace levels in twenty different agricultural soils using high resolution gas chromatography (HRGC) and negative-ion chemical ionization mass spectrometry (NCI-MS), electron impact mass spectrometry (EIMS) and electron capture detection (ECD). In NCI PCBs generated simple mass spectra with the molecular ion as base peak. The dissociative electron capture mechanism increased for higher chlorinated PCBs. After ion source optimization (pressure, temperature) detection of the tri-and tetrachloro-PCBs became possible. NCI-MS showed comparable sensitivity with the ECD for most of the PCBs analyzed, excellent linearity and good repeatability. A comparison of the PCB soil concentrations obtained with the three detection techniques revealed that NCI-MS gave values closest to the overall mean with the smallest deviations.