High sensitivity of ortho-substituted polychlorobiphenyls in negative ion mass spectrometry (NCI-MS): A comparison with EI-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 usi ng high resolution gas chromatography (HRGC) and negative-ion chemical ioni zation mass spectrometry (NCI-MS), electron impact mass spectrometry (EI-MS ) and electron capture detection (ECD). In NCI PCBs generated simple mass s pectra with the molecular ion as base peak. The dissociative electron captu re mechanism increased for higher chlorinated PCBs. After ion source optimi zation (pressure, temperature) detection of the tri-and tetrachloro-PCBs be came possible. NCI-MS showed comparable sensitivity with the ECD for most o f the PCBs analyzed, excellent linearity and good repeatability. A comparis on of the PCB soil concentrations obtained with the three detection techniq ues revealed that NCI-MS gave values closest to the overall mean with the s mallest deviations.