Electronic spectra congeners

ECD to TCBT isomers was a factor of two lower than for the corresponding tetra- and higher chlorinated PCB congeners [85]. Therefore, most practically successful TCBT analyses were done by GC-MS, especially with SIM mode [84-86,89-91]. The most useful EI-MS ions of TCBT are those of (high resolution) m/z (Int%) values 319.9508(46.5), 317.9537(60.0), 284.9819(97.1), and 282.9848(100), two M+ and two (M-C1)+ peaks, respectively. Model electron impact mass spectrum (upper part) of a TCBT isomer is presented in Fig. 7. 

Both electron impact (El) and negative chemical ionization (NCI) techniques can be used for MS detection of PCTs. The use of El results in a more fragmented spectrum, which may provide more structural information [34]. NCI provides a higher sensitivity [8]. Only lower chlorinated congeners (<4 chlorine atoms) show a lower sensitivity with NCI. However, lower chlorinated PCTs are hardly present in Aroclor 5442, and even less so in Aroclor 5460. Hale et al. [17] reported the presence of lower chlorinated PCTs in sediments and shellfish from the Chesapeake Bay due to a specific discharge of Aroclor 5432. Monsanto has, however, produced substantially less Aroclor 5432 than Aroclor 5460 [8]. El and NCI spectra of a deca PCT are shown in Fig. 3. 

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