Statistical method to evaluate clean-up procedures in polychlorinated biphenyl analysis

The clean-up procedure involved in the trace analysis of polychlorinated biphenyls (PCBs) was evaluated by studying GC-MS chromatograms of PCB mixtures after the subsequent steps of the procedure. The complex chromatograms obtained were evaluated using two methods: the individual PCB congener method and a chemometric approach based on a study of the autocovariance function. The results obtained are statistically comparable, proving that the statistical approach is able to determine the total PCB content in the sample quantitatively. Moreover, since the autocovariance method is based on statistical evaluation of the whole complex chromatogram, it can overcome the problems that usually arise because of peak overlapping in PCB mixture chromatograms. It also provides accurate results when the chromatogram shows interfering peaks and low resolution. This is the case with Aroclor 1242, where some compounds released by the cartridges strongly interfere with the analysis, resulting in errors in the quantification of individual PCBs. Highly chlorinated PCBs (i,e., Aroclor 1260) can be quantitatively recovered (mean recovery, 100 ± 1%). In contrast, lower proportions (less than 75%) of the less chlorinated compounds (i.e., those containing two and three chlorine atoms) are recovered because they are selectively retained by silica and alumina columns.