Multi-Column Complementary Separation And Analysis For PCBs By High Performance Gas Chromatography

Polychlorinated biphenyls (PCBs) is a group of organochlorine chemicals whichare extremely persistent and widespread environmental contaminants. The difficultyfor separation and analysis of PCB is caused by large numbers of congeners (possible209) and large differences in concentration between some congeners. Comprehensive,quantitative, congener-specific analysis for each PCB congener is required for topresearches.The retention values of about 150 PCB congeners were measured on three kindsof capillary GC columns with different polarities and corresponding A and Bparameters which describe the retention behavior for each PCB congener in gaschromatography were obtained accurately. Basing on the relative retention indexmethod, the predicted retention times of PCBs are calibrated accurately in differenttemperature programmed conditions. Meanwhile, a novel method has been applied toobtain A and B parameters rapidly for each congener on DB-1701 column with threelinear temperature programmed (TP) conditions only in order to overcome theinconveniences for isothermal methods. It is proved that accurate retention times canbe predicted basing on the A and B parameters from TP conditions in selecteddifferent TP conditions. According to the structures of co-eluted PCB congeners, atriple column system with non, week and middle polarity phases is suggested to getcomplementary separation for PCB congeners.In order to get reliable, accurate quantification result for overlapping PCBcongeners, the rule of peak shape parameters σand τin EMG model that welldescribe a chromatographic peak had been investigated in this study. The overlappingpeaks with two, three and more PCB congeners have been resolved. The resolutionresults were proved to be more accurate and reliable than conventional method. The complementary, quantitative determination for PCB congeners wasperformed on three columns with full chromatogram curve-fitting method. Theresults show that 67% of PCB congeners can be accurately determined on DB-5column; other 20% and 9% of PCB congeners can be accurately determined onDB-1701 and DB-1, respectively; the remained 4% of PCB congeners can becalculated after the complementary results by full chromatogram curve-fitting on allthree columns were obtained. According to this study, it is worth noting again that noavailable capillary column today can meet the requirement of separation andquantification for all about 150 PCB congeners which present in Aroclor andClophen samples. However, the triple column system adopted in this study is able tosolve these problems with the assistance of curve fitting method. Applying the method proposed in this study, the identification and quantificationresults of PCBs have been obtained accurately during the dechlorination of PCBs intransformer oil with nano-scale NaH. The relationship between dechlorination rateand chlorine atoms in PCB congeners has been found. The dechlorination activitiesof PCB congeners with different chlorine atoms distribution at two phenyl rings andchlorine atoms at ortho, meta and para position in PCB molecular have beeninvestigated.