A Comparative Assessment of Low- and High-Resolution Gas Chromatography / Mass Spectrometry Methods for Polychlorinated Biphenyl Congener Analysis in Industry Wastewater

A comprehensive study was conducted to understand the performance of USEPA Method 1628 for the testing of Polychlorinated Biphenyl (PCB) Congeners by low-resolution Gas Chromatography-Mass Spectrometry (GC-MS). Method performance was compared to USEPA Method 1668C, USEPA’s high-resolution GC-MS method, using nine pulp and paper wastewater samples. USEPA Method 1628 was designed to make PCB analysis more feasible in standard, mid-sized environmental laboratories. This method, which analyzes all PCB congeners, is less sensitive and less expensive to implement than USEPA’s high-resolution GC-MS, Method 1668C. The analysis of wastewater samples revealed several potential concerns with Method 1628, including the likelihood of false positive or positively biased identifications of certain congeners. The multi-laboratory validation study conducted by the USEPA indicated that similar problems might have arisen, although a comparison with Method 1668C was not included in that study. The Quality Assurance (QA) aspects of Methods 1628 and 1668C were compared and key issues were identified. Method 1628 can yield results that differ from those obtained with Method 1668C, sometimes quite substantially. Comparison of quantitated results between the two methods could only be applied to those individual analytes that had homologous labeled isotope standards for each method. The percent difference of the reported concentration of the same analyte compared between each method ranged from -16% to 6241%. Furthermore, there is a significant risk that Method 1628 may produce false positives and/or positive bias, which could impact the utility of this method if used for some regulatory purposes.