PCB Analysis (Aroclors, Congeners, Homologs)
Traditionally, most PCB analysis has been performed by either of two approaches - aroclor analysis utilizing gas chromatography with an electron capture detector (GC-ECD) or congener/homolog analysis utilizing high resolution gas chromatography/mass spectrometry (GC/HRMS). While each approach has its advantages and disadvantages, there is a very wide gap between these techniques in terms of the type, depth, breadth, and quality of information that each procedure provides. Alpha offers both aroclor and congener/homolog analysis; however, we utilize a gas chromatography/low resolution mass spectrometry (GC/LRMS) approach for PCB congeners and homologs that may be a very cost effective option for some project applications.
PCB Aroclor Analysis
Historically, the vast majority of PCB analyses conducted in support of remedial investigations and feasibility studies were determinations of PCB aroclors utilizing gas chromatography-electron capture detector (GC-ECD). While this is still the case today, as the inadequacies of aroclor determination for human health and ecological risk assessment became more apparent, particularly for sediment and tissue analysis, regulatory criteria and guidance has shifted towards PCB congener and homolog analysis.
However, PCB aroclor analysis still has its place, primarily due to its relatively low cost. This is especially true for sites that have been previously well characterized, where the site-specific limitations of the aroclor analyses are known and the sample matrix is not overly challenging. At a minimum, aroclor analysis can be used as a screening tool to direct subsequent congener and/or homolog analysis.
Alpha Analytical performs PCB aroclor analysis in accordance with EPA Method 8082. Sediment samples are generally extracted utilizing EPA Method 3570 - Microscale Solvent Extraction (MSE). Sample extracts can then be 'cleaned up' to minimize interferences using silica gel or gel permeation chromatography (GPC), as necessary.
PCB Congener & Homolog Analysis
The primary disadvantages of aroclor analysis by GC-ECD are qualitative in nature, due to the fact that chromatograhic patterns and peak ratios are subject to change in the environment due to "weathering". PCB aroclors may be reported as not detected due to a lack of pattern recognition; however, PCB congeners may actually be present or quantified as a different aroclor. Quantitatively, it can also be difficult to determine a total PCB concentration using the aroclor approach. This is especially true when more than one aroclor is determined to be present. As the individual aroclors represent mixtures of PCB congeners, there is a possibility that "double counting" of PCBs could also occur.
PCB analysis utilizing GC/LRMS can be a good alternative for some data collection applications and it represents a good compromise between the two options discussed above. Alpha Analytical utilizes a GC/LRMS procedure for PCB congener and homolog analysis based on EPA Method 680 and EPA Method 8270, as well as the NOAA Technical Memorandum NMFS-NWFSC-59, March 2004.
This procedure can determine all 209 PCB congeners or a subset of congeners (WHO, NOAA or custom list). The GC/LRMS method can be a very cost effective option for characterizing contaminated samples for PCB congeners. In addition, this method can also measure groupings of PCB congeners as a function of their level of chlorination (e.g. homologs/homlogues). The homolog determination provides another, more representative option for the determination of "total PCBs". Homolog analysis can be included with the congener analysis or reported separately.
Additionally, the GC/LRMS method can also estimate PCB aroclor concentrations from the same sample aliquot as the congener/homologs, allowing for the simultaneous measurement of congeners, homologs and aroclors. This approach eliminates the potential variability associated with the analysis of multiple aliquots. As a consequence, PCB contaminated sites with years of existing aroclor data do not have to incorporate GC-ECD aroclor analysis into their current sampling programs, for comparison with historical data. In addition to the increased cost involved for two separate analyses, this approach also requires separate sample aliquots, or separate sample containers in some cases. Given the non-homogeneity often observed, particularly with sediment samples, the separate sample aliquots can introduce significant variability into the data set.