Article written by Wade DeLong, Lab Manager, Analytical Products Group, Inc.
Complete article from Edition 31 APG eNewsletter
The implementation of the revised Fields of Testing on June 1, 2005 brings a new potential issue for reporting PCB results on Proficiency Testing (PT) samples. Prior to June 1, 2005, laboratories were not required to distinguish between Aroclor 1242 and Aroclor 1016 when reporting PT results. The chromatographic patterns of these two aroclors are very similar, but it is possible to correctly identify each aroclor. There are key differences that can be identified by analyzing the individual aroclors and overlaying the chromatograms. In general, the chromatographic pattern of Aroclor 1242 extends beyond that of Aroclor 1016. (View Figure 1 in PDF format.)
Another identification tool that is sometimes overlooked comes from the way some laboratories combine Aroclor 1016 and Aroclor 1260 in the same calibration standard (as described in SW-846 Method 8082). This would not be possible if the pattern for Aroclor 1016 extended into the pattern for Aroclor 1260. So, an analysis of Aroclor 1260 being overlayed with an unknown that is potentially Aroclor 1016 or Aroclor 1242 could be useful because the pattern for Aroclor 1016 should stop before Aroclor 1260 starts and Aroclor 1242 would extend into the area of Aroclor 1260. SW-846 Method 8082 also requires analysis of the other five aroclors individually to aid in identification; however, one additional analysis of either Aroclor 1016 or Aroclor 1260 may also prove to be helpful.
It is always useful to maintain a "reference library" of PCB patterns to help in identification of unknowns whether it is on paper or electronically. This library should include all aroclors individually and various combinations for those rare occasions when the identification of an unknown sample presents a challenge. Field (or real world) samples sometimes present their own unique challenge in proper identification due the "weathering" process. These chromatograms are also useful to maintain as part of the "reference library". Of course, the library should be updated after any major change to the analytical system (e.g. column changes or temperature program changes).
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