The unreliability of direct gas chromatographic analysis of polychlorinated biphenyls.

detected in these blank determinations that we were not certain whether it came from the Soluene or other sources. You may note that the blood of control rats which was analyzed with the use of Soluene did not contain detectable amounts of asbestos and zero fibers per gram was reported. We have since repeated this work (as yet unpublished) in an experiment in which asbestos was fed to rats and the tissues analyzed by a low temperature ashing technique similar to that reported for fecal asbestos (2). Essentially similar results were obtained as in the original work with significantly higher levels of asbestos fibers found in treated than in control animals. Polychlorinated biphenyls (PCBs), ubiquitous environmental pollutants, are usually assayed by gas chromatography of cleaned-up extracts with electron capture detection. Quantitation is relative to some arbitrary standard, usually one of the commercial PCB mixtures (Aroclors, Clo-phens, etc.). The mixtures recovered from environmental samples (soil, feces, various animal tissues, milk and the like) almost never match the PCB standard mixture in composition, but the commercial mixture best approximating the unknown in general distribution of peaks on the chromatograms is necessarily selected as quan-titation reference. Although it is well known (1,2) that electron capture detectors respond differently to different PCBs, the assumption is usually made that the errors in comparing an unknown mixture with a more-or-less similar standard mixture will cancel out. Accordingly, the literature is replete with data on "PCB content" of all sorts of environmental samples (3). In a few cases (4), the numbers reported were roughly confirmed by perchlorina-tion to the single compound decachlorobeiphenyl (which can be accurately quantitated with an electron capture detector), but in the vast majority of cases, there has been no confirmation. To illustrate the unreliability of the more common direct gas chromatography of PCBs versus an Aroclor standard, we performed the following simple experiment. A 1-g portion of Aroclor 1260 was chromatographed on 50 g of Florisil PR, eluting with ligh petroleum ether. Under these conditions, the PCBs tend to "tail". The portion eluting between 200 and 300 ml of petroleum ether weighed about 4 mg and showed all of the same peaks as the original Aroclor 1260 during gas chromatography. However, the relative proportions of the peaks differed from those of stock 1260. Three preparations were supplied for gas chro-matographic analysis; the original Aroclor 1260, for use as reference standard, cottonseed oil spiked …