Radioisotope Dilution Assay (RIDA) for the Estimation of Polychlorinated Biphenyls (PCBs)

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Abstract
A radioisotope dilution assay (RIDA) having an accountability of 94–99% for the estimation of total polychlorinated biphenyls (PCBs) is described. Biological samples are spiked with a radioactive PCB of known specific activity. Lipids and PCBs are extracted from the samples by the use of chloroform:methanol (2:1 v/v). PCBs are separated from lipids either by sulfuric acid treatment or by gel permeation chromatography. The PCB fraction is further cleaned up using Florisil PR-60 and is perchlorinated. Decachlorobiphenyl is estimated by gas chromatography and radioactivity assayed by liquid scintillation counting. Because dilution of radioactivity is taken into consideration, the complete recovery of PCBs is not required for their estimation; thus, this method overcomes the handling losses in the cleanup, perchlorination, and preparation of samples.