CBs in fish oil

Chlorobiphenyls (CBs) are a class of 209 discrete chemical compounds in which between one to ten chlorine atoms are attached to the biphenyl nucleus. The commercial products are complex mixtures used widely in industry, including transformers, capacitors. 

Series of interlaboratory studies were carried out prior to certification in order to evaluate the performance of current analytical techniques [15]. The group of participating laboratories examined the repeatability and reproducibility of the final determination of CBs calibrant solutions. Once the detection systems were optimised, the reproducibility of the calibrant solutions was checked with independent primary calibrants. 

An eel extract and a sewage sludge were prepared and half the extracts cleaned-up by a single laboratory. The second half of the extracts were cleaned-up by each laboratory using the different methods later employed in this certification project in an optimised form. Both sets of samples were analysed for the seven CB congeners to determine the level of variance amongst the clean-up procedures. 

Finally, a series of laboratory reference materials were examined to determine the interlaboratory reproducibility. At each stage, recommendations were made for improvement in the analytical method and are briefly summarised below. 

Calibrant solutions should be made from high purity materials and dissolved in iso-octane. In general, it is recommended that an internal standard is used which is pure, thermally and photochemically stable and which is not present in the environment (e.g. DCBEs). This should be added to the calibrant solutions and to the samples prior to injection. If the internal standard used is a synthetised CB that is not present in industrial PCB mixtures it may be added at the commencement of the analysis (prior to the clean-up procedure). There was no significant difference in the results obtained using different internal standards, but some interferences of tetrachloronaphtalene (TCN) was detected in the chromatogram of some samples. 

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