A polybromlnated biphenyl (PBB) mixture was fractionated by normal-phase preparative high-performance liquid chromatography. The hexane fractions were concentrated and applied to rabbit ears. Only the most polar fraction produced hyperkeratosis on the rabbit ears. This active fraction was subfractionated by using the same procedure. Again, the extent of hyperkeratotic activity increased with increasing polarity. The PBBs of the largest concentration levels in the active fraction were purified by preparative gas chromatography and tested on rabbit ears. The major compounds did not demonstrate hyperkeratotic activity.
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