Polymeric materials PAHs

Untreated silica column can be advantageously used for HPLC preseparation of PAHs from triglycerides. The capacity of a silica column to retain fat (for columns of the same particle size) depends on the column size, the mobile phase composition, as well as the type and by-products (free acids and polymerized material) of the fat injected [706,713]. Off-line HPLC-HPLC, employing silica column (250 X 4.6 mm i.d., 5 pm of particle size) for sample preparation before RP-HPLC and spec-trofluorometric detection, was successfully applied for PAH determination in edible oils [659,691] and fish [714]. After PAH elution, the silica column needs to be backflushed with dichloromethane to remove the fat. The entire sample preparation step can be automated by using a backflush valve and a programmable switching valve box [691]. 

Moreover, because of the presence in the tank of many types of materials (including natural organic particulates, polymeric devices, semi-permeable membranes and solid sorbents used for other types of measurements), a partial adsorption of PAHs leading to concentration depletion, at least at the beginning of the exercise, of the dissolved (free) PAHs is also highly plausible. This may also contribute to some extent to the low concentrations found for the four PAHs (ANTH, BaA, CHRY, and PYR) from samplings T4 to T9. 

The failure of classical ring closure methods - often effective for the formation of planar PAHs - may be attributed to the strain present in the bowl-shaped product (corannulene) as compared to the (almost) strainless starting materials (fluoranthenes). Hence the relatively high energy transition states leading to corannulene formation are avoided in favor of lower energy intermolecular processes including polymerizations. 

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