Isomeric PAHs

In the analysis of complex PAH mixtures obtained from environmental samples, reversed-phase LC-FL typically provides reliable results for only 8-12 major PAHs (Wise et al. 1993a). To increase the number of PAHs determined by LC-FL, a multidimensional LC procedure is used to isolate and enrich specific isomeric PAHs that could not be measured easily in the total PAH fraction because of interferences, low concentrations, and/or low fluorescence sensitivity or selectivity. This multi-dimensional procedure, which has been described previously (Wise et al. 1977 May and Wise 1984 Wise et al. 1993a, 1993b), consists of a normal-phase LC separation of the PAHs based on the number of aromatic carbon atoms in the PAH, thereby providing fractions containing only isomeric PAHs and their alkyl-substituted isomers. These isomeric fractions are then analyzed by reversed-phase LC-FL to separate and quantify the various isomers. 

GC-MS Analysis. PAHs produce stable molecular ions upon electron impact very little subsequent fragmentation takes place. This is advantageous in determining molecular weight and hence the empirical formula and ring system of a PAH molecule. However, lack of fragmentation makes it usually impossible to differentiate between structural isomers. Chromatographic separation is therefore essential for identification isomeric PAHs by GC-MS. 

Oehme (1983) and Low et al. (1986) employed capillary GC coupled with negative ion chemical ionization MS for detecting and differentiating isomeric PAHs (including PAHs on EPA s priority pollutant list). This procedure was successfully used to differentiate the isomers... 

Polynuclear aromatic hydrocarbons (PAH) are formed by pyrosynthesis during the combustion of organic matter and have widespread occurrence in the environment. PAHs are found as trace pollutants in soil, air particulate matter, water, tobacco tar, coal tar, used engine oil, and foodstuffs such as barbequed meat. Many PAHs are carcinogenic in experimental animals (e.g., benzo(a)pyrene) and are implicated as causative agents in human cancers. Analytical techniques include HPLC and GC. Advantages of HPLC are the ability to resolve isomeric PAHs, and the selective and sensitive quantitation by UV and fluorescence detection. U.S. EPA methods for PAH are 550.1,610, and 8310. 

The formation of isomers has been reported if the silyl enol ether of 1-tetral-one (104) is used instead of the corresponding cyclohexanone derivative. It is assumed, that the intermediate cation 105 can undergo a double Wagner-Meer-wein rearrangement, which does not influence the overall result in the reaction towards 103, but finally furnishes the two isomeric PAHs 106 and 107 starting from 104. 

The great power of this column to separate isomeric PAHs and the use of a photodiode array detector to gather peak spectra make it possible to find previously unseen compounds in reaction mixtures that have been thoroughly investigated by conventional methods (4). This situation has been shown in this set of new PAHs by detection of the newly found isomer (compound 20) in the product mixture from 6H-benzo[de]pyren-6-one condensation. The potential to separate and identify new PAHs could be used to identify many other new compounds in other product mixtures. 

In addition, highly-ordered poly(octadecylacrylate) grafted silica particles prepared in both methods performed eomplete separation for mixtures of various isomeric PAHs polycyclic aromatic hydrocarbons in a methanol-water as a mobile phase as mentioned in many of our previous investigation [59]. Their elution orders are the same as those that can be observed with ODS. It is also showed that the retention factor k) increases with an increase in mobile phase polarity. The performance of Sil-to-ODA and Sil-from-ODA is imique because of its attractive temperature dependencies behavior. As shown in Fig. 7, both Sil-to-... 

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