Polyaromatic preservation

In addition to preserving structure, a soft ionization technique such as chemical ionization (Cl) has a further advantage in ms /ms. By minimizing the number of ions generated from each molecular species the complexity of the (ionic) mixture which has to be separated is minimized. It is for this reason that electron impact ionization is seldom a good choice for ms/ms, although for compounds such as the polyaromatic hydrocarbons which give predominantly one ion in their electron impact spectra this complication is minimized. 

To prevent oxidation, either ascorbic acid or sodium thiosulfate is often added to samples to remove free chlorine that could otherwise form trichloro-methane. Polyaromatic hydrocarbons (PAHs), in particular benzo[a]-pyrene, are unstable in chlorinated water and sodium thiosulfate is added to preserve the analytes from degradation by chlorine. To ensure stability of the PAH analytes, the water sample is also acidified, again showing that often a single preservative is not always effective for some analytes. 

Preferred orientation of the polymer carbon can be achieved by preorientation of the chain molecules in the polymer precursor fibre. Polyacrylonitrile has been proved as the most suitable and economic precursor. This thermoplastic polymer, however, needs a cross-linkage treatment before carbonization to preserve the fibre morphology. Simultaneously, cyclization of the side chains and dehydrogenation occur resulting in nuclei for the formation of the planar polyaromatic layers... 

Despite an apparent simplicity, the functionalization of polyaromatic conjugated polymers puts stringent requirements on the possible structural modifications of the precursor. As a matter of fact, the structure of the modified precursor must remain compatible with both the polymerization reaction and the preservation of the relevant electronic, electrochemical, and electrical properties of the 7r-conjugated backbone in the resulting polymer. Such conditions imply in turn a detailed knowledge of the consequences of the electronic and steric effects of substitution both on the polymerization reaction and on the structure and properties of the polymer. 

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