Contents Terphenyls

Stationary phases with a high density of bonded alkyl groups can differentiate between two molecules of identical size where one is planar and the other twisted out of plane. This shape selectivity has been described by Sander and Wise [53] for polymeric stationary phases, where in the preparation, water has been added on purpose and trichloro alkyl silanes have been used. The selectivity for the retention of tetrabenzonaphthalene (TEN) and benzo[a]pyrene (BaP) was taken as a measure to differentiate between polymeric and standard RP columns. With standard ( monomeric ) RP columns, the twisted TBN elutes after the planar BaP, which on the other hand is more strongly retarded as TBN on polymeric stationary phases. In these cases the relative retention of TBN/ BaP is smaller than 1, whereas with monomeric phases the value is >1.5. The separation of the standards on three different phases is shown in Figure 2.9. These stationary phases have superior selectivity for the separation of polyaromatic hydrocarbons in environmental analysis. Tanaka et al. [54] introduced the relative retention of triphenylene (planar) and o-terphenyl (twisted), which are more easily available, as tracers for shape selectivity. However, shape selectivity is not restricted to polymeric phases, monomeric ones can also exhibit shape selectivity when a high carbon content is achieved (e.g., with RP30) and silica with a pore diameter >15 nm is used [55]. Also, stationary phases with bonded cholestane moieties can exhibit shape selectivity. 

Fig. 3.9. Stoichiometric analysis. Acetylene content (O in low-molecular-weight gases of laser pyrolysis versus molar hydrogen/carbon ratio for different samples. Substances analysed 1 = phen-anthrene 2 = terphenyl 3 = naphthalene 4 = 1,2-diphenylethane 5 = polystyrene 6 = durene 7 =...

Polychlorinated (not mono- and dichlorinated) biphenyls (PCB), biphenyls, polychlorinated terphenyls (PCT), and preparations including waste oils with a PCB or PCT content higher than 0.005 % by weight may not be used. 

Fig. 4. Glass transition temperature dependence on the EBBA content for PC-EBBA system (curve 1). For comparison the plots Tg vs. contents of chlorinated terphenyl, chlorinated diphenyl and dibutyl phthalate in PC also are presented (curves 2, 3 and 4 respectively).

While the specific surface area and the carbon content are responsible for the retention behavior, these properties of the phases are not significant with respect to the selectivity, even in the case of typical RP analytes such as ethylbenzene/ toluene, and for triphenylene/o-terphenyl ( shape selectivity ) they are not relevant at all. 

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