Phenyl-type phases

With comprehensive GC, we can now choose a rational set of columns that should be able to tune the separation. If we accept that each column has an approximate isovolatility property at the time when solutes are transferred from one column to the other, then separation on the second column will largely arise due to the selective phase interactions. We need only then select a second column that is able to resolve the compound classes of interest, such as a phase that separates aromatic from aliphatic compounds. If it can also separate normal and isoalkanes from cyclic alkanes, then we should be able to achieve second-dimension resolution of all major classes of compounds in petroleum samples. A useful column set is a low polarity 5 % phenyl polysiloxane first column, coupled to a higher phenyl-substituted polysiloxane, such as a 50 % phenyl-type phase. The latter column has the ability to selectively retain aromatic components. 

Phenyl-Type Phases. Phenyl-type phases have been studied for a long time [58,59]. The presence of a phenyl ring on the surface of a bonded phase introduces so-called n-n interactions with some analytes that are capable of these types of interactions. This introduces an additional specificity for HPLC separations on these stationary phases. Compared to common alkyl-type phases, phenyl columns show lower methylene selectivity in other words, the separation of members of homologous series will be less selective on phenyl columns than on alkyl-modified phases. 

KayiUo, S., Deimis, G.R., and ShaUiker, R.A., An assessment of the retention behaviour of polycyclic aromatic hydrocarbons on reversed phase stationary phases selectivity and retention on C18 and phenyl-type surfaces, J. Chromatogr. A, 1126, 283, 2006. 

Powers and Sadee preferred a chemically bonded alkyl phenyl stationary phase over an octadecyl phase, because of the poor chromatographic behaviour of the latter type. 

As noticed by other authors, Pettitt and Damon117 found that a phenyl-bonded phase gave better peak shapes for the alkaloids than an octyl or octadecyl type of stationary phase. However the addition of N,N-dimethyloctylamine to the mobile phase was found to be essential in order to greatly reduce tailing of opium alkaloids (Fig. 7.9). 

Noordam et al. with a phenyl type of stationary phase reduced the analysis time, whilst Improving peak shapes and resolution of pilocarpine and its degradation products. As mobile phase, 5% potassium dihydrogen phosphate (pH 2.5) in water was found to be the most suitable. 

Beaufour, M., Morin, P., Ribet, J.-P. and Maurizot, J.-C. FIPLC quantitation of the four stereoisomers of benzoxathiepin derivatives with cellulose phenyl type chiral stationary phase and circular dichroism detection. J. Pharm. Biomed. Anal 41 544, 2006. 

Two GC columns of different polarity, stationary phase and film thickness have been evaluated. The first column was a medium polar cyanopropylphenyl phase (6% cyanopropylphenyl/94% dimethylpolysiloxane, 30 mX 0.32 mm ID, 1.8 pm film thickness, e.g. TraceGOLD TG-624) and as a second column a low polar 5%-phenyl stationary phase (5% diphenyl/95% dimethylpolysiloxane, 30 m x 0.25 mm ID, 0.25 pm film thickness, e.g. TraceGOLD TG-5MS). The TG-624 column type is a mid-polarity column ideally suited for the analysis of volatile analytes, whereas the TG-5MS column is more commonly used especially for pesticide analysis and mostly available with all laboratories. Both columns were thus tested for the applicability of the method. Either column can be used for DTC analysis (Figure 4.40). 

The spiro-type phase-transfer catalyst (188, Ar = H) possessing a C2-symmetry axis provides a single type of asymmetric environment in contrast, a newly designed spiro-type phase-transfer catalyst (188, Ar H) has two different asymmetric environments. The substituents of the binaphthyl subunits affect enantioselectiv-ity, and the 3,5-bis[3,5-bis(trifluoromethyl)phenyl]phenyl group is the best substituent of those evaluated in the anti-selective aldol reactions of glycine SchifF base 186 with aldehydes (35) (Scheme 28.21) [94]. Similarly, simpMed chiral phase-transfer catalyst 189 bearing the 3,5-bis[3,5bis(trifluoromethyl)phenyl] phenyl substituent, which is prepared in a combinatorial approach from the readily available (S)-l,l -binaphthyl-2,2 -dicarboxylic acid, effectively catalyzes syn-selective aldol reactions [95]. 

The chromatographic resolution of bi-naphthol enantiomers was considered for simulation purposes [18]. The chiral stationary phase is 3,5-dinitrobenzoyl phenyl-glycine bonded to silica gel and a mixture of 72 28 (v/v) heptane/isopropanol was used as eluent. The adsorption equilibrium isotherms, measured at 25 °C, are of bi-Langmuir type and were proposed by the Separex group ... 

In some cases a cyano-phenyl overlapping of type II was found in the solid phase of the cyanobiphenyl compounds (Fig. 30). 

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