Cyanopropyl-bonded phase

A more or less opposite goal was pursued by de Smet et al. (574], who attempted to reduce the number of stationary phases to a single one, by choosing a cyanopropyl bonded phase of intermediate polarity, which can be used in both the normal phase and the reversed phase mode (see figure 3.8). Furthermore, because of a clever choice of modifiers, the total number of solvents required was restricted to six n-hexane, dichloromethane, acetonitrile and THF for NPLC and the latter two plus methanol and water for RPLC. A variety of drug samples could be separated with a selected number of binary and ternary mobile phase mixtures. 

In RPC systems, the retention is weaker on weakly or moderately polar stationary phases such as on phenyl- or cyanopropyl-bonded phases than on an alkylsilica phase. RPC separations on phenyl or cyanopropyl columns may show selectivities differing from those observed on Cix or Cs phases, but their main advantage is lower concentration of organic solvent required to elute weakly polar samples, which may potentially reduce the separation time. For the great majority of samples, however, the selectivity of separation is generally better on alkylsilica-bonded phases. On the other hand, retention of hydrophilic samples can be increased and their separation improved on columns with a high amount of bonded carbon (polymeric bonded phases) or on hydrophobic organic polymeric materials such as styrene-divinylbenzene copolymers. 

The aminoalkyl and the cyanopropyl bonded phases are commonly used in that they can be equally well used in either the normal phase or the reversed phase mode. The versatility of the cyanopropyl column was exploited in the development of an expert system for HPLC, allowing a single column to be used for all solutes. 

A new HPLC technique has been developed for the rapid analysis of sesquiterpene phytoalexins such as capsidiol, rishitin, luminin, and phytuberol. This method employs a cyanopropyl-bonded phase column with an isocratic mixture of hexane and isopropanol. Flame ionization and UV detection were used for the analysis of capsidiol, rishitin, lubimin, phytuberol, and debneyol. Although both detectors proved to be useful, the signal response with the flame ionization detector was proportional to the mass of each of the phytoalexins, while the signal with the UV detector was proportional to the number of carbon—carbon bonds in each of the compounds. 

A cyanopropyl bonded phase has been used for the separation of the four major cinchona... 

Decrease the strength of the interaction between the compound and the solid phase. For example, if a C-18 sorbent is being used for a reversed-phase mechanism, decrease the energy of the interaction by going to a C-8 or a C-2 bonded phase or even a cyanopropyl bonded phase. 

Musch, G. and Massart, D. L. 1988. Isolation of basic drugs from plasma using solid-phase extraction with a cyanopropyl-bonded phase, 7. Chromatog., 432 209-222. 

The most popular bonded phases for normal-phase chromatography are aminopropyl, cyanopropyl, and diol. Other polar bonded phases, including bonded ion exchangers, can be used as well. Another, less commonly used polar bonded phase is the nitrophenyl bonded phase. The retentivity of the aminopropyl and the diol phase is comparable to that of the oxides. Cyanopropyl and nitrophenyl phases have a smaller retentivity. Although differences in selectivity can be found for the different bonded phases, they are typically small. Thus the elution order of most members in a family of related compounds is largely preserved from packing to packing. For example, in a study of the elution behavior of steroids on silica, and aminopropyl and cyanopropyl bonded phases, an inversion in elution order was ol rved only for two to four pairs out of IS analytes (16). 

The concentration of surfactant in the solutions used as mobile phases in ion-pair chromatography should not pass the cmc value. It was known that the solute retention was different when micelles were present in the mobile phase [5-10]. Figure 3.3 illustrates the dramatic retention change observed when the surfactant cmc is passed [11]. The retention factor of benzyl trimethylammonium bromide (BTAB), a cationic solute, is plotted versus the amount of SDS adsorbed on the stationary phase (a cyanopropyl bonded phase). The BTAB retention factor is directly proportional to the SDS... 

Berthod studied the adsorption of SDS on five different Hypersil stationary phases [11]. Five 10 cm x 4.6 mm i.d. LC columns were specially selected for the study. All experiments were done in a thermostatic bath at 30°C. The amount of SDS adsorbed on the phases was determined by crosschecking the results obtained with (i) the breakthrough method, (ii) controlling the concentration of the effluent solution, and (iii) by the stripping method. The 3 results were in agreement within an 8% experimental error. Figure 4.2 presents the SDS adsorption on bare Hypersil , CPS Hypersil , a cyanopropyl bonded phase, SAS Hypersil , a methyl bonded phase, MOS Hypersil , an octyl bonded phase and ODS Hypersil , an octadecyl bonded phase. The physicochemical properties of these phases are listed in Table 4.1. A very differing behavior was obtained... 

The structure of SDS and CTAB surfactant layer adsorbed on porous silica was studied by NMR. The C18 (Microsorb ODS, 5 pm, 6 nm pore diameter) and C8 (Microsorb) bonded phases were studied first [17]. The cyanopropyl bonded phase (Microsorb), was also studied [18]. Cross polarization (CP), magic angle spinning (MAS) with high power proton... 

B.L. Lavine, S. Hendayana, Y. He and W.T. Cooper, Solid-State NMR Studies of Ionic Surfactants Adsorbed on Cyanopropyl Bonded Phases Implications for MLC, J. Colloid Interface Sci., 179 341 (1996). 

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