Cyano phase

Diiren, Germany) BTR Separations (Wilmington, DE) Zorbax Pro 10/60 CN Alkyl cyano phase on silica 10 p, 60 A ... 

Silica monolithic columns with a cyano phase 103 O n... 

Among bonded phases of intermediate polarity the so-called cyano phases eqjoy the greatest popularity. Some sflanizing agents which can be used for the preparation of cyano phases are listed in Table VI. Cy-... 

Retention on these supports is adaquetely described by the adsorption displacement model. Nevertheless, the adsorption sites are delocalized due to the flexible moiety of the ligand, and secondary solvent effects play a significant role. The cyano phase behaves much like a deactivated silica toward nonpolar and moderately polar solutes and solvents. Cyano propyl columns appear to have basic tendencies in chloroform and acidic tendencies in methyl tertiobutyl ether (MTBE)... 

Acidic solutes can localize on cyano groups of the bonded phase. The cyano phase is very versatile and has been proposed as the unique stationary phase in an expert system (22). In re-versed-phase mode, CN-bonded silica exhibits better selectivities than alkyl-bonded silica toward proteins and peptides. 

In addition to reversed-phase separations, two examples were found for analysis on non-end-capped cyano-modihed columns (Spherisorb CN, Waters) separating TA of highest hydrophobicity, namely bemesetron (log P 4.19, Table 1, Fig. 1) [37] and benztropine (log P 4.27, Table 1, Fig. 1) [59], Cyano-phases are of low hydrophobicity, allow dipolar and ionic interactions and are thus in principle suitable for normal- and reversed-phase applications. 

FIGURE 4-9. Comparison of retention of antihistamines on different columns. Sample components 1. phenylephrine 2. phenylpropanolamine 3. naphazoline 4. chlorpheniramine. Columns 4 mm ID x 30 cm /xBondapak phase, (a) Cyano phase. (b) Phenyl phase, (c) C18 phase. Mobile phase methanol/water containing 0.005 M heptane sulfonic acid (PIC-B-7). Flow rate 2 mL/min in a and 3 mL/min in b and c. Detector UV at 254 nm, 0.1 AUFS. 

Different polar functional groups bonded onto silica can also be used for normal phase. The most frequently used bonded phases are amino-, diol-, cyano-, and nitro-groups. These phases, when used in the normal mode, are similar to adsorption onto silica gel. The use of bonded-phase columns in the normal phase mode is shown in Figure 5-44. There is a different order of elution on the amino-bonded phase compared to the cyano phase and different elution than on silica (ortho < meta < para), which is not shown. This is due to interactions with the functional groups on the packing rather than solely with the hydroxyl groups on the silica gel. 

Having determined that the high polarity cyano phase and the liquid crystal phase provide the best separation of the compounds likely to be found as components of the pheromone blend of H. virescens and H. subflexa, we analyzed a complex mixture of positional and geometrical isomers of 16 carbon aldehydes, alcohols, and acetates on these two columns (Figure 7). As noted earlier, the elution order of Z- and JE-isomers is opposite on the two phases. Aldehydes elute first on both phases. The alcohols are retained more than the acetates on the high polarity cyano phase, but the elution order of alcohols and acetates is reversed on the liquid crystal phase. While neither phase separated all of the synthetic mixture, the combination of separations obtained on both columns enabled us to pursue the... 

The cyano phase may physically collapse in solvents of intermediate polarity and it is recommended to be used solely with nonpolar or polar solvents. If solvents of intermediate polarity are to be used, the flow should not be changed or stopped, because the back-pressure holds the bonded phase in place and this helps prevent the collapse of the packed bed [13]. 

The specific chemical interactions from the stationary phase have been approached in the same manner. Snyder (95) first proposed that the three types of bonded phases should provide maximum differences in selectivity. He assigned the amino-phase to group I, the cyano- phase to group VI, and the diol-phase to group IV. Cooper and Smith (98,99) have extensively studied the three common types of normal-phase, bonded-phase columns and, using extended solubility parameters, have experimentally located the three columns on a stationary-phase selectivity triangle, shown in Fig. 20. Both the amino-phase and the cyano-phase fall near the predictions however, the diol-phase shows significantly less... 

Because of the popularity of the technique, much work has been devoted to understanding the retention mechanism of reversed-phase chromatography. The conditions of reversed-phase chromatography require a nonpolar stationary phase, but this condition can be met by many different ligands. In fact, there are commercially available columns of at least Ci, C2, C4, C8, Ci8, C30, phenyl, and cyano functionalities, where the carbon numbers refer to the length of a fully saturated hydrocarbon chain. While the cyano phases are not highly nonpolar, they can behave in a reversed-phase manner. The question then arises as to how these different phases affect retention and the retention mechanism. 

Here it is the functional groups which dominate retention. The amino and diol phases will retain compounds with pronounced hydrogen bonding potential more strongly, while the cyano phase interacts most strongly with analytes whose polar interactions result from strong dipole moments. Complex structures may interact in a combination of these mechanisms, so relative retention is less easy to predict than with the reversed phase columns. 

The above results demonstrated the possibility of the quantitative analysis of retention times in reversed-phase liquid chromatography. In addition, a cyano-group-bonded silicone phase was constructed, and MI energy values were calculated. The sum of the MIFS and cnMIES (cyano phase) energies... 

CYANO PHASE. Silica gel chemically bonded with a CN functional group through a hydrophobic spacer. The layer has polarity between amino and di-methylsiloxane reversed-phase plates and can function with normal- or re-versed-phase mechanisms, depending on the mobile phase. 

Since the PC1-PC2 analysis only explained 61% of the variation of the database, the PC1-PC3 plots were evaluated (see Fig. 5). PCS contributed an extra 15% of the variability of the data and a plot of PC1-PC3 further differentiated between the phases. The acidic phases such as Resolve Cjg, Spherisorb ODSl, and Platinum EPS Cjg (column nos. 87, 91, and 75) could be grouped together (group E) as these possessed high acidity and total silanol activity (agp, at pH 2.7 and 7.6). Within the non-Cjg phases (group D), the majority of cyano phases could be located as a subgroup H. The PC1-PC3 plotalso differentiated the perfluorophenyl... 

D = non-C18 phases E = acidic phases F = perfluorophenyl phases G = highly hydrophobic phases H = cyano phases... 

All r values are small, which refleds the minor difference between the stationary and mobile phases with respect to this interaction. The r values of the polar embedded phases (symmetry shield) are dearly higher than those of all the other columns, confirming the n-/jr-electron activity of the incorporated carbamate moieties. The nitrile phase also shows a relatively prominent r parameter, which is easily traceable from the electronic structure of the surface groups. Whilst all other parameters of the cyano phase resemble those of the C4 and Cg phases, the r parameter indicates a higher contribution of electron interactions than with any other of the tested columns. Nevertheless, the nitrile phase r parameter is the smallest in its parameter set, whereas its n parameter is 5.5 times the size. It can be concluded that the Zorbax SB 300 CN column mainly behaves as a reversed phase in the given system. 

The dipolarity/polarizability parameter s closes the list of the interaction parameters from Eq. (5). Again, the data show a negative sign, indicating more pronounced dipole or induced-dipole activity in the eluent than in the stationary phase. Principally, phases with higher carbon load show weaker dipolar interactions and thus more strongly negative s parameters. As expected, the polar embedded phases and the cyano phase exhibit smaller values. The difference between Symmetry Shield Cjg and Cg reflects the differences in the steric effects of the alkyl chains. 

---