Separator cyanopropyl-bonded silica

Haliclonacyclamine F (25), arenosclerin D (26), and arenosclerin E (27) have been recently isolated from the sponge Pachychalina alcaloidifera endemic in Brazil [26]. The alkaloids 25-27 were isolated from the cytotoxic, antibiotic, and antituberculosis MeOH crude extract of P. alcaloidifera by a series of separations on silica-gel and cyanopropyl-bonded silica-gel columns. The structures of compounds 25-27 were established by the same approach employed for the structural elucidation of haliclonacyclamine E (13) and arenosclerins A-C (14-16) [18], as well as by comparison with NMR data for this last series of alkaloids. The alkaloids 25-27 displayed moderate cytotoxic activity against SF295 (human CNS), MDA-MB435 (human breast), HCT8 (colon), and HL60 (leukemia) cancer cell lines. 

Smith and Sanagi reported the packed-column SFC of benzodiazepines (diazepam, lorazepam, lormetazepam, nordazepam, temazepam, es-trazolam, chlordiazepoxide, triazolam, cloxazolam, ketazolam, and lopra-zolam) with methanol-modified carbon dioxide as the mobile phase [29]. The effect of methanol concentration on separation was studied on three columns polystyrene-divinylbenzene, octadecylsilane, and cyanopropyl-bonded silica columns. They concluded that proportion of methanol has marked effect on the selectivity of compounds containing different functional groups. 

In the liquid chromatographic methods, separation of nitrofurans is generally carried out on nonpolar reversed-phase columns, the preferred sorbent being octadecyl bonded silica (Tabic 29.5). Polar columns containing cyanopropyl-based sorbents (164, 165) have also been used for die isocratic separation of nitrofuran residues isolated from edible animal products. A literature survey shows that there exists a clear preference for acidic mobile phases containing acetonitrile as the organic modifier (Fig. 29.5.1). 

Polar bonded phases for normal-phase separations have recently gained popularity. These include the dihydroxypropyl propyl ether (diol), aminopropyl, cyanopropyl, and nitrophenyl bonded silicas. These phases are advantageous to silica because they are less active and, yet, produce similar interactions, require shorter equilibration times, and are influenced less by the water content of the mobile phase. The retention of most analytes upon the diol and amino phases is similar to that of the parent silica and alumnia, whereas the cyanopropyl and nitrophenyl phases generally show less retention. 

Chemically bonded silica gels with cyanopropyl, aminopropyl, and diol functional groups are also available and each has been used for normal-phase as well as reversed-phase separations. Polymeric-based packings are available and can be used for ion-exchange or reversed-phase applications. Cross-linked polymeric based packings have been combined with ion-exchange materials to create a more pH-stable stationary phase. Graphitized carbon... 

An ion-pair reagent was not wholly essential for separation, and it was found that the optimum concentration was probably below 0.01 mole/liter. Different chain lengths up to C4 caused minor modifications in the order of / / values for the eight acids. For the aromatic dicarboxylic acids in chloroform-tetrahydrofuran (2 1) on silufol (175), the Ry order found was isophthalic (0.5), terephtha-lic acid (0.49), 2-hydroxyethyl isophthalate (0.33), 2-hydroxyethyl-terephthalate (0.35), and the bis ester (both 0.18). Cj and cyanopropyl-bonded high performance silica gel layers in conjunction with ion-pair reagents have been employed to separate dihydroxybenzoic acids (175a,175b). 

Silica has often been modified with silver for argentation chromatography because of the additional selectivity conferred by the interactions between silver and Jt-bonds of unsaturated hydrocarbons. In a recent example, methyl linoleate was separated from methyl linolenate on silver-modified silica in a dioxane-hexane mixture.23 Bonded phases using amino or cyano groups have proved to be of great utility. In a recent application on a 250 x 1-mm Deltabond (Keystone Scientific Belief onte, PA) Cyano cyanopropyl column, carbon dioxide was dissolved under pressure into the hexane mobile phase, serving to reduce the viscosity from 6.2 to 1 MPa and improve efficiency and peak symmetry.24 It was proposed that the carbon dioxide served to suppress the effect of residual surface silanols on retention. 

Are the primary differences in polarity Partition columns are available that vary in polarity from nonpolar (octyldecyl), through intermediate polarity (octyl and cyanopropyl), to polar (silica). Some columns have similar polarities, but differ in their specificity. Qg and the phenyl column have similar polarities, but Ci8 separates on carbon chain length, while phenyl separates fatty acids on both carbon number and number of double bonds. Phenyl columns also resolve aromatic compounds from aliphatic compounds of similar carbon number. In another example of similar polarities, C8 is a carbon number separator while cyanopropyl selects for functional groups. 

Bonded phases may be used in both normal and reverse phase chromatography. When normal phase chromatography is done on bonded phase packings, the packing is more polar than the mobile phase. Polar bonded phases such as the cyanopropyl and aminopropyl functionalities are popular for this use. These bonded phases are less subject to changing retention times of compounds because water is adsorbed from the mobile phase onto the stationary phase, a frequent concern when using bare silica packings for normal-phase separations. 

By LSC we include separations on any polar, nonionic phase, e.g., alumina, silica, or bonded-phase packings such as cyanopropyl, aminopropyl, and diol-phase. 

In order to accomplish the desired separation, the selection of appropriate stationary phase and eluent system is imperative. The most commonly used stationary phases in normal-phase chromatography are either (a) inorganic adsorbents such as silica and alumina or (b) moderately polar chemically bonded phases having functional groups such as aminopropyl, cyanopropyl, nitrophenyl, and diol that are chemically bonded on the silica gel support [16]. Other phases that are designed for particular types of analytes have also... 

The extraction of aromatic hydrocarbons (Fig. 5.5) from crude oil uses two sorbents in series, first a cyanopropyl column attached to a second silica column. In this procedure, aromatic hydrocarbons are sorbed on both the cyanopropyl sorbent and on the silica sorbent. The heteroatom hydrocarbons (containing nitrogen, oxygen, and sulfur) are trapped on the cyanopropyl sorbent and eluted as a separate fraction from the silica column. Because the major interaction of aromatic heterocyclic hydrocarbons is through hydrogen bonding to the surface of the sorbent, the cyanopropyl sorbent is easier to elute than a silica sorbent alone. For this reason, the cyanopropyl column is used before the silica column. The separation of hydrocarbons from crude oil is an example of normal-phase chromatography that has been performed for many years on silica gel prior to the introduction of SPE. 

The extraction of A-nitrosopyrrolidine (Fig. 5.8) from bacon involves the use of a cyanopropyl column, and the mechanism is hydrogen bonding between the amino nitrogen of the A-nitrosopyrrolidine and the underlying silica surface, as well as an interaction between the propyl carbons and the analyte. The sample is applied as a solution of hexane and methylene chloride, which solubilizes the bacon and does not interfere with the separation of the analytes by hydrogen bonding. The eluent contains methanol, which breaks up the bonding and effectively solubilizes the A-nitrosopyrrolidine. 

NMR-guided fractionation yielded benzomalvin C (7) from P. raistrickii in our study. The methylene chloride extract of H10BA2 was resolved by LH-20 size exclusion chromatography (chloroform/methanol, 1 1) into ten fractions. Fraction 2 was further resolved by reverse-phase HPLC (Rainin C8 semipreparative, 50% methanol/water - 100% methanol), yielding eighteen fractions. Fraction 13 of this separation exhibited most of the aromatic peaks of interest in the HNMR, so it was applied to a silica gel HPLC colunm (10% isopropanol/hexane) and was ultimately purified by HPLC, using a bonded phase cyanopropyl column (Rainin CNPr, 20% isopropanol/hexane). 

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