Organic modifiers nature

Gonnet, C., and Marichy, M. (1980). Chromatographic analysis of pharmaceutical products of toxicological interest in chemically bonded thin layers. Influence of the organic modifier nature on selectivity. J. Liquid Chromatogr. 3 1901-1912. 

Flash chromatography is widely employed for the purification of crude products obtained by synthesis at a research laboratory scale (several grams) or isolated as extracts from natural products or fermentations. The solid support is based on silica gel, and the mobile phase is usually a mixture of a hydrocarbon, such as hexane or heptane, with an organic modifier, e.g. ethyl acetate, driven by low pressure air. (Recently the comparison of flash chromatography with countercurrent chromatography (CCC), a technique particularly adapted to preparative purposes, has been studied for the separation of nonchiral compounds [90].)... 

The nature of the modifier and the modifier concentration impact both retention and selectivity in packed column SFC. SFC offers considerable flexibility in modifier selection because nearly all commonly used organic modifiers, including methanol and acetonitrile, are miscible with CO,. In contrast, methanol and acetonitrile are rarely used as modifiers in normal phase LC because they are immiscible with hexane [68]. 

The CHI parameter approximates the percentage of organic modifier in the mobile phase for eluting the compounds and can be used for high-throughput determination of physicochemical properties (50-100 compounds per day). CHI is a system property index, and depends on the nature of the stationary phase and the organic modifier as well as the pH of the mobile phase for ionizable compounds. 

Much LC-MS work is carried out in a qualitative or semi-quantitative mode. Development of quantitative LC-MS procedures for polymer/additive analysis is gaining attention. When accurate quantitation is necessary, it is important to understand in depth the experimental factors which influence the quantitative response of the entire LC-MS system. These factors, which include solvent composition, solvent flow-rate, and the presence of co-eluting species, exert a major influence on analyte mass transport and ionisation efficiency. Analyte responses in MS procedures can be significantly affected by the nature of the organic modifier used in the RPLC... 

The retention depends on the nature of both the stationary phase and the organic modifier in the mobile phase. Therefore CHI values obtained using different systems show different sensitivities towards solute characteristics. This has been studied systematically and used for the quantitative calculation of solute molecular descriptors (H-bond donor capacity, H-bond acceptor capacity and dipolarity/polarizability) for application in a general solvation equation [21]. 

Organo-modified natural zeolites as new tailored natural materials for removal of cations, anions and even organic pollutants may present fairly large potential for water utility companies. The topic of this study was to examine the oxyanions removal from waters by octadecylammonium-enriched inland clinoptilolite. The 18-carbon chain consisting surfactant attached on the clinoptilolite surface, as to the organic acids of living bodies comparable substances, makes the treatment process economic on scale and cost-effective as well.7... 

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

Organic modifiers have been frequently employed in CE to increase the solubility of hydrophobic solutes in the aqueous buffer system. Unfortunately, many organic modifiers are UV absorbent and cannot be used without considerable loss of sensitivity of detection. A contactless conductivity detection system has been developed which extends the application range of UV-absorbing solvents [ 119]. As both natural pigments and synthetic dyes absorb in the visible part of the spectra, the application of UV-absorbing organic modifiers in their CE analysis does not cause detection problems. 

At present, the selection of an organic modifier is estimated from the aliphatic or aromatic nature of analytes. However, the properties of analytes often cannot be easily obtained. Examples of quantitative structure-retention relationships based on the log-P and van der Waals volume of analytes are demonstrated in Chapter 6. 

Gritti, F. and Guiochon, G., Adsorption mechanism in RFLC. Effect of the nature of the organic modifier, AnaZ. Chem., 11, 4257, 2005. 

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