Influence Of Organic Modifier Research Articles

Capillary zone electrophoresis and micellar electrokinetic capillary chromatography of some nonsteroidal antiinflammatory drugs (NSAIDs)

The possibilities of capillary electrophoresis (CE) and micellar electrokinetic capillary chromatography (MEKC) were investigated for the qualitative analysis of some non-steroidal antiinflammatory drugs. In CE the influence of the pH of the buffer and its ionic strength were investigated for a test mixture of six compounds. Also the influence of organic modifiers was studied. The best conditions were applied to the separation of 15 drugs. In MEKC the influence of the concentration of SDS in buffers with pH ranges of 8.0–9.0 was investigated. The influence of an organic modifier, namely acetonitrile was discussed, whereby an interesting phenomenon of change in retention behaviour was noted. A combination of CE and MEKC allows the separation of the 15 above-mentioned compounds and forms an interesting alternative to HPLC.

Description of retention mechanism by solvophobic theory : Influence of organic modifiers on the retention behaviour of homologous series in reversed-phase liquid chromatography

The retention behaviour of different homologous series (2 ⩽ n c ⩽ 22) was studied on three different bonded chain lengths (C 1, C 14 and C 18) and in aqueous—organic solvent mixtures commonly used in reversed-phase liquid chromatography [methanol, acetonitrile and tetrahydrofuran (THF)]. For all solutes (ligands) without π electrons, and regardless of bonded chain length, the plots log k′ vs. ϕ (organic modifier ratio) in methanol—water or acetonitrile—water are correlated with the evolution of surface tension of these mixtures. On the other hand, for ligand which possess π electrons, there is a modification in these curves which is due to specific π—π interactions added to the pure solvophobic effect. In this respect, pure methanol was found to be a better eluent than pure acetonitrile excepted for the ligands with π electrons, for which the opposite was observed. For the THF—water mixtures, the plots of log k′ vs. ϕ were always below those for methanol—water or acetonitrile—water. Moreover, the plots of log k′ vs. n c did not increase linearly. In this pure solvent, retention is due to an exclusion mechanism. These results were in agreement with conformational infrared studies of alkyl chains in THF, methanol and acetonitrile. The overall results could rationalize the fact that retention prediction based on methylene selectivity was often erroneous when THF was used. Nevertheless, they show the possibility of optimizing separations of homologous series from the results obtained from a single gradient experiment with any commonly used organic modifier.

Polyalkylenes used as stationary phases for preparative reversed-phase liquid chromatography

Polyethylene and polypropylene were employed as stationary phases for preparative liquid chromatography and compared with LiChroprep RP-18. Polyalkylene phases are chemically stable and have homogeneous hydrophobic surfaces, but they are physically less resistant than silica-based phases. The influence of organic modifiers and salt ions on the capacity factors of aromatic hydrocarbons and peptides was determined. Peptides prepared by solid-phase peptide synthesis were purified on polypropylene. The results demonstrate the usefulness of polyalkylenes in preparative reversed-phase liquid chromatography, particularly for basic peptides.

Influence of organic modifiers on the isocratic reversed-phase high-performance liquid chromatography of flavonol glycosides from brewer's hops

The elution order in reversed-phase high-performance liquid chromatography of certain flavonol glycosides found in hops was influenced by the concentration of tetrahydrofuran (THF) used under isocratic conditions. Whereas acceptable resolution of all compounds of interest was obtained with the appropriate water—THF mixtures, solvent mixtures containing methanol instead of THF were much less satisfactory. The solvent strength of acetic acid, when included in eluent mixtures was found to be greater than that of THF, which was in turn greater than that of methanol.

Influence of organic modifiers on the rentention behaviour in reversed-phase liquid chromatography and its consequences for gradient elution

In a previous paper it was shown that the key to the description and understanding of retention behaviour under gradient conditions in reversed-phase liquid chromatography lies in the relationship between the isocratic capacity factor ( K) and the volume fraciton of organic modifier (ϕ). Hence, the presentation of extensive data on this relationship in different organic modifier systems offers possibilities for evaluating and refining existing gradient elution models, such as the one of Snyder and co-workers. An extensive study of 32 aromatic compounds in aqueous system containing 10–100% of methanol, acetonitrile and tetrahydrofuran as organic modifiers under isocratic conditions is described. Two major conclusions are drawn that have consequences for gradient elution. Firstly, the relationship between in k and (ϕ) is generally non-linear, in accordance with previous statements. Secondly, the rate of change of in k and (ϕ) can be solute dependent. Systematic changes in the slope of the in k versus (ϕ) curves with absolute retention are observed for methanol and tetrahydro- furan as organic modifiers. It is shown that this conclusion leads to optimal gradients, which are convex rather than linear.