Download or read book Investigating a Model Reversed phase Liquid Chromatography Stationary Phase with Vibrationally Resonant Sum Frequency Generation Spectroscopy written by Arthur D. Quast and published by . This book was released on 2011 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reversed-phase liquid chromatography (RPLC) is a widely used technique for analytical separations but routinely requires empirical optimization. Gaining a better understanding of the molecular reasons for retention may mean more efficient separations with fewer trial and error runs to obtain optimized separations. Vibrationally resonant sum frequency generation (VR-SFG) is a surface specific technique that has allowed for in situ examination of model RPLC stationary phases under various solvent and pressure conditions. In order to improve on past work with model RPLC stationary phases two challenges had to be overcome. First, improved vibrational mode assignments of the C18 stationary phase were needed for proper understanding of this model system. Second, the synthesis of back-surface reference mirrors used in these VR-SFG experiments allowed us to better correct the relative intensities of the various spectral peaks present in typical spectra. After examination of model RPLC systems under various conditions, we have found that these model substrates have a significant amount of interference from nonresonant signal. This interference of resonant and nonresonant signals on fused silica surfaces has not been previously examined and further studies of the model RPLC stationary phase must properly deal with the non-negligible nonresonant interference that is present. We have seen changes in the VR-SFG spectra of these model systems under a variety of conditions including elevated pressure, however the changes are mostly due to nonresonant interference. These spectral changes, although apparently not solely from structural changes, need to be investigated further to better understand the molecular basis of retention in model RPLC systems.
Download or read book Reversed Phase High Performance Liquid Chromatography written by Ante M. Krstulovic and published by . This book was released on 1982-05-04 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive problem-solving approach to reversed-phase high-performance liquid chromatography covering the theoretical aspects and practical information needed in diverse areas of research. Also reviews RPLC applications in the biomedical/biochemical field.
Download or read book Chromatographic and Nuclear Magnetic Resonance Investigations of Reversed phase Liquid Chromatographic Stationary Phase Conformation and Mobility written by Scott T. Shearer and published by . This book was released on 1997 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Spectroscopic Study of Compressible Mobile Phase and Stationary Phase Behavior in Chromatography written by Lawrence R. Baker and published by . This book was released on 2008 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: Raman spectroscopy, laser-induced fluorescence, and sum-frequency generation (SFG) spectroscopy are used to investigate the behavior of compressible mobile phases and stationary phases under a variety of chromatographic conditions. Efforts to understand and optimize separations employing compressible mobile phases have been limited by a lack of understanding of the mobile phase density gradient. Mobile phase compressibility leads to gradients in linear velocity and solute retention and affects separation speed and efficiency, especially in packed columns. This work describes on-column density measurement of CO2, a common carrier fluid for SFC and SGC, in packed capillary columns using Raman microspectroscopy. On-column detection by laser-induced fluorescence is used to observe the effect of the mobile phase density gradient on separation speed and efficiency, and experimental efficiency is compared to a theoretical model. Additionally, SFG spectroscopy allows for probing the structure of model monomeric and polymeric C18 stationary phases under pressure; this provides a basis for correlating selectivity with pressure-induced structural changes in stationary phase materials. Together, this work provides a more complete understanding of the role of column pressure and fluid compressibility on the speed, efficiency, and selectivity of chemical separations.
Download or read book Liquid Chromatography written by R. Kaliszan and published by Elsevier Inc. Chapters. This book was released on 2013-01-08 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: In view of linear free-energy relationships, LFER, chromatographic systems are “free-energy transducers,” translating differences in the structure of analytes into quantitative differences in physicochemical properties, like retention parameters. Hence, quantitative structure property (retention) relationships, QSP(R)R, bear valuable information on analytes and the separation systems involved. We illustrate here what can be achieved from the statistically valid and physically meaningful quantitative structure-retention relationships, QSRR. In particular, one can predict retention data, confirm identification, and optimize conditions of separation of given structurally defined analytes. Also, QSPR can shed light on the molecular mechanism of separation operating on specific stationary phases. Additionally, one can assess such properties of drug analytes of pharmacokinetic importance, like lipophilicity and acidity. Also, differences in interactions of xenobiotics with biomacromolecule components of chromatographic systems can conveniently be quantified. By means of QSRR, the chromatographic behavior of analytes in diverse separation systems can be related to their pharmacological properties.
Download or read book Synthesis and Characterization of Stationary Phases for Reversed phase Liquid Chromatography written by Dale Allen Shoemaker and published by . This book was released on 1992 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluation of PS DVB Stationary Phase in Reversed phase High Performance Liquid Chromatography written by Susan Pedigo and published by . This book was released on 1987 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Supercritical Fluid Chromatography And Micro hplc written by M. Yoshioka and published by VSP. This book was released on 1989 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: First published in 1988. Routledge is an imprint of Taylor & Francis, an informa company.
Download or read book Investigation and Applications of Micellar Mobile Phases in Reversed Phase Liquid Chromatography written by Jun-Liang Lin and published by . This book was released on 1988 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigating Reaction Schemes for Improving Silica Based Monomeric Bonded Stationary Phases for Reversed Phase Liquid Chromatography written by Michael David Bair and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: Central to the advancement of reversed-phase high-performance liquid chromatography (RPLC) is to develop new synthetic strategies for manufacturing stationary phase materials. Methods to improve the efficiency, retention properties, and chemical stability of stationary phases are always being investigated. The work presented focuses on two new synthesis schemes aimed at improving monomeric silica-based stationary phases in these respects. The first study involves "pre-capping" Type-B silica. Previous work showed that monomeric stationary phases made by pre-treating the silica surface with small amounts of trimethylsilane (TMS) reagents prior to C18 silanization showed vast improvements in the chromatographic efficiency, phase loading, and retention with a maximum at approx. 5% pre-capping. It was concluded that this pre-capping step improved efficiency by selectively neutralizing the most reactive highly-acidic silanol sites, so-called silanol "hot spots," producing a more energetically-homogenous surface prior to exhaustive C18 derivatization that subsequently yielded a more evenly-distributed alkyl bonding arrangement. These previous studies were performed on Type-A silica, an older variety of silica gel material containing higher levels of metal impurities than the Type-B silica used today. It has since been argued that metallic impurities are the primary cause of silanol hot-spots, and that pre-capping Type-B silica would have little or no effect, however the experimental evidence has yet to be produced, and there exists the potential for heterogeneous silanol reactivity inherent in the amorphous silica gel regardless of purity. The purpose of the work presented here is to determine the effects of TMS pre-capping on Type-B silica as compared to the previous Type-A results, with the goal of establishing pre-capping protocol for Type-B silica and to form a better understanding of its chemistry. The current work performed on three Type-B silica substrates of various physical and chemical properties demonstrated optimal TMS pre-capping at approximately 2.5%. The results at this level show only a slight improvement in efficiency for non-polar compounds ( 25%) was observed for some drug compounds and bases under buffered conditions, with the magnitude of the improved efficiencies correlating with metal impurity content and physical parameters of the silica substrate. Pre-capping also resulted in a slight decrease in retention and hydrolytic stability due to a decrease in bonded phase density. The results lend supporting evidence that metal impurities are the primary source of highly acidic silanols, but they also suggest a means to improve efficiency of basic analytes on certain Type-B silica substrates. It was concluded that TMS pre-capping Type-B silica is best done at low levels (
Download or read book Characterization of Stationary Phases for Reversed phase Liquid Chromatography written by Hendrikus Antonius Claessens and published by . This book was released on 1999 with total page 283 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Synthesis and Characterization of Reversed Phase Stationary Phases for High Performance Liquid Chromatography written by Karen Wink Barnes and published by . This book was released on 1986 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reversed phase liquid chromatography (RPLC) is a widely used separation technique today. The stationary phase, composed of hydrocarbon moieties chemically bound to a silica support, is commonly prepared by refluxing the silica with a reactive silane in an appropriate solvent. Siloxane bonds, Si-O-Si, are formed. There are limitations to RPLC in that nonhomogeneous surface coverages, detrimental to efficient separations, result from the bonding process, and because the reaction is never complete due to steric restrictions. Also, silica is soluble at high pH values, and the Si-C bond binding the hydrocarbon to the silica is labile at low pH ranges. Thus, the usable pH range for silica stationary phases is 2.5 to 7.5, and often this range is too narrow to allow the separation of a mixture. The use of ultrasonic cavitation to catalyze silane bonding was investigated to dtermine whether the vigorous ultrasonic process would drive reagents into the surface pores and better distribute the hydrocar bonaceous reagent, thereby producing a more efficient stationary phase. Tandem reactions proved that ultrasonic bonding procedures are as effective as the refluxed, and that the chromatographic efficiency of the ultrasonic phases was comparable, if not superior, to the refluxed. Chromatographic tests also indicated the ultrasonic phases were comparable to commercially available phases. The reproducibility of the reactions and the effect of acoustic power and heat were also investigated. A second set of experiments investigated substitution of alumina for silica because the alumina crystalline structure remains intact over a pH range of 2 to 12. A trifunctional modification scheme generating a thick cross-linked hydrocarbon matte was used because the Al-0 bond is susceptible to hydrolysis, which strips the bound hydrocarbons, by polar RP solvents. Five aluminas were bonded and tested for chromatographic utility. Reaction conditions were optimized, and ultrasonic bonding was investigated. It was found that alumina with a sufficiently active surface is modifiable, and that the modified surface is remarkably stable for use with acidic and basic buffers and in neutral, polar solvent mixtures. The chromatographic utility of alumina phases was demonstrated and compared with the silica results.
Download or read book Investigation of Diamond packed Columns for Reversed phase Liquid Chromatography written by Anuttra Nuamthanom and published by . This book was released on 2002 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation and applications of micellar mobile phases in reversed phase liquid chromatography pluralistic era written by Jun-Liang Lin and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Phenomenological Investigation of N ALKLY Bonded Phases in Reversed phase Liquid Chromatography written by Shih Hsien Hsu and published by . This book was released on 1986 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Investigation of Factors Affecting the Reversed Phase Ion Pairing Approach to High Performance Liquid Chromatography written by Sat Paul Sood and published by . This book was released on 1976 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of the Interactions in Normal phase Liquid Chromatography by Chromatographic and Ultraviolet Spectral Techniques written by Larry Dean Olsen and published by . This book was released on 1990 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
