Chromatographic systems reverse phase

Retention factor A measure of the amount of time an analyte spends in the stationary phase relative to the mobile phase Retention time The time taken for an analyte to travel from the point of injection to the point of detection within an HPLC system Reverse phase chromatography Describes the chromatographic separation in which the stationary phase is nonpolar and the mobile phase is composed of an aqueous, moderately polar liquid Robustness A measure of a method s ability to withstand small but deliberate changes in the method parameters it provides an indication of its reliability during normal usage Selectivity factor See separation factor... 

The sulfanes are soluble in carbon disulfide, benzene, tetrachloromethane, and dry diethylether (decreasingly so in that order) while alcohols and aqueous systems initiate rapid decomposition. For this reason a report on the chromatographic separation of the sulfanes H2S by reversed-phase HPLC using methanol as an eluent [35] was shown to be in error The peaks observed in the chromatogram have to be assigned to bismethoxy oligosulfanes... 

From the general framework of the Snyder and Soczewinski model of the linear adsorption TLC, two very simple relationships were derived, which proved extremely useful for rapid prediction of solute retention in the thin-layer chromatographic systems employing binary mobile phases. One of them (known as the Soczewinski equation) proved successful in the case of the adsorption and the normal phase TLC modes. Another (known as the Snyder equation) proved similarly successful in the case of the reversed-phase TLC mode. 

Zarzycki and coworkers [77] studied the influence of temperature on the separation of cholesterol and bile acids using reversed-phase stationary phases. The best chromatographic conditions for the separation of mnlticomponent samples of steroids were chosen. Experiments were performed on wettable plates with RP-18W and at the temperatnres of 5, 10, 20, 30, 40, 50, and 60°C. The studies showed (Figure 9.9) that the degree of separation in the high-temperature region can be increased by an improvement of the efficiency of the chromatographic system. However, a relatively weak retention-temperatnre response for the studied steroids was observed. 

The choice of the chromatographic system depends on the chemical character of the extracts being separated. The mobile phase should accomplish all requirements for PLC determined by volatility and low viscosity, because nonvolatile components (e.g., ion association reagents and most buffers) should be avoided. It means that, for PLC of plant extracts, normal phase chromatography is much more preferable than reversed-phase systems. In the latter situation, mixtures such as methanol-ace-tonitrile-water are mostly used. If buffers and acids have to be added to either the... 

Radke et al. [28] described an automated medium-pressure liquid chromatograph, now commonly called the Kohnen-Willsch instrument. At present, the method is widely used to isolate different fractions of soluble organic matter (for instance, as described in Reference 29 to Reference 31). A combination of normal phase and reversed-phase liquid chromatography has been used by Garrigues et al. [32] to discriminate between different aromatic ring systems and degrees of methylamine in order to characterize thermal maturity of organic matter. 

De Jong, G. J. Optimization and characterization of silica-based reversed-phase liquid chromatographic systems for the analysis of basic pharmaceuticals./. Chromatogr. A 2000, 897,1-22. 

Welerowicz, T., Buszewski, B. The effect of stationary phase on lipophilicity determination of 3-blockers using reverse-phase chromatographic systems. Eiomed. Chromatogr. 2005, 39, 725-736. 

The PRISMA model was developed by Nyiredy for solvent optimization in TLC and HPLC [142,168-171]. The PRISMA model consists of three parts the selection of the chromatographic system, optimization of the selected mobile phases, and the selection of the development method. Since silica is the most widely used stationary phase in TLC, the optimization procedure always starts with this phase, although the method is equally applicable to all chemically bonded phases in the normal or reversed-phase mode. For the selection of suitable solvents the first experiments are carried out on TLC plates in unsaturated... 

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

A number of recommendations have been made in the development of quantitative chromatographic methods. The American Society for Testing Materials — using as a benchmark the reversed phase separation of benzyl alcohol, acetophenone, benzaldehyde, benzene, and dimethylterephthalate — discovered substantial laboratory-to-laboratory differences in quantitative analysis.53 These compounds are routinely used to test column performance or for system suitability testing. A followup study, using benzyl alcohol, acetophenone, p-tolualdehyde, and anisole, showed that measurement of... 

Gilpin, R. K., Jaroniec, M., and Lin, S., Dependence of the methylene selectivity on the composition of hydro-organic eluents for reversed-phase liquid chromatographic systems with alkyl bonded phases, Chromatographia, 30,393, 1990. 

McKern, N. M., Edskes, H. K., and Shukla, D. D., Purificatiion of hydrophilic and hydrophobic peptide fragments on a single reversed phase high performance liquid chromatographic system, Biomed. Chromatogr., 7, 15, 1993. 

Jandera, P., Holcapek, M., Theodoridis, G. (1998). Investigation of chromatographic behavior of alcohol ethoxylate surfactants in normal-phase and reversed-phase systems using high-performance liquid chromatography-mass spectrometry. J. Chromatogr. A 813(2), 299-311. 

Relative retention times for niclosamide and 570 drugs and related compounds on eight chromatographic systems were reported. Reversed-phase high-pressure chromatography employing octadecylsilanized columns was described [69]. 

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