Mass Transfer in High Performance Liquid Chromatography

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Protein and alkaloid patterns of the floral nectar in some solanaceous species

The family Solanaceae includes several melliferous plants, which tend to produce copious amounts of nectar. Floral nectar is a chemically complex aqueous solution, dominated by sugars, but minor components such as amino acids, proteins, flavonoids and alkaloids are present as well. This study aimed at analysing the protein and alkaloid profile of the nectar in seven solanaceous species. Proteins were examined with SDS-PAGE and alkaloids were analyzed with HPLC. The investigation of protein profile revealed significant differences in nectar-protein patterns not only between different plant genera, but also between the three Nicotiana species investigated. SDS-PAGE suggested the presence of several Nectarin proteins with antimicrobial activity in Nicotiana species. The nectar of all tobacco species contained the alkaloid nicotine, N. tabacum having the highest nicotine content. The nectar of Brugmansia suaveolens, Datura stramonium, Hyoscyamus niger and Lycium barbarum contained scopolamine, the highest content of which was measured in B. suaveolens. The alkaloid concentrations in the nectars of most solanaceous species investigated can cause deterrence in honeybees, and the nectar of N. rustica and N. tabacum can be considered toxic for honeybees

Overloading study of zwitterionic chiral stationary phases based on cinchona alkaloids

Nowadays, chirality has great importance in the life sciences as well as in the pharmaceutical industry. Usually the enantiomers have diverse activity in the living systems: one of the enantiomers possesses positive effect, while the other may be inactive or toxic. Thus, the separation of the enantiomers is very important. On the Cinchona alkaloid-based ZWIX(+) and ZWIX(-) zwitterionic chiral stationary phases, simultaneous anion- and cation-exchange takes place. These stationary phases are good choice for the separation of the enantiomers of chiral acids, amines, amino acids and peptides. Nonlinear chromatography was used for the investigation of the retention mechanisms. The stationary phases were overloaded by large volume injection of DL-tert-Leucine. BiLangmuir isotherm was used for modeling the adsorption because of the heterogeneous surface of the zwitterionic stationary phases. The isotherm parameters were determined by the inverse method. In the optimization of the enantioseparation, the acid and base additives play an important role, they ensure the ionization of the selector and the selectand. Therefore, the effect of the nature and the ionic strength of the additives on the overloaded chromatographic bands were investigated

Inverse Size-Exclusion Chromatography

The most preferred method to separate sample molecules based on their size relative to the pore size is size exclusion chromatography (SEC) (also referred to as gelpermeation, gel-filtration, molecular sieve, or simply gel chromatography) because using a strong solvent, there will be no interaction between the solute molecules and the stationary phase. The inverse version of SEC, inverse size-exclusion chromatography (ISEC) was also described in the middle of the 1970s [1,2], where the pore sizes were determined in the knowledge of the molecule size. Some sources attributed the first description of the ISEC technology incorrectly to Ogston [3] or to Aggerbrandt [4]. There is a plethora of information on the theoretical and experimental aspects of SEC and ISEC and also a number of great reviews have been published. The porous structure of the chromatographic particles is of great complexity and that has a number of consequences during the separation process. The physicochemical properties of high-performance liquid chromatography (HPLC) stationary phases play an important role on column performance and efficiency. The proper characterization of the pore structure and the pore size distribution (PSD) is relevant, because the mass transfer across the particles is greatly affected by the nature of the pores. SEC allows getting a more accurate picture of the impact of the distributions (pore size distribution and polydispersity) on the separation efficiency from ISEC measurements using a proper model. In this chapter, we summarize the most important theories and the newest applications regarding ISEC

Polydispersity in size-exclusion chromatography: a stochastic approach

Abstract We investigate the impact of polydispersity of the sample molecules on the separation process and on the efficiency of size-exclusion chromatography. Polydispersity was integrated into the molecular (stochastic) model of chromatography; the characteristic function, the band profile and the most important moments of the elution profiles were calculated for several kind of pore structures. We investigated the parameters affected by polydispersity on the separation for a number of pore shapes. Our results demonstrate that even a small distribution in the molecular size (i.e. polydispersity) can contribute substantially to the total width of the chromatographic peak. The pure effect of polydispersity can only be investigated via mathematical modeling, because its contribution to an experimental chromatogram cannot be separated from other band-broadening effects

Retention mechanism on phosphodiester stationary phases in hydrophilic interaction liquid chromatography and purely aqueous mobile phase part II: Overloading with limited soluble samples

The adsorption behaviour of caffeine and theophylline under hydrophilic interaction chromatography and purely aqueous conditions was investigated on four phosphodiester stationary phases. Solute adsorption isotherms were determined by frontal analysis or inverse method. The bi-Langmuir model was found to be the best choice to describe the behaviour of caffeine and theophylline adsorption in purely aqueous conditions, whereas the bi-Moreau model describes the adsorption phenomena in HILIC conditions. The results obtained demonstrate that the interaction of caffeine and theophylline with the stationary phase surface varies depending on the mobile phase composition. Both in pure aqueous mobile phase and in HILIC mode, the heterogeneity of the surface of the studied stationary phases is confirmed. In hydrophilic solutions, the sample molecules interact with the stationary phase only. In hydrophobic conditions, a lateral interaction occurs between caffeine or theophylline molecules, which are poorly soluble in acetonitrile-rich solvents. This confirms that the same compound on the same stationary phase can behave rather differently, depending on the mobile phase composition. Thus, the mobile phase may govern and control the retention mechanism