Size-exclusion chromatography mobile phase selection

Most size exclusion chromatography (SEC) practitioners select their columns primarily to cover the molar mass area of interest and to ensure compatibility with the mobile phase(s) applied. A further parameter to judge is the column efficiency expressed, e.g., by the theoretical plate count or related values, which are measured by appropriate low molar mass probes. It follows the apparent linearity of the calibration dependence and the attainable selectivity of separation the latter parameter is in turn connected with the width of the molar mass range covered by the column and depends on both the pore size distribution and the pore volume of the packing material. Other important column parameters are the column production repeatability, availability, and price. Unfortunately, the interactive properties of SEC columns are often overlooked. 

Conductivity detectors, commonly employed in ion chromatography, can be used to determine ionic materials at levels of parts per million (ppm) or parts per bUHon (ppb) in aqueous mobile phases. The infrared (ir) detector is one that may be used in either nonselective or selective detection. Its most common use has been as a detector in size-exclusion chromatography, although it is not limited to sec. The detector is limited to use in systems in which the mobile phase is transparent to the ir wavelength being monitored. It is possible to obtain complete spectra, much as in some gc-ir experiments, if the flow is not very high or can be stopped momentarily. 

In size exclusion chromatography, the mobile phase must be selected to totally solubilize the sample and eliminate all interactions of the solutes with the... 

The separation of chemical species by size exclusion chromatography is more reproducible than any other type of chromatography. Once the SEC columns, the mobile phase (most often a pure solvent like THF or toluene), and the flow rate are selected, the retention volume (or retention time assuming the flow rate does not change) is primarily a function of linear molecular size, which can be obtained from the valence bond structure if the compound is known. Some of the chemical species can interact with the solvent forming complexes with an effective linear size greater than that of the molecule. This causes the expected retention volume, based on "free" molecular structure, to shift to a lower but very reproducible retention volume. Phenols in coal liquids form 1 1 complex with THF (9,10) and carry the effective linear molecular size to increase. As a result phenolic species elute sooner than expected from their... 

Size-exclusion chromatography (SEC) differs from the other methods in that the separation is based on physical sieving processes and not on chemical phenomena. The stationary phase is chemically inert and there is selective diffusion of solute molecules into and out of the mobile phase-filled pores in a three-dimensional network which may be a gel or a porous inorganic solid. The degree of retention is dependant on the size of the solvated solute molecule relative to the size of the pore. Smaller molecules will permeate the smaller pores, intermediate-sized molecules will permeate some pores and... 

The first step in the selection of the size-exclusion separation system is the choice of the mobile phase. We need to select a mobile phase in which the analytes, usually polymers, are soluble. This, in turn, determines the selection of the stationary phase, spedfically, whether we select a padring designed for organic or aqueous size-exclusion chromatography (the term aqueous may include polar solvents). If the goal of the separation is a molecular-weight determination, the requirements for the mobile phase-column combination are quite stringent ... 

Cycloaliphatic resins were prepared by complete hydrogenation of selected aromatic resins. Molecular weight data were obtained by size exclusion chromatography, using a Styragel column set with THF as the mobile phase. Calculations were based on a polystyrene calibration. Glass transition temperatures were obtained by differential scanning calorimetry from the first break on the second heat. 

MOBILE PHASE SELECTION Size Exclusion Chromatography... 

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