Pore diameter, liquid chromatography

SynChropak GPC supports were introduced in 1978 as the first commercial columns for high-performance liquid chromatography of proteins. SynChropak GPC columns were based on research developed by Fred Regnier and coworkers in 1976 (1,2). The first columns were only available in 10-yu,m particles with a 100-A pore diameter, but as silica technology advanced, the range of available pore diameters increased and 5-yu,m particle diameters became available. SynChropak GPC and CATSEC occasionally were prepared on larger particles on a custom basis, but generally these products have been intended for analytical applications. 

This is liquid-solid chromatography in which the surface of microparticulate silica or other adsorbent constitutes the polar stationary phase. The silica particles are characterized by their shape (irregular or spherical), size and size distribution, and pore structure (mean pore diameter,... 

The products obtained were analyzed for composition using high-performance liquid chromatography (HPLC) (LC -10AT Shimadzu, Kyoto, Japan), which consisted of a column (STR ODS-II, 25 cm in length x 4.6 mm in id Shinwa Chemical, Osaka, Japan) operated at 40°C at a flow rate of 1.0 mL/min with methanol as a carrier solvent. The column was packed with silica particles (5-pm particle diameter and 12-nm pore diameter). The cloud and pour points of the obtained biodiesel were then determined by a mini-cloud/pour point tester (Model MPC-102 Tanaka Scientific, Tokyo, Japan) based on ASTM D2500 for cloud point and ASTM D6749 for pour point (14). 

Knudsen diffusion becomes predominant when the mean-free path of the molecular species considered is larger than the pore diameter and hence, when the effects of the molecule-wall collisions become important. In liquid chromatography, Knudsen diffusion is negligible. 

Separation by liquid-liquid partition chromatography is the result of the difference in the distribution between two immiscible liquid phases of the individual components of a mixture. The liquid stationary phase is coated on a solid support, which is ideally inert. As the support relatively large pore silica (10-50 nm pore diameter) is most often used. 

Porous silica (or silica gel) is by far the most important adsorbent for liquid-solid chromatography and is also the substrate used to prepare most chemically bonded phases, giving it a preeminent position in modem column technology [3-15]. Silica particles are mechanically strong and easily prepared in a wide range of particle size ranges and pore diameters suitable for chromatography. As a substrate for the... 

Porous graphitic carbon is synthesized by a multistep chemical and thermal treatment from organic monomers deposited in the pores of a silica gel particle template and subsequently subjected to polymerization, carbonization, dissolution of the silica template and graphitization [170,172]. The silica gel template allows optimization of the adsorbent particle size, porosity and surface area for liquid chromatography. The selection of monomers and thermal treatment is responsible for the mechanical strength, high purity and absence of significant microporosity. Commercially available materials have particle sizes of 5 or 7 xm, a mean pore diameter of 25 nm and a surface area of 100-120 m /g. 

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