Particle size of the stationary phase

The main differences between TLC and PLC are due to the layer thickness and particle size of the stationary phase and the amount of sample applied to the plate. 

It was known from gas chromatographic theory that efficiency could be improved if the particle size of the stationary phase materials used in lc could be reduced. High performance liquid chromatography developed steadily during the late 1960s as these high efficiency materials were produced, and as improvements in instrumentation allowed the full potential of these materials to be realised. As hplc has developed, the particle size of the stationary phase used has... 

The particle size of the stationary phase material plays a very vital and crucial role in HPLC. In fact, high-elficiency-stationary-phase materials have been researched and developed exclusively for HPLC having progressively smaller particle size termed as microparticulate column packings. These silica particles are mostly uniform, porous, with spherical or irregular shape, and having diameter ranging from 3.5 to 10 pm. 

The speed of a chromatographic separation is fixed by the particle size, the stationary phase characteristics, the available pressure, the solvent viscosity, the solute diffusivity, the a values of the critical pair, and extracolumn dispersion. One way to achieve faster separations is to reduce the particle size of the stationary phase. However, if material of smaller diameter is packed into a conventional size column, the backpressure will become prohibitively high. Thus, in a compromise between speed and optimum performance, narrow (<2 mm) columns packed with small 3-5 ju.m diameter particles have been developed. 

The separation efficiency is related to the particle size of the stationary phase material. A higher pressure is required when the particle size is reduced. With a typical linear velocity in the range of 2-10 mm/s, a pressure drop over the coluttm can exceed 10 MPa, obviously depending on the colunm length as well. 

Other factors that affect efficiency are characteristics of the stationary support particles, mobile phase viscosity, column temperature, and noncolumn contributions. In general a decrease in (1) mobile phase flow rate, (2) average particle size of the stationary phase, (3) particle size distribution, and (4) volume of sample will increase efficiency. Increases in column length, temperature, and sample viscosity also increase efficiency. 

Mobile phase mass-transfer coefficient, CmU A quantity that affects band broadening and thus plate height nonlinear in solvent velocity u and influenced by the diffusion coefficient of the analyte, the particle size of the stationary phase, and the inside diameter of the column. 

The optimized pressure concept can be extended. Figures 2.29 and 2.30 show nomograms for well packed columns operated at their van Deemter curve minima. The nomograms show the interrelationship between column length, pressure, number of theoretical plates, particle size of the stationary phase and breakthrough time. Two of these five parameters may be selected at random, the other three being geared to the optimum flow rate. 

The smaller the particle size of the stationary phase the greater is the peak capacity of the column and the better and faster are the separations. ... 

In contrast to these considerations. Figure 24.1 shows the influence of column diameter and separation performance (or particle size of the stationary phase) on peak shape if a constant volume of a solution with a given concentration is injected. 

This equation tells us that in order to obtain a high H-value, the thickness and the particle size of the stationary phase must be small to favour mass transfer and that Dl (diffusion coefficient in the hquid phase) must be large. 

The smaller the particle size of the stationary phase the greater is the peak capacity of the column and the better and faster are the separations. Size-exclusion chromatography is generally subdivided further into mobile phase categories. The mobile phase is aqueous in GFC (gel filtration chromatography) and is an organic solvent in GPC (gel permeation chromatography). 

The theoretical plate height curve has a minimum that corresponds to the optimal flow rate. The minimal theoretical plate height is influenced by the average particle size of the stationary phase. The smaller the average particle size the smaller the H and the better the resolution is [35,36]. Current technologies can provide columns... 

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