Open tubular columns surface coated

Porous-layer- open tubular (PLOT) and support-coated open tubular (SCOT) columns are prepared by extending the inner surface area of the capillary tube. A layer of particles can be deposited on the surface or the column wall can be chemically treated to create a porous adsorbent layer. Obviously some of the wall-modified open tubular columns discussed in section 2.3.3 could be... 

An open-tubular column is a capillary bonded with a wall-supported stationary phase that can be a coated polymer, bonded molecular monolayer, or a synthesized porous layer network. The inner diameters of open-tubular CEC columns should be less than 25 pm that is less than the inner diameters of packed columns. The surface area of fused silica tubing is much less than that of porous packing materials. As a result, the phase ratio and, hence, the sample capacity for open-tubular columns are much less than those for packed columns. The small sample capacity makes it difficult to detect trace analytes. 

Surface tension modifications for producing wall-coated open tubular columns... 

One type of column is the wall-coated open tubular column (WCOT) in which the stationary phase is applied and bound directly to the walls of the column. Porous-layer open tubular columns (PLOT) are columns in which the stationary phase is deposited on fine particles of absorbent, absorbed on the walls of the column, increasing the available surface area of the column wall. Support-coated open tubular (SCOT) columns are those... 

Open tubular columns are simply capillary tubes in which the inside of the column wall is used as the support for the liquid phase. These wall-coated open tubular columns (WCOT) have the stationary phase distributed in the form of a thin film on the inside surface of the open capillary tube, the walls thus serving as the support. In order to reduce the thickness of the liquid phase film, a porous layer may be formed on the inside wall of the capillary tubing and then coated with the liquid phase to produce a support-coated open tubular column (SCOT). Porous-layer open tubular colunms (PLOT) are similar to SCOT colunms, the difference being that in the former, the stationary phase is deposited on fine crystalline particles or glass powder which is adsorbed onto the walls of the tube. In both cases, the available surface area of the wall is increased, and allows an increased amount of liquid phase to be accommodated in the same length and diameter of tubing. The whisker-walled (WW) colunm consists of whiskers chemically etched on the surface of the wall, which also result in a significant increase in the available surface area. Wall-coated, porous-layer, and support-coated capillary columns are all available as whisker-walled, i.e., WWCOT, WWPLOT, and WWSCOT, respectively. 

The pioneering gas-liquid chromatographic studies in the early 1950s were carried out on packed columns in which the stationary phase was a thin film of liquid retained by adsorption on the surface of a finely divided, inert solid support. From theoretical studies made during this early period, it became apparent that unpacked columns having inside diameters of a few tenths of a millimeter could provide separations that were superior to those of packed columns in both speed and column efficiency. In such capillary columns, the stationary phase was a film of liquid a few tenths of a micrometer thick that uniformly coated the interior of capillary tubing. In the late 1950s, such open tubular columns were constructed the predicted... 

With packed columns, losses through adsorption and peak tailing are greater (due to the larger surface area) than with capillary wall coated open tubular columns. The latter is preferred because it provides the required inertness, high resolution, and sharp signals. 

While the developments in capillary GC were slow in coming in the late 1960 s, many researchers then considered the support-coated open tubular and micropacked columns to be viable alternatives to the conventional capillaries. Although some interesting results were reported about 10 years ago [94,95] on the performance of such columns, they were largely overshadowed by the rapid advances in technology of wall-coated columns. The limited column permeability of micropacked columns and an excessive surface activity of support-coated open tubular columns are the major drawbacks of these column types. However, they may still offer a suitable compromise between sample capacity and column efficiency in certain special instances. 

Open tubular, or capillary, columns are of two basic typos wall-coated open tubular (W( OT) and support-coated open tubular (SCOT) columns. Wall-coated columns are simply capillary tubes coated with a thin layer of the stationary phase. In support-coated open tubular columns, the inner surface of the capillary is lined with a thin film (—.30 pm) of a support material, such as diatomaceous earth. This type of column holds several times as much stationary phase as docs a wall-coated column and thus has a greater sample capacity. Generally, the efficiency of a SCOT column is less than that of a WCOT column but significantly greater than that of a packed column. 

The internal surface of an open tubular column usually requires deactivation and/or cleaning before it can be coated with stationary phase. Deactivation procedures used for commercial columns are seen by many to be "shrouded with mystery" and the procedures are usually considered as highly proprietary. Although some unique or special samples may, indeed, need select and complete column deactivation. 

Open tubular columns can be coated internally with the appropriate stationary phase dissolved in a suitable solvent, or, alternatively, with monomeric materials that are subsequently polymerized to form a relatively rigid polymer film on the column walls. There are two basic methods for depositing the stationary phase as a surface film on a capillary column, dynamic coating and static coating, the latter being the most commonly used. 

The original capillary column, invented and patented by Dr. Marcel Golay [1], consisted of a tube with a thin film of liquid phase coated on the inside surface. This is properly called a wall-coated open tubular column or WCOT, shown in Figure 6.2. The tube can be made of fused silica, glass, or stainless steel. Almost all commercial capillary columns are now made of fused silica. 

Nowadays only three of the four possible types of columns are mainly used open capillary columns with a non-porous wall surface coated with a stationary liquid pheise (wall-coated open tubular (WCOT) open capillary columns with a porous layer of adsorbent on the inside walls or adsorption layer open tubular columns (ALOT) open capillary columns with a porous layer impregnated with a... 

On the other hand, the coating of capiiiary columns is a very complicated process and therefore the characteristics of open tubular column vary greatly, depending on the surface properties of the fused-... 

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