Porous-layer open-tubular column

The overall method for gasoline requires no sample preparation other than the addition of internal references. The method is fast since samples may be run at 3-min intervals, interference-free and specific for MMT. Analysis time comparison is favourable with respect to atomic absorption analysis which typically required about 15 min per sample when run in batches. Further, the procedure is readily adapted for use with open tubular columns. Porous layer open tubular columns (PLOY) are best suited to accommodate the direct injection of gasoline samples. The improvement in analysis time for MMT determination by the latter method may outweigh the somewhat poorer limit of detection resulting from limitations on the sample size. 

In addition, support-coated open tubular (SCOT), porous-layer open tubular (PLOT), and wall-coated superior capacity open tubular (WSCOT) columns are applied. In a SCOT column, the column wall is coated with a thin layer of small inert particles that serve as a support for the stationary-phase liquid. The SCOT column provides a higher sample loadability at the expense of separation efli-... 

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... 

Figure 2.15 Separation of a mixture of saturated and unsaturated hydrocarbons on a 50 m x 0.32 mm fused silica porous-layer open tubular column coated with alumina modified wl potassium chloride. The separation was performed by temperature programming from 70 to 200°C at 3 C/mln. (Reproduced with permission fr

PA(S) Photoacoustic (spectroscopy) PLOT Porous-layer open-tubular column... 

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. 

Huang, X., Zhang, J., and Horvath, C. (1999). Capillary electrochromatography of proteins and peptides with porous-layer open-tubular columns.. Chromatogr. A 858, 91-101. 

These phases are composed of adsorbing materials molecular sieves, alumina, porous glass and gels (such as Chromosorb 100, Porapak and PoraPLOT1 ), and graphitised carbon black. They are mainly used to separate gases or volatile compounds. Capillary columns made by deposition of these materials in the form of very fine particulates are called PLOT (porous layer open tubular) columns. 

PLOT. Porous Layer Open Tubular column. 

PLOT Columns. Porous-layer open tubular columns wherein the internal wall is coated with a layer of adsorbent support. If the support is then coated with a liquid phase it is referred to as a SCOT Column (i.e., support-coated open tubular column). 

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... 

L. Ghaoui, E. Dessai, et al., Analysis of perfluoroalkanes and fluor-obenzenes using an aluminum oxide porous-layer open tubular column, Chromatographia, 20(2) 75-78 (1985). 

J. de Zeeuw, R. C. de Nijs, et al., PoraPLOT Q A porous layer open tubular column coated with styrene-divinylbenzene copolymer, HRC CC J. High Res. Chromatogr. Chromatogr. Commun., 11 162-167(1988). 

For a period of time, OT columns that had characteristics intermediate between those of WCOT and packed columns were popular. There were two types, but they were similar. Support coated open tubular (SCOT) columns had a thin layer of solid support coated on the inside wall of a capillary tube of larger diameter than that used for WCOT columns. This layer was coated with stationary liquid similar to packed columns. Porous layer open tubular (PLOT) columns were similar but made differently for example, the solid support was added while the capillary tube was being drawn. With a few exceptions, SCOT and PLOT columns are no longer popular because wide diameter WCOT fused silica columns are as good, more stable (no layer to flake off), and easier to use. Subsequent discussion will be restricted to WCOT columns. 

PLOT porous layer open tubular (column)... 

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. 

Several other stationary phases made from different proportions of typical phases (methyl, phenyl, cyanopropyl), or from special compounds such as polytrifluropropyl-siloxane, or different columns such as PLOT (porous layer open tubular), columns coated with a modified graphitized carbon or with a silicone based polymer with chiral groups incorporated into the polymeric chain, columns coated with derivatized cyclodextrins (for the separation of chiral compounds), etc. are also utilized. 

Support-coated open tubular column (also called porous layer open tubular or PLOT). 

Gas-solid chromatography is performed with both packed and open tubular columns. For the latter, a thin layer of the adsorbent is affixed to the inner walls of the capillary. Such columns are sometimes called porous-layer open tubular columns, or PLOT columns. Figure 31-16 shows a typical application of a PLOT column. 

Colloidal Alumina Alumina is available in a colloidal form which can be deposited on firebrick or glass beads, or on the wall of an open tubular column, to give a porous adsorptive layer which may be modified by addition of a liquid or other adsorbent such as colloidal silica. This way a wide variety of selective separating layers can be prepared. 

GSC is carried out using a different type of open tubular column. The stationary phase in such columns has the form of a layer of porous material coated on the walls of the tube. Such columns are... 

PLOT Porous layer open tubular column used in capillary GC, consists of a thin layer (1-5 pm) of solid stationary phase material, e.g. modified alumina, coated onto the inner wall of silica capillary tubing see capillary GC. 

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