Wall-coated open-tubular column

A successful analysis is obtained when the components in a sample are adequately separated. This is achieved by optimising the retention characteristics that is, K and k, by selecting the most appropriate variables  

Column material Si02 AI2O3 NajO CaO MgO B2O3 BaO 

WCOT columns. The stationary phase coating was susceptible to column bleed and damage by solvents and high boiling contaminants. PLOT columns with alumina, molecular sieve or copolymer surface coatings have been developed particularly for the separation of Ci-Q alkanes and alkene and atmospheric gases [22-24]. 

Current column technology utilises the surface properties of pure silica tubing to immobilise the stationary phase producing extremely stable inert columns which are not degraded by solvents and have minimum column 

---

Before discussing column preparation procedures a few comments on nomenclature are in order. Open tubular columns are also widely known as capillary columns. The characteristic feature of these columns is their openness, which provides an unrestricted gas path through the column. Thus open tubular colximn rather than capillary column is a more apt description. However, both descriptions appear frequently in the literature and can be emsidered interchangeable. The type of columns discussed so far are also known as wall-coated open tubular columns (WCOT). Here the liquid phase is deposited directly onto the column wall without the inclusion of any additive that might be considered as... 

WCOT Wall-coated open-tubular column... 

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

The chromatographic column used was a wall-coated, open tubular column (WCOT) (J W Scientific) with a DB-1 Durabond chemically bonded stationary phase that had a nominal film thickness of 0.25 pm. The column was 60 m long X 0.32 mm i.d. The DB-1 stationary phase has chromatographic properties similar to SE-30. 

Table 23-3 Comparison of packed and wall-coated open tubular column performance0...

Wall-coated open tubular column (WCOT) liquid stationary phase on inside wall of column... 

Figure 24-12 Separation of two polyaromatic hydrocarbons on a wall-coated open tubular column with different carrier gases. Resolution. R. increases and analysis time decreases as we change from N2 to He to H2 carrier gas. [Courtesy J W Scientific, Folsom, CA.]...

WCOT. Wall Coated Open Tubular column. 

WCOT Columns. Wall-coated open tubular columns wherein the internal wall is coated with a thin layer of liquid (liquid substrate). ... 

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... 

Houtermans, W. J., and Boodt, C. P. (1979). Increased thermostability of non-polar wall coated open tubular columns. J. High Resolut. Chromatogr. Chromatogr. Commun. 2,249-250. 

Carrier gas flow should be optimised for a particular column and a particular carrier gas. This is most important for open tubular columns. Fig. 5 shows the relationship between efficiency expressed as the height equivalent of a theoretical plate versus carrier gas velocity (Van Deemter plot) for a 28 m by 0.25 mm internal diameter wall-coated open tubular column of Carbowax 20M. 

Fig. 5. Van Deemter plots for a 28 m by 0.25 mm internal diameter wall-coated open tubular column coated with Carbowax 20M run with different carrier gases.

WCOT wall-coated 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. 

Two types of columns are used in SFC packed columns containing solid particles of small inner diameter or wall-coated open-tubular columns (WCOT), usually called just capillary columns. Packed columns have been preferred when capacity is the most relevant issue capillary columns are selected when efficiency is the goal. 

URL USEPA UV WCOT WWW uniform resource locator United States Environmental Protection Agency ultraviolet wall-coated open tubular (column) World Wide Web... 

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. 

Fused silica, wall coated open tubular column Wall-coatud open lubular melal, plastic, ur glass columns. 

Wall-coated open tubular columns (WCOT columns), or simply capillary columns, and classical packed columns dominate the practice of gas-liquid chromatography today. Porous layer open tubular columns (PLOT columns) and classical packed columns dominate the practice of gas-solid chromatography. WCOT columns are typically up to 100 m... 

The introduction of capillary columns for GC analysis produced a breakthrough in the analysis of environmental pollutants due to their high separation efficiency. For environmental applications, fused-silica wall-coated open-tubular columns with internal diameters from 0.1 to 0.32 mm and film thickness of 0.1-0.2 pm, and lengths from 25 to 60 m are currently used. The wide range of stationary phases commercially available with different polarities and high thermal stabiHty provides the tool required to maintain the prominent position of GC in environmental analysis. In addition, the availability of chiral stationary phases gives GC the capability to perform GC enantiomer separations. Table 1 gives the recommended columns used in routine analysis of some selected pollutants. 

---