Support-coated open-tubular column

Support-coated open tubular column (SCOT) liquid stationary phase coated on solid support attached to inside wall of column... 

SCOT. Support Coated Open Tubular column. 

FLOW. The rate at which zones migrate down the column is dependent upon equilibrium conditions and mobile phase velocity on the other hand, how the zone broadens depends upon flow conditions in the column, longitudinal diffusion, and the rate of mass transfer. Since there are various types of columns used in gas chromatography, namely, open tubular columns, support coated open tubular columns, packed capillary columns, and analytical packed columns, we should look at the conditions of flow in a gas chromatographic column. Our discussion of flow will be restricted to Newtonian fluids, that is, those in which the viscosity remains constant at a given temperature. 

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). 

Cramers et al5 described high resolution gas chromatography for the quantitative determination of underivatized anti-convulsant drugs with support coated open tubular columns. 

B. Caddy, F. Fish, and D. Scott, Chromatographic screening for drugs of abuse using capillary columns, part 1, comparison of open tubular columns and support coated open tubular columns for the analysis of central nervous system stimulant drugs, Chro-matographia, 6 251 (1973). 

Fig. 7.1 shows the trace obtained from the analysis of undegraded linear alkylbenzene sulphonate (LAS) mixture (sodium dodecylbenzene sulphonate). Peak identifications were made by co-injection with pure undegraded linear alkylbenzene sulphonate compounds and confirmed by analysis of the undegraded linear alkylbenzene sulphonate mixture by desulphonation followed by gas chromatography of the resultant alkylbenzenes on a 15m OV-1 support coated open-tubular column. 

Figure 5 compares chromatograms of A8- and A9-THC-TMS and 11-hydroxy-A8-THC-TMS obtained on a glass capillary column and a 6ft. x 2mm I.D. packed column. The retention times of the cannabinoids are comparable, but the resolution and sensitivity achieved on the capillary column is far superior. The capacity of the capillary column is of course far less than that of the packed column. Nevertheless, by using a Grob-type splitless injector (7) we are able to inject several microliters of solution containing up to 50 ng of each cannabinoid without overloading the column. Use of a support-coated open tubular column should increase the column capacity, but at some sacrifice of resolution and sensitivity. 

SCOT Support 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. 

Figure 5. Gas chromatogram of methyl esters from the aqueous Na2Cr20y oxidation of Illinois No. 2 bituminous coal (separated on an OV-17 support coated open tubular column (SCOT), temperature...

The benzene fraction was initially examined by GLC using 100 ft. support coated open tubular columns containing Carbowax 1540 polyethylene glycol) and squalane (Figure 3) as the liquid phases. Quantitative data were obtained at 45 °C. on the squalane column with a helium flow of 3.0 ml./min. The Perkin Elmer Model 880 gas-liquid chromatograph, equipped with a stream splitting device and hydrogen flame... 

Besides the stationary-phase selectivity, the phase ratio (volume of the mobile phase/volume of the stationary phase) is an important consideration in practical chromatography. Thus, within the available arsenal of GC columns, the efficiency increases in the following direction packed column < micropacked column < support-coated open tubular column (or wide-bore capillary column) < conventional... 

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. 

Figure 4.19 Separation of four hydrocarbons at different temperatures. 45-m X 0.5-mm-i.d. support-coated open tubular column coated with squalane. Peak identification (1) methylcyclohexane, (2) 2,5-dimethylhexane, (3) 2,4-dimethylhexane, and (4) 2,2,3-trimethylpentane.

SCOT = support-coated open tubular column. These columns are less popular today since thicker WCOT phases are now available. PLOT = porous layer open tubular column. 

The other types of capillary columns are shown in Figure 6.3, the SCOT or support-coated open tubular column, on the left, and the PLOT or porous layer open tubular column, on the right. SCOT columns contain an adsorbed layer of very small solid support (such as Celite ) coated with a liquid phase. SCOT columns can hold more liquid phase, and have a higher sample capacity than the thin films common to the early WCOT columns. However, with the introduction of cross-linking techniques, stable thick films are possible for WCOT columns, and the need for SCOT columns has disappeared. A few SCOT columns are still commercially available but only in stainless steel tubing. 

Retardation factor in column chromatography fraction of a sample component in a mobile phase Gas constant Peak resolution Detector sensitivity Support-coated open tubular (column)... 

Abuse Using Capillary Columns. III. Quantitative Analysis of CNS (Central Nervous System) Stimulant Drugs in Urine Using Support Coated Open Tubular Columns... 

Quantitative Determination of Underiv-atized Anti-Convulsant Drugs by High ResolutionGas Chromatography with Support-Coated Open Tubular Columns Clin. Chim. Acta 73(1) 97-107 (1976) CA 86 3745Iz... 

Study on the Efficiency of Support Coated Open Tubular Columns for Steroid Analysis... 

Open tubular or capillary columns have open unrestricted path for the gas within the column. These columns are about 15-30 meters in length with an inside diameter of about 0.25 mm. The inner wall of these columns is coated with the liquid stationary phase to about 1 m in thickness. The open tubular columns are of two kinds. One is known as the wall coated open tubular column [WCOT) in which the liquid phase is coated on the column wall. These columns have limited sample capacity and are unsuitable for large-scale separations. The second type is known as support coated open tubular columns (SCOT). In these columns a porous layer is formed on the inside wall of the tubing. The porous layer can either be formed by chemical treatment of the inner wall or is deposited on the inner wall. The support is coated in such a way that the inherent property of the capillary columns, i.e., the unrestricted gas flow is retained. The inert porous layer is then impregnated with the liquid stationary phase. These columns have a higher sample capacity. 

SCOT. An acronym for support-coated open tubular column. These are capillary columns in which the liquid substrate is on a solid support that coats the walls of the capillary column. 

WWSCOT. An acronym for whisker-wall-support-coated open tubular column. It is a SCOT column in which the walls have been etched before depositing of the support. 

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