Open column diatomaceous earths

Capillary columns are of two principal types. Wall-coated open tuhular columns (WCOT) contain a thin layer of stationary phase, typically 0.25 pm thick, coated on the capillary s inner wall. In support-coated open tuhular columns (SCOT), a thin layer of a solid support, such as a diatomaceous earth, coated with a liquid stationary phase is attached to the capillary s inner wall. 

Two types of columns are used. A packed column is one filled with inert, solid particles coated with a liquid stationary phase. Standard tubing is about 0.5 cm in diameter, with lengths ranging from 1 m to 20 m however, columns for large-scale preparative work may be up to 5 cm in diameter and several meters long. Commonly used solid supports are diatomaceous earth, Teflon powder, and glass beads. The stationary liquid must be chosen on the basis of the compounds to be analyzed. A more recently developed and more widely used type of column is the open-tubular or capillary column. This is prepared by coating the inner wall of the column with the stationary liquid phase. The inside diameter of a typical capillary tube is 0.25 mm, and... 

Accurately quantifying the amount of provitamin A carotenoids in a food product is essential for determining nutritional value of foods. The AO AC method for determination of vitamin A (974.29) and carotenoids (941.15 and 970.64) in foods utilizes open column chromatography combined with a colorimeter (vitamin A) or spectrophotometer (carotenoids) (Horwitz, 2006). It is recommended to extract with acetone-hexane followed by filtration, then remove the acetone by rinsing with water. The extracts in hexane are applied to an activated Mg02 diatomaceous earth column and eluted using acetone and hexane... 

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. 

There are two basic disadvantages to the coated capillary column. First, the hmited solute retention that results from the small quantity of stationary phase in the column. Second, if a thick film is coated on the column to compensate for this low retention, the film becomes unstable resulting in rapid column deterioration. Initially, attempts were made to increase the stationary phase loading by increasing the internal surface area of the column. Attempts were first made to etch the internal column surface, which produced very little increase in surface area and very scant improvement. Attempts were then made to coat the internal surface with diatomaceous earth, to form a hybrid between a packed column and coated capillary. None of the techniques were particularly successful and the work was suddenly eclipsed by the production of immobilize films firmly attached to the tube walls. This solved both the problem of loading, because thick films could be immobilized on the tube surface, and that of phase stability. As a consequence, porous-layer open-tubular (PLOT) columns are not extensively used. The PLOT column, however, has been found to be an attractive alternative to the packed column for gas-solid chromatography (GSC) and effective methods for depositing adsorbents on the tube surface have been developed. 

There are two general types of GC column packed and capillary (also known as open tubular). Packed columns contain a finely divided, inert, solid support material (commonly based on diatomaceous earth) coated with a viscous liquid stationary phase. Most packed columns are 1.5-lOm in length and have an internal diameter of 2-4mm. The original glass capillary columns had an internal diameter of a few tenths of a millimeter and were also one of two types, wall-coated open tubular (WCOT) and support-coated open tubular (SCOT). WCOT columns consist of a capillary tube whose walls are coated with liquid stationary phase. In SCOT columns the inner wall of the capillary is lined with a thin layer of support material such as diatomaceous earth, onto which the stationary phase has been adsorbed. Both of these types of capillary column provide greater separation efficiency than packed columns, but since 1979 they have... 

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