Diatomaceous earth, stationary phase

Cabon tetrachloride, n-hexane, chloroform, ACN, acetone, THF, pyridine, acetic acid, and their various mixtures were applied as mobile phases for adsorption TLC. Methanol, 1-propanol, ACN, acetone, THF, pyridine and dioxane served as organic modifiers for RP-TLC. Distilled water, buffers at various pH (solutions of and dipotassium hydrogen phosphate or potassium dihydrogen phosphate) and solutions of lithium chloride formed the aqueous phase. Carotenoids were extracted from a commercial paprika sample by acetone (lg paprika shaken with 3 ml of acetone for 30 min), the solution was spotted onto the plates. Development was carried out in a sandwich chamber in the dark and at ambient temperature. After development (15 cm for normal and 7cm for HPTLC plates) the plates were evaluated by a TLC scanner. The best separations were realized on impregnated diatomaceous earth stationary phases using water-acetone and water-THF-acetone mixtures as mobile phases. Some densitograms are shown in Fig.2.1. Calculations indicated that the selectivity of acetone and THF as organic modifiers in RP-TLC is different [14],... 

The most widely used particulate support is diatomaceous earth, which is composed of the silica skeletons of diatoms. These particles are quite porous, with surface areas of 0.5-7.5 m /g, which provides ample contact between the mobile phase and stationary phase. When hydrolyzed, the surface of a diatomaceous earth contains silanol groups (-SiOH), providing active sites that absorb solute molecules in gas-solid chromatography. 

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. 

No expensive equipment is required for OCC however, the separation efhciency depends on the analyst s experience since a new column has to be packed for each analysis. In addition, depending on the packing type (powder or slurry), stationary phase, and purpose of the separation, the separation can take from 30 min to 4 hr. The AOAC official method for the determination of carotenoids still uses OCC." Separation of carotenoids from many foods was developed on a column packed with a mixture of MgO and HyfloSupercel (or celite or diatomaceous earth) at 1 1... 

In a partition system the stationary phase is a liquid coated onto a solid support (p. 97). Silica gel, kieselguhr (diatomaceous earth) or cellulose powder are the most frequently used. Conditions closely resemble those of counter-current distribution so that in the absence of adsorption by the solid support, solutes move through the system at rates determined by their... 

The liquid stationary phase in a GLC packed column is adsorbed on the surface of a solid substrate (also called the support). This material must be inert and finely divided (powdered). The typical diameter of a substrate particle is 125 to 250 ft, creating a 60- to 100-mesh material. These particles are of two general types diatomaceous earth and Teflon . Diatomaceous earth, the decayed silica skeletons of algae, is most commonly referred to by the manufacturer s (Johns Manville s) trade name, Chromosorb . Various types of Chromosorb, which have had different pretreatment procedures applied, are available, such as Chromosorb P, Chromosorb W, and Chromosorb 101-104. The nature of the stationary phase as well as the nature of the substrate material are both usually specified in a chromatography literature procedure, and columns are tagged to indicate each of these as well. 

Chromosorb is the trade name given to diatomaceous earth, the decayed silica skeletons of algae. It is the substrate material on which the liquid stationary phase is adsorbed in packed columns. Low-molecular-weight alcohols are highly polar, thus FFAP or Casterwax would be useful in their separation. 

The efficacy of various normal and RP-TLC systems for the separation of the colour pigments of Capsicum annuum was compared. Neutral aluminium oxide, silica gel, diatomaceous earth, silica gel-diatomaceous earth 1 1, cellulose, cyano, diol- and amino modified silicas were employed as stationary phases for adsorption TLC. Polyamide and modified silica layers were used for RP-TLC as received, the other stationary phases were impregnated by overnight predevelopment in n-hexane - paraffin oil, 95 5 v/v. 

The columns are usually made from glass which is silanized to remove polar silanol Si-OH groups from its surface that can contribute to the peak tailing of the peaks of polar analytes. These columns have internal diameters of 2-5 mm. The columns are packed with particles of a solid support which are coated with the liquid stationary phase. The most commonly used support is diatomaceous earth (mainly calcium silicate). This material is usually acid washed to remove mineral impurities and then silanized as shown in Figure 11.4 to remove the polar Si-OH groups on the surface of the support, which can lead to tailing of the analyte peak. 

The first type consist of relatively short tubes, with an inner diameter of several millimetres, packed with an inert support on which the stationary liquid phase is held. The preferred sorbents are variously calcined, acid- or base-washed and silanized forms of diatomaceous earth (Chromosorb, Gas Chrom Q, Supelcoport)165,168,178,180-184,191,184,195,197,200,... 

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... 

A number of metal and metalloid halides have been separated with rather conventional arrangements. For example, Keller and Freiser separated SnCl4, TiCl4, NbClj, and TaCIs at 200°C using a copper column packed with squalane on Chromsorb P (a modified diatomaceous earth).51 A variety of chlorosilanes and methylchlorosilanes have been separated using silicone oil plus diethyl ph-thalate as the stationary-phase and thermal conductivity detectors.52... 

According to our earlier classification, the stationary phase can be a solid, a liquid, or a bonded phase. In the latter two cases, the phase must be coated on, or bonded to, particles of a porous solid support. Only a few materials have found widespread use as stationary solid supports they are silica, synthetic polymers such as the styrene-divinylbenzene copolymer, diatomaceous earths, and some polysaccharides. The most common types and uses are given in Table 2. 

The distinguishing features of gas chromatography are a gaseous mobile phase and a solid or immobilized liquid stationary phase. Liquid stationary phases are available in packed or capillary columns. In the packed columns, the liquid phase is deposited on a finely divided, inert solid support, such as diatomaceous earth or porous polymer, which is packed into a column that typically has a 2- to 4-mm id and is 1 to 3 m long. In capillary columns, which contain no particles, the liquid phase is deposited on the inner surface of the fused silica column and may be chemically bonded to it. In gas-solid chromatography, the solid phase is an active adsorbent, such as alumina, silica, or carbon, packed into a column. Polyaromatic porous resins, which are sometimes used in packed columns, are not coated with a liquid phase. 

Chromosorb Wisa diatomaceous e tii calcined with the addition of sodium carbonate. It is less dense than Chromosorb P, with a packed density of approximately 0.3 g/cm, and is softer with a greater tendency to produce fines. The surface M-ea is about 1 mVg. Celite 545 is simile to Chromosorb W. Chromosorb G is a calcined diatomaceous earth witii a density similar to that of Chromosorb P but tiie surface area is much less, about 0.5 mVg, and it is the least reactive of tiie Chromosorbs. The high resistance to mechanical damage together with the density and inertness m e it very suitable for low-loaded columns. The amount of stationary phase... 

Column packing consists of two essential ingredients—the inert supporting phase and the stationary liquid phase. The solid supporting phase is usually an insert material of uniform particle size. Diatomaceous earth is a frequently used solid support, although celite, firebrick, and glass beads are also used. The particle size is important in achieving the maximum separation or efficiency. However, smaller particles inhibit the flow rate of gas due to the increased resistance of the denser medium. 

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