Teflon glass beads

Solid supports should be chemically inert and exhibit a large surface area. Support materials used are diatomaceous earths. Teflon , glass beads, and various polymers. Since the surface of the diatomaceous materials consist of silanol (Si—O—H) and siloxane (Si—O—Si) groups, compounds capable of hydrogen bonding (alcohols, acids, amines, etc.) can interact with these media, which results in tailing. This problem may, however, be minimized by silanization ... 

Once separated, the supports are washed using acid (HCl) and sdanized, ie, treated with dimethyl dichi orosilane [75-78-5] (DMCS), to reduce the polarity. Sdanizing replaces adjacent SiOH groups with nonpolar CH caps. In addition to diatomaceous earths, supports of carbon (qv), halocarbons, eg. Teflon, and glass beads are in use by various chromatographers. 

The most commonly used column support materials are made from diatomite. Other materials include sand. Teflon, inorganic salts, glass beads, porous layer beads, porous polymers, carbon blacks, etc. We will discuss the diatomite supports in some detail and additional information may be obtained in Chapter 3. 

Substitution of a less reactive support material. For example, the use of Teflon or glass beads in place of diatomaceous earth. 

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... 

Kim and Kim [67] Isocitrate Apple, grape, strawberry and tomato juices Isocitric dehydrogenase/in aminopropyl glass beads with glutaraldehyde and packed in a Teflon tube Potentiometric CO -selective electrode -... 

Maroulis and Bandy ( ) determined DMS in air at Wallops Island by cryotrapping air drawn through a teflon tube packed with glass beads immersed in liquid argon. The DMS was thermally desorbed onto a GC column with polyphenyl ether/H PC liquid phase coated onto a teflon substrate and was detected via doped "FPD. No mention was made in that paper of sampling losses, however it has been suggested that the presence of the glass beads may have served to remove co-trapped oxidants (D. Thornton, personal communication). 

The acid concentration should be as low as possible. The nebuliser fitted as standard may have a stainless steel capillary tube which will be attacked by acid over a period of time. Solutions containing more than 5% mineral acid should be nebulised using a nebuliser having a platinum/iridium capillary. A corrosion-resistant nebuliser having a plastic throat is required for solutions containing hydrofluoric acid. Additionally, in this instance, a teflon impact bead must replace the standard glass one where these are employed. 

Fig. 9.9 depicts some of the results from such trials. Despite some scatter in the angle range 95°-105°, it is readily seen that at 9< 95° none of the films ruptures, while at 0> 105° all the films rupture. Experiments with suspensions of solid particles (Teflon, hydrophobed glass beads and ground glass) showed that in the case of smooth particles, the defoaming... 

Specially treated glass beads have been used as supports for high-molecular-weight compounds. The beads are usually etched and silanized prior to coating with the liquid phase. Teflon is a useful support material for the analysis of short chain polar substances, which tail on diatomaceous supports, and is particularly indicated for the analysis of corrosive substances such as halogenated acids. 

It is also possible to use the support in a packed column without coating it. Firebrick tends to be acidic and reacts with basic substrates. Other materials that have been used without coatings are Teflon, nylon, graphite, micro glass beads, and carborundum. There appears to be little advantage to supports without coatings, and they are not widely used. 

Fig. 28. Time domain waveforms and power spectra (right) of Teflon composite containing 10% of indicated sizes of glass beads...

Fig. 29. Frequency dependence of ratios of spectral amplitude for Teilon/glass bead composites (10% bead content) to that for pure Teflon...

Special supports are popular for particular applications. Very lightly loaded glass beads are preferred when very rapid separations are desired. Very often powdered teflon is used as a support for very polar solutes. Graphitized carbon and carborundum are other supports for special applications. 

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