Quartz

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During the period of soft glass capillary use the optical fiber industry had developed methods for drawing flexible quartz fibers by coating then directly after drawing with a temperature resistant polimide plastic. The product was quite unique in that loose knots could be tied in such fibers without their breaking and yet the natural form of the fibers was straight. The technique for quartz fiber production was used by Dandenau (3) to produce flexible quartz capillary tubes. As the quartz capillaries were intrinsically straight they could be easily connected to the sample injection system and the detector using appropriate ferules but, at the same time, the column itself could be formed into a neat coil to fit into a relatively small oven. Initially, some minor problems were experience in coating these columns, but these were soon over come and today, most stationary phases can be coated as thin films on the walls of quartz capillaries. An

columns, but their permanent circular shape, made them difficult to fit to unions connecting columns to injector and column to detector. By careful surface treatment the rigid glass tubes could be coated with polar stationary phases such as CARBOWAX�. Dandenau (5) introduced flexible fused silica capillary columns using the quartz fiber drawing technique. The solid quartz rod used in quartz fiber drawing was replaced by a quartz tube and the drawing rates adjusted appropriately. The quartz tubes had to be coated on the outside with polyimide to prevent moisture attacking the surface and producing stress corrosion. Coating the capillary tube with a polyimide polymer immediately after drawing prevents moisture coming in contact with the surface and thus stabilizes the tube. Soft glass capillaries can be produced by the same technique at much lower temperatures (6) but the tubes are not as mechanically strong or as inert as quartz capillaries. Surface treatment is still

can exist in both crystalline and amorphous forms, it usually occurs as quartz, cristobalite or tridymite crystals. Quartz, when crushed by earth movement and weathered by air and water forms sand. Each silicon atom in both quartz and cristobalite is associated with four oxygen atoms but, in cristobalite the silicon atoms are thought to be oriented in a similar manner to the carbon atoms in diamond where the oxygen atoms would be considered to be situated half way between the ‘carbon’ atoms. In quartz, the silicon atoms adopt a helical configuration, and consequently, the crystals are enantiomorphic and, thus, optically active. Silica, (SiO2) can be considered to be the anhydride of silicic acid, and in its naturally occurring crystalline form, does hydrate to silicic acid and, as a consequence, is very slightly soluble in water. However, the hydration is very slow and it is not practical to produce silica gel, for example, by directly hydrating quartz. The Preparation of Silica Gel

The UV adsorption system consists of a low pressure mercury lamp (major emission at 254 nm) and a solid state photo cell with quartz windows so it responds to light in the UV region. The cell is 3 mm long and is terminated at on end by a cylindrical quartz window and at the other by a quartz lens. The lens focuses the transmitted light on to the photo cell. There are two stainless steel discs separated by a 1 cm length of Pyrex tube adjacent to the quartz windows. Mobile phase enters and leaves the detector cell through radial holes in the periphery of the stainless steel discs. The steel discs act as the electrodes

Open Tubular Columns The majority of contemporary open tubular columns are made from fused quartz although, even today, in some applications (mainly hydrocarbon mixtures) stainless steel columns are still used providing equivalent performance. Nevertheless, fused quartz columns are perceived as “state of the art” columns. The internal surface of an open tubular column normally requires some deactivation and/or cleaning before it can be coated with stationary phase. Deactivation procedures (although usually very simple) are usually considered as highly proprietary. Under

array spectrometer. A diagram showing the basic principles of the helium plasma atomic emission spectrometer is shown in figure 21. The plasma is microwave induced into a helium stream employing a water-cooled transducer. The sample, mixed with the pure helium make-up gas, enters the plasma and the elements present in the solute emit light, the wavelength of which is characteristic for each element. The sample residue subsequently passes to waste. The light emitted is transmitted through a quartz window, and is then focused by a quartz lens and spherical mirror onto a diffraction grating.