Fused silica, speciality

The stationary phase consists of a thin layer (ca. 0.2 pm) of a non-volatile liquid, such as methylsilicone or methylphenylsilicone, tightly adsorbed to the inert surfaces of the column. The liquid stationary phases are classified according to their polarity, non-polar phases are used most often because they are easier to handle and are stable over a wide temperature range. The mobile phase is an inert carrier gas such as nitrogen, helium or hydrogen which flows at a constant, but adjustable rate through the column. Current capillary columns, with internal diameters between 0.1-0.6 mm, are constructed of fused silica, specially prepared from pure silicon tetrachloride, and formed into spirals up to 100 m long. Injectors, columns and detectors are located in separately thermostatable compartments. 

Cabot 1882 1.2 Carbon black/ natural gas Carbon black, fused silica, specialized high- performance materials Related diversification in 1950s unrelated diversification in 1960s retreat to core business in 1980s with selective, highly specialized remnants of diversification era... 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

The fluffy product is extremely finely divided (particle size typically 7-40 nm, powder density 0.03-0.06 g cm-3) but nonporous (surface area ca. 200-400 m2 g-1). Like fused silica, silica fume is amorphous, and this, together with the small particle size, gives it relatively high solubility. It is used as a thixotropic thickening agent for epoxy resins, in special high strength... 

Raman probes constructed from fused silica optical fibers have gained much attention recently. Typically, low-OH content fibers are utilized to reduce the fiber fluorescence. The probe design also includes filters at the distal end to suppress the fused silica Raman signal from the excitation fiber and suppress the elastically scattered fight entering the collection fibers.25 Commercial probes are now available and they offer ruggedness and easy access to samples with various special or geometrical constraints. 

On-column injection into columns of 320 pm or less is more difficult and not easily automated. This usually requires the use of a fused silica needle of sufficiently small outer diameter or a needle capable of entry into the analytical column. The column is usually placed into a specially designed injection port fitted with duck bill or isolation-valve-type septa. A second approach which has shown great success is the use of a precolumn of a wide-bore capillary (530 pm ID) which is connected to the analytical... 

One exception is the special types of photostructurable glass. For the construction of microreactors, the borosilicate types of glass as well as fused silica are the most important ingredients. 

Physical properties Fused silica Borosilicate glass Photoetchable special glasses... 

Solid-Phase Microextraction. Solid-phase microextraction (SPME), used as a sample introduction technique for high speed gc, utilizes small-diameter fused-silica fibers coated with polymeric stationary phase for sample extraction and concentration (33). The trapped analyte can be liberated by thermal desorption. By using a specially designed dedicated injector, the desorption process can be shortened to a fraction of a second, producing an injection band narrow enough for high speed gc. A modified system has been investigated for the analysis of volatile compounds listed in EPA Method 624. Separation of all 28 compounds by ion trap mass spectrometric detector is achieved in less than 150 seconds. 

Glassware that has bends and/or has been fused to other pieces of glass will be either common laboratory borosilicate glass or fused silica. Any soft glass made into laboratory apparatus is for special application or, more likely is very old (and ought to be in a museum). 

All the samples were further purifred by removing dust particles through 0.2 pm Millipore filter and sealed in fused silica cells or P x cells. The sample cell was embedded in a specially designed home-made cryostat or furnace. The temperatures were measured with a chromel-constantan thermocouple closely attached to a cell. The accuracy of the temperature control is within 0.1 K. The thermocouples were prepared at Chemical Thermodynamics Laboratory, Osaka University. 

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