Fiber silica

Solid-phase microextractions also have been developed. In one approach, a fused silica fiber is placed inside a syringe needle. The fiber, which is coated with a thin organic film, such as poly(dimethyl siloxane), is lowered into the sample by depressing a plunger and exposed to the sample for a predetermined time. The fiber is then withdrawn into the needle and transferred to a gas chromatograph for analysis. 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Fused-silica fiber coated with stationary phase... 

A solid-phase extraction in which the solid adsorbent is coated on a fused-silica fiber held within a syringe needle. 

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

Microscopic sheets of amorphous silica have been prepared in the laboratory by either (/) hydrolysis of gaseous SiCl or SiF to form monosilicic acid [10193-36-9] (orthosihcic acid), Si(OH)4, with simultaneous polymerisation in water of the monosilicic acid that is formed (7) (2) freesing of colloidal silica or polysilicic acid (8—10) (J) hydrolysis of HSiCl in ether, followed by solvent evaporation (11) or (4) coagulation of silica in the presence of cationic surfactants (12). Amorphous silica fibers are prepared by drying thin films of sols or oxidising silicon monoxide (13). Hydrated amorphous silica differs in solubility from anhydrous or surface-hydrated amorphous sdica forms (1) in that the former is generally stable up to 60°C, and water is not lost by evaporation at room temperature. Hydrated sdica gel can be prepared by reaction of hydrated sodium siUcate crystals and anhydrous acid, followed by polymerisation of the monosilicic acid that is formed into a dense state (14). This process can result in a water content of approximately one molecule of H2O for each sdanol group present. 

This design was closely followed in the experimental model and in the later instruments. The experimental model (October, 1940) had as test body a dumbbell of two thin-walled glass spheres 4 mm. in diameter sealed to a glass rod 6 mm. long. A silica fiber 8 fi in diameter was stretched between the prongs of a silica fork, and the glass dumbbell was cemented with shellac to the middle of the fiber, perpendicular to it. A plane glass mirror 2 mm. square was also cemented near the middle of the fiber. The suspension was balanced... 

We are grateful to.Professor H. Victor Neher of the Norman Bridge Laboratory of Physics for advice and instruction in silica-fiber technique. 

A four-ounce Alnico permanent magnet was mounted in a brass yoke. Two wedge-shaped pole pieces of soft iron, each with a slot sawed part way through it, were also attached, and the dumbbell assembly was inserted with the ends of the silica fiber in the slots and the spheres of the dumbbell between the pole pieces, one sphere being a little in front and the other a little behind the plane of the pole pieces, as shown in Figure 1. 

Fig. 2.—The assembly of dumbbell, mirror, and balancing rod mounted on a taut silica fiber.

Zhong, Q., Innis, D., Kjoller, K., and Elings, V., Fractured polymer/silica fiber surface studied by tapping mode atomic force microscopy. Surf. Sci. Lett., 290, 688, 1993. 

Solid phase micro extraction (SPME) is a techniques in which a silica fiber coated with a thin film of polymer is brought into contact with an aqueous matrix where the organics in solution partition onto the fiber. The fiber is subsequently placed into the injector of a GC where the heat causes the release of analyte onto the column. This has been applied to endosulfan (a- and (3-) and endosulfan sulfate in water with limits of detection of less than 0.3 pg/L reported (Magdic and Pawliszyn 1996). 

Figure 9.2 Fiber and foam structures, (a) Knitted silica fibers catalyst. (Reprinted from [7].) (b) Woven active carbon fiber catalyst. (Reprinted from [8].) (c) Aluminum foam. (Reprinted from [9].)...

In context with methane detection during offshore oil drilling, another infrared fiber optic methane sensor was reported25. The detector comprises 3 main units a microcomputer-based signal processing and control unit, a nonconducting fiber optic gas sensor, and an optical fiber cable module. The system operates at an absorption line of methane where silica fibers have very low losses. 

Unlike methane and the other alkanes, aromatic hydrocarbons have absorptions in the UV part of the spectrum, and thus may be detected through UV spectrometry using silica fibers. This scheme is useful for "aromatic" water pollutants such as toluenes and xylenes with their absorption bands between 250 and 300 nm. Similarly, nitrate anion can be monitored (albeit with low sensitivity) in water via its UV absorption at 250 nm. 

A novel fiber optic sensor concept using antibody-antigen reactions at a glass-liquid interface was reported by Daehne146. The reaction of antibodies immobilized onto the surface of fused silica fiber optic or planar waveguides with antigens in solution was detected by interaction with the evanescent wave. By detecting in-line fluorescence, the measurement of human IgG is described. 

R. P. Belardi, J. Pawliszyn, The application of chemically modified fused silica fibers in the extraction of organics from water matrix samples and their rapid transfer to capillary columns, Water Pollut. Res. J. Can., 24, 179 191 (1989). 

Strong Photocatalytic Fiber (Titania/Silica Fiber) Produced... 

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