Fused silica optics

C. E. Arthur and J. Pawliszyn, Solid phase mia oextr action with thermal desorption using fused silica optical fibers . Awn/. Chem. 62 2145 - 2148 (1990). 

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

In our earlier study, a pure fused silica optical fiber, SF-112UV (Sumitomo Co. Ltd., Japan), was chosen to serve as both delivery and collection fibers. The fiber has a core diameter of 114 pm, a total diameter of 125 pm, and an NA value of 0.20 [28]. Table 2.1 shows fibers with smaller i b values, and they would have been satisfactory, but we were also concerned about cost and continuing availability. There was no problem with using this fiber for both 720 and 785 nm excitation wavelengths. 

Author, C.L. and J. Pawliszyn (1990). Solid phase microextraction with thermal desorption fused silica optical fibers. Anal. Chem., 62(19) 2145-2148. 

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. 

Solid-phase microextraction (SPME) — is a procedure originally developed for sample preconcentration in gas chromatography (GC). In this procedure a small-diameter fused silica optical fiber, coated with a liquid polymer phase such as poly(dimethylsiloxane), is immersed in an aqueous sample solution. The -> analytes partition into the polymer phase and are then thermally desorbed in the GC injector on the column. The same polymer coating is used as a stationary phase of capillary GC columns. The extraction is a non-exhaustive liquid-liquid extraction with the convenience that the organic phase is attached to the fiber. This fiber is contained in a syringe, which protects it and simplifies introduction of the fiber into a GC injector. Both uncoated and coated fibers with films of different GC stationary phases can be used. SPME can be successfully applied to the analysis of volatile chlorinated organic compounds, such as chlorinated organic solvents and substituted benzenes as well as nonvolatile chlorinated biphenyls. 

Two methods for the covalent immobilization of single-stranded DNA onto fused silica optical fibres using various linkers for the development of biosensors were reported by Krull and co-workers [22]. One method involved a hydrophobic and the other a hydrophilic spacer arm and it was determined which linker would provide the best immobilization efficiency, hybridization kinetics, and minimal non-specific adsorption to the surface. 

Solid-phase extraction devices and applications are evolving rapidly, and novel techniques that stretch the classical definition of SPE are becoming routine. Pawliszyn introduced solid-phase micro extraction (SPME) in 1989,5,14 and a commercial apparatus is available from Supelco (Bellefonte, PA). The SPME apparatus is merely a modified syringe that houses a fused silica optical fiber coated with an immobilized polymer film. The fiber can be exposed for extraction and then retracted for insertion or removal from the sample vial or instrument. Both manual and autosampler devices are available and each can be adjusted for proper fiber depth. Several coatings are available with varying thickness including polydimethylsiloxane, polyacrylate, polydimethylsiloxane/divinylbenzene, and carbowax/divinylben-zene. In contrast to SPE, which is an exhaustive extraction approach, SPME will extract only a fraction of an available analyte, hence it is not suitable for the isolation of impurities and degradants in most applications.15... 

Solid-phase microextraction (SPME) is a sampling and concentration technique used to increase the sensitivity of HS methods. This technique is utilized for arson analysis and environmental monitoring purposes and also for clinical and forensic procedures. Short, narrow diameter, fused-silica optical fibers coated with stationary phase polymers are either immersed in the sample or the HS and compounds are adsorbed or absorbed (depending on... 

Arthur, C. L. and Pawliszyn, J., SPME with thermal desorption using fused silica optical hbers. Anal. Chem., 62, 2145-2148, 1990. 

As noted earlier, fused silica optical fiber is used for remote NIR measurements. The same type of fiber optic probe can be used for Raman spectroscopy, and enables remote measurement of samples and online process measurements. In situ reaction monitoring by Raman spectroscopy has been used to study catalytic hydrogenation, emulsion polymerization, and reaction mechanisms. Remote sensing of molecules in the atmosphere can be performed by Raman scattering measurements using pulsed lasers. 

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