Fibres coating

Fig. 35 TEM image of peptide fibres coated with streptavidin-gold nanoparticles, (a, b) Peptides with biotin directly attached (using SAF-pl-biotin) particles are 10 nm, (c) Peptide fibre with biotinylated anti-FLAG antibody attached that was then bound to gold-labelled streptavidin particles are 5 nm. Reprinted with permission from Ryadnov and Woolfson [76]. Copyright 2004 American Chemical Society...

So the function of special optical fibres for sensing is to produce a sensitive response to changes in the fibre surroundings. Such requirements on optical hardware as durability to the analyte, transparency (i.e. minimum optical losses) in a wide spectral range and common availability should be pointed out. Related to the these requirements, the choice of the fibre material as well as of the fibre coating and fibre structure belong to fundamental tasks in the design of fibre-optic sensors. 

From Figure 13 it can be seen a typical example demonstrating the influence of the properties of the fibre coating on fibre sensing properties. 

The SPME process, adapted for solid or viscous matrix, is shown in Figure 10.1. A fused silica fibre, coated with a polymer, is installed inside a stainless steel hollow needle. In the first step, the needle is introduced in the sample vial through the septum. The fibre is then exposed to the headspace above the sample and the organic analytes adsorb to the coating of the fibre. After a variable sampling time, the fibre is drawn into the needle and the needle is withdrawn from the sample vial. Finally, in the same way, the fibre is introduced into the chromatograph injector where the analytes are thermally desorbed. 

Five SPME fibre coatings (PDMS, PDMS/DVB, CAR/PDMS, DVB/CAR/PDMS and CW/DVB) and four sampling times (20, 40, 60 and 80 min) were tested. The sampling temperature was 80°C. 

Diterpenes require more than 80 min to reach equilibrium. This is expected for compounds that exhibit low vapour pressure in combination with a high partition coefficient between the fibre coating and the gaseous phase. During headspace SPME the amount of such compounds present in the gaseous phase is absorbed by the fibre coating at a much faster rate than their release from the matrix, thus the amount of mass in the headspace at any time is small and a long time is required to reach equilibrium [58]. 

However, it was observed that, for each compound, the sampling profile was the same for the five fibre coatings. It could be deduced that the quantity of terpene trapped is independent of the nature of the fibre coating. This behaviour can be explained easily, as the interactions between compounds and fibres are not specific. This is not very surprising because of the nature of the terpenes studied, which are principally composed of carbon and hydrogen. 

Table 10.2 Values of the criterion function Fij calculated for five different fibre coatings...

Early work was based on concentrating the radium from the seawater sample by adding barium and coprecipitating with barium sulfate. This concentration procedure has been replaced by one involving the extraction of radium from seawater on acrylic fibre coated with manganese dioxide [19,20] (Mn fibres). By use of this technique, volumes of 200-2000 litres may be sampled routinely. 

The volatile substances were extracted from portions of 0. lg hair using solid-phase micro extraction (SPME). The method uses a fibre coated with an adsorbent that can extract organic compounds from the headspace above the sample. Extracted compounds are desorbed upon exposure of the SPME fibre in the heated injector port of a gas chromatograph (GC). 

Wire and cable insulation and jacketing, telecommunication wires and cables, optical fibre coating, extruded coatings... 

As with fatty acids, organo-silanes can be applied by both wet and dry coating methods. In the present context, wet coating is principally restricted to glass fibre coating, where it can be incorporated into the size, which is already applied from water. Dry coating is the preferred method for coating mica, wollastonite clays and metal hydroxides. 

An SPME unit consists of a piece of fused-silica fibre coated with a layer of a stationary phase such as non-polar poly(dimethylsiloxane) or polar polyacrylate or divinylbenzene/Carboxen/poly(dimethylsiloxane). The latter, for example, was suitable to trap the odorants (including sotolon) of soy sauce [19]. In the analytical procedure the fibre is exposed to the headspace of a food sample for 10-15 min. Then, the fibre is inserted into the injection port of a GC-mass spectrometry (MS) system. After desorption, the odorants are analysed. To improve the yields of the odorants, the fibre is placed in the effluent of a food sample purged with nitrogen [20]. 

According to the 1981-83 United States National Occupational Exposure Survey (NOES, 1997), as many as 125 000 workers in the United States were potentially exposed to dimethylformamide (see General Remarks). Occupational exposures to dimethylformamide may occur in the production of the chemical, other organic chemicals, resins, fibres, coatings, inks and adhesives. Exposure also may occur during use of these coatings, inks, adhesives, in the synthetic leather industry, in the tanning industry and in the repair of aircraft (Ducatman et al., 1986 lARC, 1989). 

Dale, J. M., Sulfur-Fibre Coatings, Sulphur Inst. J. (Fall 1965) 1 (1),... 

To cite a practical example, 20% by mass of 12/mi diameter glass fibre coated with silver (70 nm thick) mixed in a thermosetting polyester resin gave a composite conductivity of 2.5 x 104fi-lm 1. From Equation (8.37) the calculated value is 5.3 x 104fl-lm-1, which compares reasonably well with the experiment, if one takes into account that some disintegration of the fibre is inevitable in the mixing process. 

Immune cholangitis differs markedly from the early forms of PSC. In particular, the fibre coats surrounding proliferated ductuli, which are typical of PSC and which develop early, and the PAS-positive colouring of the basal membrane are absent. Biliary cirrhosis must be anticipated as the final stage. (454, 469, 471) (s. p. 644) Therapy is with UDCA, first of all as monotherapy. With non-responders, the additional administration of azathioprine plus prednisolone is recommended. In coexistent chronic IBD, the administration of mesala-zine (5 ASA) is indicated. Liver transplantation is required in the individual case. (455, 461, 463, 465)... 

Desorption from the fibre can also be accomplished by using an appropriate solvent, a condensed medium such as compressed CO, or even an aqueous solution. For example, the selective extraction of bismuth from a fibre coated with an ion-exchange polymer can be accomplished by using an acidic potassium iodide solution as a complexing reagent [206]. 

Headspace SPME involves three phases (viz. coating, headspace and matrix), the chemical potential difference of the analytes between the phases being the driving force that moves them from the matrix to the fibre coating. With aqueous samples, head-space/water partition coefficients are directly related to the Henry constants for the analytes, which are in turn determined by their volatility and hydrophobicity. 

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