Platinum coils

Small solid seuaples can be analyzed directly by dynamic headspace sampling using a platinum coil and quartz crucible pyrolyzer and cold trap coupled to an open tubular column (341,369,379). This method has been used primarily for the analysis of mineral samples and of additives, catalysts and byproducts in finished polymers which yield unreliable results using conventional headspace techniques owing to the slow release of the volatiles to the headspace. At the higher temperatures (450-1000 C) available with the pyrolyzer the volatiles are more readily and completely removed from the sample providing for quantitative analysis. 

To use the DCI probe, 1-2 xL of the sample (in solution) are applied to the probe tip, composed of a small platinum coil, and after the solvent has been allowed to evaporate at room temperature, the probe is inserted into the source. DCI probes have the capability of very fast temperature ramping from 20 to 700 °C over several seconds, in order to volatilise the sample before it thermally decomposes. With slower temperature gradients, samples containing a mixture of components can be fractionally desorbed. The temperature ramp can be reproduced accurately. It is important to use as volatile a solvent as possible, so as to minimise the time required to wait for solvent evaporation, which leaves a thin layer of sample covering the coil. The observed spectrum is likely to be the superposition of various phenomena evaporation of the sample with rapid ionisation direct ionisation on the filament surface direct desorption of ions and, at higher temperature, pyrolysis followed by ionisation. 

Pyrolysis-Gas Chromatography-Mass Spectrometry. In the experiments, about 2 mg of sample was pyrolyzed at 900°C in flowing helium using a Chemical Data System (CDS) Platinum Coil Pyrolysis Probe controlled by a CDS Model 122 Pyroprobe in normal mode. Products were separated on a 12 meter fused capillary column with a cross-linked poly (dimethylsilicone) stationary phase. The GC column was temperature programmed from -50 to 300°C. Individual compounds were identified with a Hewlett Packard (HP) Model 5995C low resolution quadruple GC/MS System. Data acquisition and reduction were performed on the HP 100 E-series computer running revision E RTE-6/VM software. 

Pellistors are used to detect flammable gases like CO, NH3, CH4 or natural gas. Some flammable gases, their upper and lower explosion limits and the corresponding self-ignition temperatures are listed in Tab. 5.1. This kind of gas sensor uses the exothermicity of gas combustion on a catalytic surface. As the combustion process is activated at higher temperatures, a pellistor is equipped with a heater coil which heats up the active catalytic surface to an operative temperature of about 500 °C. Usually a Platinum coil is used as heater, embedded in an inert support structure which itself is covered by the active catalyst (see Fig. 5.33). The most frequently used catalysts are platinum, palladium, iridium and rhodium. 

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

The variable-temperature cell in which reactive intermediates can be studied at temperatures down to — 130°C (Figure 6.18) is designed with opposed, coaxial working, and Luggin-probe electrodes surrounded by a platinum-coil counter electrode. The cylindrical symmetry provides uniform current and po-... 

Sintered metal elements as a part of a flameproof enclosure are often used for gas warning detectors for combustible gases. As a cost effective gas sensor, an electrically heated platinum coil covered with a catalyst and as a part of a... 

FIGURE 8.3. Electrolytic cell for the ECSOW system (a) O phase (b) W phase (c), (d) platinum disk electrodes connected with an electric wire (e), (f) reference electrodes with Luggin capillaries (g), (h) platinum coil electrodes (i), (j) N2 gas inlet. Reprinted from Ref. [38], with permission from Elsevier Science. 

The titrant is usually generated directly in the solution whence it can immediately react with the species to be determined. The electrodes are typically made of platinum coils or sheets. The counter-electrode is normally... 

Pyrolysis in the Presence of TMAH. A wide set of Fulvic Acids (FA), Humic Acids (HA) and related materials from different origins have been thus far studied using the TMAH/thermochemolysis procedure (9,15-17,22,24,25). The TMAH procedure has mainly been performed in pyroprobe units, in much the same way as the conventional flash pyrolysis using either quartz tubes and/or a platinum coil, by mixing the humic materii with a few drops of the reagent prior to heating. 

Use of a coil of high resistance This is the method employed in the Engelhard thermometer. The resistance of the lead wires from the coil to the thermometer head and the likely variation in resistance of the copper lead wires are extremely small compared to the 50-ohm platinum coil. Hence such variations in resistance as are likely to occur do not introduce serious error. Thus only two lead wires are necessary, from the thermometer to the indicating instrument. 

ISO ml. concentrated ammonia solution are placed in the Erlenmeyer flask. The platinum coil is attached to a piece of nickel wire and hung in the flask so tliai it is about 3 cm above the surface of the liquid. Before the spiral is intro-... 

Go to the slow combustion chamber that s the one with the platinum coil. Close the stopcock. 

The poly(oxyphenylene) was electrodeposited from freshly prepared solution containing 0.23 M of 2-allylphenol, 0.4 M of allylamine, 0.2 M of butylcellosolve (ethyleneglycol monobutylether) in water/methanol mixture (1 1 by volume) by applying a constant potential of 4 V from constant voltage power-supply (Zentro-Elektrik, Type LA 15/156 B) between the cathode (a platinum coil of 1.5 cm area) and the substrate (anode). The current was monitored with a Keithley 177 microvoltmeter and recorded with a Metrawatt, Model SE 780 recorder. The electrodeposited films of poly(oxyphenylene) formed within half of an hour (aprox. 1.5 /xm thick) were rinsed with distilled water and cured at 150°C for 30 min. 

In a study by Fanning et al. (2007) 100 intracranial aneurysms were embolized with HydroCoils in conjunction with bare platinum coils, where a basket of bare platinum coils were positioned in the aneurysm, followed by the introduction of HydroCoils. The treatment group showed a 20% increase in the mean packing density when the same number of coils was used in the control... 

Matrix detachable coils (Boston Scientific Neurovascular) are another example of modified endovascular coils, employing a stainless steel delivery wire coated with a bioabsorbable copolymer of 90% polyglycolide and 10% polylactide. In a study by Murayama et al. (2003), matrix detachable coils were shown to accelerate the rate of aneurysm healing in swine aneurysm models, specifically by promoting the formation of a thick neointimal layer at the aneurysm neck more quickly bare platinum coils (Murayama et al, 2003). Taschner et al. (2005) evaluated the use of Matrix detachable coils in 25 patients with intracranial aneurysms. Again, stable emboUzed aneurysms were achieved over a six-month period, but only when Matrix coils were used in conjunction with bare platinum coils (Taschner et al, 2005). 

Cloft, H. J. KaUmes, D. F. (2004) Aneurysm packing with HydroCoil embolic system versus platinum coils initial clinical experience. American Journal of... 

Farming, N. F., Berentei, Z., Brerman, P. R. Thornton, J. (2007) HydroCoil as an adjuvant to bare platinum coil treatment of 100 cerebral aneurysms. Neuroradiology, 49, 139-148. 

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