Window cell

Region Source Absorption cell window Dispersing element Detector... 

Useful fransparenf materials for cell windows, lenses, and so on are Pyrex glass for fhe visible and fused quartz for fhe visible and near-ulfraviolef. 

Neoprene gasket Cell window Lead spacer Cell window Neoprene gasket... 

When a beam of monochromatic radiation is passed through the windows of an infrared cell some reflection occurs on the window surfaces and interference takes place between radiation passing from the internal surface of the first window and that reflected back from the internal surface of the second window. This interference is at a maximum when 2d = (n + 1 /2)k, where d is the distance in yum between the inner surfaces of the two cell windows, X is the wavelength in m, and n is any integral number. If the wavelength k of the monochromatic radiation is varied continuously an interference pattern consisting of a series of waves (Fig. 19.7) is obtained. 

The wave-front shearing interferometric method can be applied to transparent melts which do not attack cell windows made of silicate glass. The principle of this method has been given by Gustafsson. " A thin foil is placed vertically, a laser beam passing in the -direction along the plane. The heat is transferred in a melt in the direction of x. The slope of the... 

Figure 2.112 Cyclic voltammograms of a P( electrode immersed in N2-saturated I M NaOH solution, and (a) in the absence and (b) in the presence of I M ethylene glycol. Scan rate 100mVs-1, the voltammograms were taken using the IR spectroelectrochemical cell with the electrode pulled back from the cell window. From Christensen and Hamnett (1989).

Two other types of RI monitor are based on Fresnel s laws of reflection and the principle of interferometry respectively. The former utilizes a very small volume (3 pi) sample cell and is therefore useful for highly efficient columns, but linearity is limited and the cell windows need to be kept scrupulously clean for optimum performance. The main advantages of the interferometric design are improved sensitivity and a wide linear range. 

In Figure 1 we show the PM-IRRAS spectra for a Pt electrode exposed to saturated C0/H S0 solutions which contain various concentrations of different organic nitriles. For comparison, we have also included a spectrum recorded in saturated CO/H SO with no added nitrile. The adsorption step was accomplished by pulling the electrode back into the bulk solution and cycling the potential from 0.55 V(SHE) up to 1.15 V, down to 0.0 V, and back to 0.55 V. The spectra were recorded after re-positioning the electrode against the cell window while the potential was held at 0.55 V. 

In the frequency region where the i/(0H) vibrations of interfacial H20 are observed, the normal Raman scattering from the bulk solution can obscure the SERS of interfacial H20 if appropriate precautions are not taken. In the studies reported here, the SERS of interfacial H20 was acquired with the electrode surface positioned as close to the electrochemical cell window as possible to minimize contributions from the bulk solution. When altering the electrode potential to deposit Pb onto the Ag electrode surface, the electrode was pulled away from the window several mm, the surface allowed to equilibrate at the new conditions, and the electrode repositioned near the cell window for spectral acquisition. 

Reaction of a Pt (II) carbonyl derivative with halide from the IR cell window monitored by v(CO)... 

Procedure Take about 15-20 mg of sample in a previously cleaned small agate mortar and powder it thoroughly (about 200 mesh). Add to it 2 drops of purified paraffin (commonly known as Nujol) or any other suitable mulling liquid and continue the trituration until a very smooth paste of uniform consistency is achieved. Now, transfer the slurry to a sodium chloride window, placing it carefully into the cavity made by the spacer. Consequently, place the other window on top and thus assemble the cell. With the help of a clean piece of tissue-paper wipe out the excess paste that has squeezed out from the cell windows. Finally, introduce the cell in the respective cell-compartment. 

Infrared detectors are similar in construction to those used in UV detection. The main difference is that the sample cell windows are constructed of sodium chloride, potassium bromide, or calcium fluoride. A limitation of this type of detector is caused by the low transparency of many useful solvents (Skoog et al., 1998). Recent changes to interface systems that use spraying to induce rapid evaporation of the solvent provide good sensitivity and enhanced spectral quality (LaCourse, 2000). 

HP IR transmission cells can be divided into two broad categories, namely (i) where the contents of the high pressure vessel are observed directly through IR transparent windows and (ii) where the reaction solution is circulated from the autoclave to an auxiliary observation cell. The first type is exemplified by the cell shown in Figure 3.2, developed by Whyman at ICI [2, 3]. The stirred reaction solution surrounds the cell windows in an arrangement that minimises the problem of... 

Cells of the second type were initially developed by Tinker and Morris at Monsanto [4] and subsequently by Penninger [5]. In these systems, the reaction solution is circulated from the autoclave through an external IR cell of relatively small volume. This arrangement means that the cell can be isolated from the main reaction vessel relatively easily (for example in the event of window failure) thus protecting the spectrometer. Cells of this sort can, in principle, be fitted to plants or pilot plants to monitor liquid streams. However, the circulation of solution from the main reaction vessel through an external cell introduces some potential problems. A pressure drop in the circulation system can lead to release of dissolved gas, which may accumulate between the cell windows and interfere with the spectroscopic measurement. A change in pressure may also influence the catalyst specia-tion, such that the observed spectra may not be truly representative of the bulk reaction solution. 

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

For measurements at temperatures other than ambient, cells with double walls, which can be thermostatted, are also available commercially. If measurements are required at temperatures between ca. —5°C and room temperature, the sample compartment of the spectrometer can be flushed with dry air or nitrogen to reduce condensation on the cell windows. Below ca. — 5 °C the windows can be covered with a thin polythene film, but measurements below —25 °C are very troublesome. The problems associated with low temperature spectroscopic measurements were solved by enclosing the cell in an air-tight box fitted with glass windows (Dadley and Evans, 1967). The box was so designed that it fitted into the spectrophotometer and the air inside the box was dried with phosphoric oxide which, it is claimed, stopped condensation even at temperatures as low as — 60 °C glass windows could be used because only absorptions above 380 nm were of interest. 

Alternatively, two parallel cells are used, one of which has air from which 03 has been scrubbed and the other the air containing ozone. These instruments appear to be relatively artifact-free, although interference from high concentrations of photooxidation products in laboratory studies and from contamination of the cell windows has been reported (Meyer et al., 1991 Kleindienst et al., 1993). 

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