Sample flat cell

It is especially useflil for liquid samples in flat cells, which may extend through tlie entire height of the cavity. In the cylindrical cavity a TEq mode is frequently used because of its fairly high g-factor and the very strong along the sample axis. 

An alternative solution to the dielectric water problem that applies in particular to standard TE102 rectangular resonators, is to use a flat cell a rectangular sample holder that is oversized in the vertical direction, and with one small cut-through dimension, say 1 mm, and the other dimension circa 10 mm, that is, approaching the bore of the cavity access holes (Figure 3.11). When in place in the resonator, this cell is rotated about its vertical axis to a position such that the 10 mm dimension points to a direction of minimal /i-field. 

The electrochemical cells employed in epr measurements are generally fabricated out of silica since glass contains paramagnetic impurities that can interfere with the signal. The need to minimise the interaction of the sample with the electric component of the radiation in the cavity, and the geometry and size of the cavity itself, have generally led to electrochemists employing flat cells that are c. <0.5mm thick. 

For qualitative investigations there is considerable latitude in experimental procedure. There are few limitations on solvent for reactions studied in the liquid phase, although standard considerations of susceptibility to radical attack must obviously be taken into account. With polar solvents it may be desirable to replace the normal silica sample tube with a flat cell, although spin-adduct concentrations are usually sufficiently great for this to be circumvented by the use of capillary tubes. 

Electrokinetic Measurements. Electrophoretic mobilities were measured with a flat-cell apparatus manufactured by Rank Brothers, Cambridge, England. In addition, several mobility values were checked for accuracy with a Zeta Meter, New York. Mobilities were determined with a small volume of the suspension (approximately 25 cc) that had been prepared for the adsorption experiments. The pH of the solution was measured prior to determining the electrophoretic mobilities, which involved measuring the velocities of five to ten particles in each direction. An average value of the mobilities was recorded. Samples containing the flocculated particles were dipped into an ultrasonic bath for approximately one second prior to making the pH and mobility measurements. 

The optimum orientation of the flat electrochemical cell is in the center of the rectangular cavity, so that the sample is in the region of the maximum magnetic field. In this configuration, the face of the flat cell is parallel to the end plate of the cavity. Usually the cell position along the length of the cavity... 

Cylindrical cells are easier to construct and thermostat than flat cells and dark-field illumination can be obtained by the ultramicro-scopic method of illuminating the sample perpendicular to the direction of observation (see page 52 and Figure 7.6). The volume of dispersion required is usually less for cylindrical cells than for flat cells and, owing to the relatively small cross-section, it is more often possible to use platinum black rather than reversible electrodes with cylindrical cells. However, unless the capillary wall is extremely thin, an optical correction must be made with cylindrical cells to allow for the focusing action of the tube, and optical distortion may prevent measurements from being made at the far stationary level. Cylindrical cells are unsatisfactory if any sedimentation takes place during the... 

XRF is used for the analysis of solid and liquid samples. For quantitative analysis the surface of the sample must be as flat as possible, as will be discussed in the applications section. There are two classes of sample holders, cassettes for bulk solid samples and cells for loose powders, small drillings, and liquids. A typical cassette for a flat bulk solid such as a polished metal disk, a pressed powder disk, a glass or polymer flat is shown in Fig. 8.26(a). The cassette is a metal cylinder, with a screw top and a circular opening or aperture, where the sample will be exposed to the X-ray beam. The maximum size for a bulk sample is shown. The sample is placed in the cassette. For a system where the sample is analyzed face down, the cassette is placed with the opening down and the... 

The instrumentation for dc conductivity measurements is dc power-source, sensitive electrometer (the currents are of microampere range and lower), and adequate sample cells. Such instrumentation is easily available and even the most sensitive kind is relatively inexpensive. Remote measurements are simple to perform, and parts exposed to irradiation, like reaction cells and cables, are cheap and can be easily replaced. Two types of sample cells for conductivity monitoring are most conunon flat and cylindrical coaxial. In flat cells the sample, usually solid, is sandwiched between electrodes and the interelectrode distance is kept by a spacer of chosen size. Cylindrical coaxial cells shown in Figure 13.1 are preferred for liquid samples, flow-through versions also exist (Battisti et al. 2009a). 

A round-bottomed multinecked flask is a common approach when a sealed cell is required. Fig. 2(a). The multiple ports allow for insertion of tubes for deaeration, thermometers, and the various electrodes. As mentioned above, cells that press the sample against a window are called flat cells. Flat cells are easily sealed and convenient to use. Fig. 2(b). A clamp-on cell is a type of flat cell commonly used for coated samples. Fig. 2(c). Large areas are typically needed for clamp-on cells, and crevice corrosion is not a problem. The clamp-on cell uses a common glassware... 

The characteristics of the ESR cavity (Fig.l) implies the basic restrictions in the construction of an electrochemical cell for ESR-measurements. Like any other probes the electrochemical cell is to be mounted in the center of the resonant cavity where the magnetic field has its maximum. Lossy samples like electrolyte solutions have to be restricted into the z-direction to avoid high dielectric absorption which lowers the quality-factor of the cavity and the sensitivity of the measurement or makes the measurements impossible at high absorption. Therefore a flat cell with a 0.3 to 0.5 mm thickness of the solution layer must be used. The cell has to be made of quartz because of the "sucking in effect of that material which improves the sensitivity by a factor of 2. This geometry gives the limitations of the electrochemical conditions low electrolyte volume, high cell resistance and small electrodes. For the last fact even further restrictions exist. 

The measurements were conducted using the Rank Brothers Particle Microelectrophoresis Apparatus Mark II equipped with a flat cell. Samples were prepared by diluting a lOOpl sample of the oil-in-water emulsion with 20 ml of 10 M NaCl containing Aerosol OT (0 to 100 ppm). In experiments with Duomeen C, the reagent was added to the oil phase in the desired amount prior to emulsification. The pH was adjusted using HCl or NaOH to cover the range 2.5 to 11.5. All experiments were conducted at 30 C. 

The spectra of the radicals and magnetic nanoparticles were recorded at room temperature using Bruker EMX 8/2.7 X-band spectrometer at a microwave power of 5 mW, modulation frequency 100 kHz and amplitude 1 G. The first derivative of the resonance absorption curve was detected. The samples were placed into the cavity of the spectrometer in a quartz flat cell. Magnesium oxide powder containing Mn ions was used as an external standard in ESR experiments. Average amount of spin labels on protein macromolecules reached 1 per 4-5 albumin macromolecules and 1 per 2-3 thrombin macromolecules. Rotational correlation times of labels were evaluated as well as a fraction of labels with slow motion (x > 1 ns). 

Organic nonpolar solvents can normally be used at all temperatures. Aqueous samples present difficulties at temperatures above 0°C, due to the interaction of the large electric dipole of water with the standing wave in the resonator cavity. To minimize this interaction, thin, flat cells are used for aqueous samples in X-band systems and very narrow quartz capillaries are used in Q-band systems. 

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