Electrode cells guarding

The technique of pellet preparation and the guard-ring electrode cell were described previously (8). The density of the pellets is 61% of the real zeolite density. No structural damage is observed with x-ray diffraction after pellets are made. 

Detector E, ESA Coulochem model 5100 A, Model 5020 guard cell, guard cell 0.3 V, detector 0.55 V for first electrode and 0.70 V for second electrode... 

Detector E, ESA Coulochem Model 5100A, Model 5020 guard cell 1.0 V (before iiyector). Model 5010 dual-electrode cell, screen electrode El -I- 0.7 V, sample electrode E2 -(-0.9 V,... 

Sample cells (Figure 5.16) were constructed upon the coated panels by glueing the polished end of glass tubes (internal diameter about 50 mm.) onto the coated surface with epoxy cement. The sample cells were stored at 22 2°C and a relative humidity of 55 + 5 per cent. The steel panel served as high potential electrode (H), and a mercury electrode, connected by a platinum wire, as low potential electrode (L). Guarding was achieved by using a bell-shaped brass cover which also supports the connector of the low potential electrode. 

Fig. 67. Thermometric conductivity detector with 5 electrodes 1) = reference electrode 2) = detection electrode 3) = guard electrode = cell unit 5) - cell oven 6) = 2 meters of 0.23 mm i.D. stainless steel tubing...

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

Figure 1.5 (a and b) Typical electrode configurations used for the measurements of thermally stimulated currents. The sample surface ceU (a) may be augmented by additional contacts (b)-(d) to monitor potential distribution along the sample. The sandwich cell (e)-(h) is ideally suited for the use of guard rings of either rectangular or circular shapes. 

Stray capacitances, e.g. between a lead and the opposite electrode, must be avoided by proper shielding. For this reason it is preferable to run the guarded electrode at zero potential. Then the guard electrode can be earthed and a completely shielded 3-terminal cell constructed (Fig. 5.5), where the only stray capacitances are between the electrodes and earth, giving an equivalent circuit as shown. 

Fig. 5.5 A 3-terminal specimen holder (a) diagram of shielded electrode system with guard ring, (b) equivalent electrical circuit of the cell.

In this condition, earthed screens can be used around all bridge components, and a guard electrode can be used in the sample cell. 

Fig.6. Configuration of a vertical parallel-plate cell [10]. a Side view b Cross section view (X-X ) (1) silicone tube (outer diameter, 4 mm), (2) glass plate (length x width x thickness, 50x50x3 mm), (3) copper wire (diameter, 1 mm), (4) electrode (gold-plated copper foil diameter, 20 mm thickness, 0.035 mm), (5) guard electrode (gold-plated copper foil diameter, 22 mm thickness, 0.035 mm), (6) electrode (gold-plated copper foil length x width x thickness, 50x50x0.035 mm), (7) epoxy adhesives, (8) epoxy resin (thickness, 1.5-2.5 mm)...

Eluted peaks were detected by electrochemical oxidation using the ESA 5100A coulometric detector equipped with an ESA 5010 dual electrode detector cell and a guard cell (ESA, Bedford, MA). The guard cell was placed between the pump and injector (19) and set at a potential of 0.75V. The first electrode of the analytical cell was set at a potential of 0.5V and the second electrode at which OA and N-acetyl OA are oxidized was set at 0.7V. 

Detector E, ESA 5100A Coulochem, guard cell +1 V, dual electrode analytical cell +0.7 and +0.8 V... 

Detector E, Environmental Sciences Associates Model 5100A, screen electrode -1-0.5 V, analytical cell -1-0.79 V, Model 5020 pre-column guard cell -1-0.85 V... 

Detector E, ESA 5100A detector. Model 5020 guard cell between pump and autosampler +0.7 V, Model 5011 dual electrode analytical cell, upstream (screening) electrode +0.2 V, downstream electrode +0.45 V against Ag/AgCl. 

Detector E, ESA Model 5100A Coulochem, model 5020 guard cell -1-950 mV, Model 5010 analytical cell + 400 mV, palladium reference electrode, following post-column photolysis. The effluent from the column flowed through a 20 m X 0.3 mm coil of PTFE tubing irradiated at 254 nm with a Sylvania GTE 8 W low-pressure lamp to the detector. 

Detector E, ESA Coulochem Model 5100 A, Model 5010 analjdical cell, first (screen) electrode 0.68 V, second (measuring) electrode 0.98 V, Model 5020 guard cell (before injector)... 

More recently, auxin effects on ion transport have been characterized in protoplasts from Vida faba guard cells and tobacco protoplasts. In both systems, patch clamp techniques have been used to demonstrate auxin regulation of anion channels [14,15]. Alternatively, electrode impalement of protoplasts from faba guard cells has demonstrated that low concentrations of auxin promote inward movement of K, while higher concentrations inhibit this same activity. These effects were correlated with opening and closing of the stomata, respectively [16]. 

Accurate sample thickness determination of these thin foam disks is difficult. A guarded measuring cell with two low-potential electrodes (one disk electrode for the sample and one ring electrode for the sample thickness determination) was... 

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