Thin layer cells

The most widely used amperometric detectors are based on the thin-layer and wall-jet configurations (Figure 3-22). The thin-layer cell relies on a thin layer of solution that flows parallel to the planar electrode surface, which is imbedded in a... 

Tubular Planar (parallel flow) Thin-layer cell Planar (perpendicular) Wall-jet detector 1= 1.61 nFC(DA/r)2/3U123 i = 0.68 nFCD2l3v- 6(A/b)V2UV1 i = 1.47 nFC(DA/b)2/3U123 i = 0.903nFCD2f3v- 6A3/4u 2 i = 0. mnFCD2/3v-5/ua-V2A3/tU3/4... 

Optically active molecules show circular dichroism. Their extinction coefficients f l and are different and change as a function of wavelength. Using a suitable spectroelectrochemical cell, Af = fl -which is usually small compared to conventional extinction coefficients, can be measured. Combined with the special properties of a thin layer cell kinetic data can be extracted from CD-data [01 Liu]. (Data obtained with this method are labelled CD.)... 

Significant improvements in ECALE deposit morphology and quality were reported as achieved by switching from a thin layer cell to a thick layer H-form cell, integrated in an automated deposition system [46]. Thin epitaxial films of zinc blende CdTe, CdSe, and CdS with predominate (111) orientations were grown. 

The drop in current that occurs in coulometric experiments may arise not only from the decrease in bulk concentration of the substance being analyzed, but also from a decrease in its surface concentration caused by the development of concentration gradients (see Section 11.2.1). Low values of current density and strong solution stirring are used to avoid the interference of such effects. Thin-layer cells where the electrodes are very close together (tens of micrometers) and the parameter ratio SIV is high, are often used to shorten the experiments. 

A thin-layer cell for SFG measurements is shown in Fig. 27.35 (Baldelli et al., 1999). The IR and visible beams impinge on the sample surface at different angles. 

Figure 5.12 Scheeatlc diagraM of A, a thin-layer cell, B, a wall-jet cell, and C a complete assenbly for a thin-layer ai >eronetric detector.

Fig. 9. LEED Auger electrochemical UHV system with electrochemical thin layer cell. After [39].

The system developed by O Grady is reproduced in Fig. 9. A key element of this arrangement is the electrochemical thin layer cell, using a combined Pd-hydrogen reference and counter electrode, thus minimizing the amount of electrolyte necessary for the electrochemical treatment. This type of cell is particularly useful for double layer studies but cannot be used for gas evolution or corrosion experiments at higher current densities. For a collection and discussion of other transfer systems the reader is referred to the review article by Sherwood [43]. 

Fig. 1.6. Thin layer cell for in situ IR absorption-desorption measurements based in a model proposed by Seki et al. [32]. WE = working electrode, W = window, L=lead, M = micrometer screw, S = steel spring, SM = simmer gasket.

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. 

External reflectance. The most commonly applied in situ IR techniques involve the external reflectance approach. These methods seek to minimise the strong solvent absorption by simply pressing a reflective working electrode against the IR transparent window of the electrochemical cell. The result is a thin layer of electrolyte trapped between electrode and window usually 1 to 50 pm. A typical thin layer cell is shown in Figure 2.40. 

In 1985, Feldman et al. reported in situ conductivity measurements on polypyrrole. These were obtained using a twin electrode, thin-layer cell... 

Figure 3.75 Schematic illustration of a twin electrode thin layer cell used for static conductivity measurements. From Feldman et ai (1985). Copyright 1985, American Chemical Society.

CdSe Flow cells, large thin layer cell 2000 [164]... 

Films of CdSe have been grown with the automated flow-cell systems, both using the H-cell [111] (Figure 3B), and recently with the large thin-layer cell (Figure 3C) [164], Comparisons of X-ray diffraction patterns (XRD) have suggested that in both cases,... 

Scaling analysis has also been applied to quasi-2D deposits in thin layer cells where the images were obtained by optical microscopy. These studies focus on length scales up to hundreds of micrometers, and find a clear non-local instability, but also report KPZ like behavior on smaller scales [79-81],... 

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