Gold flow-through electrode

The molecular models are in a sense a subset of the geometrical ones - we assume that we know which molecules are present and we assume that we know their geometries (indeed sometimes we assume more than that, such as the usual assumption that thiol end groups lose their protons when forming their asymmetric bond with gold). In this we also necessarily assume that there are no other species, either on the electrode surface or in the surrounding media, that influence the current flow through the system. 

Castner turned his interest to gold extraction, which required high-quality sodium hydroxide. Castner developed a three-chambered electrolytic cell. The two end chambers contained brine and graphite electrodes. The middle chamber held water. The cells were separated excepted for a small opening on the bottom, which contained a pool of mercury that served as the cell s cathode. When current flowed through the cell and the cell was rocked, sodium reduced from the brine came into contact with water in the middle cell to produce a sodium hydroxide solution. As Castner built his mercury cell, Kellner was working on a similar design. Rather than compete with each other, Castner and Kellner joined forces to establish the Castner-Kellner Alkali Company to produce sodium hydroxide, which competed with soda ash and potash as an industrial base, and chlorine, which was used primarily to make bleach. 

Flow electrodes. Rather than move the electrode past the solution, the sample solution can be flowed past a stationary electrode. The tubular platinum electrode (Figure 5.34) and the gold micromesh flow-through electrode (Figure 5.35) are both ingenious attempts to produce electrodes that are useful for the measurement of electroactive materials in a continuously flowing stream. Ap-... 

Figure 5.35 Gold micromesh flow-through electrode (a) cell system (b) detail of gold micromesh screen.

Electronic accumulation represents probe interaction within electric fields. Small electrodes are arranged in an array and are addressed by electric circuits. Thus, charged capture probes are mutually attached or appealed in the discharged flow-through cell [50]. The capture probe concentration is enhanced on positive or negative electrodes. Nanogen uses Streptavidin coated gold electrodes to couple biotinylated capture probes after electronic accumulation (Fig. 18). 

Another cell for gold recovery is the Mintek cell. It has a rectangular configuration with alternating anodes and cathodes in parallel. The anodes are perforated stainless steel plates. The cathodes are removable plastic baskets with perforated sides, packed with steel wool. The electrodes fit the cell sides and bottom, so that the electrolyte has to flow through the electrodes. Packed cathodes of steel wool... 

H. Ma, L. Jin, and H. Yan, Studies on the Application of an Amperometric Gold Tube Electrode Flow Through Detector. II. The Determination of Micro Quantities of Cyanide in Surface Waters [in Chinese]. Huanjing Huaxue, 2 (1983) 58. 

The electrochemical potential of such an electrode is, ideally, independent of the amount of current flowing through it. Therefore any changes in potential difference imposed on or measured across the cell can be attributed to changes at the other electrode. The working electrode is usually some noble metal such as platinum, silver or gold. 

Several sample-handling techniques are employed for SERS, In one technique, colloidal silver or gold particles are suspended in a dilute solution (usually aqueous) of the sample. The solution is then held or flowed through a narrow glass tube while it is excited by a laser beam. In another method, a thin film of colloidal metal panicles is deposited on a glass slide and a drop or two of the sample solulion spotted on the film. The Raman spectrum is then obtained in the usual manner. Alternatively, the satnple may be deposited electrolytically on a roughened metal electrode, which is then removed from the solulion and exposed to the laser excitation source. 

I-V curves for these artificial ion channels were obtained by mounting the membrane sample between the two halves of a U-tube conductivity cell. Each half-cell was filled with 5 mL of a 10 mM pH = 7 phosphate buffer that was also 100 mM in KCl. A Ag/AgCl reference electrode was inserted into each half-cell solution, and a Keithley Instruments 6487 picoammeter/voltage source was used to apply the desired transmembrane potential and measure the resulting ionic current flowing through the gold nanotube. 

Bixler, J.W., Bond, A.M., Lay, P.A. et al. (1986) Instrumental configurations for the determination of sub-micromolar concentrations with carbon, gold and platinum microdisc electrodes in static and flow-through cells. Analytica Chimica Acta, 187, 67. 

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