Double tubular electrodes

Couto et al. [11] developed a flow injection system with potentiometric detection for determination of TC, OTC, and CTC in pharmaceutical products. A homogeneous crystalline CuS/Ag2S double membrane tubular electrode was used to monitor the Cu(II) decrease due to its complexation with OTC. The system allows OTC determination within a 49.1 1.9 x 103 ppm and a precision better than 0.4%. A flow injection method for the assay of OTC, TC, and CTC in pharmaceutical formulations was also developed by Wangfuengkanagul et al. [12] using electrochemical detection at anodized boron-doped diamond thin-film electrode. The detection limit was found to be 10 nM (signal-to-noise ratio = 3). 

In bioanalytical practice the channel systems and tubular electrodes seem to be more useful. Such equipment can be easily attached to a reaction vessel (e.g., fermentation kettle) like a through-flow (bypass) tubing. A general computational approach [73] to the simulation of current-time transients was applied to double-potential step chronoam-perometry at a single-channel electrode. 

Fig. 2b represents a simultaneous recording obtained with a Cl -selective microelectrode. As the double-barreled microelectrode impales the peritubular membrane, there is a steep rise in the membrane potential of about - 70 mV associated with a fall in the Cl potential. The fall in the chloride potential is less steep than the rise in the peritubular membrane PD. This is due to the fact that the chemical sensor has a slower response time than the electrical cell. After recording a stable peritubular membrane PD and cell Cl potential, the double-barreled electrode was advanced a few micra into the lumen of a late proximal tubule to record two stable potentials a transepithelial PD of about 10-15 mV and a tubular fluid Cl potential roughly equivalent to the Cl" potential in the amphibian Ringer s solution covering the kidney. 

In the case of pipe flow (tubular flow, also tubular or tube electrode), the electrolyte solution is pumped through a circular tube at a rate (flow rate V"f) low enough to secure laminar flow (for the distinction from turbulent flow, see below). The working electrode is embedded as a ring (annulus) in the wall of the pipe a double ring can be mounted also to enable mechanistic studies like with a ring-disc electrode (see above). 

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