Electrodes detection

L. Basini, C.A. Cavalca, and G.L. Haller, Electrochemical Promotion of Oxygen Atom Back-Spillover from Yttria-Stabilized Zirconia onto a Porous Platinum Electrode Detection of SERS Signals,/. Phys. Chem. 98, 10853-10856 (1994). 

Jorg, E. and Sontag, G. (1992). Determination of phenolic acids in honey by HPLC using coulometric dual electrode detection. Dtsch. Lebensm. Rundsh. 88,179-183. 

L.-C. Chang, M.E. Meyerhoff, and V.C. Yang, Electrochemical assay of plasminogen activators in plasma using polyion-sensitive membrane electrode detection. Anal. Biochem. 276, 8-12 (1999). 

Despite the importance of the ORR and long history of study, very little is known about the reaction mechanism.126,130,131 Mechanistic information has been derived almost exclusively from rotating disk electrode (RDE)131,132 and rotating ring disk electrode (RRDE)133-136,62,128 studies. The rotating electrode minimizes mass transfer effects and allows a kinetic current density to be extracted. In the RRDE setup, the ring surrounding the disk electrode detects species weakly adsorbed to the electrode that are ejected due to electrode rotation. The ORR reaction (eqn 4) is... 

The anode-cathode assembly generates the iodine. The dual-pin platinum electrode detects the end point. 

Figure 4.19 A constant current coulometry titration cell. The reagent is produced at the working electrode and reacts with the sample. The indicator electrodes detect the changing potential or conductivity of the solution and the amount of change that takes place is measured and related to the concentration of the reactant in the sample.

The black curve in Figure 15-21 is typical of many liquid-based ion-selective electrodes. The response of this Pb2+ electrode levels off at an analyte concentration around 10 6M. The electrode detects changes in concentration above 10 (> M, but not below 10-6 M. The solution in the internal electrode compartment contains 0.5 mM PbCl2. 

Dual-electrode detection for CE is much simpler to implement in the microchip format and offers additional sensitivity and selectivity due to the ability to monitor reversible redox reactions as well as help for identifying peaks in complex mixtures. Dual detection with serial gold [90,91] and carbon paste [92], fibre [93] and pyrolysed photoresist [94] working electrodes was reported. 

Guijt et al. [69] reported four-electrode capacitively coupled conductivity detection in NCE. The glass microchip consisted of a 6 cm etched channel (20 x 70 pm cross-section) with silicon nitride covered walls. Laugere et al. [70] described chip-based, contactless four-electrode conductivity detection in NCE. A 6 cm long, 70 pm wide, and 20 pm deep channel was etched on a glass substrate. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection set up. Jiang et al. [71] reported a mini-electrochemical detector in NCE,... 

The FID earns the name from a high temperature flame fueled with a flow of hydrogen and air that burns inside the detector body. Two electrodes detect the background electrical current from ions and electrons produced in the flame. Organic compounds that elute from the column are burned in the flame and create an influx of new ions and electrons, elevating the background current. The change in the current is proportional to the number of burned molecules. 

To avoid fouling of the Au working electrode, it is cleaned by applying a bipolar square wave voltage to the electrode after 25 injections however, more than 10 repeated applications will still destroy the electrode [748]. The LOD of catechol (single-electrode detection) was found to be 4 lM [748], which was three times lower than a previous report [745], possibly because of the application of the bipolar square wave voltage between injections to clean the electrode [748]. 

Chen, H., Fang, Q., Yin, X.F., Fang, Z.L., A multiphase laminar flow diffusion chip with ion selective electrode detection. Micro Total Analysis Systems Proceedings pTAS 2002 symposium, 6th Nara, Japan, Nov. 3-7, 2002, 371-373. 

Technique Working Electrode Detection Limit (M) Speed (Time per Cycle) (min) Response Shape... 

Acetylcholineesterase and choline oxidase Immobilized by cross linking with glutaraldehyde vapor on the exposed end (diameter 0.2 mm) of a silica-sleeved Pt electrode. Detection limit for ACh and Ch were 20 and lOpmol, respectively. Sensor was used successfully in the FIA and for detection in HPLC. [84]... 

Alternatively, a sharp change in temperature induced by an intermittent light beam of high intensity causes pressure fluctuations in the vicinity of the electrode. Detection of this pressure change is known as... 

HPLC carbon paste electrode detection limit 0.4-0.6 ng/ml 26/... 

W.A. Bartlett, Effects of mobile phase composition on the chromatographic and electrochemical behaviour of catecholamines and selected metabolites reversed-phase ion-paired high-performance liquid chromatography using multiple-electrode detection, J. Chromatogr, 493, 1-14 (1989). 

While selectivity in certain instances has been excellent (i.e., the above glutamine sensor), most tissue and bacterial electrodes are plagued by simultaneous response to several biochemical species. This is because there are often several enzymes present in a given cell which liberate the electrode-detectable product. Consequently, in situ type measurements with such... 

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