Carbon liber electrodes

Hgure 5 Disk and carbon liber electrodes used in amperometric and voltammetric CE detectors. 

XOD is one of the most complex flavoproteins and is composed of two identical and catalytically independent subunits each subunit contains one molybdenium center, two iron sulfur centers, and flavine adenine dinucleotide. The enzyme activity is due to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties at or near the active site [260], It can be used to detect xanthine and hypoxanthine by immobilizing xanthine oxidase on a glassy carbon paste electrode [261], The elements are based on the chronoamperometric monitoring of the current that occurs due to the oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The biosensor showed linear dependence in the concentration range between 5.0 X 10 7 and 4.0 X 10-5M for xanthine and 2.0 X 10 5 and 8.0 X 10 5M for hypoxanthine, respectively. The detection limit values were estimated as 1.0 X 10 7 M for xanthine and 5.3 X 10-6M for hypoxanthine, respectively. Li used DNA to embed xanthine oxidase and obtained the electrochemical response of FAD and molybdenum center of xanthine oxidase [262], Moreover, the enzyme keeps its native catalytic activity to hypoxanthine in the DNA film. So the biosensor for hypoxanthine can be based on... 

Because there is LC-EC, it is only logical that there should be CE-EC and capillary electrochromatography (CEC)-EC. This area was pioneered by Andrew Ewing at the Pennsylvania State University. Richard Zare (Stanford University) and Susan Lunte (Kansas University) have explored this idea in a number of unique ways. The basic technology has been recently reviewed [3]. There are several fundamental problems that do not occur with LC-EC. First, the capillaries must be of small diameter to properly dissipate resistive heating. Thus, the electrodes used in CE-EC are normally carbon libers or metallic wires placed in or at the capillary end. 

Besides plasma treated metal electrodes, carbon libers also adhere well to these PM A based EAPs. PMA based EAPs with embedded carbon fibers, arranged in long linear patterns or in grid patterns, respond very well to electricity, with marked contraction at 50 V with over 50% contraction by weight loss in a minute or less. Small cylindrical EAPs with embedded carbon fibers (Fig. 4.16) contracted and expanded when the polarity was reversed, albeit slowly, at voltages even as low as 1 V. 

Oxidation of NO on classical conductive materials such as noble metals (platinum, gold, etc.) or carbon, which are used as electrodes, produces a relatively low current at neutral pH. This is due to a strong absorption of NO to the electrode surface and a slow rate of electron transfer between NO and the electrode. Typical differential pulse voltammograms (DPV) of NO on carbon liber covered with Nafion, and carbon fiber covered with porphyrinic film and Nafion are shown in Fig. 3. There is about a 190 mV difference between the oxidation potential of NO on carbon fiber and porphyrinic film. A concentration of 0.1-pM NO produces a very small current on the carbon fiber electrode operating in the DPV mode (Fig. 3a). However, this same carbon fiber covered with a layer of polymeric porphyrin produces a much larger current (Fig. 3b) for NO oxidation. The current generated on polymeric porphyrin is mass transport controlled and is linearly proportional to the concentration of NO. The linearity is observed over four orders of magnitude of NO concentration [45]. 

Flexible supercapacitors were also made from carbon libers by Shi et al. [20]. They prepared flexible electrodes in different ways mainly to have the conductive carbon network within them. 

In 2002, Jin et al. investigated the precapillary derivatization of 20 amino acids with naphthalene-2,3-dicarboxaldehyde (NDA) and CN [10]. All these derivatized amino acids could be oxidized on the carbon liber microdisk bundle electrode except proline at a detection potential of 1.15 V (vs. SCE). CZE with ECD was employed for the analysis of 19 amino acids (including arginine, lysine, ornithine tryptophan, histidine isoleucine, leucine phenylalanine, methionine, glutamine, tyrosine, valine, threonine, serine, alanine, glycine. 

Adding Teflon emulsion, conductive polymers, carbon liber, and rutile structured oxidate to PAM as adhesives can promote the transformation of a-Pb02 into p-Pb02, enhancing electrode performance. 

The main advantage of using this type of working electrode is the possibility for miniaturization that carbon liber is capable of, which can be demonstrated in many interesting examples such as detection of neurotransmitters in extracellular space of the brain. 

Frequency analysis of NP collisions is not simple because the shape and frequency of the current transients are affected not only by the NPs but also by the material and nature of the surface of the measuring electrode. For example, the current transient frequency of citrate-stabilized IrO NPs differed by the electrode material current transients for IrO, NP collisions were frequent on bare An, rare on bare Pt, and not observed at all on carbon liber UMEs. The electrocatalytic redox recycling behavior also depends strongly on the electrode material. The current spikes are sensitive to the electrode surface, and we find that the current transient behavior can be modified with different surface treatments, for example, by immersing the Pt UME in a 10 mM aqueous NaBH4 solution for 5 min. The influence of the electrode surface properties on NP behavior is still not well understood, but the single NP collision detection techniques described here can be useful tools to study such phenomena. 

Wunsche An electrolytic process for liberating bromine from a bromide solution. It uses carbon electrodes and a porous clay separator. Developed in Germany in 1902. See also Kossuth. 

In 1807 Sir Humphry Davy (1778-1829) devised an electrolysis apparatus that used electrodes immersed in a bath of melted sodium hydroxide. When he passed an electric current through the system, metallic sodium formed at the negative (cathode) electrode. He first performed this experiment with molten potassium carbonate to liberate the metal potassium, and he soon followed up with the sodium experiment. Today, sodium and some of the other alkali metals are still produced by electrolysis. The types of electrolytes may vary using a mixture of sodium chloride and calcium chloride and then further purifying the sodium metal. 

Sulfates are precipitated as BaS04, and then reduced with carbon at 1,000°C to produce CO2 and CO. The CO is either measured directly or converted to CO2 by electrical discharge between platinum electrodes (LonginelU and Craig 1967). Total pyrolysis by continuous flow methods has made the analysis of sulfate oxygen more precise and less time-consuming than the off-line methods. Bao and Thiemens (2000) have used a C02-laser fluorination system to liberate oxygen from barium sulfate. 

The electrolytic aluminium rectifier includes an aluminium electrode and mother electrode of carl ion, iron or load. Both electrodes are suspended so that they face one another and are immersed in a solution of alkali borates, phosphates or carbonates. In a tantalum rectifier a solution of potassium carbonate, ammonium carbonate or sulphuric acid is used the othev electrode being made of lead. The maximum voltage of the alternating current to be rectified must of course be lower than the breakdown voltage of the rectifier. When the rectifier cell is working, hydrogen is evolved at the tantalum or aluminium electrode while at the lead electrode oxygen is liberated. 

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