Dropping carbon electrode

For everyone who has watched the field from the very beginning, it is a pleasure to see a couple of reports from Japanese authors [91, 92], concerning the successful revival of the already introduced dropping carbon electrode, DCE [1-3]. Reportedly, the new prototype was wholly functional for its primary purpose - polarographic oxidations in aqueous solutions - when a three-component mixture of graphite, dioctyl phthalate, and triiodomethane acted as the true DCE with a periodically renewable surface. 

Tatsumi, H. and Shiba, M. (2012) Polarography with a dropping carbon electrode. Electrochem. Commun., 20, 160-162. 

Carbon electrodes are the normal choice for the link in the connection chain to deflver power to the arc tip. Graphite may be used in special apphcations, but the higher cost of graphite favors the use of carbon electrodes. Carbon possesses properties ideal to its appHcation as an electrode. These properties include no softening point, no melting point, electrical conductivity, strength increases with increasing temperature, resistivity drops as temperature increases, available in the size and purity desired, and cost effectiveness. 

These reactions proceed very rapidly, so that the overall reaction corresponds to the transfer of two electrons. As reaction (5.7.9) is very slow in acid and neutral media, the electrode reaction is irreversible and the polarization curve does not depend on the concentration of hydrogen ions. In weakly alkaline media, reoxidation of H02 begins to occur. At pH > 11, the polarization curve at a dropping mercury electrode becomes reversible. In this way, the process proceeds in water and water-like solvents. On the other hand, for example in carbonate melts, the step following after the reaction (5.7.9) is the slow reaction 02 + e = 022-. 

Batley [780] examined the techniques available for the in situ electrodeposition of lead and cadmium in seawater. These included anodic scanning voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen, and in situ electrodeposition on mercury-coated graphite tubes. 

At the glassy carbon electrode, using both in situ and preformed mercury films, similar results were obtained, but the sloping baseline interference observed at the hanging mercury drop electrode was less evident because of the higher stripping currents. 

Batley [28] examined the techniques available for the in situ electrodeposition of lead and cadmium in estuary water. These included anodic stripping voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen and in situ electrodeposition on mercury coated graphite tubes. Batley [28] found that in situ deposition of lead and cadmium on a mercury coated tube was the more versatile technique. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals were then determined by electrothermal atomic absorption spectrometry, Hasle and Abdullah [29] used differential pulse anodic stripping voltammetry in speciation studies on dissolved copper, lead, and cadmium in coastal sea water. 

Substrates DME = dropping mercury electrode FTO = fluorine-doped tin oxide G = graphite GC = glassy carbon GrC = graphic carbon ITO = indium tin oxide-coated glass SC = single crystals SS = stainless steel TCO = transparent conducting oxide VC = vitrious carbon. Miscellaneous ECALE = electrochemical atomic layer epitaxy ED = electrodeposition ML = monolayer RT = room temperature SMD = sequential monolayer deposition V = vacuum. 

Zhao et al. prepared magnetite (FesO nanoparticles modified with electroactive Prussian Blue [44]. These modified NPs were drop-cast onto glassy-carbon electrodes. They observed the redox processes commonly observed for PB (similar to that seen in Figure 4.8), and also demonstrated that the Prussian White material produced by PB reduction at 0.2 V served as an electrocatalyst for Fi202 reduction. They also prepared LbL films in which PB NPs and glucose oxidase were alternated between PD DA layers [99]. These were demonstrated to act as electrocatalysts for Fi202 reduction. Based on the ability to sense the product of the enzymatic reaction, these structures were shown to act as glucose sensors. 

Ebel et al. have used a microliter vessel in the voltammetry and polarographic determination of small sample volumes of chlorpromazine [166]. The concentration of cells in glass or PTFE was described for use with a dropping-mercury electrode (sample volume 180 pL), a rotating disc electrode (sample volume 1 mL), or a stationary vitreous-carbon electrode (sample volume 80 pL). Chlorpromazine was determined using oxidative voltammetry at a 3 mm vitreous-carbon or a rotating electrode. 

Long-term tests on CoTMPP carbon electrodes with polyethylene as binder showed a drop in potential of about 5 mV per day, even after several hundred hours operation. 

Although the carbon-paste electrode is quite effective for readily oxidizable analytes, a full range of electrochemical response is only available with the mercury electrode, particularly the versatile version called dropping mercury electrode. Witli this electrode, analyses are conducted at a frequently renewed mercury... 

Fig. 8.7 Cyclic voltammograms of cobalticinium ion in 1 mM (tj-C5H5)2CoPF6-0.1 M Bu4NBF4-AN [30a]. Recorded using a hanging mercury drop electrode (a) and a glassy carbon electrode (b) at 100 mVs-1 and at 25 °C.

Figure 9.3 Stationary solution voltammetry cells, (a) Platinum wire loop auxiliary electrode, (b) reference electrode or reference electrode probe tip, (c) carbon paste working electrode, (d) graphite auxiliary electrode, (e) dropping mercury electrode, (0 platinum wire contact to mercury pool working electrode, (g) nitrogen gas inlet tube, (h) magnetic stirrer, (i) mercury pool working electrode, (j) glass frit isolation barrier.

Table VIM Is an index to the indicator electrodes employed It provides access to all of the data obtained with mercury-pool, carbon-paste, rotating disc, and each of the numerous other electrode materials and configurations represented in Table I, with the single exception of the dropping mercury electrode, which is omitted here for the same reason that polarography is omitted from Table VII.

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