Coated wire electrodes preparation

Satake et al. reported the use of a coated wire electrode sensitive to procaine and other local anesthetic cations, and their application to potentiometric determination [73]. Electrodes were constructed from a copper wire (0.8 mm diameter), coated with a PVC membrane comprising a mixture of the drug-tetraphenylborate ion-pair, dioctyl phthalate, polyvinyl chloride, and tetrahydrofuran. Potential measurement was made with respect to a Ag-AgCl reference electrode. The electrodes showed linear responses with a Nemstian slope for procaine over the concentration range investigated. The method was used for analyses of the drug in pharmaceutical preparations. 

Coated-wire electrodes (CWEs), introduced by Freiser in the mid-1970s, are prepared by coating an appropriate polymeric film directly onto a conductor (Fig. 5.18). The ion-responsive membrane is commonly based on poly(vinyl... 

Coated-wire electrode (CWE)-type devices for in vivo monitoring have also been described. For example, workers at General Electric Inc. (N3), have patented a catheter for in vivo pH measurements which was based on the approach used by the Miles workers to prepare the previously mentioned K CWE. The ISE portion of the pH catheter consisted of a Ag/AgCl wire coated first with a hydrophilic polymer containing bufifer components and chloride ions and then with a polymer membrane containing a H" carrier molecule. A second tube with appropriate Ag/AgCl wire and electrolyte served as the external reference element. Once again, stable potentials can only be obtained if the osmolarity of the hydrophilic polymer layer matches that of whole blood. 

ISEs can be prepared by simply coating a bare electrode wire with a selective PVC membrane such as those described above. These coated wire electrodes are very easy to prepare and use. A THE solution of the membrane ingredients is simply coated onto the wire and allowed to evaporate. 

With regard to simple miniaturization, coated-wire ISEs are an attractive approach (39- 0). This involves coating the corresponding conventional polymer membrane onto a platinum or other wire. Numerous coated-wire electrodes selective to different ions have been prepared (i41-j 2), despite the lingering controversy over the performance of these devices in terms of... 

In attempts already made in the early 1970s, the ion-selective polymeric membrane was directly applied to a metal wire. From a theoretical point of view, this is an unsatisfactory situation because in all but a few exceptions these membranes contain neither a redox-active cation of the metal of which the wire is made nor an electron acceptor/donor pair that determines the redox potential. As a result, the phase boundary potential at the membrane/metal interface of most coated-wire ISEs is poorly defined. It is still not well understood why in real life freshly prepared coated-wire electrodes sometimes perform surprisingly well under circumstances when they can be recalibrated relatively frequently. However, formation of a water layer at the metal-membrane interface leads eventually to memory effects and, after delamination of the sensitive membrane, to catastrophic failure. 

The electrochemical behavior of chlorpromazine hydrochloride in 0.2M H2SO4 was studied by cyclic and linear sweep voltammetry at an oxidized and a non-oxidized ruthenium wire electrode [173]. Preparation of a stable and permanent coating of RuOj on the electrode was very time-consuming, but the resulting curves were highly reproducible. The... 

The development of the reductive mode LCEC technique has been slow because of difficulties in preparing convenient and reliable working electrodes for use with a high efficiency chromatographic separation. In addition, problems are encountered with dissolved oxygen and heavy metals. Solid electrodes have been used with limited success for reductive LCEC. Mercury pool electrodes (44-47), the DME (48-53), and platinum wire electrodes coated with mercury (49) are generally not satis-... 

Acetylcholineesterase and choline oxidase Coated wire enzyme electrode was prepared by coating a Ag wire with a homogenized solution of CH2C12 containing 0.28 gm of polyvinyl bytyral, 0.15 gm of di-n-amylphthalate, 10 mg of tridodecy-lamine and 2 mg of sodium tetraphenylborate. Three different methods for immobilizing the enzyme on the coated electrode are described with use of AChE. The model electrode was used to determine ACh from 0.1 to 10 mM. Response time was 3-6 min. [94]... 

Preparation of Electrodes. The Ag/AgBr and Ag/AgI electrodes were prepared by anodic electrolysis of the appropriate sodium salt solution (IN) at 6.5 ma. per sq. cm. for 5 minutes. The two electrodes to be coated were connected and dipped into the solution a wire of pure silver was used as the cathode. In the case of the Ag/AgCl electrode IN HC1 was used. Just after preparation the electrodes were immersed in the appropriate halide solution (10-3 M). The Ag/Ag halide electrodes prepared in this manner showed a difference of potential of 0.3 to 0.5 mv. in the presence of 10 5 M solution of sodium halide. This potential will be referred to as rest or nonflow potential. 

The role of C104 as a ligand in solution has been reviewed by Johansson.144 Perchlorate-ion-selective electrodes prepared using liquid ion-exchangers in PVC are said145 to exhibit approximately the same characteristics as the commercially available electrode the selectivity of the new electrode was claimed to be superior. The ion-exchanger was mixed with PVC dissolved in THF and the mixture dried as a membrane disc or used to coat a Pt electrode the useful life ranged from 2 weeks, for a wire electrode, up to a month. 

The silver-silver chloride reference electrode, can be prepared by electroplating with silver a platinum wire sealed into a glass tube. The silver coating is then converted partly into silver chloride by making it anode in dilute hydrochloric acid. Alternatively, a silver wire can be chloridized as just described. More details on electrode preparation are available elsewhere [7], When the silver-silver chloride electrode is immersed in a chloride solution, the following equilibrium is established ... 

The slice is electrically stimulated with an enamel-coated bipolar wire electrode causing action potentials that evoke DA release. In the slice preparation, the stimulation is applied directly at the neuron terminals. This is in contrast to an in vivo experiment, where the stimulation is performed at the cell body of the neuron and the DA release is monitored remotely at the presynaptic terminals. DA concentration in the extracellular fluid rises and quickly returns to baseline at the cessation of the stimulation [3]. Fast scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes is used to detect the resulting concentration changes in the extracellular fluid. This analytical technique provides a method for the determination of uptake kinetics in intact brain tissue. Thus, the secretion and subsequent clearance of DA in the tissue is observed in real time. 

Nanometer-sized disk-shaped SECM tips were prepared from etched Pt wires insulated with a polyimide layer [69]. Polymerization of the polyimide insulating flhn was thermally triggered the etched Pt wire was immersed into a A,A-dimethylacetamide solution containing 1,2,4,5-benzenetetracarboxylic anhydride and 4,4 -diaminodiphenyl ether and the electrode body was heated np nntil an insnlating film formed. The apex of the electrode was exposed by dipping the coated wire in 0.01 M NaOH for a few minntes. 

For accurate work, the silver electrode is coated with a fresh film of silver. A current is passed through a solution of KAg(CN)2 (freshly prepared from silver nitrate and potassium cyanide) between the electrode to be plated, which is the cathode, and a silver anode. An electrode prepared from 22S.W.G. silver wire is adequate for most purposes. 

The previous examples used the three-electrode electrochemical system. An alternative was utilized by Ajayan et al. to prepare Ag NP coated SWCNTs [217]. An electrode was fabricated consisting of SWCNTs attached to a Ti cathode and a silver contact pad as a sacrificial anode (Fig. 5.16(a)). The electrode was submerged in an aqueous solution and a potential was applied resulting in oxidation of Ag metal to Ag2+ ions which then subsequently deposited onto the SWCNT cathode. Although experimentally complicated, silver NPs, wires and patterns were controllably deposited on the SWCNTs (Fig. 5.16(a), (b)) [217],... 

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