Electrodes cleaning/polishing

Acetylcholineesterase and choline oxidase A rotating graphite-disc electrode was polished, defatted, cleaned and oxidized by immersion in 10% HN03/2.5%, K2Cr207 at 2.2 V versus SCE for 10 s. AChE was covalently immobilized on to the electrode using a standard method. Measurements were made in 0.1 M-universal buffer of pH 7 at 0.8 V versus SCE. Calibration graphs were linear from 0.6-10 pM substrate. RSD were 5% (n = 10). The detection limit was 10 pM acetylthiocholine, electrode response time was 15 s. [89]... 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

Electrode Preparation. Pt electrodes were polished with alumina polishing powder (1, 0.3, and 0.05 xm) to a mirror finish and cleaned electrochemically by cycling the potential between hydrogen and oxygen evolution potentials in 1-M... 

Electropolymerization A 1 x 1cm ITO glass plate (purified with soap solution, water, ethanol) was used as the working electrode. A Pt wire counter electrode was purified with H2SO4/H2O2, water and ethanol. The Ag wire as reference electrode was polished and then cleaned with water and ethanol. The solution for the electropolymerization of the phthalocyanine derivative contains 6.30 mg (10 mol) 51a (M = Ni) and 342 mg (10" mol) tetrabutylammonium perchlorate in 10 mL dry DMF, and for the electropolymerization of the porphyrin derivative 49h (M = Zn) 7.4 mg (10 mol) 49h and 342 mg (10 mol) tetrabutylammonium perchlorate in 10 mL dry methylene chloride. 4.5 mL of one of the solutions was filled into the glass cell under a stream of nitrogen. The ITO electrode was connected to a copper holder. The potential was scanned continuously between -0.4 V and +0.8 V for 51a or 0.0 and 0.9 V for 49h, respectively, vs. SCE at a rate of 10 mV/s. For calibration of the reference electrode, the porphyrin derivatives were replaced by ferrocene (E° = 0.4 V vs. SCE) in the same electrolyte. 

Burnish electrode with polishing paper or cloth until a clean, polished silver surface diows. 

Glassy carbon electrodes polished with alumina and sonicated under clean conditions show activation for the ferrl-/ ferro-cyanlde couple and the oxidation of ascorbic acid. Heterogeneous rate constants for the ferrl-/ ferro-cyanlde couple are dependent on the quality of the water used to prepare the electrolyte solutions. For the highest purity solutions, the rate constants approach those measured on platinum. The linear scan voltammetrlc peak potential for ascorbic acid shifts 390 mV when electrodes are activated. 

Electrochemical Instrumentation. For the Ru complexes, a 1 cm diameter platinum disk brazed onto a brass holder was used as a working electrode. It was masked with ChemGrip (a teflon based epoxy) except for the upper face. Prior to use, it was polished with 1 micron diamond paste (Buehler) and rinsed with water, acetone and methanol. The working electrode for each Os complex was the uppermost platinum layer of a platinum/carbon layered synthetic microstructure (LSM) (Energy Conversion Devices). The LSM consisted of 200 layer pairs of carbon and platinum whose thicknesses were 24.4 and 17.0 A, respectively and where platinum was the outermost layer. The LSM was placed in 1.0 M H2SO4 and cleaned... 

A known volume of KBr solution is pipetted into a clean beaker and a freshly polished silver electrode is then immersed in this solution. After a potentiometric titration with AgNOj solution at 298 K, the electrode potential at the equivalence point (EAg+,Ag) is determined to be 0.441 V. What is for the pale yellow AgBr that is formed ... 

Moreover, the oxidation process is strongly dependent on the state of the electrode surface. At a freshly cleaned and polished lead the oxidation of 5b occurs at p/2 = — 1.52 V on the first sweep, but on subsequent cycles the potential shifts in the cathodic direction approaching E j2 = —1.72 V. 

Most problems with 02 electrode assays can be traced back to dirty or leaking membranes the membrane and KC1 electrolyte should be replaced and the assay should be repeated. A small piece of single-thickness facial tissue between the cathode and the membrane will ensure that there is always a thin film of electrolyte present. The Pt cathode may be cleaned by gently polishing with paper tissue. Inadequate stirring and poor temperature control will also lead to erratic results. 

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