Poly reference electrode

In the dual-electrode techniques, the potential of each electrode is controlled with a bipotentiostat so that a small constant potential difference is maintained across the polymer film as its potential is slowly scanned, relative to a reference electrode. Figure 10 shows the results of this type of experiment for poly(3-methylthiophene) in SO20).37... 

Figure 4 shows the application (6) of potentials to the Pt and Au electrodes of the sandwich (vs. a reference electrode elsewhere in the contacting electrolyte solution) so that they span the E° of the poly-[Co(II/I)TPP] couple (Fig. 4B). There is a consequent redistribution of the concentrations of the sites in the two oxidation states to achieve the steady state linear gradients shown in the inset. Figure 4C represents surface profilometry of a different film sample in order to determine the film thickness from that the actual porphyrin site concentration (0.85M). The flow of self exchange-supported current is experimentally parameterized by applying Fick s first law to the concentration-distance diagram in Fig. 4B ...

The integrated planar silver chloride electrode uses a thin layer of 150 pm polymer that consists of a heat curing epoxy resin poly-hydroxy-ethylmethacrylate (PHEMA) to immobilize the KC1 electrolyte. The potential drift of the reference electrode reduced to 59 pV/h after a conditioning phase of several hours. However, this reference electrode was only used for P02 measurement, while an external reference electrode was used for pH measurement. 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

Hamada et al. used a poly (vinyl chloride) matrix membrane ion-selective electrode for the analysis of procaine [76]. Procaine flavianate (10 mg, prepared by precipitation from an equimolar mixture of procaine hydrochloride and flavianic acid), was mixed with PVC powder (150 mg), dioctyl phthalate (370 mg), and tetrahydrofuran (4 mL). This mixture was used to produce membranes (3 cm diameter), from which discs were cut to prepare ion-selective electrodes. The electrodes were used in conjunction with a double-junction Ag-AgCl (KNO3) reference electrode for the potentiometric determination of procaine hydrochloride at 25°C. 

Electrochemical doping of insulating polymers has been attempted for polyacetylene, polypyrrole, poly-A/-vinyl carbazole and phthalocyaninato-poly-siloxane. Significantly, Shirota et al. [91] claim to have achieved the first synthesis of electrically conducting poly(vinyl ferrocene) by the method of electrochemical deposition (ECD) [91]. This is based on the insolubilization of doped polymers from a solution of neutral polymers. A typical procedure applied [91] for polyvinyl ferrocene is to dissolve the polymer in dichlorometh-ane and oxidize it anodically with Ag/Ag+ reference electrode under selective conditions. The modified polymer [91] (Fig. 28) is a partially oxidized mixed valence salt containing ferrocene and ferrocenium ion pendant groups with C104 as the counter anion. 

Sharma et al. [44] Lactose Milk and dairy products Lactase and galactose oxidase (GaO)/in Langmuir-Blodgett (LB) films of poly(3-hexyl thiophene) (P3HT)/stearic acid (SA) Indium-tin-oxide coated glass plates/0.4 V vs. Pt reference electrode ... 

All potentials vs. screen-printed pseudo Ag/AgCl reference, except values marked with double-dagger (J), which are vs. screen-printed Ag/Pd, and 02 those marked with asterisk ( ), which are vs. Ag/3M AgCl double-junction reference electrode. Abbreviations LDH lactate dehydrogenase, LOD lactate oxidase, PVA-SbQ styrlpyridinium-modified poly(vinyl alcohol), FIA flow injection analysis. aLinear ranges using a dialysis system. 

Nicotinic receptor from Torpedo californica Receptor was fixed into a cross-linked poly(vinylbutyral) membrane covering the gate of an ISFET which was mounted in a sample cell with a reference ISFET and Ag-AgCl reference electrode. Sensitive to ACh, H +, Na + and K +. Steady state reached after 2 min. Initial rate of change of the voltage was a rectilinear function of log ACh concentration was a from 0.1 to 10 pM. When receptor was immobilized in the membrane by using lecithin an amplified response was obtained which was due to Na + flux across receptor channel. [65]... 

A platinum electrode coated with a film of poly(vinylferrocene), which was electrodepos-ited in its oxidized form and later partially reduced, was found to be a stable reference electrode in MeCN (but not in DMF) [220]. Polymer films containing other redox systems may also be used. 

A similar electrode based on Fe(CN)g adsorbed on a cross-linked polymer (poly-ethyleneimine/l,4-dibromobutane) has been proposed as a reference electrode in organic solvents [221]. 

Other reference electrodes have been proposed for use in the nonaqueous solvents that are widely used in coordination chemistry. Their main advantage is that they allow one to work with a single solvent. Among these electrodes, the Ag+/Ag electrode is reversible in many solvents.4 Ag+ ions are introduced as salts, such as AgCl or AgBF4. However, the inner solution has to be refreshed due to the reactivity of Ag+. Another class consists of redox electrodes in which the two components are in solution, such as ferrocenium ion/ferrocene Fc+/Fc.5 Since the potential is dependent on the concentration ratio of the redox couple, this ratio must be kept constant. An attractive solution to prevent the use of a junction lies in the preparation of a functionalized-polymer coated electrode such as poly(vinylferrocene).6 The polymer is deposited by electrooxidation in its oxidized form, polyFc+, and then partially reduced to yield poly Fc+/Fc. Their use is limited by their relative stability in the different solvents. 

Figure 4.19. Double-step potential chronoabsortiometric curves recorded for regioregular poly(3-octylthiophene) (a) 2 = 520 nm (b) 2 = 860 nm (c) 2 = 1150 nm. (E measured vs Ag/AgCI reference electrode),...

Figure 4.21. Raman spectra of regioregular poly(3- octylthiophene) registered for different potentials of the electrode (E measured vs Ag/AgCI reference electrode, = 514.5 nm).

An interesting approach to miniature electrodes is the coating of a fine platinum wire with a mixture of a liquid ion-exchanger and poly(vinyl chloride) or poly(methyl methacrylate) [14]. Although the mechanism by which these electrodes function is not known (there is no internal reference electrode), they do appear to function almost as well as the larger commercial varieties. 

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