Poly matrix membrane electrodes

Khalil, S. Borham, N. Phenothiazine drug poly(vinyl chloride) matrix membrane electrodes and their use in pharmaceutical analysis. Microchem. J. 1999, 63, 389-397. 

The 14-membered macrocyclic phosphine 77 and corresponding sulfide 78 were prepared by the macrocyclization under high dilution conditions and further oxidation with sulfur (Scheme 12.29). Both ligands were used as ionophores in an all-solid state poly(vinylchloride) matrix membrane electrode. The sulfide 78 based electrode exhibited a Nemstian response towards copper (II) ions with a cationic slope of 30.7 mV/pCu and a detection limit of 5.97 x 10 M. The potential response remains almost unchanged over the pH range 3.9-6.4 at least 7 months. Sensors based on the macrocycles 77 and 78 demonstrate the copper (11) ion sensitivity over other metal ions [83]. 

R. Yuan, Y.Q. Chai, and R.Q. Yu, Poly(vinyl chloride) matrix membrane pH electrode based on 4,4 -bis[(N,N-diakylamino)-methyl]azobenzene with a wide linear pH response range. Analyst 117, 1891-1893 (1991). 

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. 

When water is used as a medium for CO2 reduction, it is important to suppress proton reduction to produce H2, which is more favorable in water than CO2 reduction. A hydrophobic polymer environment can provide such conditions by suppressing proton reduction to selectively carry out CO2 reduction. In an electrocatalytic CO2 reduction by CoPc confined in a poly(vinylpyridine) membrane coated on an electrode, selective CO2 reduction takes place, producing CO [119]. It is of further interest that in the electrocatalytic system, a third electron is injected into the Co(I)Pc(-3) - CO2 intermediate to produce CO and Co(I)Pc(-2) complex after the starting Co(II)Pc(-2) complex is reduced by two electrons to Co(I)Pc(-3) to form Co(I)Pc(-3) - CO2 with CO2. Such a mechanistic scheme can be represented by Fig. 20 [119]. Path I is the previously accepted scheme, and path II is the proposal of a new two-electron reduction pathway. Note also that for the CO2 reduction, a proton is also involved in an equilibrium process. It was inferred that in the polyvinylpyridine matrix, protonation and deprotonation takes place easily with the help of the pendant pyridine groups in a concerted fashion, resulting in favorable CO production (see also Fig. 20) [119]. 

A Quinoline Yellow determination procedure was developed using a direct poten-tiometric method [29]. A Quinoline Yellow-coated graphite electrode and a polymeric membrane electrode, based on the use of the ion-pair complex of tetraphenylphospho-nium-Quinoline Yellow embedded in a poly(vinyl chloride) matrix as the electroactive substance, were successfully used in this analysis. 

Alegret, S. and A. Florido. 1991. Response characteristics of conductive polymer composite substrate all-solid-state poly(vinyl chloride) matrix membrane ion-selective electrodes in aerated and nitrogen-saturated solutions. Analyst 116 473-476. 

Various authors have prepared multilayer membranes from hydrogenated polymers, but few surveys exist involving such a system with fluoropolymers. Park et al. [192] prepared a trilayer membrane from a copolymer matrix composed of a poly(VDF-co-HFP) copolymer doped with a 5% Nafion /hydrated tungstcnic phosphoric acid solution. This constitutes the central thickness of the membrane (60 pm). Then, a 5% Nafion solution was deposited on each side to obtain a trilayer membrane of 70 pm. Finally, that membrane was pressed and laminated to obtain a composite membrane of 30 pm thickness. The Nafion layer deposited on both sides of the membrane improved the conductivity at the membrane/electrode interface and also limits the oxidation of hydrogen on the central polymer. Furthermore, Nafion acts as an adhesive to ensure better contact between the membrane and the electrode [192]. Such composite membrane allows to limit the methanol crossover for its use in DMFC, which is the main drawback of that standard polymer. 

Davies G, Moody GJ, Thomas JDR (1988) Optimization of poly(vinyl chloride) matrix membrane ion-selective electrodes for ammonium ions. Analyst 113 497-500... 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

Poly(urethane) can be substituted for PVC in nitrate sensor membranes (67). Nonetheless, such materials are unlikely to usurp the well-proven poly(vinyl chloride) matrix. It is essential to employ a proven PVC, e.g. Breon III EP, Flowell 470 or Fluka S 704, otherwise non-functional or poor-quality ISEs may be produced even with a well-tried cocktail. However, Silopren (a silicone rubber) offers a distinct advantage in that lipophilic anions do not interfere with its valinomycin electrode, and it is considered to have universal applicability for body fluids (41). 

Activated carbon powder is dispersed in a plasticized copolymer matrix solution which is then dried to form membrane. Examples of copolymers are poly(vinylidene fluoride-co-hexafluoropropylene) and poly(vinylidene fluoride-co-chlorotrifluoroethylene. The composite is thermally laminated to aluminum current collector as electrode. 

Ion-selective electrodes are widely used in pharmaceutical analysis. Numerous ion-selective electrodes based on poly(vinyl)chloride (PVC) have been constructed in order to determine various pharmacologically active substances in pharmaceutical preparations. The inherent advantages of ISE-s are simple design, construction and manipulation, reasonable selectivity, fast response time, low cost, adequate detection limit and adequate precision and accuracy. Therefore, the ISE potentiometric method is very attractive for pharmaceutical analysis. The first part of this chapter describes the properties and uses of PVC, as well as the general characteristics and preparation of the polymer membranes of ion-selective electrodes. The second part deals with the development of solid contact electrodes formed on non-crystal electrodes with a microporous matrix (e.g., vinyl polychloride dissolved in an appropriate modifier) selective for various nonsteroidal anti-inflammatory drugs (NSAlD-s) and their applications in pharmaceutical research. 

V.J. Wotring, PK. Prince, L.G. Bachas, Evaluation of poly(vinylidene chloride) as a matrix for polymer membrane ion-selective electrodes. Analyst, 116, 581-584,1991. 

Trogadas and Ramani summarized the modification of PEM membranes, including Nafion modified by zirconium phosphates, heteropolyacids, hydrogen sulfates, metal oxides, and silica. Membranes with sulfonated non-fluorinated backbones were also described. The base polymers polysulfone, poly(ether sulfone), poly(ether ether ketone), polybenzimidazole, and polyimide. Another interesting category is acid-base polymer blend membranes. This review also paid special attention to electrode designs based on catalyst particles bound by a hydrophobic poly-tetrafluoroethylene (PTFE) structure or hydrophilic Nafion, vacuum deposition, and electrodeposition method. Issues related to the MEA were presented. In then-study on composite membranes, the effects of particle sizes, cation sizes, number of protons, etc., of HPA were correlated with the fuel cell performance. To promote stability of the PTA within the membrane matrix, the investigators have employed PTA supported on metal oxides such as silicon dioxide as additives to Nafion. 

Here, we will consider changes in the accessibility of electrodes to electroactive substances by switchable polymer films, which are not directly redox-sensitive. A gating of hexacyanoferrates could be modulated by the presence of cholesterol, which complexes the collapsed poly(vinyl pyridine) matrix (hydrophobic at the pH used) [425]. The preparation of this membrane leads to pores that are filled upon complexation with cholesterol. At the same time, the accessibility of the electrode... 

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