Ion-selective carbon-paste electrodes for halides and silver(I) ions

The behaviour of a simple type of ion-selective electrode for halogens and silver has been studied. The electrode consists of a plastic body filled with carbon paste, the surface of which can be easily renewed. The paste composition is based on carbon-nujol (5:1, w/v) or carbon-paraffin wax (3:1,w/w) containing a prepared mixture of silver halide-silver sulphide (1–30%). The electrodes have low ohmic resistance and show a rapid Nernstian response (within 2–5 mV) for halide and silver ions down to 5·10^-5M chloride, 1·10^-5M bromide and 5·10^-7M iodide with the respective electrodes. Ions forming very stable complexes with halide or silver and those having strong oxidizing or reducing action interfere.     

Ion-selective electrodes based on p-tert-butyl-homooxacalixarene di(ethyl)amides

The diethyl amides of p-tert-butyldihomooxacalix[4]arene (1), p-tert-butylhexahomotrioxacalix[3]arene (2) and p-tert-butylcalix[4]arene (3) were used as active materials in ion-selective membrane electrodes to check the detection of different kinds of cations (Na⁺, K⁺, Cs⁺, Mg^2 + , Ca^2 + , Mn^2 + , Cu^2 + , Zn^2 + , Cd^2 + , Pb^2 +  and tetramethylammonium cation). The electrode characteristics and selectivity coefficients were determined and compared. Optimisation of the PVC membrane composition was achieved using three different plasticisers (bis(2-ethylhexyl) adipate, o-nitrophenyl octyl ether and bis(2-butylpentyl) adipate). Amide 3 shows selectivity for Na⁺, whereas compounds 1 and 2 exhibit the highest selectivity for Pb^2 +  among all the studied cations. The X-ray crystal structure of dihomooxacalix[4]arene tetra(diethyl)amide (1) was determined, revealing it to be in the cone conformation.     

Surface-layer properties of glass electrodes responsive to sodium and hydrogen ions

Cation-sensitive glasses exhibit an alkali-metal ion concentration profile and an electrical conductivity profile which increase smoothly with the distance in towards the bulk glass, as a result of interaction with aqueous solutions. In a pH-sensitive glass, however, a stepwise alkali-metal ion-distance profile is obtained and a low electrical-conductivity region is restricted to a thin film near the gel-layer/bulk-glass transition region. The replacement of silicon by aluminium causes the degree of H(+)-M(+) ion-exchange to decrease, and consequently favours alkali-metal ion selectivity of the glass. Lower conductivity is attributed to a low proton-interdiffusion coefficient. The conductivity is lowest where the SiOH concentration is high, i.e., where the water concentration and the SiO(-) concentrations are low. High conductivity of the gel-layer of pH-sensitive glasses is caused by the presence of water which depolymerizes the glass structure. The network of alkali-sensitive glasses is less affected by water owing to the aluminium decreasing the concentration of terminal oxygen atoms in the structure. A low-conductivity surface layer on the latter glasses contributes to the sluggishness in the response of the electrodes.     

Ion-selective electrodes for determination of organic ammonium ions: Ways for selectivity control

The influence of the ISE membrane composition on the selectivity for primary, secondary, tertiary, and quaternary alkylammonium cations, as well as for cations of physiologically active amines, has been investigated. Factors studied include the effect of plasticizer (2-nitrophenyl octyl ether, o-NPOE; dibutyl phthalate, DBP; dinonyl adipate, DNA; tris(2-ethylhexyl) phosphate, TEHP) and ion exchanger (potassium tetrakis(4-chlorophenyl)borate, K(TpClPB); potassium tris(nonyloxy)benzenesulfonate, K(TNOBS)), as well as that of the lipophilic cationic additive (tetradecylammonium nitrate, (TDA)NO(3)) and neutral carrier (dibenzo-18-crown-6) presence in membrane. It has been established that plasticizer nature affects K(i,j)(pot) values both when the target and/or foreign ions have non-ionic polar groups capable of specific interaction with plasticizer, and when the only difference consists in the substitution degree of their ionic groups. K(i,j)(pot) values for quaternary alkylammonium cations over primary-tertiary ones change in the following order: TEHP>DBP approximately DNA>o-NPOE. The highest K(i,j)(pot) value change is achieved for the primary-quaternary alkylammonium cation pair, amounting to 3 and 4.7 orders for membranes containing K(TNOBS) and K(TpClPB) as ion exchangers, respectively. In its turn, the ion exchanger influence on the selectivity depends on plasticizer nature, it being maximal for o-NPOE (about 2 orders) and practically non-existent for TEHP. On the whole, as compared to K(TpClPB)-based ISEs, those based on K(TNOBS) show higher selectivity for primary-tertiary alkylammonium cations over quaternary ones. Incorporation of (TDA)NO(3) into membrane causes further improvement of selectivity for primary-tertiary alkylammonium cations in the case of K(TNOBS) only. The maximal total effect of the ion exchanger and lipophilic ionic additive is observed for ISEs with DNA-plasticized membranes and is over 3 orders. The influence of crown ether on the selectivity also depends significantly upon ion exchanger and plasticizer nature. For ISEs with o-NPOE-plasticized membranes the K(i,j)(pot) value changes can be as great as 3 (ion exchanger K(TNOBS)) and even 4.5 (ion exchanger K(TpClPB)) orders. On the contrary, for ISEs with TEHP-plasticized membranes the crown ether effect on the selectivity is unessential. The results obtained are explained by peculiarities of organic ammonium cations solvating by plasticizer and association of cations with ion exchangers.     

Ion-selective electrodes for basic drugs

Coated-wire ion-selective electrodes based on dinonylnaphthalene sulfonic acid (DNNS) are prepared for methadone, methylamphetamine, cocaine and protriptyline in protonated form. In each set, nearly-Nernstian responses are obtained while detection limits range from 10^-5.5M for cocaine and methylamphetamine electrodes, to 10^-6.0M for methadone, and 10^-6.5 M for protriptyline electrodes. Selectivity is found to decrease in the order methadone, protriptyline, cocaine and methylamphetamine; these results are consistent with systematic selectivity studies reported earlier for electrodes in this family.     

Ion-selective electrodes under galvanostatic polarization conditions

The application of ion-selective electrodes (ISE) with ionophore-based membranes under galvanostatic polarization conditions is briefly reviewed. The possibilities offered by polarization for expanding the working range of ISE and for varying their selectivity and the type of electrode response (cationic or anionic) are discussed.     

Ion-selective electrodes – istory and conclusions

 The working mechanism of ion-selective electrodes has been investigated. The contradictions of theories deduced from so-called analogous phenomena are discussed in detail. Based on experiments made by the author’s research group the conclusion was drawn that only the surface (the active groups located there) takes part in the potential-determining reaction and the bulk resistance of the membrane plays a role only in the selection of the instrument used for potential measurement. Received: 15 May 1995/Revised: 12 August 1995/Accepted: 11 August 1995     

Copper(I) sulphide-impregnated silicone rubber membranes as selective electrodes for copper(II) ions

Silicone rubber membranes impregnated with copper(I) sulphide have been developed as selective electrodes for coppefr(II) ions. The internal electrode and solution were eliminated. The Nernst equation was satisfied in the concentration range from 10(-1) to 10(-6)M copper(II) and the analytical range was from 10(-1) to 10(-7)M. The interference of other ions was examined. Other resins were compared with silicone rubber as inert matrices.     

Ion-selective electrodes based on silver sulphide

A series of electrodes with membranes of silver sulphide have been prepared. Their standard potentials and their response to sulphide and silver ions are measured and compared with those of a single-crystal silver sulphide electrode. The selectivity parameters against heavy metal ions and halides, as well as cyanide, are discussed. It is concluded that only interferences from cyanide ions and mercury(II) ions are detrimental to the practical use of the electrodes for measuring pAg and pS.     

Ion-selective electrodes – istory and conclusions

 The working mechanism of ion-selective electrodes has been investigated. The contradictions of theories deduced from so-called analogous phenomena are discussed in detail. Based on experiments made by the author’s research group the conclusion was drawn that only the surface (the active groups located there) takes part in the potential-determining reaction and the bulk resistance of the membrane plays a role only in the selection of the instrument used for potential measurement. Received: 15 May 1995/Revised: 12 August 1995/Accepted: 11 August 1995     

Ion-selective electrodes in titrations involving azo-coupling reactions

An organic cation-selective indicator electrode based on a PVC membrane plasticized with 2-nitrophenyl 2-ethylhexyl ether can be used in potentiometric titrations of aromatic hydroxy compounds, amines, and compounds containing active methylene groups, with 4-methyl-, 4-bromo-, or 4-nitro-benzenediazonium chloride solutions as titrants. Useful results were obtained in determinations of 16 passive components, including 2-naphthol, some 2-naphthol sulfonic acids, 8-quinolinol and its 5-sulfonic acid, ammo-1-naphthol-3-sulfonic acids, 1-naphthylamine sulfonic acids, resorcinol, 2,4-toluylenediamine, two acetanilide derivatives, and two substituted sulfophenyl pyrazolone derivatives. 4-Bromobenzenediazonium chloride proved to be the best titrant of the diazonium salts tested.     

Ion-selective electrodes for gold and silver determination

Some new ion-selective electrodes for silver and gold are described. They are based on the ion-associate species formed by the cyanide, chloride or thiourea complexes of the metals, with hydrophobic anions or cations, as appropriate. The electrodes have been applied to the determination of gold and silver in various technological process solutions in industry.     

Ion-selective electrodes and enzyme electrodes in environmental and clinical studies.

Electrodes have been developed for the assay of glucose, urea, amino acids, uric acid, phosphate, nitrate and perchlorate. The electrodes for the organic compounds are enzyme electrodes which are prepared by chemically immobilizing an enzyme over the outside of a conventional ion-selective electrode. These electrodes will be discussed in depth. The progress and the development of the electrodes that show sensitivity and selectivity for phosphate, nitrate and perchlorate will be outlined. The basis of these sensors is a complex of a transition metal of either an analog of thiourea or an organic chelator, such as 1,10-phenanthraline. Such electrodes respond linearly to phosphate, nitrate or perchlorate, and show selectivity over sulphate, halides and acetate. The linear range of all these electrodes is approx. 10(-1)-10(-5) M with a near Nernstian slope and a reproducibility of 1%. The electrodes are stable and can be used continuously.     

Asymmetric Schiff base as carrier in PVC membrane electrodes for manganese (II) ions

Manganese(II) complex of (E)-2-(hydroxyl-5-methoxybenzylideneamino) phenol was synthesized and used as a suitable Mn(II) – selective membrane in PVC matrix. The plasticized membrane sensor exhibits a nersian response for Mn(II) ions over a wide concentration range of 6 × 10^?6–2 × 10^?2 M with slope of 29 ± 1 mV per decade. It has a response time of <11 s and can be used for 2 months without any measurable divergence in potential. The response of the proposed sensor is independent of pH between 4 and 9.5. The proposed sensor shows a fairly good discriminating ability towards Mn(II) in comparison with some hard and soft metals. The electrode was used in the determination of Mn(II) in aqueous solutions and as an indicator electrode in potentiometer titration of manganese ions against EDTA.     

Ion-selective electrodes in organic analysis-determination of xanthate

A PVC membrane xanthate-selective electrode has been developed for the direct determination of xanthates of primary and secondary alcohols. The xanthate electrode is highly selective and exhibits a Nernstian response in the range 5.0 x 10(-2)-7.1 x 10(-5)M xanthate with a slope of 58.6 mV per concentration decade. The electrode has a wide working pH range (5.0-11.5), a fast response time (less than 30 sec) and is stable for at least two months.