Performance Of Ion-selective Electrodes Research Articles

Cheap and effective potentiometric PVC sensor for the determination of imidazolium based ionic liquids in aqueous and aqua-organic media

Owing to the extensive research on imidazolium based ionic liquids; the present study aims to design a potentiometric sensor for alkyl methylimidazolium ion. For this, poly(vinyl chloride) PVC membrane based on the neutral ion-pair complexes of cetylpyridinium chloride and sodium dodecyl sulfate (CPy+DS−) has been developed. The synthesized ion selective electrode (ISEs) have been found to show linear response with near-Nernstian slope for CnMeImCl (C10MeImCl, C12MeImCl and C14MeImCl). The proposed ISEs show quick response (5–6 s) and provide wide pH range for working. The influence of various ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined by separate solution method. The performance of synthesized ISE in examining the critical micellar concentration (cmc) of CnMeImCl in aqueous, aqua-organic media and in the presence of amino acids (glycine, L-glutamic acid and L-phenylalanine) has been found to be satisfactory and confirmed through conductivity and fluorescence measurements. This emphasizes its worth for in-situ analysis of alkyl methylimidazolium ions, during an organic reaction, and hence possible reaction mechanism evaluation. Different thermodynamic parameters such as Standard Gibbs energies of micellization (ΔGm∘), degree of counterion dissociation (α), amphiphile tail transfer Gibbs free energy (ΔGm,trans∘) have been evaluated. Further, the analytical application of synthesized electrode as end point indicator in the potentiometric titration of C14MeImCl with SDS has also been explored, which compared well with improved two-phase titration method. The current study is novel as it involves the use of a cheaper material (CPyCl) as ionophore and that the same electrode can be used for different chain alkyl methylimidazolium ions simply by changing the internal reference solutions.

Silver ion recognition using potentiometric sensor based on recently synthesized isoquinoline-1,3-dione derivatives

The four derivatives of isoquinoline-1,3-dione based on β-lactum (I-IV), have been explored as neutral ionophores for preparing poly(vinylchloride) based polymeric membrane electrodes (PME) selective to silver(I) ions. The addition of sodium tetraphenylborate (NaTPB) and dioctylsebacate (DOS) as a plasticizer was found to improve the performance of ion selective electrodes. The best performance was obtained with PME-1 based on ionophore I having composition: ionophore (9.2 mg), PVC (100.1 mg), DOS (201.1 mg) and NaTPB (1.5 mg) in 5 mL tetrahydrofuran. The electrode response was linear with Nernstian slope of 58.44 mV/decade in the concentration range of 1.0 x 10 -1 M to 5.0 x 10 -6 M and detection limit of 5.83 x 10 -6 M. It performs satisfactorily over wide pH range of 1.0-5.5. The proposed sensor can be used over a period of more than three months without any significant drift in potential and shows good selectivity to silver(I) ion over a number of cations especially with no interference of mercury(II) ions. Sharp end point was obtained when the sensor was used as an indicator electrode for the potentiometric titration of silver(I) ions with chloride ions and therefore this electrode (PME-1) could be used for quantitative determination of silver(I) ion in synthetic water, silver foil and dental amalgam samples.

Novel surfactant selective electrochemical sensors based on single walled carbon nanotubes

New poly(vinyl chloride) PVC membrane electrodes selective to the hexadecyltrimethylammonium ion (CTA +) and sodium dodecyl ion (SD −) have been constructed using a modified single walled carbon nanotube (SWCNT). This sensor was used as a sensing material and incorporated into the plasticized PVC-membrane. The membrane electrodes exhibited a Nernstian response (59.5 mV/decade) for SDS and a near-Nernstian response (57.2 mV/decade) for CTAB over a wide concentration range below their critical micelle concentrations (CMC). The electrodes showed a fast response time (t90% = 30 s) and could be used for 3 months without any divergence in potentials. The SD − ion selective electrode (ISE) can determine monomer units down to concentrations as low as 1.9 × 10 − 6 M and 5.2 × 10 − 6 M for CTA +. The effect of foreign anions along with primary ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined using the fixed primary method (FPM) at 5.0 × 10 − 5 M concentration of surfactant ions. The two proposed potentiometric sensors revealed acceptable selectivities for surfactant ions over a wide variety of other common inorganic and organic anions. The lifetime of the sensor is more than three months. This method for determining of anionic surfactants was found to be quite accurate when compared with classical methods.

Effects of architecture and surface chemistry of three-dimensionally ordered macroporous carbon solid contacts on performance of ion-selective electrodes.

The effects of the architecture and surface chemistry of three-dimensionally ordered macroporous (3DOM) carbon solid contacts on the properties of ion-selective electrodes (ISEs) were examined. Infiltration of the plasticized poly(vinyl chloride) (PVC) membrane into the pores of the carbon created a large interfacial area between the sensing membrane and the solid contact, as shown by cryo-scanning electron microscopy (cryo-SEM) and elemental analysis. This large interfacial area, along with the high capacitance of the 3DOM carbon solid contacts (as determined by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) results in an excellent long-term stability of the potentiometric response, with drifts as low as 11.7 muV/h. The comparison of 3DOM carbon solid contacts with an untemplated carbon solid contact shows that the pore structure is an essential feature for the excellent electrode performance. However, the surface chemistry of the 3DOM carbon cannot be ignored. While there is no evidence for an aqueous layer forming between the sensing membrane and unoxidized 3DOM carbon, electrodes based on oxidized 3DOM carbon exhibit potentiometric responses with the typical hysteresis indicative of a water layer. A comparison of the different techniques to characterize the solid contacts confirms that constant-current charge-discharge experiments offer an intriguing approach to assess the long-term stability of solid-contact ISEs but shows that their results need to be interpreted with care.

Potentiometric determination of the chloride ion activity in cement based materials

The chloride content at the reinforcement is one of the decisive factors for the initiation and propagation of localised corrosion in concrete structures. A monitoring technique for the chloride concentration which is accurate, non-destructive and continuous would thus be highly desirable. For this reason, the performance of ion selective electrodes (ISEs) was investigated both in alkaline solutions and embedded in mortar. The Ag/AgCl electrodes used in this work showed Nernstian behaviour with a slope of –59 ± 1 mV per decade and a detection limit for chloride ions below 10−2 mol dm−3 even at pH close to 14; the selectivity coefficient for hydroxide interference was estimated at $$ k_{{{\text{Cl}}^{ - } ,{\text{OH}}^{ - } }}^{\text{pot}} \approx 4 \cdot 10^{ - 3} $$ . The Ag/AgCl membranes show good long-term stability over more than 6 months even in highly alkaline solutions as long as chloride ions are present; in the complete absence of chloride the measured potentials were affected by the pH of the solution. The sensors are, however, able to recover fast as soon as they come into contact with chloride. When using ISEs embedded in concrete, diffusion potentials between the reference electrode and the ISE, as arising e.g. from gradients in pH, significantly affect the potential measurement and present a most important error source for the application of direct potentiometry to concrete. To minimise such errors, the reference electrode has to be positioned as close to the ISE as possible.

Effect of various additives on the performance of a newly developed PVC based potentiometric sensor for anionic surfactants

A new poly(vinyl chloride) PVC membrane electrode to determine monomer concentrations of dodecylbenzenesulphonate ions (DBS −) based on a neutral ion-pair carrier complex of dodecyltrimethylammonium–dodecylbenzenesulphonate (DTA +–DBS −), is reported here. The electrode exhibits a slope of 51.25 mV per decade for DBS − ions. The DBS − ion selective electrode (ISE) can determine monomer units down to concentrations as low as 3.32 × 10 −4 M. The effect of three kinds of additives, i.e. alcohols, glycols and triblock polymers on the performance of the surfactant selective electrode is studied systematically. The effect of foreign anions along with primary ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined using the fixed interference method (FIM) at 1.0 × 10 −2 M concentration of foreign anions. The sensor responds well to the surfactant ions in the presence of additives at lower concentration. The Gibbs free energy of micelle formation (Δ G m) of sodium dodecylbenzenesulphonate (SDBS) in the presence of various additives is calculated and found to vary differently with respect to the increase in the amount of additives. The sensor worked in the acidic pH range with a short response time of 30 s. The lifetime of the sensor is more than three months. The sensor was further used to determine the amount of DBS − in local detergents. This method of determining anionic surfactants was found to be quite accurate when compared with classical methods.

The use of ion-selective electrodes in manual and computer-controlled plow injection systems

The performance of ion-selective electrodes in a flow injection system under manual or active computer control is discussed. The response of the fluoride-selective membrane electrode was not Nemstian, and depended on several parameters. With appropriate standardization, the results were quite satisfactory. Precision was typically 3%; 60 determinations per hour are possible in the concentration range 20–200 ppb. The detection limits of the electrodes are below the values found m other measurement modes.