Quantitive binding constants of H(+)-selective chromoionophores and anion ionophores in solvent polymeric sensing membranes

The binding properties of neutral or charged chromoionophores and anion ionophores in solvent polymeric membranes were characterized in situ by the so-called sandwich membrane method. Acidity constants (pK(a)) of eight chromoionophores (ETH 5294, ETH 2439, ETH 5350, ETH 5418, ETH 5315, ETH 7061, ETH 7075, ETH 2412) were measured in bis(2-ethylhexyl)sebacate (DOS) and o-nitrophenyloctylether (NPOE) plasticized poly(vinyl chloride) (PVC) membranes commonly used in optical and potentiometric ion sensors. The pK(a) values of all chromoionophores in DOS membranes are by 2-3 orders of magnitude smaller than in NPOE membranes. The weak alkali metal ion binding properties with neutral H(+)-chromoionophore and anion binding with electrically charged chromoionophores were also studied quantitatively. The complex formation constants of the commercially available Co(III)cobyrinate nitrite ionophore and the organomercury chloride ionophore, ETH 9009, were also measured. The very low stability constant observed for ETH 9009 (logbeta(2)=3.60+/-0.03 in PVC-DOS and 3.61+/-0.01 in PVC-NPOE) was explained by the decomposition of the ionophore in contact with chloride samples. On the other hand, the electrically charged nitrite ionophore showed strong complexation with nitrite ions, with logbeta=10.58 and 10.59 in DOS and NPOE membranes, respectively. In contrast to cation ionophores, the stability constant of the NO(2)(-) ionophore does not change with different plasticizers.     

Quality control criteria for solid-contact, solvent polymeric membrane ion-selective electrodes

After a long history and conflicting views, solid-contact (SC) solvent polymeric membrane ion-selective electrodes (ISEs) emerged as reliable potentometric-sensing devices with unique advantages. From the large variety of proposed SCs inherently conductive polymers emerged as the materials of choice. In our view, the most attractive feature of SC ISEs is their compatibility with thin- and thick-film microfabrication technologies that can provide cheap, mass-produced sensors and sensor arrays that can be integrated with the measuring, data acquisition, and control electronics in a straightforward way. However, despite the impressive properties of certain SC electrodes and their potential advantages, they remained primarily in the research laboratories. To make the jump from the research laboratories into commercial devices, it would be essential to prove that miniaturized SC ISEs can indeed match or surpass the performance characteristics of the conventional, liquid-contact macroelectrodes. In addition, it would be important to settle on the quality control criteria and testing protocols for assessing the performance characteristics of SC electrodes. It could help in interpreting the sometimes-inconsistent experimental data. Once cheap, miniaturized, SC ISEs will mach the performance characteristics of macroscopic-size electrodes, it is expected to have an important impact in a variety of applications requiring robust, maintenance-free, or single-use ISEs, e.g., in homecare or bedside diagnostics, environmental analysis, and quality control assessment. In addition, reliable SC ISEs are expected to revitalize the field of ion-selective field effect transistors and open new possibilities in combination with nanowire-based devices.     

Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

Flow injection determination of ketotifen fumarate using PVC membrane selective electrodes

In this study a PVC membrane electrode for determination of ketotifen fumarate is reported, where ketotifen tetraphenylborate (Keto-TPB) was used as ion exchanger. The electrode has linear range of 5.6 × 10^− 6–1.0 × 10^− 2 and 1.0 × 10^− 5–1.0 × 10^− 2 mol/L, with detection limits 2.37 × 10^− 6and 4.60 × 10^− 6 mol/L in batch and flow injection analysis (FIA), respectively. The electrodes show a Nernstian slope value (58.40 and 61.50 mV/decade in batch and FIA, respectively), and the response time is very short (≤ 10 s). The potential is nearly stable over the pH range 2.0–8.0. Selectivity coefficient values towards different inorganic cations, sugars and amino acids reflect high selectivity of the prepared electrodes. These are used for determination of Ketotifen using potentiometric titration and standard addition methods in pure samples and its pharmaceutical preparations (Zaditen tablets and syrup). The average recovery values are 99.5 and 99.2% with RSD 1.4 and 1.2% for potentiometric titrations and standard addition methods, respectively. The electrode response at different temperatures was also studied.     

Chemically modified polymeric filtration membranes for the selective elimination of active pharmaceutical ingredients from water

Poly(ether sulfone) (PES) filtration membranes were chemically modified by ultraviolet‐assisted graft polymerization radical reactions using two monomers, namely acrylic acid (AA) and N‐vinyl‐2‐pyrrolidone (NVP). The reaction kinetics was assessed by applying increasing irradiation durations keeping the monomer concentration constant, and the degree of substitution of the produced materials was monitored by attenuated total reflection‐Fourier transform infrared spectroscopy. The selective binding properties of the produced chemically modified membranes of a series of active pharmaceutical ingredients (APIs), namely 4‐acetamidophenol (APAP), ofloxacin (OFX), ciprofloxacin (CFX), tetracycline (TC), chloramphenicol (CHPH), (±)‐propranolol (PRO) and diclofenac (DF) were evaluated by means of high‐performance liquid chromatography. It was observed that native PES membranes showed specific elimination of some of the selected pharmaceuticals (i.e. PRO, OFX, CFX and DF), and this elimination was improved after chemical modification with AA (except for DF). After chemical modification by NVP, the binding properties were partially improved for several pharmaceuticals, namely TC, CHPH and PRO, and partially reduced for OFX and CFX. The selective elimination of PRO was significantly improved with both AA‐ and NVP‐modified membranes. The reported results demonstrated that the chemical modification of PES filtration membranes allowed improving significantly their API retention properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes

The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N′-[bis(pyridin-2-yl)formylidene]butane-1,4-diamine (S₁) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S₂) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S₁) (2.15%):PVC (32.2%):o-NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M Cd²⁺ with limit of detection 5.0 × 10⁻⁸ M, performs satisfactorily over wide pH range (2.0-8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

Neutral carriers based polymeric membrane electrodes for selective determination of mercury (II)

The potentiometric response characteristics of mercury ion-selective membrane electrodes based on 2-amino-6-purinethiol (I₁) and 5-amino-1, 3, 4-thiadiazole-2-thiol (I₂) were described. Ion selectivities were tested for various plasticizers, which were used as solvent mediators to incorporate the ionophores into the membrane. Effects of experimental parameters such as membrane composition, nature and amount of plasticizers and additives, pH and concentration of internal solution on the potential response of Hg²⁺ electrodes were investigated. The best performance was obtained with the electrode having a membrane composition (w/w) of (I₁) (3.17%): PVC (31.7%): DOP (dioctylpthalate) (63.4%): NaTPB (sodium tetraphenylborate) (1.58%). The proposed electrode reveals a Nernstian response over Hg²⁺ ion in the concentration range of 7.0 × 10⁻⁸-1.0 × 10⁻¹ M with limit of detection 4.4 × 10⁻⁸ M. The electrode shows good discrimination toward Hg²⁺ ion with respect to most common cations. It shows a short response time (10 s) for whole concentration range and can be used for 2 months without any considerable divergence in potentials. For evaluation of the analytical applicability, the electrode was used in the determination of Hg²⁺ ion in different environmental and biological samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

Development of polymeric membranes for zinc ion-selective electrodes

Several polymeric membranes for zinc ion-selective electrodes have been investigated. By optimizing the choice of solvent mediator and ligand, selectivity for zinc ions can be obtained. The applicability of a theory proposing membrane selectivities as a result of both solvent and site properties is demonstrated. The concept of solubility parameters is used in discussing the detection limits obtained. The best electrode found is based on a PVC membrane containing the zinc salt of di(2-ethylhexyl)phosphoric acid dissolved in tri(2-ethylhexyl)phosphate. It is the first ion-selective electrode which responds primarily to zinc. The sensor, which has a lifetime of at least two months, is characterized by a rapid response, potential stability and good sensitivity caused by a super-Nernstian slope (43.8mV/p Zn); the detection limit is 4.5 ± 0.1 pZn.     

丝素膜修饰电极pH电荷选择效应的研究

研究了丝素膜的带电特性,其等电点在pH4.5附近,利用丝系膜在等电点前后的两性荷电特性和电荷之间的静电作用,研制了丝素膜修饰石墨电极,多巴胺在膜中的表观扩散系数为2.65×10^-7cm^2/s,其电极反应异相电子转移速率常数为8.9×10^-6cm/s,电极用于神经递质类化合物体系的测定中,验证了此修饰电极的pH电荷选择效应。     

PVC membrane electrodes for potentiometric determination of tripelennamine

The construction of PVC matrix type tripelennamine ion selective electrodes and their use for direct potentiometry, potentiometric titration and flow injection analysis of tripelennamine cation are described. The membranes of these electrodes consist of tripelennamine-tetraphenylborate, reineckate and picrylsulfonate ion-association complexes dispersed in PVC matrix with tributyl phosphate (TBP) plasticizer. The electrodes exhibit near-Nernstian response over the concentration range of 10^–1-10^–4 M tripelennamine over the pH range 4.5–8.0. Selectivity coefficients data obtained for 17 different organic and inorganic ions are presented. The results obtained for the determination of 29 g/ml-29 mg/ml of tripelennamine with the proposed electrodes show average recoveries of 99.5–99.9% and mean standard deviations of 0.6–1.2%. The data agree well with those obtained by the standard methods.     

PVC-碳糊修饰电极的研制

研制了二茂铁修饰PVC-碳糊电极，采用循环伏安法研究了在pH7．4 KH2PO4-Na2HPO4缓冲溶液中该修饰电极的电化学特性和该修饰电极对抗坏血酸和邻苯二酚的电催化作用，测定结果具有较好的灵敏度和线性关系。研制了α-安息香肟修饰PVC-碳糊电极，研究了该电极对铜(Ⅱ)的特殊选择性。同时初步探讨了电极与铜(Ⅱ)的反应机理。     

Ionic liquids promote selective responses towards the highly hydrophilic anion sulfate in PVC membrane ion-selective electrodes

A remarkable enhanced response towards the hydrophilic anion sulfate using plasticized PVC membranes containing the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and a polyazacycloalkane derivative as ionophore has been found.     

Enzymatic detection of glucose using fluoride-selective electrodes with polymeric membranes

The feasibility of using polymeric membrane fluoride-selective electrodes based on zirconium(IV) 5,10,15,20-tetraphenylporphyrin as a detector in a flow-injection analysis (FIA) system for glucose determination was examined. The optimization of enzymatic reactions, FIA system configuration and enzyme-immobilization process was performed. It was shown that the resulting flow-injection system exhibits good working parameters, such as reproducibility, linear range of glucose concentration (3 × 10⁻³–10⁻¹ M), sampling rate (60 samples per minute) and lifetime (over 1 month). The performance of the polymeric membrane electrode was similar to that of a crystalline LaF₃ electrode. The results of glucose determination in synthetic samples with the proposed system show good agreement with real glucose concentrations.     

Properties of ion-selective electrodes with polymeric membranes for ketoprofen determination

The aim of the research was to create electrodes based on PVC membrane with solid contact. The membranes were plasticized with bis(2-ethylhexyl)sebacate, (DOS), dibutylphthalate (DBP) diisobutylphthalate (DIBP), tris(2-ethylhexyl) phosphate (TEHP), and 2-nitrophenyloctyl ether (o-NPOE) in which the active substance tetraoctylammonium 3-benzoyl-??-methylbenzeneacetate (KET-TOA) was dissolved. The basic analytical parameters of the ketoprofen electrode such as measuring range, detection limit, response time, lifetime, and selectivity coefficients for some organic and inorganic anions were determined. For all electrodes similar potentiometric responses were obtained: measuring range 1 × 10^?4 ?1 × 10^?1 M, and Nernstian slope of characteristics of about 55?C60 mV/decade. The electrode was used to determine ketoprofen in the synthetic sample and pharmaceutical preparations, in injections, tablets and capsules in the concentration range of 0.025?C25 mg/mL in aqueous solution at pH 5.5?C8.5.     

The role of PVC in ion selective electrode membranes

The behaviour of a solution of NaBPh₄ in a PVC membrane plasticized by di-octyl sebacate is compared with a solution of NaBPh₄ in pure liquid di-octyl sebacate. In the liquid the NaBPh₄ is present as ion pairs with ~ 0.2% of these dissociated in a 1 mM solution. By contrast in the membrane 1 mM solution is 74% dissociated. This difference in behaviour arises chiefly from the higher dielectric constant of the membrane phase.     

Selective coulometric release of ions from ion selective polymeric membranes for calibration-free titrations

Coulometry belongs to one of the few known calibration-free techniques and is therefore highly attractive for chemical analysis. Titrations performed by the coulometric generation of reactants is a well-known approach in electrochemistry, but suffers from limited selectivity and is therefore not generally suited for samples of varying or unknown composition. Here, the selective coulometric release of ionic reagents from ion-selective polymeric membrane materials ordinarily used for the fabrication of ion-selective electrodes is described. The selectivity of such membranes can be tuned to a significant extent by the type and concentration of ionophore and lipophilic ion-exchanger and is today well understood. An anodic current of fixed magnitude and duration may be imposed across such a membrane to release a defined quantity of ions with high selectivity and precision. Since the applied current relates to a defined ion flux, a variety of non-redox active ions may be accurately released with this technique. In this work, the released titrant's activity was measured with a second ionophore-based ion-selective electrode and corresponded well with expected dosage levels on the basis of Faraday's law of electrolysis. Initial examples of coulometric titrations explored here include the release of calcium ions for complexometric titrations, including back titrations, and the release of barium ions to determine sulfate.     

Performance of a highly lipophilic Li+ lonophore in solvent polymeric membranes

Ionophores based on non-cyclic triamides exhibiting Li⁺ selectivity in solvent polymeric membranes are described. Their lipophilicity (water/1-n-octanol partition coefficient) is up to 10^13.8 so that they can be used in ion-selective electrodes with a lifetime of up to 40 000 h even in permanent contact with whole blood or undiluted blood serum.On leave from the Department of General Chemistry, Technical University of Gdansk, PL-80-952 Gdansk, Poland     

Adsorptive fouling of modified and unmodified commercial polymeric ultrafiltration membranes

The fouling tendency, due to adsorption on the pore walls, of two pairs of modified and unmodified ultrafiltration membranes, with similar observed retentions determined by dextran and gel permeation chromatography, was studied. The membranes investigated were made of modified and unmodified polyaramide (PA) and modified and unmodified polyvinylidene fluoride (PVDF). The PVDF membrane was surface-modified and the PA membrane was made from a modified polymer solution. Membrane modification was used to reduce fouling by adsorption. Octanoic acid was used as the fouling substance, representing a large number of small, hydrophobic compounds. It is demonstrated in this investigation that membrane modification is not always successful. It was determined that at lower concentrations of octanoic acid, the modified PA membrane exhibits a smaller fouling tendency than the unmodified PA membrane, while the result is reversed for concentrations above 60% of the saturation concentration. The fouling tendency of the unmodified PVDF membrane is much lower than that of the modified PVDF membrane at all concentrations. The cross-sections of the membranes were visually examined with scanning electron microscopy, but no difference could be observed between the modified and unmodified membranes. The membranes were also examined with Fourier transform infrared spectroscopy. The spectra of the two PA membranes were different, while no difference was observed for the unmodified and surface-modified PVDF membranes. Remains of octanoic acid were found in the membranes, although they had been thoroughly rinsed with deionized water and the initial pure water flux was recovered.