Potentiometric Performance Research Articles

Selective Determination of Zn2+ Ion in Various Environmental, Biological and Medicinal Plant Samples Using a Novel Coated Graphite Electrode

AbstractNovel Zn2+ ion‐selective PVC based coated graphite electrodes were fabricated using the ionophores N‐((1H‐indol‐3‐yl)methylene)thiazol‐2‐amine (I1), N‐((1H‐indol‐3‐yl)methyl)‐thiazol‐2‐amine (I2) and 1‐((1H‐indol‐3‐yl)methylene)urea (I3). Their potentiometric performance was examined in dependence of the addition of plasticizers and anion excluders and compared. It is found that the coated graphite electrode with the composition I1:KTpClPB:o‐NPOE:PVC=9 : 1.5 : 51 : 38.5 is the best with respect to the wide working concentration range (4.2×10−8–1.0×10−1 mol L−1), low detection limit (1.6×10−8 mol L−1) and wide pH range of 3.0–8.0. The proposed electrode was successfully applied to quantify Zn2+ in various environmental, biological and medicinal plant samples and used as indicator electrode.

Screen-Printed Potentiometric Strip for Calcium Ion Determination in Water and Milk

<abstract><title><italic>Abstract. </italic></title> In this study, a novel type of calcium ion potentiometric strip was fabricated using a screen-printing technique. Commercial ink was first printed onto the ceramic substrate in order to construct the reference electrode and working electrode. Then modification of the graphene film on the surface of the working electrode was performed using a one-step electrodeposition technique. A calcium ion-selective membrane was coated onto the surface of the graphene film with a simple drop-casting method. Dynamic response testing was employed to characterize the potentiometric performance of the developed disposable strip, which showed a Nernstian slope of 29.1 mV decade^-1, low detection limit of 10^-5.9 mol L^-1, and short response time (less than 10 s). Furthermore, the potential response of the developed strip was insensitive to oxygen, redox species, and light. The use of the disposable potentiometric strip for water and milk sample analysis was performed with a one-point calibration procedure. The detection limits were 8.6 × 10^-5 mol L^-1 for tap water samples, 8.2 × 10^-5 mol L^-1 for mineral water samples, and 9.8 × 10^-5 mol L^-1 for milk samples. This method could be used as an effective tool in real sample analysis, which makes it a promising alternative in routine sensing applications.

High-performance flexible potentiometric sensing devices using free-standing graphene paper.

The development of cost-effective, robust, and rugged biochemical sensing devices is of great interest for point-of-care testing and on-spot monitoring. Here we reported a facile approach to build high-performance flexible potentiometric sensing devices by using free-standing graphene paper (GNP) as electrode substrate. The transduction mechanism of the GNP-based electrode was investigated systematically, revealing that GNP acts as both electric conductor and ion-to-electron transducer of the potentiometric signals. Three GNP-based ion-selective electrodes (GNP-ISEs) were constructed, which exhibited excellent potentiometric performance. Furthermore, a paper-type reference electrode (RE) was presented for the first time in which the photo-polymerised reference membrane is directly coated onto the GNP. Results show that the GNP-based RE (GNP-RE) displayed low potential variability for a wide range of biochemical species in a wide calibration range. On the basis of these excellent results, integrated potentiometric sensing devices using GNP-ISE and GNP-RE were built that possess comparable performance with common types of potentiometric detection system. High-performance, easy fabrication, low cost, and excellent flexibility make the GNP-based potentiometric sensing devices very attractive as 'vanguard analytical tools' for routine sensing applications.

A New Validated Potentiometric Method for Batch and Continuous Quality Control Monitoring of Oseltamivir Phosphate (Taminil) in Drug Formulations and Biological Fluids

AbstractA new validated potentiometric method is described for batch and continuous quality control monitoring of the drug oseltamivir phosphate (Taminil) (OST). The method involves the development of a potentiometric sensor responsive to the drug based on the use of the ion‐association complex of (OST+) cation with phosphomolybdate anion (PMA−) as an electroactive material in a poly(vinyl chloride) matrix membrane plasticized with o‐nitrophenyloctyl ether (o‐NPOE). Optimization of the performance characteristics of the sensor is described. A membrane incorporating the OST‐PMA‐NPOE complex in a tubular flow through detector is used in a two channel flow injection set up for continuous monitoring of the drug at a frequency of ∼30 samples h−1. The sensor shows fast near‐Nernstian response for OST over the concentration range 5.2×10−5–0.8×10−2 M (21.34 µg mL−1–3.23 mg mL−1) with a detection limit of 9.1×10−6 M (3.73 µg mL−1) over the pH range 4.6–6.1. The sensor displays good selectivity for OST drug over some basic drugs, inorganic cations, excipients and diluents commonly used in the drug formulations. Validation of the assay method is tested by measuring the lower detection limit, range, linearity, bias, trueness, accuracy, precision, and between‐day‐variability, within day reproducibility, selectivity and ruggedness (robustness). The results reveal good potentiometric performance of the proposed sensor for determination of OST in pharmaceutical capsules and in biological fluid matrices as well as for testing the dissolution profile of the drug and drug homogeneity.

The Potentiometric Performances of the Cation Selective Electrodes based on Tetracycline and Chemically Modified Tetracycline

Metal-binding antibiotics are very attractive choices as cation selective ionophores. The ability of tetracycline (TC) antibiotics to bind to metal ions has obtained much attention. TCs exhibit the potentiometric performance changes for various cations dependant on several experiment conditions. In this report, we investigated the potentiometric performance changes of TC as the modification of TC`s possible metal binding site. We found that the selectivity alter with the blocking main binding site of ionophores for cations. And, additionally it is possible to control the selectivity of sensors with chemical modification of ionophores.

The Potentiometric Performances of the Cation Selective Electrodes based on Tetracycline and Chemically Modified Tetracycline

The Potentiometric Performances of the Cation Selective Electrodes based on Tetracycline and Chemically Modified Tetracycline

Sulfadiazine-selective determination in aquaculture environment: Selective potentiometric transduction by neutral or charged ionophores

Solid-contact sensors for the selective screening of sulfadiazine (SDZ) in aquaculture waters are reported. Sensor surfaces were made from PVC membranes doped with tetraphenylporphyrin-manganese(III) chloride, α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin ionophores that were dispersed in plasticizer. Some membranes also presented a positive or a negatively charged additive. Phorphyrin-based sensors relied on a charged carrier mechanism. They exhibited a near-Nernstian response with slopes of 52mVdecade−1 and detection limits of 3.91×10−5molL−1. The addition of cationic lipophilic compounds to the membrane originated Nernstian behaviours, with slopes ranging 59.7–62.0mVdecade−1 and wider linear ranges. Cyclodextrin-based sensors acted as neutral carriers. In general, sensors with positively charged additives showed an improved potentiometric performance when compared to those without additive. Some SDZ selective membranes displayed higher slopes and extended linear concentration ranges with an increasing amount of additive (always <100% ionophore). The sensors were independent from the pH of test solutions within 2–7. The sensors displayed fast response, always <15s. In general, a good discriminating ability was found in real sample environment. The sensors were successfully applied to the fast screening of SDZ in real waters samples from aquaculture fish farms. The method offered the advantages of simplicity, accuracy, and automation feasibility. The sensing membrane may contribute to the development of small devices allowing in locus measurements of sulfadiazine or parent-drugs.

Ag+-selective poly(vinyl chloride) Membrane Electrode Based on [N,N- ethylenebis-(3-methoxy salicylaldimine)

A solid state silver selective poly (vinyl chloride) (PVC) membrane electrode was developed by using recently synthesized [N, N-ethylenebis-(3-methoxy salicylaldimine)] as an active component of the membrane. The best sensitivity and selectivity for Ag+ ions were obtained for the electrode membrane containing ionophore-NPOE-PVC and KTpClTB in composition of 4:62:33:1 (w/w). The proposed electrode had a Nernstian response (56.0 mV/decade) to Ag+ within the concentration range 1.0 ×10-6 to 1.0×x10-1 mol L-1and with a detection limit of 8.3×10-7 mol L-1. The electrode worked well between pH 3.0 and 8.0 and had a fast response time of 15 s. The electrode was used along 3 months without any significant change in its sensitivity. Potentiometric performance of the electrode in partially non-aqueous medium (up to 10 % (v/v) alcohol) was found satisfactory. The electrode was successfully used in the potentiometric titration of silver ions with standard solution of potassium iodide, and in the direct determination of silver ion in spiked waste water and photographic film developing solutions.

Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes.

A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Cl− ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes.

Flow-injection potentiometric applications of solid state Li+ selective electrode in biological and pharmaceutical samples

A solid state polyvinyl chloride (PVC) membrane Li+-selective electrode was prepared and used as a detector in a low-dead volume flow through cell for the determination of Li+ in pharmaceutical formulations and human serum samples. The potentiometric performance characteristics of the electrode were calculated under the optimized flow conditions. The electrode had near-Nernstian behavior in the concentration range of 0.1–100 mM (R 2 = 0.9981) with a slope of 61.34 mV decade−1 and detection limit of 0.080 mM. The relative standard deviation of the electrode response for eight replicate measurements of 100, 10, and 1 mM Li+ was 0.43%, 0.45%, and 0.99%, respectively. The designed flow-through cell detector system revealed sampling rates of approximately 70 injections per hour. Flow injection potentiometry (FIP) results obtained for the pharmaceutical formulations were in good harmony with the atomic emission spectrophotometry results. However, the electrode could not be used successfully for the direct analysis of real serum samples in FIP.

A sensitive and highly stable polypyrrole-based pH sensor with hydroquinone monosulfonate and oxalate co-doping

A polymer-based pH electrode has been successfully fabricated via a simple electropolymerization of pyrrole on stainless steel using a co-doping system. Hydroquinone monosulfonate (HQS) was selected as a functional dopant while oxalic acid was used as a co-dopant. A combination of cyclic voltammetry and X-ray photoelectron spectroscopy revealed that passive layers of iron oxalate and chromium oxalate formed on the stainless steel surface at the initial stage of electropolymerization. The potentiometric characteristics of the co-doped polypyrrole (PPy) electrode exhibited a response slope of −54.67 ± 0.70 mV/pH at 28 °C, a linearity range from pH 2 to 12 and correlation coefficient greater than 0.995. The open-circuit potential was stable in buffer solutions with a response time less than 10 s, regardless of the age of electrode. The co-doped PPy electrode could be used as a multi-use pH sensor up to 60 days without any effect to the potentiometric response. Interferences from most of common ions are acceptably small. In comparison with a HQS-doped PPy electrode, the co-doped PPy electrode provides a superior pH measurement in solution due to the higher pH sensitivity and longer lifetime. Co-doping results in an improvement in the adhesion strength of the co-doped PPy film with the stainless steel electrode. Easy fabrication and the low production cost of the co-doped PPy electrodes offer an alternative to pH sensors having a comparable potentiometric performance with commercial glass electrodes.

Iodide recognition by the N,N-bis-succinamide-based dendritic molecule [CH 2C(O)NHC(CH 2CH 2C(O)OtBu) 3] 2

Ion selective membrane electrode doped with amide functionalized dendritic [CH 2C(O)NHC(CH 2CH 2C(O)OtBu) 3] 2 macromolecule was evaluated as anion sensor. The ability of the membrane has been explored by incorporating it into a plasticized PVC matrix on glassy carbon electrode. The effects of membrane composition, pH and the influence of anion additives, and also the nature of the plasticizers on the response characteristics of the electrode were investigated. The resulting electrode exhibits an anti-Hofmeister selectivity pattern with remarkable specificity towards iodide over other lipophilic inorganic anions. The optimum membrane composition for best potentiometric performance was achieved with a DPE-plasticized membrane (DPE = diphenyl ether) doped with 15% TBAB (TBAB = tetrabutyl ammonium bromide), suggesting that the ionophore operates via a neutral carrier mechanism. It has a linear response to iodide with a detection limit of 4.46 × 10 −7 M and a slope of 59.6 mV/decade, a satisfactory reproducibility and a rapid response time. The selectivity coefficients for I − towards interferences from ClO 4 −, NO 3 − and Cl − were estimated to be K I − , anio n − pot = 1.25 × 10 − 4 , 1.99 × 10 −4 and 7.94 × 10 −5, respectively. Application of the electrode to the potentiometric titration of iodide ion with silver nitrate is also reported.

The Potentiometric Performances of Ion-selective Electrodes based on Tetracycline and Modified Tetracyclines

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The Potentiometric Performance of Mercury (II) Ion-Selective Electrode Based on Tetracycline Antibiotics

Poly (vinylchloride) (PVC) membrane electrodes based on neutral carrier, tetracycline was prepared as an active sensor for Hg(II) ion, and tested in different contents of the potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as lipophilic salt. Bis (2-ethylhexyl) sebacate (DOS), bis(l-butylpentyl) adipate (BBPA), 2-nitrophenyl octyl ether (NPOE) and dibutyl phthalate (DBP) were used as diverse plasticizing solvent mediators. This electrode shows excellent potentiometric response characteristics and display good linearity with log <TEX>$[Hg^{+2}]$</TEX> versus EMF response, over a range of concentrations between <TEX>$10^{-7}$</TEX> and <TEX>$10^{-3}M$</TEX>. With 30.8mV/decade Nernstian slope, the detection limit was <TEX>$6.9{\times}10^{-9}M$</TEX> and the response time was less than 20s. The proposed electrode yields very good selectivity for mercury (II) ion over many cations such as alkali, alkaline earth, transition and heavy metal ions. And it shows a very stable potential values in a wide pH range. This reliable electrode prepared was kept at least a month without considerable alteration in their response to Hg (II) ion.

The Composition Dependence Selectivity Changes by Plasticizer at the Cation Sensors Based on Tetracycline Antibiotics

The performances of tetracycline based cation selective polymeric membrane electrodes of many sets with different plasticizers were investigated as the selectivity of ion-selective electrodes and optodes are greatly influenced by membrane solvent and also controlled by plasticizers. The membrane 1 with Bis(2-ethylhexyl) sebacate (DOS) and additive shows good potentiometric performance toward Ca2+ (slope: 27.8 mV per decade; DL: -4.52) including selectivity. Contrastingly, membrane 4 with Dibutyl phthalate (DBP) shows near-Nernstian response, it has also shown the best measuring range and detection limit for Ca2+ (29.5 mV and -5.10) and Mg2+ (24.4 mV and -5.04) and the least selectivity has been also observed between Ca2+ and Mg2+. When the membrane 1 and 4 were used together to flow system, we could determine the concentration of Ca2+ and Mg2+, simultaneously.

Cation selectivity of ionophores based on tripodal thiazole derivatives on benzene scaffold

The synthesis and potentiometric evaluation of new 1,3,5-tris(thiazolylcarbethoxy)-2,4,6-trimethylbenzene ( 3), 1,3,5-tris(thiazolylhydroxy)-2,4,6-trimethylbenzene ( 4), 1,3,5-tris(thiazolylmethyl)-2,4,6-trimethylbenzene ( 5), and 1,3,5-tris(thiazolylphenyl)-2,4,6-trimethylbenzene ( 6), toward mono and divalent cations under various pH conditions are outlined. The ion-selective properties of the newly synthesized compounds were studied by measuring the potentiometric responses of the 3-, 4-, 5-, and 6-based membrane electrodes to alkali metal, alkaline earth metal, ammonium, and transition metal ions, under various pH conditions. The 3-based electrode exhibited a Nernstian response to ammonium and potassium under alkaline pH conditions, while the other three electrodes showed a poor potentiometric performance. All electrodes showed substantial responses to silver ion under acidic condition, but there was almost nil response to other transition metal ions (Fe 2+, Co 2+, Zn 2+, Ni 2+, Pb 2+, Cd 2+, Cu 2+ and Hg 2+). The 3- and 5-based electrodes resulted in near Nernstian responses (51.3 mV and 59.5 mV/pAg +, respectively) with low detection limits (∼100 ppt), while the 4- and 6-based ones showed sub-Nernstian below 40 mV/pAg +. The results were interpreted with semi-empirically modeled structures.

Potentiometric performance of 2-aminothiophenol based dipodal ionophore as a silver sensing material

A new sensing material has been used for fabricating a liquid membrane electrode for silver determination. The electrode has been systematically characterized by the electrode response, measuring range (1 × 10 −4 to 1 × 10 −1 M), detection limit (6 × 10 −5 M), pH range (3.3–8.0) and selectivity coefficients for the closely related metal ions. The electrode shows a good response to silver ions in the presence of mercury ions. The electrode works well in mixed solvents media also. The electrode is used extensively as an indicator electrode for the determination of Ag + in various synthetic samples and also used for the determination of SCN −, CN −, S 2− and I −.

Potentiometric Performance of Silver Ion-Selective Electrodes Based on Tridentate Schiff Base Derivatives

To examine the directivity for improving the silver ion discrimination ability of a Schiff base, three kinds of tridentate ligands were synthesized and compared with the similar quadridentate ligand as the silver ionophore. Among the Schiff base derivatives tested, 3-(2-pyridylethylimino)-2-butanoneoxime, having one oxime and a pyridine substituent, was found to be the best ionophore for a silver-ion electrode. The electrode based on this derivative exhibited good silver-ion selectivity, -log Kpot(Ag+,K+) = 3.8, comparable to that of a quadridentate Schiff base, N,N'-bis(2'-hydroxyimino-1'-phenylpropyleden)-1,3-propanediamine, reported previously, except for a pseudo Nernstian response (35.6 mV decade(-1)) with a wide silver-ion activity change in the activity change from 5.0 x 10(-7) to 7.9 x 10(-2) mol dm(-3).

The potentiometric performances of cyclotetrahydroxysiloxane containing ferrocenyl moiety as an anion-selective membrane electrode

A test electrode based on cyclotetrasiloxane containing ferrocenyl, hydroxide and amine moiety exhibits very good potentiometric performance toward anions. Especially, acetate ion shows non-Hofmeister behavior on selectivity. The addition of the tetraalkylammonium salt provides lipophilic cationic sites within the membrane and enhances the response to more lipophilic anions. As expected, potentiometric performances of slopes and detection limits for the most of lipophilic anions, such as ClO 4 − and SCN −, are the most enhanced. However, the response to acetate ion was significantly decreased. In our knowledge, this is the first report that cyclic siloxane containing functional groups such as ferrocenyl moiety and hydroxyl group shows possible usage as a neutral carrier for an anion sensor.

Selective fluoride recognition and potentiometric properties of ion-selective electrodes based on bis(halodiphenylstannyl)alkanes

A series of bis(halodiphenylstannyl)alkanes (Ph 2XSn) 2(CH 2) n , (X: Cl, Br, OAc, n=1–4) have been evaluated as fluoride ionophores in polymeric-membrane ion-selective electrodes. It is shown that the selectivity pattern of these molecules is governed by their structural characteristics. An entirely non-Hofmeister selectivity sequence with a remarkable preference towards fluoride is obtained for bis(chlorodiphenylstannyl)methane, (Ph 2ClSn) 2CH 2. The latter compound was utilised for further studies on the improvement of the ISEs selectivity towards fluoride. The optimum membrane composition for best potentiometric performance was achieved with DOS-elasticised membranes doped with 10 mol% KTpClPB, suggesting that this compound operates via a charged-carrier mechanism. This membrane composition results in a preference to fluoride over several lipophilic anions, such as perchlorate, nitrate and iodide.