Development of low-cost metal oxide pH electrodes based on the polymeric precursor method

In this work, the polymeric precursor method was used to prepare low-cost solid-state sensors for pH determination based on iridium oxide as the main pH sensitive material. The iridium content was reduced with addition of TiO₂, forming the binary system IrO_x–TiO₂, whose electroanalytical properties were evaluated in comparison with a commercial glass pH electrode. The minimum iridium content which gave suitable results was 30 mol%, and the electrode presented Nernstian and fast response in the pH range from 1 to 13, with no hysteresis effect observed. Besides, the electrode showed high selectivity in the presence of alkali ions as Li⁺, Na⁺ or K⁺. The amount of iridium in the prepared electrodes was very small (<0.1 mg), supporting the efficiency of this method on the simple preparation of functional low-cost pH electrodes.     

Developing an Iridium Oxide Film Modified Microelectrode for Microscale Measurement of pH

Iridium oxide film modified microelectrode was fabricated by anodic oxidation method onto the tip of an etched iridium wire in diluted sulfuric acid solution by cyclic voltammetry. The iridium oxide film microelectrode exhibited very promising pH sensing performance, with an ideal Nernstian in the tested pH range of 0 to 14. This method for preparing microelectrode allowed accurately control of the deposited amount and the rate of the iridium oxide film growth. The electrodes demonstrated advantages of long lifetime, good selectivity and fast response with a relative time less than 0.2 s for pH changes in a large scale. The microelectrode was not interfered by a wide variety of inorganic ions and organic compounds. Furthermore, the electrodes were successfully applied to the measurement of pH in microscale of apples.     

基于双氨基三唑硫醚为中性载体的汞离子选择性电极的研究

研制了基于双氨基三唑硫醚为中性载体的阳离子选择性电极。实验表明,该电极对Hg2 具有良好的电位响应特性,在pH 2.0硝酸盐缓冲液中,电极电位呈近能斯特响应,线性响应范围为4.0 mg/L~20 g/L,斜率为33.4 mV/dec.(25℃),检出限为1.7 mg/L。该电极响应时间短(<10 s),pH范围较宽(1.3~3.3)。将该电极用于实际水样和二元混合溶液中Hg2 的检测,其结果令人满意。     

Potentiometric Iodide Selectivity of Polymer‐Membrane Sensors Based on Co(II) Triazole Derivative

The 3‐amion‐5‐mercapto‐1,2,4‐triazole cobalt(II) [Co(II)AMETR] was used as a new carrier for preparing polymeric membrane selective sensor which exhibited high affinity for iodide ion. The effects of membrane composition, pH, the influence of lipophilic ion additives and plasticizer on the response characteristics of the sensor were investigated. The sensor showed a near Nernstian slope of ?56.6 mV/decade for I^? ion over a wide concentration range from 8.5×10^?7 to 1.0×10^?1 M with a low detection limit of 5.1×10^?7 M. The sensor has a fast response time and could be used over a wide pH range of 2–8. The response mechanism is discussed in view of the AC impedance technique. The sensor was successfully applied to direct determination of iodide content in environmental water samples and mouth wash samples.     

Optimization of polymeric triiodide membrane electrode based on clozapine-triiodide ion-pair using experimental design

Central composite design (CCD) and response surface methodology (RSM) were developed as experimental strategies for modeling and optimization of the influence of some variables on the performance of a new PVC membrane triiodide ion-selective electrode. This triiodide sensor is based on triiodide-clozapine ion-pair complexation. PVC, plasticizers, ion-pair amounts and pH were investigated as four variables to build a model to achieve the best Nernstian slope (59.9 mV) as response. The electrode is prepared by incorporating the ion-exchanger in PVC matrix plasticized with 2-nitrophenyl octal ether, which is directly coated on the surface of a graphite electrode. The influence of foreign ions on the electrode performance was also investigated. The optimized membranes demonstrate Nernstian response for triiodide ions over a wide linear range from 5.0 x 10(-6) to 1.0 x 10(-2)mol L(-1) with a limit of detection 2.0 x 10(-6) mol L(-1) at 25 degrees C. The electrodes could be used over a wide pH range 4-8, and have the advantages of easy to prepare, good selectivity and fast response time, long lifetime (over 3 months) and small interferences from hydrogen ion. The proposed electrode was successfully used as indicator electrode in potentiometric titration of triiodide ions and ascorbic acid.     

Cobalt(II)-selective membrane electrode based on a recently synthesized benzo-substituted macrocyclic diamide.

A PVC-membrane electrode based on a recently synthesized 18-membered macrocyclic diamide is presented. The electrode reveals a Nernstian potentiometric response for Co2+ over a wide concentration range (2.0 x 10(-6)-1.0 x 10(-2) M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for Co2+ over a wide variety of other metal ions, and could be used over a wide pH range (3.0-8.0). The detection limit of the sensor is 6.0 x 10(-7) M. It was successfully applied to the direct determination and potentiometric titration of cobalt ion.     

Silver(I)-selective coated-wire electrode based on an octahydroxycalix[4]arene derivative.

The performance of octahydroxycalix[4]arene derivative used as a neutral carrier for silver polymeric membrane electrode was studied. The sensor gave a good Nernstian response of 58 +/- 1 mV per decade for silver ion in the activity range 3.3 x 10(-6) to 3.3 x 10(-2) M Ag+. The limit of detection reached 2.1 x 10(-6) M Ag+ and exhibited high selectivity for silver ion against the alkali, alkaline earth and transition metal ions. The sensor can be used in wide pH range from 1.5 to 6.5. The response time of the sensor is less than 20 s. The potentiometric sensor was used as the indicator electrode in the titration of Ag+ ions by sodium chloride solution.     

Preparation of a novel iodide-selective electrode based on iodide-miconazole ion-pair and its application to pharmaceutical analysis.

An iodide-miconazole ion-paired complex was used as a suitable ion-exchanger for the preparation of a plasticized-PVC membrane electrode. Among different solvent mediators tested, dioctylsebacate exhibited the proper response characteristics, including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of -59.8 +/- 0.5 mV decade(-1) for I- ion over a concentration range of 1.0 x 10(-5) - 1.0 x 10(-2) M with a limit of detection of 7.0 x 10(-6) M. The electrode displays a good selectivity for I- with respect to a number of inorganic and organic species. It canbe used over a pH range of 2.5 - 8.5. The membrane sensor was successfully applied to the determination of iodide in water samples and blood serum, as well as in pharmaceutical products such as iodoquinol and thyroxin.     

Ni selective sensors based on meso-tetrakis-{4-[tris-(4-allyl dimethylsilyl-phenyl)-silyl]-phenyl}porphyrin and (sal)2trien in poly(vinyl chloride) matrix

PVC-based membranes of meso-tetrakis-{4-[tris-(4-allyl dimethylsilyl-phenyl)-silyl]-phenyl}porphyrin (I) and (sal)₂trien (II) as electroactive material with dioctylphthalate (DOP), tri-n-butylphosphate (TBP), chloronapthalene (CN), dibutylphthalate (DBP) and dibutyl(butyl) phosphonate (DBBP) as plasticising solvent mediators have been found to act as Ni²⁺ selective sensor. The best performance was obtained with the sensor having a membrane of composition of I: sodium tetraphenyl borate: PVC in the ratio 5:5:150. The sensor exhibits Nernstian response in the activity range 2.5 × 10⁻⁶ to 1.0 × 10⁻¹ M, performs satisfactorily over wide pH range (2–5.5) with a fast response time (8 s). The sensor was found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol or ethanol and acetone and could be used over a period of 4 months. Potentiometric selectivity coefficients determined by matched potential method (MPM) indicate excellent selectivity for Ni²⁺ ions. The sensors could be used successfully in the estimation of nickel in different brand of chocolates and also as an indicator electrode in potentiometric titration.     

Highly Selective PVC‐Based Membrane Electrode Based on 2,6‐Diphenylpyrylium Fluoroborate

A highly selective PVC‐membrane electrode based on 2,6‐diphenylpyrylium fluoroborate is presented. The electrode reveals a Nernstian potentiometric response for sulfate ion over a wide concentration range (5.0 × 10^?6‐1.0 × 10^?1 M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for sulfate over a wide variety of common organic and inorganic anions and could be used over a wide pH range (2.5–9.5). The detection limit of the sensor is 3.0 × 10^?6 M. It was successfully applied to the direct determination of salbutamol, paramomycin tablets, and as an indicator electrode for potentiometric titration of sulfate ions with barium ions.     

Copper(II) Ion‐Selective Electrodes Based on Dithiosalicylic and Thiosalicylic Acids

Potentiometric carbon paste electrodes for copper(II) based on dithiosalicylic and thiosalicylic acids are described. The sensor based on dithiosalicylic acid (DTS) exhibits a linear response with a nearly Nernstian slope of 27.7 mV per decade, whereas the electrode based on thiosalicylic acid (TS) shows a super‐Nernstian slope. The limits of detection for the DTS sensor and the TS sensor are 10^?7.9and 10^?6.3 M for copper(II) activity, respectively. Selectivity coefficients are tabulated, and the influence of the pH on the response of these ISEs is studied. The DTS electrode is successfully used for potentiometric titration of humic acids with copper in order to get more information about complexing properties of these acids.     

A novel pH sensing membrane based on an ionic liquid-polymer composite

A novel pH sensing membrane was developed that consists of the ionic liquid n-cetylpyridinium hexafluorophosphate (CPFP), poly(vinyl chloride), and quinhydrone. The membrane is stable and flexible and can be easily deposited on the electrode. Electrochemical impedance spectroscopy was used to study the interfacial charge transfer of this membrane. Compared to a traditional plasticizer-based membrane electrode, the new electrode possesses excellent potentiometric characteristics for monitoring pH, such as a response time of less than 10 s, high sensitivity, stability, and reproducibility. The response is almost Nernstian, with a slope of ?57.5?±?0.2 mV pH^?1 in the pH range from 2 to 9.5. The new electrode was used for direct monitoring of pH in real food samples.

Novel potentiometric sensor for monitoring beryllium based on naphto-9-crown-3.

A novel poly(vinyl chloride) (PVC) membrane electrode based on naphto-9-crown-3 was prepared and tested for the selective detection of beryllium ions. A suitable lipophilicity of the carrier and appropriate coordination ability were found to be essential for designing an electrode with good response characteristics. A PVC membrane with 9% naphtho-9-crown-3 carrier, 58% o-NPOE plasticizer, 3% tetraphenylborate anionic excluder and 30% poly(vinyl chloride) satisfied these requirements. The proposed sensor displayed a linear response to beryllium over a wide concentration range of 1.0 x 10(-1)-8.0 x 10(-6) M with a Nernstian slope of 29.5 mV per decade. The electrode showed very short response time (<15 s) and could be used in the pH range 3.5-9.0. The selectivity coefficient for alkali, alkaline earth, transition and heavy metal ions was smaller than 4.0 x 10(-4). The sensor was successfully used as an indicator electrode in the potentiometric titration of Be2+ with EDTA. The proposed Be(II) sensor was also used for the determination of Be2+ ions in binary mixtures.     

Cesium-selective membrane electrode based on a recently synthesized 16-membered macrocyclic diamide

A PVC membrane sensor for the Cs+ ion based on 1,5-diaza-2,3,4-naphthyl-8,11,14-trioxacyclohexadecane-6,16-dione (L) has been prepared. The sensor has a linear dynamic range of 5.0 x 10(-1) - 6.9 x 10(-6) mol L(-1), a Nernstian slope of 59.5 +/- 0.8 mV decade(-1), and a detection limit of 4.7 x 10(-6) mol L(-1). It has a fast response time of <15 s and can be used for at least 8 weeks without any considerable divergence in potentials. The selectivity of the proposed electrode relative to alkali, alkaline earth, and transition metal ions was comparatively good. The electrode could be used in the pH range 4.5-11.0.     

A New pH Sensor Based on a Glassy Carbon Electrode Coated with a Co/Al Layered Double Hydroxide

A glassy carbon electrode has been coated by electrodeposition with a thin film of cobalt based layered double hydroxide (LDH) and used as a pH sensor. The developed electrode displays a linear super‐Nernstian response (?76.2±0.6 mV/pH) in the pH range between 2 and 14 and it is particularly suitable to operate in strongly alkaline solution. The reproducibility of the sensor construction is good with a relative standard deviation of the calibration curve slopes of±2.5 % (n=4). The electrode has a response time comparable to that exhibited by commercial glass electrodes in the pH range examined and is not affected by interference from the most common anions and cations.     

A polystyrene based membrane electrode for cadmium(II) ions

A polystyrene based membrane of 3,4:12,13-dibenzo-2,5,11,14-tetraoxo- 1,6,10,15-tetraazacyclooctade-cane shows a Nernstian response to Cd(II) ions over a wide concentration range (3.16 x 10(-6) - 1.00 x 10(-1) mol L(-1) with a Nernstian slope of 29.8 mV/decade of concentration, between pH 2.0 and 6.0. This electrode has been found to be chemically inert and of adequate stability with a response time of 20s. The electrode gives reproducible results with a lifetime of 130 days. The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 35% (v/v) content of methanol and ethanol. The practical utility of the proposed chemical sensor has been observed by using it as end-point indicator in the titration of Cd(II) ions with EDTA. The potentiometric selectivity coefficient values indicate that the membrane sensor is highly selective for Cd(II) ions over a number of cations. Small amounts of surfactants do not disturb the functioning of the sensor. This electrode has also been used to estimate cadmium ions in real samples.     

Intra- and Inter-molecular Sulf- hydryl Hydrogen Bonding: Facilitating Proton Transfer Events for Determination of pH in Sea Water

This work presents the electrochemical response of a 2-(methylthio)phenol glassy carbon based electrode for a promising voltammetric pH sensor in both buffered and low-buffered solutions. Electropolymerization of the redox species was performed with the resulting polymer presenting a Nernstian response in buffered media, with a sensitivity of 51 mV/pH unit. The effectiveness of the sulfhydryl bond to facilitate proton transfer from the bulk solution to the phenol molecules has been confirmed, providing an accurate pH measurement of 8.28 in sea water media, compared to that measured with a calibrated glass pH probe of 8.30.     

Ketoconazol‐Triiodide Ion Pair Complex as a Suitable Carrier in an Iodide Selective Membrane Electrode

A novel membrane sensor for selective monitoring of iodide, consisting of a triiodide‐ketoconazole ion pair complex dispersed in a PVC matrix, plasticized with a mixture of 2‐nitrophenyl octyl ether and dioctylphtalate with unique selectivity toward iodide ions, is described. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The optimized membrane demonstrates a near‐Nernstian response for iodide ions over a wide linear range from 1.0 × 10^?2 to 1.0 × 10^?5 M, at 25 ± 1 °C. The electrode could be used over a wide pH range 3–10 and has the advantages of high selectivity, fast response time and good lifetime (over 4 months). It was successfully used as indicator electrode in potentiometric titrations and direct potentiometric assay of iodide ions.     

Copper(II)-selective membrane electrodes based on some recently synthesized mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit

Three different mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit were investigated to characterize their abilities as copper(II) ion carriers in PVC-membrane electrodes. The electrode based on L1 exhibited a Nernstian response for Cu²⁺ ions over a wide concentration range (2×10⁻¹ to 1×10⁻⁵ M) with a limit of detection of 8.0×10⁻⁶ M (0.5 p.p.m.). The response time of sensor is 15 s, and the membrane can be used for more than 3 months without observing any deviation. The electrode revealed comparatively good selectivities with respect to many alkali, alkaline earth, transition and heavy metal ions, and could be used in a pH range of 2.5–5.5. It was applied to the direct determination and potentiometric titration of the copper(II) ion.     

A new diclofenac membrane sensor based on its ion associate with crystal violet. Application to diclofenac determination in urine and pharmaceuticals

A novel diclofenac ion-selective electrode has been prepared and used in pharmaceutical analysis. The ion-associate of diclofenac with basic dye (crystal violet) was used as the membrane carrier. Among the four different solvent mediators tested, dibutylphthalate (DBP) exhibited proper behavior including the Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of 59 ± 1 mV decade^?1 for diclofenac in the concentration range 5.0 × 10^?5-5.0 × 10^?2 M with the limit of detection of 2.5 × 10^?5 M. The electrode displays good sensitivity with the respect to a number of common inorganic and organic species. It can be used in a pH range of 6–11. The membrane sensor was successfully applied to the determination of diclofenac in capsules and for its recovery from urine samples.