Potentiometric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate indirect determinations

Ferrous ethylenediamine sulphate has been used as a reducing agent to determine indirectly potassium dichromate, hydrogen peroxide, potassium permanganate, potassium persulphate, potassium chlorate, potassium bromate, and ceric sulphate by a potentiometric method. An excess of ferrous ethylenediamine sulphate added to each of the substances in an acid medium is titrated with a standard solution of potassium permanganate, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

Potentiometric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate ceric sulphate method

Ferrous ethylenediamine sulphate has been used as a reducing agent to determine indirectly potassium permanganate, ceric sulphate, potassium chlorate, hydrogen peroxide, potassium persulphate, potassium dichromate and potassium bromate by a potentiometric method. An excess of ferrous ethylenediamine sulphate added to each of the substances in acid medium was titrated with a standard solution of ceric sulphate, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

金电极上L-半胱氨酸短链分子自组装单层的电化学性能和拉曼光谱研究

用循环伏安法分别测定了金电极表面L-半胱氨酸(L-Cys)和十二硫醇自组装单分子层的电化学行为, 实验发现虽然单层结构排列致密, 但并不能有效地阻碍铁氰化钾与电极间异相电子转移过程, 同时观察到十二烷基硫醇自组装层能较好地阻碍电子转移作用. 运用表面增强拉曼散射光谱技术, 以十二烷基硫醇作为缺陷探针, 从分子水平上证实了L-半胱氨酸自组装单层的稳定性和致密性.     

Needle-type ultra micro silver/silver chloride reference electrode for use in micro-electrochemistry.

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.     

Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a calix[4]arene.

A hydrogen ion-selective poly(vinyl chloride) membrane electrode was constructed using 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetracyanomethoxycalix[4]arene as a neutral carrier. The electrode showed an apparent Nernstian response in the 2-11.5 pH range with a slope of 54.0 +/- 0.2 mV/pH at 20 +/- degrees C. This electrode showed a rapid response of the emf to changes in the pH, high ion selectivity with respect to lithium, sodium and potassium, and characteristics similar to those reported for the conventional pH glass membrane electrode. It can be used as a potentiometric indicator electrode in hydrofluoric acid solutions. The effects of iodide, thiocyanate, perchlorate and bromide on the characteristics of the electrode were also considered.     

Electrogenerated chemiluminescence for potentiometric sensors

We report here on a generic approach to read out potentiometric sensors with electrogenerated chemiluminescence (ECL). In a first example, a potassium ion-selective electrode acts as the reference electrode and is placed in contact with the sample solution. The working electrode of the three-electrode cell is responsible for ECL generation and placed in a detection solution containing tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] and the coreactant 2-(dibutylamino)ethanol (DBAE), physically separated from the sample by a bridge. Changes in the sample potassium concentration directly modulate the potential at the working electrode, and hence the ECL output, when a constant-potential pulse is applied between the two electrodes. A linear response of the ECL intensity to the logarithmic potassium concentration between 10 μm and 10 mM was found.     

Determination of potassium in fatty acid methyl esters applying an ion-selective potassium electrode

An easy and inexpensive method of potassium determination in fatty acid methyl esters (FAME) applying an ion-selective potassium electrode (ISE-K) is presented. FAME are considered alternative fuel for diesel engines. Simple apparatus and procedure were developed to avoid contact of ester samples with the sensitive ISE-K membrane, which can damage the ISE membrane surface in long time operation. Using different FAME samples with a wide range of known potassium content a calibration curve was constructed. Among all samples, ISE-K satisfactory predicted potassium content in FAME as identified by the AAS reference method.     

Highly Selective Potassium Ion Responsive Liquid-Membrane Electrode

Abstract

The performance of a new liquid-membrane electrode using valinomycin as membrane component is described with respect to selectivity, working range, speed of response and accuracy. The electrode makes possible the measurement of potassium ion activities in the range of 10^?1 M to at least 10^?6 M in unbuffered systems with a selectivity of potassium over sodium ions of more than 4,000. The electrode was used for the direct titration of potassium ions.     

重力驱动多相层流分离离子选择性电极检测集成化微流控芯片系统

将微流控芯片多相层流分离技术与离子选择性电极检测技术联用,利用重力驱动的芯片多相层流分离系统,在线净化生物(血液)试样.同时,在芯片上加工微离子选择性电极进行待测物的在线检测,实现整体分析系统的芯片集成化,并将其用于血样中K⁺的测定.对5.5×10^-3mol/L钾溶液5次平行测定的相对标准偏差(RSD)为5.6%,检出限为6.8×10^-5mol/L,线性范围10^-4～10^-1mol/L.     

Photo-cured polymers in ion-selective electrode membranes : Part 4. An Ultraviolet Laser Cured Membrane for Potassium

The preparation of an ultraviolet-laser cured polymer membrane electrode selective for potassium is reported. The epoxyacrylate membrane in this valinomycin-based electrode is cured without using a photoinitiator. This leads to improved compatibility of the membrane components and to better response characteristics for the electrode, particularly for use in flow injection, compared with an earlier procedure in which a photoinitiator was used in the curing process. An improved method for preparing very thin films on the metallic substrate of the electrode provides a very fast electrode response.     

A Solid Potassium Ion Selective Electrode

Abstract

A solid membrane potassium selective electrode has been developed. The following parameters of the potassium ion electrode were investigated; Nernstian response to potassium ion activity, response time to step changes in potassium ion activity, the effect of pH on potassium response, and the electrode response to other cations.     

Studies on bis(crown ether)-based ion-selective electrodes for the potentiometric determination of sodium and potassium in serum

Bis(crown ether)-based ion-selective electrodes for sodium and potassium are described, based on the bis[(12-crown-4)-2-ylmethyl]-2-dodecyl-2-methyl malonate sensor(I) for sodium and the bis[(benzo-15-crown-5)-15-ylmethyl] pimelate sensor(II) for potassium. The best results were obtained when the sensors were used in association with 2-nitrophenyl octyl ether as plasticising solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anion excluder in poly(vinyl chloride) matrices. Electrode slopes were near-Nernstian, with detection limits of less than 10(-5) M. The electrode features are compared with those of a sodium glass membrane electrode, for sensor I, and with a valinomycin-based potassium electrode, for sensor II. The electrodes are also discussed in relation to others reported for sensors I and II and are shown to be superior. However, although the electrodes described offer promising alternatives to glass electrodes for sodium and valinomycin electrodes for potassium, data for sodium and potassium measurements in blood serum indicate a need for further research in order to improve the correlation with flame photometric measurements.     

钾离子电池负极的高性能潜在材料:锑

近年来随着对储能器件的需求增加,钾离子电池受到越来越多的关注。钾的物理化学性质与锂相似,且在地壳中的储量丰富,在储能领域中具有广阔的发展前景。但由于电极材料实际容量远小于理论容量等问题的存在导致应用在钾离子电池的性能仍有不足。金属锑(Sb)具有较高的理论容量被广泛应用在电极材料上,然而在充放电过程体积变化过大导致稳定性较差,需要通过形貌控制、合金化、与碳材料复合等形式来提高结构稳定性。本文主要介绍了Sb材料在钾离子电池负极材料的研究进展,并展望了Sb电极材料的应用前景。     

Freestanding film formed with Sb-nanoplates embedded in flexible porous carbon nanofibers as a binder-free anode for high-performance wearable potassium-ion battery

Antimony-based materials are considered as promising anodes for potassium ion batteries due to their high theoretical capacity and low electrode potential. However, the aggregation and bulk expansion of Sb particles in cycling will cause capacity attenuation and poor rate performance. In this paper, Sb nanoplates were designed to be embedded in flexible porous N-dopped carbon nanofibers (Sb@PCNFs) by a simple electrospinning deposition (ESD) method. In this structural design, Sb nanoplates of high capacity were employed as active materials, N-dopped carbon nanofibers were used to improve conductivity and structural stability. The introduction of pore-forming agent enables the nanofibers to possess porous structure, thus buffering the huge volume change and promoting the transfer of electrolyte/ions. More importantly, the freestanding film can be directly used as a working electrode, reducing the redundancy in the battery and the cost. Benefitting from the favorable structure, the freestanding flexible Sb@PCNFs electrode shows excellent potassium storage performance with a capacity of 314 mAh/g after 2000 cycles at 500 mA/g. This strategy of employing active material with high capacity in porous and conductive flexible nanofibers represents an effective method of achieving binder-free electrode with good electrochemical performance towards wearable energy storage devices.     

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.     

Effect of yeast pretreatment on the characteristics of yeast-modified electrodes as mediated amperometric biosensors for lactic acid

Carbon paste electrode modified with baker' and wine yeast Saccharomyces cerevisiae (a source of flavocytochrome b(2)) were investigated as amperometric biosensors for L-lactic acid. Before immobilization on the electrode surface, yeast cells were pretreated with various electrolytes, alcohols and weak organic acids. Electrode responses to L-lactic acid were tested in the presence of various mediators (potassium ferricyanide, phenazine methosulfate, 2,6-dichlorophenolindophenol sodium salt hydrate, 1,2-naphthoquinone-4-sulfonic acid sodium salt). The highest (144+/-7 nA per 0.2 mM L-lactic acid) and the most stable responses were obtained after yeast pretreatment with 30% ethanol using potassium ferricyanide as a mediator. Different electrode sensitivities with mediator phenazine methosulphate probably reflected diverse changes in yeast membrane (and/or cell wall).     

In vivo measurements with a potassium ion-selective microelectrode based on a new bis(crown ether)

Potassium ion-selective microelectrodes with a tip diameter of 10 μm are described. The ionophore used is 2,2′-bis[3,4-(15-crown-5)-2-nitrophenylcarbamoxymethyl] tetradecane in a conventional mixture with sodium tetraphenylborate, an ether and PVC. The electrode provides Nernstian response over the range 10^?5?10^?1 M potassium activity. Its selectivity is shown to be similar to that of a valinomycin-based microelectrode. After the electrode has aged for 24 h, the 95% response time at the 10^?3 M potassium ion level is 2.0 ± 0.5 s. The applicability of the bis(crown ether) electrode for measurements in vivo is proved by monitoring the changes in potassium activity in different areas of the brain of anaesthetized rats after administration of veratrine.     

Flow injection analysis of potassium using an all-solid-state potassium-selective electrode as a detector

The concentration of potassium was determined by a combination of flow injection analysis (FIA) with an all-solid-state potassium sensor detection. The all-solid-state potassium-selective electrode possessing long-term potential stability was fabricated by coating an electroactive polypyrrole/poly(4-styrenesulfonate) film electrode with a plasticized poly(vinyl chloride) membrane containing valinomycin. The simple FIA system developed in this laboratory demonstrated sensitivity identical to that in the batch system and achieved considerably rapid assay (150 samples h⁻¹). Analyses of soy sauce and control serum samples by this FIA system yielded results in good agreement with those obtained by conventional measurements.     

First-principles calculations of stability of graphene-like BC_3 monolayer and its high-performance potassium storage

With increasing demand for renewable energy,graphene-like BC_3 monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently.However,its structural stability,potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet.In this work,phonon spectra,AIMD simulations and elastic constants of graphene-like BC_3 monolayer are investigated.Our results show that graphene-like BC_3 monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653 mAh/g with the corresponding open circuit voltages 0.66 V.Due to potassium atom can be effectively adsorbed at the most energetically favorable h-CC site with obvious charge transfer,making adsorbed graphene-like BC_3 monolayer change from semiconductor to metal which is really good for electrode utilization.Moreover,the migrations potassium atom on the graphene-like BC_3 monolayer is rather fast with the diffusion barriers as low as 0.12 eV,comparing lithium atom with a relatively large diffusion barrier of 0.46 eV.Additionally,the tensile strains applied on the graphene-like BC_3 monolayer have marginal effect on the adsorption and diffusion performances of lithium,sodium and potassium atoms.     

An agar-based silver|silver chloride reference electrode for use in micro-electrochemistry

A miniaturised Ag|AgCl reference electrode is described which can be easily set up. Its electrochemical behaviour was proven by micro-polarisation curves, electrochemical impedance spectroscopy and potential transients. A saturated potassium chloride solution was used which was solidified by adding agar. The electrode is as small as 800 μm in diameter and 5 mm in length, with further potential for down-sizing. A modified version includes an agar salt bridge in the same capillary. After an induction period of 6 h the potential becomes stable within 1 mV for more than 6 weeks. The electrode shows a slightly different reference potential, which is discussed in terms of the production process.