Electrometric titrations with a single polarised electrode Determination of hydrogen peroxide and manganese

A simple electrometric method for end-point detection, based on the lack of response of the indicator electrode in the titrated irreversible system has been described. The end-point is reached at the beginning of depolarisation of the electrode, when the equilibrium in the pre-balanced circuit is destroyed, producing an offbalance current.     

Electrometric titrations with two polarized second-order electrodes

Electrometric titrations at constant resistance with two polarized second-order electrodes are shown to be possible. The polarization curve of the silver/silver chloride electrode is investigated theoretically and experimentally in order to find the best conditions for chloride titrations.Directions are given for the preparation and manipulation, of electrodes which enable quick titrations with rather dilute standard solutions (up to 0.001N AgNO₃). The titration apparatus used and some practical applications of the amperometric titration are described.     

Potentiometric titrations with a mercury-mercury sulphide electrode

Platinum foil coated with a film of mercury and mercury sulphide is recommended as electrode for potentiometric titrations with thioacetamide.     

Potentiometric titrations of selenium with a fluoride-selective electrode

Selenite can be determined with a fluoride-selective electrode by two methods: a direct procedure based on the joint titration of selenite and standard fluoride with lanthanum and an indirect method based on precipitation of selenite with excess of lanthanum followed by back-titration with fluoride. In the first case the end-point is located by the second derivative method, and in the second case by means of a Gran plot. Direct titrations are suitable for selenite concentrations above 5 mM; indirect titrations are useful for concentrations as low as 0.5 mM.     

Electrometric titrations of silver with alkali pyrovanadate and of vanadium (V) with silver ions

Summary An amperometric method has been developed for the titration of silver with vanadate ions and vice versa. The method permits the determination with an accuracy of ±1%. The composition of the precipitation is discussed.

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Zusammenfassung Eine amperometrische Titration von Silbermit Vanadationen wird vorgeschlagen. Auch die umgekehrte Titration ist möglich. Die Genauigkeit ist besser als ±1%. Die Zusammensetzung des Niederschlags wird diskutiert.

     

Potentiometric titrations in non-conducting solutions with an interfacial antimony electrode

The micro interfacial device described is based on an antimony/antimony scratch/ 0.1 M KCl/Hg₂Cl₂/Pt cell. Acid—base reactions occurring in solvents such as dry ligroin, benzene, cyclohexane, dichloroethane, chloroform and pentyl acetate are readily monitored.     

The influence of halides on amperometric complex-formation titrations with the rotating mercury electrode

The interference of halides with complexometric titrations, indicated by means of the anodic wave of the ligand at a rotating mercury electrode, has been studied theoretically. The effect of halides strongly depends on the pH of the solution. In alkaline solutions there appears to be no interference by chloride at all. A critical value for the halide concentration can easily be found for any medium. The theoretical predictions have been verified experimentally.     

The aluminium indicator electrode in acid-base potentiometric titrations

Aluminium has been employed as an indicator electrode in potentiometric acid-base titrations. The titration curves obtained were approximately 3.6 times broader than those obtained with the antimony electrode.     

On the use of the mercury electrode in chelatometric potentiometric titrations

Summary Information is given on the applicability of the mercury electrode in chelatometric potentiometric titrations. The influence of ternary complex formation, the formation of precipitates on the electrode and possible errors, due to the asymmetric shape of the titration curves are discussed.

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Über die Verwendung der Quecksilberelektrode bei chelatometrisch-potentiometrischen Titrationen

Zusammenfassung Einige Betrachtungen werden angestellt über die Anwendung der Quecksilberelektrode für komplexometrische Titrationen mit potentiometrischer Endpunktsanzeige. Der Einfluß der Bildung ternärer Komplexe, die Bildung von Niederschlägen auf der Elektrode und die Fehler infolge der Asymmetrie der Titrationskurven werden besprochen.

     

Amperometric complex-formation titrations with a dropping bismuth amalgam electrode in halide medium

The use of the dropping bismuth amalgam electrode has been investigated for the selective determination of metal ions in the presence of large concentrations of halides by means of amperometric complex-formation titrations, using normal pulse polarography. Concentrations of metal ions down to 3 x 10(-7)M have been determined with adequate accuracy in the presence of about 0.1M chloride or 0.01M bromide. Calculated and experimental current-voltage curves have been compared and found to be in reasonable agreement.     

Amperometric complex-formation titrations with a dropping indium amalgam electrode in halide medium

The applicability of a dropping indium amalgam electrode for the determination of metal ions in the presence of large concentrations of halides by means of amperometric complex-formation titrations using normal pulse polarography has been investigated. Titrations appear to be possible in the presence of 4M potassium iodide, 1M potassium bromide and 1M potassium chloride.     

Amperometric titrations with rotated platinum electrode: Determination of hydrazine by potassium bromate

The reaction between hydrazine and potassium bromate is studied amperometrically at rotating platinum electrode. The bromate titration is performed at an applied e.m.f. of zero (versus S.C.E.) and in the presence of bromide and 1–5N sulfuric acid or 0.5–4N hydrochloric acid. Quantities ranging from 30 μg to 3 mg of hydrazine can be estimated accurately by this method. Determination of phenylhydrazine, Semicarbazide and other oxidizable materials on similar lines is suggested.     

Label-free immunosensing of microcystin-LR using a gold electrode modified with gold nanoparticles

The hepatotoxic microcystins, especially microcystin?CLR (MC?CLR), are causing serious problems to public health and fisheries. We describe here a label-free amperometric immunosensor for rapid determination of MC?CLR in water sample. The sensor was prepared by immobilizing antibody on a gold electrode coated with L-cysteine-modified gold nanoparticles. The stepwise self-assembly of the immunosensor was monitored and characterized by means of electrochemical impedance spectroscopy and differential pulse voltammetry. A 0.60?mmol L^?1 solution of hydroquinone was used as the electron mediator. The immunosensor was incubated with MC?CLR at 25?°C for 20?min, upon which the differential pulse voltammetric current changed linearly over the concentration range from 0.05 to 15.00???g L^?1, with a detection limit of 20?ng L^?1. The developed biosensor was used to determine MC?CLR in spiked crude algae samples. The recovery was in the range from 95.6 to 105%. This method is simple, economical and efficient, this making it potentially suitable for field analysis of MC-LR in crude algae and water samples.

Nanostructured gold colloid electrode based on in situ functionalized self-assembled monolayers on gold electrode

A novel method for fabricating nanostructured gold colloid electrode based on in situ functionalization of self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) on gold electrode is proposed. The in situ functionalization of 4-ATP SAMs yields a redox active monolayer of 4′-mercapto-N-phenylquinone diimine (NPQD). When the amino-rich surface is exposed to gold colloid, the citrate-stabilized gold nanoparticles (GNPs) can be anchored onto the surface of the in situ functionalized electrode by the electrostatic interactions and a new nanostructured gold colloid surface was obtained. The mixed monolayers of in situ functionalized product, NPQD, and 1,4-benzenedimethanethiol (BDMT) can provide a more compact and order platform to fabricate GNPs on the electrode surface. The film formed by this technique has the advantages of high organization and uniformity, which could provide a desirable microenvironment to assemble GNPs and facilitate the concentration of the analyte from the bulk solution to the electrode surface. The nanostructured gold colloid electrode has favorable effect on the electrochemical oxidation of naphthol isomers.     

Mercury-mercurous acetate indicator electrode for potentiometric titrations in anhydrous acetic acid

The authors describe a metallic mercury electrode covered with a mercurous acetate coating, its preparation, its use as an indicator electrode in anhydrous acetic acid neutralization titrations and its properties as compared with other electrodes used for the same purpose.     

Natural monocrystalline pyrite as electrode material for potentiometric titrations in water

The possibility of applying natural monocrystalline pyrite as sensor for the potentiometric titration of acids in water was investigated. The potential of this electrode in aqueous solutions exhibits a sub-Nernst dependence. In fresh solutions the slope (mV/pH) is 33.9. The potential jumps at the titration end-point obtained in titrations of HCl, H(3)PO(4) and CH(3) COOH do not differ much from those obtained by the application of the glass electrode as the indicator one. The potentials in the course of the titration and at the titration end-point (TEP) are rapidly established. The results obtained in the determination of the investigated acids deviated for 0.16-0.34% with respect to those obtained by using the glass electrode as the indicator one.     

Iodine--iodide reference electrode for potentiometric titrations of bases in acetic acid

The suitability of the half-cell Pt/I2, KI in glacial acetic acid as reference electrode for potentiometric titrations of weak bases in the same medium was investigated. This electrode is easily prepared. It has been found very convenient in use and performing at least as well as the best electrodes used for the same purpose. Some phenomenological aspects of the behaviour of the above half-cell, of interest for the use as the reference electrode in the laboratory practice have been observed, that show important differences respect aqueous medium and other organic solvents.     

Sensing phenothiazine drugs at a gold electrode co-modified with DNA and gold nanoparticles.

DNA and gold nanoparticles are co-immobilized at a gold electrode through elaborate self-assembly processes. This configuration has proven to be useful as a sensor for phenothiazine drugs, taking advantage of the well-known, relatively large surface area of gold nanoparticles and the strong intercalation between dsDNA and phenothiazine drugs. This modified electrode has demonstrated good sensitivity and stability towards the oxidation of two model phenothiazine drugs: promethazine and chlorpromazine. A linear dependence between the concentration of phenothiazine drugs and the peak current is observed, with a concentration range of 2.0 x 10(-5)-1.6 x 10(-4) M and 1.0 x 10(-5)-1.2 x 10(-4) M, and a detection limit of 1.0 x 10(-5) M and 7.0 x 10(-6) M, for promethazine and chlorpromazine, respectively.     

Layer-by-layer immobilization of horseradish peroxidase on a gold electrode modified with colloidal gold nanoparticles

An amperometric biosensor, based on layer-by-layer self-assembly of colloidal gold nanoparticles, cysteine and horseradish peroxidase on Nafion modified electrode surface by electrostatic adsorption, has been used for the determination of hydrogen peroxide. The electrochemical behavior of the multilayer film was studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The step layer-by-layer adsorption interface morphology was further characterized by means of electrochemical impedance spectroscopy and cyclic voltammetry. The performance and factors influencing the resulted biosensor were studied in detail. The sensor displayed an excellent electrocatalytic response to the reduction of H₂O₂ without the aid of an electron transfer mediator. Linear response to H₂O₂ was obtained for the concentration range from 1.6 μM to 2.4 mM under optimized conditions. The detection limit of the biosensor was 0.5 μM (S/N = 3), and the sensor achieved 95% of the steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability. Correspondence: Yan Liu, College of Chemistry, Chongqing Normal University, Chongqing 400047, P.R. China