A potentiometric study of the oxidation of cobalt(II) with gold(III) chloride in presence of 1,10 phenanthroline or 2,2'-bipyridine : A new titration of cobalt (II) and its application to nickel-base alloys

The redox reaction between cobalt(II) and gold(III) chloride in the presence of 1.10-phenanthroline or 2,2'-bipyridine was studied, and a titration of the cobalt(II) complex with a gold(III) chloride solution was developed. A 4-fold amount of 1,10-phenanthroline or 2,2'-bipyridine was necessary for rapid quantitative reaction; the permissible pH range was 1.5–5. The oxidation of the cobalt(II) complex proceeds rapidly at 40–50°C, and a direct potentiometric titration was possible. The following maximum errors were obtained: 3.3% for 0.2–1.0 mg Co, 2.0% for 1–5 mg Co, and 0.70% for 10–40 mg Co. The following ions did not interfere: Ni(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(II), Cr(III), Al(III), Th(IV), Se(IV), Ti(IV), U(VI), Mo(VI), SO^2-₄ and PO^3-₄. Even small quantities of silver(I), copper(II), palladium(II), mercury(II)and iron(III) interfered. The method was applied to the determination of high cobalt contents in high-temperature nickel-base alloys.     

On the reaction between iodide and mercury(II)

A survey on the iodide-mercury(II) reaction and its analytical uses is given. Titrations of iodide with mercury(II) in various acidities, using nitrate, acetate, and chloride as titrants and silver or platinum amalgam as the indicator electrode, showed that mercury(II) nitrate is the best titrant giving 0.46 V/0.1 ml potential break in comparison with 0.14 V/0.1 ml of mercury(II) chloride and 0.35V/0.1 ml of mercury(II) acetate, all titrants being 0.05 M in mercury(II).     

Functionalized di- and tetrathia-crowns and their use to quantitatively separate and recover gold(III), palladium(II), silver(I) and mercury(II) Ions

Two new dithia-crowns containing a hydroxy group and 1,4,7,10-tetrathia-18-crown-6 containing an allyl-oxymethyl substituent were prepared in good yields. Two of these crowns were covalently attached to silica gel. The silica gel-bound thia-crowns were used to separate gold( III ), palladium( II ), silver( I ) and mercury( II ) ions from an aqueous 0.1 M nitric acid solution which also contained 1.0 M ferric chloride.     

Amperometric titration of palladium, silver and copper with benzimidazol-2-ylmethanethiol, and its application to non-ferrous materials

A method is described for the determination of mg amounts of palladium, silver and copper by amperometric titration with benzimidazol-2-ylmethanethiol in acetate buifer medium (pH 4-5) at an applied potential of -0.2 V vs. the saturated calomel electrode. Direct titrations are possible in the presence of a number of foreign ions. Copper and palladium interfere mutually and in the determination of silver. Mercury(I), mercury(II) and platinum(IV) also interfere. Silver does not interfere in the determination of copper and palladium if it is first precipitated as chloride. The method has been successfully applied to the analysis of non-ferrous materials.     

Pyridine-2-aldoxime and 6-methylpyridine-2-aldoxime as gravimetric reagents for estimation of palladium(II) and uranium(VI)

Pyridine-2-aldoiumc (I) has been found to be a sensitive reagent for the gravimetric determination of palladium(II). From chloride medium, precipitation is complete at pH 3.0-11.0, and in solution containing 1NHNO(3) to pH6.0. The compositions of the precipitates (dried at 130 degrees ) correspond to PdL(2), and PdL(2). HNO(3) (HL representing the reagent) respectively. Pd(II) can be estimated gravimetncally in presence of acetate, oxalate, tartrate, phosphate, fluoride borate, perchlorate, Cu(II), Cd, Co(II), Fe(II), Ni, Zn, Pb, Bi, Sb(III), Pt(IV), Ir(IV), Ru(III), Rh(III); Os(IV) in quantities more than twice that of Pd(II), and Ag(I), Au(III) and Fe(II) even m traces cause serious interference. The yellow uranium(VI) complex with (I) is precipitated quantitatively over the pH range 3.5-10.5 and, after washing and drying corresponds to the composition (c(6)h(5)n(2)o)(2)uo(2), The uranium(VI) complex with 6-methylpyridine-2-aldoxime (II) is precipitated quantitatively over the pH range 3.0-10.5, and after washing and drying at 120-130 degrees corresponds to UO(2),(C(7),H(7),N(2)O)(2). Both (I) and (II) are suitable for the estimation of 1-50 mg of uranium(VI) in the presence of up to 10-fold quantities ofTh(IV), La(III) and Ce(III) even when present together. Ce(IV) in quantities more than three times that of U must be reduced to Ce(III). Tartrate, citrate, phosphate, Ti(IV) and Zr interfere, but acetate, oxalate, and borate do not.     

Maßanalyse und Katalyse

The application of the therinometric method to the catalytic endpoint indication in volumetric determinations by precipitation reactions is discussed. The direct titration of silver, mercury(II) and palladium(II) as well as the determination of several anions (Cl^?, Br^?, J^?, SCN^?, CN^?, [Fe(CN)₆]^4? and S^2?) by backtitration with iodide standard solution is described. The well known reaction between cerium(IV) and arsenic(III), catalysed by iodide, serves as an indicator. The ions mentioned can thus be determined in the microgram range with good accuracy.     

Applications,involving the iodide ion: VIII. Direct and indirect determination of mercury(I) and analysis of mixtures. Analysis of chromium(VI)-chromium (III) mixtures. Determination of hypochlorite

Mercury(I), down to 3 ppm, has been accurately determined by direct titration with iodide or by back-titrating excess of iodide with mercury (II) using silver amalgam as the indicator electrode. The direct method and additional volumetric ones were applied to the rapid analysis of various mixtures involving mercury(I) with fair accuracy and precision. Analysis of Cr(VI)-Cr(III) mixtures involved potentiometric back-titration of excess iodide and of excess EDTA separately with mercury(II). Back-titration of excess iodide was successfully applied to the determination of hypochlorite.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999     

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium--VII. Photometric titration of vanadium(IV) and of cerium(III) alone and in mixtures with iroN(II)

Vanadium(IV) can be accurately titrated with potassium dichromate in media containing phosphoric acid of 3-12M concentration: the change in absorption of vanadium(IV) is followed in the region 660 mmicro using a red filter. It is more convenient to carry out the titration in 3M phosphoric acid because at higher concentrations chloride, nitrate, cerium(III) and manganese(II) may interfere. Photoelcetric titration is more convenient than potentiometric because the former can be made in a 3M phosphoric acid medium, whereas the latter is possible only in 12M phosphoric acid. The simultaneous differential photometric titration of iron(II) and vanadium(IV) is also possible. Conditions have been found for the photometric titration of cerium(III) and of cerium(III) plus iron(II). The titration is carried out (at 450 mmicro or with a blue filter) in about 10.5M phosphoric acid. Application of the method to a cerium mineral is considered.     

Potentiometric titration and differentiation of cyano and nitrito complexes of Ir(III), Pt(II), and Pd(II)

Summary The precipitation titration of the nitrito complexes of Ir(III), Pt(II), and Pd(II) vs. cetylpyridinium chloride is reported. The corresponding cyanide complexes of these precious metals are also precipitated by silver nitrate, which does not react with the nitrito complexes. Differentiation of the 2 types of complexes is, therefore, possible. Sequential estimation of the cyanide complexes and some anions such as bromide, cyanide, and aurocyanide is feasible with silver nitrate.

---

Potentiometrische Titration und Differenzierung von Cyano- und Nitrito-Komplexen von Ir(III), Pt(II) und Pd(II)

---

Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48     

Back titration with mercuric nitrate in alkaline medium analysis of tertiary mixtures of mercury(II) with some other metals

Summary Tertiary mixtures each containing mercury(II) were analysed by simple procedures involving combination between the recent method of back titration with mercuric nitrate in alkaline medium, and the volumetric methods which make use of masking agents as cyanide. The content of mercury(II) in most mixtures is determined potentiometrically with potassium iodide using the silver amalgam as indicator electrode. End points are attended with fair accuracy within 0.02 ml titrant and with reasonable jumps from 60 to 90 mv per 0.1 ml of mercuric nitrate solution or from 170 to 200 mv per 0.1 ml of potassium iodide solution.     

Silver(I) and Copper(II) Catalysis for Oxidation of Histidine by Cerium(IV) in Acid Medium: A Comparative Kinetic Study

The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm⁻³ and at 25°C. In both uncatalyzed and metal ions‐catalyzed paths, the reactions exhibited first‐order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first‐order dependences with respect to [His] and [H⁺]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2‐imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second‐order rate constants were evaluated.     

Semiautomatic and automatic catalytic amperometric and catalytic constant-current potentiometric titrations of gold(III)

Semiautomatic and automatic amperometry and constant-current potentiometry were used to follow the course of catalytic titration of gold(III) with potassium iodide. The Ce(IV)-As(III) system in the presence of sulfuric acid was used as the indicator reaction. The possibilities of the application of two types of graphite electrodes were investigated. The effect of concentration of the indicator reaction components, and the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 80–900 μg of gold(III) were determined with a relative standard deviation less than 1.1%. The results obtained are in good agreement with those of comparable methods.     

Determination of mercury(II) ion by electrochemical cold vapor generation atomic absorption spectrometry.

A technique for determination of mercury is described; it is based on electrolytic reduction of Hg(II) ion on a graphite cathode, the trapping of mercury vapor and its volatilization into a quartz tube aligned in the optical path of an atomic absorption spectrometer. The electrochemical cell consisted of a graphite cathode and an anode operating with constant direct current for the production of mercury atoms. A pre-activated graphite rod was used as the cathode material. The optimum conditions for electrochemical generation of mercury cold vapor (the electrolysis time and current, the flow rate, the type of electrode and electrolyte) were investigated. The characteristic electrochemical data with chemical cold vapor using NaBH4-acid were compared. The presence of cadmium(II), arsenic(III), antimony(III), selenium(IV), bismuth(III), silver(I), lead(II), lithium(I), sodium(I) and potassium(I) showed interference effects which were eliminated by suitable separation techniques. The calibration curve is linear over the range of 5-90 ng ml(-1) mercury(II). The detection limit is 2 ng ml(-1) of Hg(II) and the RSD is 2.5% (n = 10) for 40 ng ml(-1). The accuracy and recovery of the method were investigated by analyzing spiked tap water and river water.     

A silver electrode in the potentiometric titration of thiols

A silver wire immersed in a thiol solution gives a potential responsive to the thiol concentration, and is a sensitive indicator electrode in the potentiometric titration of thiols with mercury(II) chloride, p-chloromercuryphenyl sulphonate, and silver nitrate at pH 4.5-9.5, 7-9.5 and 9.5 respectively. Titrations of simple thiols such as cysteine or a protein such as albumin are equally successful, but the potential break was smaller for the protein. The end-point could be determined within an increment of titrant equal to 5 nmole of thiol. An inert atmosphere is needed for titration at pH 7.     

Preconcentration of Nickel(II) in White Wine Using Quinoxaline-2,3-dithiol and a Finely Divided Anion-Exchange Resin for the Determination by Solid-Phase Spectrophotometry

A simple and sensitive method for the determination of trace amounts of nickel(II) is described. The method is based on the adsorptive enrichment of nickel(II) as the complex with quinoxaline-2,3-dithiol using a finely divided anion-exchange resin, collection of the resin on a membrane filter by filtration, and direct measurement of the absorbance of the resultant circular thin layer by reflective spectrophotometry at 605 nm. In the presence of interfering cations such as copper(II) and cobalt(II) a sample solution is first filtered, after the addition of ammonium thiocyanate and Zephiramine, to extract these cations onto a membrane filter as the ion-pair precipitate formed between the metal-thiocyanate complex anions and Zephiramine cations, then nickel(II) in the filtrate is determined. Interferences from iron(III), silver(I), bismuth(III), cadmium(II), mercury(II), indium(III), palladium(II), platinum(IV), tin(IV), and zinc(II) can also be eliminated. The proposed method was applied to the determination of nickel in white wine. The concentrations of nickel found in 5-ml aliquots of 10 different wine samples were in the range 16.1-68.0 ng ml⁻¹.     

Formation of silver nanoparticles in the redox reaction of silver(I) nitrate with crystalline macrocyclic nickel(II) compounds

The redox reaction of crystalline macrocyclic nickel(II) carboxylates with silver(I), gold(III), and palladium(II) salts leads to the formation of nanoclusters of the corresponding metals. The reaction with silver nitrate was used to show that the size of the nanoparticles formed depends both on the chemical and crystal structure of the solid matrix and the reaction time. The results open the possibility of forming noble metal nanoparticles with desired dimensions and dispersion.     

Influence of Masking Agents on the Color Reactions of Dithizone with Pd(II), Hg(II), and Ag(I) Ions after the Sorption of Their Chloride Complexes on the Fibrous Filled Anion Exchanger AV-17

The influence of masking agents (acetate, thiosulfate, tartrate, and iodide ions; thiourea; and ethylenediaminetetraacetic acid (EDTA)) in a dithizone solution on the complexation of Hg(II), Pd(II), and Ag(I) ions on the solid phase of the fibrous anion exchanger filled with AV-17 was studied. Mercury, palladium, and silver were adsorbed as chloride complexes. The possibility of the simultaneous group determination of the three elements and the selective determination of palladium in the presence of mercury and silver by measuring the diffuse reflection coefficient at two wavelengths (580 and 680 nm, respectively) was demonstrated. A mixture of dithizone with EDTA, acetate, iodide, or thiosulfate can be used for masking concomitant elements. The reaction of palladium with dithizone on the solid phase can be used for the test determination of palladium with the detection limit 0.01 mg/L.     

A simple thermometric technique for reaction-rate determination of inorganic species, based on the iodide-catalysed cerium(IV)-arsenic(III) reaction

A very simple reaction-rate thermometric technique is used for determination of iodide (5-20 ng ml ), based on its catalytic action on the cerium(IV)-arsenic(III) reaction, and for determination of mercury(II) (1.5-10 ng ml ) and silver(I) (2-10 ng ml ), based on their inhibitory effect on this reaction. The reaction is followed by measuring the rate of temperature increase. The method suffers from very few interferences and is applied to determination of iodide in biological and inorganic samples, and Hg(II) and Ag(I) in pharmaceutical products.     

Adsorption of mercury(II) on macroreticular styrene-divinylbenzene copolymer beads

The adsorption characteristics of mercury(II) on several kinds of styrene-divinylbenzene copolymer beads having different surface properties were studied. It was found that the polymer beads selectively adsorbed mercury(II) from solutions over a wide range of pH with high efficiency. The amount of mercury(II) adsorbed increased with increase in specific surface area of the polymer beads and the adsorption behaviour was found to be of the Langmuir type. The presence of chloride strongly reduced the adsorption, but this interference was not observed with nitrate, sulphate, perchlorate, cadmium(II), cobalt(II), copper(II), nickel(II), silver(I) and zinc(II). More than 95% of the mercury(II) adsorbed on a column of polymer beads could be recovered with dilute hydrochloric acid.