Potentiometric titration of gold in ores with potassium iodide

Summary A direct potentiometric titration method for the determination of gold in ores and alloys is described. It is based on the reduction of Au(III) with iodide ions yielding accurate and reproducible results. Detection limit and sensitivity were 0.06 and 0.032 mg/l Au, respectively. The linear response range was between 0.1 and 120 mg/l Au. The method can be used for the routine assay of gold in different kind of samples.     

The potentiometric titration of mercury(II) with cetylpyridinium chloride

Summary New precipitation titrations have been evaluated for the determination of mercury(II) in acid solution and for mercuric cyanide solutions. In acid or neutral solutions the mercuric ion was converted to the bromo complex by addition of excess potassium bromide. Mercuric cyanide was converted to the tetracyano complex by addition of an excess of potassium cyanide. In both cases the complex anions were titrated potentiometrically vs. 0.01M cetyl-pyridinium chloride. Emf's were monitored with a home-made graphite sensor coated with a solution containing poly(vinyl chloride) and dioctylphthalate in tetrahydrofuran and a single-junction reference electrode.

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Über die potentiometrische Titration von Hg(II) mit Cetylpyridiniumchlorid

Zusammenfassung Neue Verfahren zur Fällungstitration von Hg(II) in saurer Lösung sowie von Lösungen von Quecksilbercyanid wurden angegeben. Quecksilberion wird in saurer oder neutraler Lösung durch Zusatz überschüssigen Kalium-bromids in den Brom-Komplex übergeführt. Quecksilbercyanid wird durch Zusatz überschüssigen Kaliumcyanids in den Tetracyanokomplex umgesetzt. In beiden Fällen werden die komplexen Anionen potentiometrisch gegen 0,01M Cetylpyridinium-chlorid titriert. Die EMK wird mit Hilfe eines selbst hergestellten Graphitsensors, der mit einer Lösung von Polyvinylchlorid und Dioctylphthalat in Tetrahydrofuran überzogen ist, sowie einer Single-junction-Bezugselektrode gemessen.

     

Potentiometric microdetermination of cadmium and mercury as their iodo complexes with cetylpyridinium chloride

The precipitation titrations of cadmium and mercury(II) as their iodo complexes vs cetylpyridinium chloride and tetraphenylarsonium chloride have been evaluated. Electromotive forces were monitored with a graphite rod coated with a solution of poly(vinylchloride) and dioctylphthalate in tetrahydrofuran and a double-junction reference electrode. Cadmium can be determined in the presence of a large excess of zinc.     

Constant-current potentiometric titration of orthophosphate with cetylpyridinium chloride: a feasibility study

The feasibility of constant-current potentiometric titration of orthophosphate with cetylpyridinium chloride has been studied. The phosphate solution is acidified with hydrochloric acid to pH 1.1-1.3 and an excess of molybdate solution added. For l mg of phosphorus (as phosphate) the optimum Mo:P ratio is about 40. Cetylpyridinium chloride reacts stoichiometrically with 12-molybdophosphate, in 3:1 ratio. The optimum cathodic polarizing current is 1.1 muA. The blanks for molybdate are relatively small, constant and non-stoichiometric.     

Chelometric titration of gallium in the presence of indium and other metals by chloride masking

Summary In solutions containing high concentrations of ammonium chloride, indium is masked as the chloro complex and gallium can be titrated in boiling solution with EDTA to a visual end-point using Xylenol Orange as the indicator. Up to a mole ratio InGa of about 300 good results are obtained. The influence of some other metal ions on the titration has been investigated.

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Zusammenfassung Indium wird in Lösungen, die hohe Konzentrationen an Ammoniumchlorid enthalten, als Chlorokomplex maskiert und Gallium kann in kochender Lösung mit ÄDTA titriert werden. Xylenolorange dient als Indicator. Gute Resultate werden noch bei In: Ga-Verhältnissen von ungefähr 300 erhalten. Der Einfluß einiger anderer Metalle wurde untersucht.

     

Precise coulometric titration of precious metals III. Determination of gold (III) with electrogenerated chlorocuprous ion in KCl-Cu-EDTA buffer medium

A method for the precise coulometric titration of gold (III) with electrogenerated chlorocuprous ion in KCl-Cu-EDTA buffer medium is described. 7.45-16.8 mg of gold can be determined with potentiometric end-point detection (RSD = 0.04%). The method is applied to precise analysis of gold in pure gold, jewellery and gold alloys with good selectivity. The mechanism of electron exchange at the gold-plated platinum cathode-electrolyte interface during the process of titration and the reversibility of the electrode in the proposed electrolyte are discussed.     

Spectrographic determination of gold and platinum metals in geological and other materials by fire-assay preconcentration

A method is described for the determination of gold, platinum, palladium, rhodium and iridium at microgram levels in geological and other materials by a combination of fire-assay preconcentration and emission spectrography. The noble metals are collected into 4-mg silver or platinum prills by a normal fire-assay technique. These prills are arced between graphite electrodes at 12 A d.c. No buffer is required to prevent ejection of the prill. Gold, platinum and palladium are determined in the silver prills and gold, palladium, rhodium and iridium in the platinum prills. Low, but reproducible, results are found for iridium. At the 0.08 ppm level an overall coefficient of variation of 11% is found. This technique is simple and rapid for the determination of the precious metals.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Potentiometric titration of cyanide and chloride, using the silver specific-ion electrode as an indicator

Conditions are given for consecutive potentiometric titration of cyanide and chloride in mmole amounts, a silver-specific electrode being used as indicator electrode.     

Determination of some precious metals by neutron activation analysis

A neutron activation procedure for the determination of Ru, Pd, Os, Ir, Pt and Au in a single irradiation in silicate rocks, meteorites and sulfide ores has been developed. An alkali fusion was used to dissolve and mix 100 to 200 mg powder samples with appropriate carriers. The individual metals were separated and brought to a state of high radiochemical purity by distillation, ion exchange and solvent extraction techniques. Precious metal activities were counted by both γ and β-methods. The procedure was evaluated by replicate analyses of the granite and diabase rock standards, G-1 and W-1 and a Cu−Ni sulfide matte which had previously been analysed by emission spectrographic and spectrophotometric methods. The results were compared with previously published data. A major discrepancy was found only for Ir in W-1.     

Simultaneous spectrophotometric determination of thorium and rare earth metals with pyrimidine azo dyes and cetylpyridinium chloride

Thorium and rare earth elements (REE) react with 5-(2',4'-dimethylphenylazo)6-hydroxypyrimidine-2,4-dione (I) and 5-(4'-nitro-2',6'-dichlorophenylazo)6-hydroxypyrimidine-2,4-dione (II) in the absence of cetylpyridinium chloride (CPC) to form red complexes. The molar absorptivity and Sandell sensitivity were calculated in absence of CPC. In its presence, REE - complexes are not formed due to miceller masking, whereas Th(4+) has a sensitive reaction with the studied reagents I and II, with enhancement of the color intensity of the complex. Most of the foreign ions are tolerated in considerable amounts; 150-2400-fold amounts of rare earth do not interfere with the determination of thorium. The optimum experimental conditions of the complex formation reactions and the compositions of thorium complexes are described. A simple method is proposed for simultaneous determination of thorium and rare earth element without previous separation.     

Sequential titrations of anions with cetylpyridinium chloride

Summary The recently reported sequential titration of perchlorate and iodide vs. nitron was critically examined and improved. Some possible sequential titrations of anions vs. cetylpyridinium chloride were examined. Up to four separate endpoint breaks for four groups of anions were obtained. Under optimum conditions, these may be used for the estimation of certain anions or groups of anions.

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Sequentielle Titrationen von Anionen mit Cetylpyridiniumchlorid

     

Potentiometric titration of permanganate with resacetophenone oxime

Milligram amounts of permanganate can be titrated with resacetophenone oxime (4-acetylresorcinol oxime) as a reducing titrant in the presence of phosphoric acid (0.5 M). The stoichiometry between permanganate and the oxime is 3:1 (MnO₄^-:oxime). The titration is successful in the presence of large amounts of dichromate or vanadate or moderate amounts of cerium(IV).     

Simultaneous spectrophotometric determination of thorium and rare earth metals with m-carboxychlorophosphonazo (CPAmK) and cetylpyridinium chloride

Th and rare earth elements (REE) react with m-carboxychlorophosphonazo (CPAmK) in the absence of cetylpyridinium chloride (CPC) to form colour complexes. The molar absorptivities for Th and Ce are 1.03 x 10(5) and 1.06 x 10(5) 1.mole(-1).cm(-1) respectively. In the presence of CPC, REE-complexes are not formed because of micellar masking, while Th gives a more sensitive reaction with CPAmK ( = 1.50 x 10(5)). Most of the foreign ions are tolerated in considerable amounts; 360-1000-fold amounts of rare earths do not interfere with the determination of Th. The optimum conditions of the complex-formation reactions and the compositions of Th-CPAmK complexes are described. A simple method is proposed for simultaneous determination of Th and rare earths without previous separation.     

Comparison of some analytical performance characteristics in inductively coupled plasma spectrometry of platinum group metals and gold

The limits of detection, precision and matrix effects in the inductively coupled plasma spectrometry of platinum group metals (PGMs) and gold were measured and evaluated for four ICP-AES and one ICP-MS instrument. The sample matrix was a cationic surfactant used for the PGMs and gold preconcentration on a modified silica gel (C18). A sorption of ion associates of PGMs and gold chlorocomplexes with the cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide was considered. The calibration curves, limits of detection and matrix effects were evaluated in the presence of 0.003 mol dm(-3) of onium salt (1.3 mg cm(-3)) and 0.1 mol dm(-3) HCl. The values of limits of detection (3 sigma(bl)) of PGMs for all axial ICP instruments were mostly below 10 ng cm(-3). Lateral observation on dual view ICP instrument yielded only 3 times higher detection limits in comparison to the axial mode of the same spectrometer and the detection limits for ICP-MS instrument were on the levels of units or tens of pg cm(-3). These limits of detection did not significantly differ from values obtained with pure solutions. Matrix effects in the presence of onium salt did not exceed 12% depression in the analytical signals. Besides the coefficients of correlation, the uncertainties on centroids of concentrations were calculated for calibration graphs obtained by linear regression.     

Stability constants of some metal complexes of triethylenetetraminehexa-acetic acid and complexometric titration of rare earths and other metals

The stability constants of some non-protonated 1:1 metal complexes of triethylenetetraminehexa-acetic acid are reported; log K values are Cd 19.8, Co(II) 20.4, Ni 19.9, Pb 19.5, Sm(III) 24.3, Zn 20.1.     

Chemical microscopy of platinum metals and gold: Reactions with 4,4′-dipyridyldihydrochloride

Summary It has been shown that an acid solution of 4,4-dipyridyldihydrochloride can serve to identify low concentrations of most of the platinum metals and gold in 1-N hydrochloric acid solutions of their chlorides by the separation of characteristic micro crystalline precipitates. The reagent was most effective for palladium(II) and platinum(IV), which could be identified in a 20-l drop of sample containing less than 0.6g of metal. Under the conditions imposed, rhodium (III) was the only platinum metal which failed to yield a precipitate. By contrast, under similar conditions 2,2-dipyridyl failed to yield a crystalline precipitate with rhodium(III), ruthenium (III), and iridium(III). Cupric ion caused the separation of a crystalline complex with 4,4-dipyridyl reagent only at a relatively high metal concentration.

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Zusammenfassung Eine saure Lösung von 4,4-Dipyridyldihydrochlorid eignet sich zum Nachweis geringer Konzentrationen der meisten Platinmetalle und des Goldes in 1-n salzsauren Lösungen ihrer Chloride durch charakteristische Mikrokristallfällungen. Am wirksamsten ist das Reagens gegenüber Pd(II) bzw. Pt(IV), von denen sich weniger als 0,6g in einem 20-l-Tropfen nachweisen lassen. Unter den angegebenen Bedingungen gibt Rh(III) als einziges Platinmetall keinen Niederschlag. Dagegen gibt 2,2-Dipyridyl unter diesen Bedingungen außer mit Rh(III) auch mit Ru(II) und Ir(III) keine kristalline Fällung. Kupfer(II)-ionen bilden mit 4,4-Dipyridyl erst in relativ hoher Konzentration eine kristallisierte Komplexverbindung.

     

Interaction of cetylpyridinium chloride with giant lipid vesicles

The interaction of cationic surfactant cetylpyridinium chloride, CPC, with giant lipid vesicles prepared from 1-palmitoyl-2-oleoylphosphatidylcholine, POPC, was examined at various concentrations of the lipid component. The lipid concentration was determined by a spectrophotometric method. The potentiometric method based on surfactant-selective electrode was used for the determination of surfactant concentration in the external water solution. From these results, moles of surfactant incorporated in the membrane per mole of lipid (parameter beta) and two kinds of partition coefficients were calculated. Their values were found to be considerably larger than the available literature data. A three stage process of surfactant-induced solubilization of lipid vesicles was observed. First, stable mixed bilayers form, which become saturated with CPC at a value beta(sat) larger than 0.8, which then gradually disintegrate. Just prior to the breakdown of the vesicular structure, formation of ellipsoidal vesicles was observed by optical microscopy. This phenomenon was attributed to the cooperative incorporation of surfactant into the bilayer. Fluorescence measurements have shown that the second stage in the solubilization process of POPC by the C16 chain-length surfactant does not involve mixed micelles. These are formed only in the third stage, which is the complete solubilization of POPC bilayers. The corresponding critical micellization concentration decreases with increasing concentration of the lipid component.     

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.