Determination of selenium and tellurium in electrolytic copper by anodic stripping voltammetry at a gold film electrode

A simple procedure for the determination of selenium and tellurium in electrolytic copper is described. These two elements are first separated from copper by passing an ammoniacal solution of the sample through Chelex-100 resin. Voltammetric interferences from nitrite liberated during the dissolution of the metal sample in nitric acid and from arsenic and antimony present in the metal are eliminated by addition of hydrogen peroxide. Excess of peroxide is quickly decomposed by the copper(II) ions present. As little as 0.01 μg Se g^-1 and 0.02 μg Te g^-1 can be determined; relative standard deviations (n = 5) are in the ranges 1.4–3.7% for selenium concentrations of 7.3–0.6 ppm in copper and 1.6—3.1% for tellurium concentrations of 4.6—0.5 ppm.     

Fast determination of molybdenum and tellurium by neutron activation analysis

The utilization of 14.6-min ¹⁰¹Mo and 25-min ^101gTe for the determination of molybdenum and tellurium in biological materials by radiochemical neutron activation analysis is described for the first time. Radioisotopes were separated from the samples activated in a thermal neutron flux of about l0¹⁴n cm^-2 s^-1. The radiochemical procedure for molybdenum involves extraction of Mo⁺⁺ from 6 M HCl into diethylether, re-extraction into water, precipitation as oximate, and measurement of the gamma activity of ¹⁰¹Tc. The tellurium was separated by reduction to the element with SO₂ in 3 M HCl, dissolution in HNO₃, and reprecipitation as the element for the measurement of radioactivity. The sensitivity was estimated at ca. 10 ng at the level of confidence of 95%. The methods were tested by analyzing NBS- standard Bovine Liver and Orchard Leaves for molybdenum; the concentrations found were 3.2 ± 0.1 μg g^-1 and 300 ± 60 ng g^-1, respectively. The tellurium content of bovine liver was estimated at 90 ± 15 ng g^-1.     

Determination of bismuth,lead and tellurium in copper by atomic absorption spectrometry with introduction of solid samples into an induction furnace

Atomic absorption spectrometry with an induction furnace is used for the determination of bismuth (0.015–10 μg g^-1), lead (0.2–15 μg g^-1) and tellurium (0.04–5 μg g^-1) in 2–30-mg samples of copper and low-alloy copper dropped into the furnace. Calibration graphs of peak area versus mass of element were constructed by use of standardised alloys. The accuracy, precision and limits of detection of the method are described for numerous copper samples. With alloys containing more than 0.1 μg Bi g^-1, 0.2 μg Pb g^-1 and 0.8 μg Te g^-1, average relative standard deviations are 7%, 6% and 8%, respectively. The limits of detection for bismuth, lead and tellurium are 0.01, 0.1 and 0.02 μg g^-1, respectively.     

Determination of Iodine in Cereal Grains and Standard Reference Materials by Neutron Activation Anaylsis

Abstract

Trace amounts of iodine in thirty-eight cereal grain samples cultivated at different locations in Austria were determined for the first time in this study by radiochemical neutron activation analysis. For the dissolution of cereal grain samples and standard reference materials, two different procedures, alkaline and acidic dissolution, were applied in the presence of an iodine carrier. Rapid and simple dissolution procedure with acidic solution was demonstrated in this study. The analytical values in the cereal grain as well as in the standard reference materials obtained by the different dissolution procedures were in good agreement within one standard deviation. The iodine in cereal grains and the standard reference materials ranged from 0.002 to 0.03 μg g^?-1 and 0.0015 to 0.30 μg g^?-1, respectively. The distribution of relative standard deviation (RSD) for iodine concentration below 0.01 μg g^?-1 were 21% and 24% of all data for the range 1–10% RSD and 11–20% RSD, respectively. The RSD for 0.1 μg g^?1 of iodine concentrations were around 10%     

Thermal stabilization of inorganic and organically- bound tellurium for electrothermal atomic absorption spectrometry

The thermal stabilization of inorganic tellurium(IV) and organically-bound tellurium for electrothermal atomic absorption spectrometric determination of the element was studied with the use of the isotope tellurium-127m. Of the 19 metals and potassium iodide tested, 15 metals had a stabilizing effect on inorganic tellurium; among the 9 metals tested with organically-bound tellurium, only 3 exhibited an effect. The most effective metals for stabilizing inorganic tellurium were cadmium, copper, palladium, platinum and zinc, while the best agents for stabilization of organically-bound tellurium were silver, palladium and platinum; in the presence of palladium and platinum, tellurium in both forms could be heated in the graphite tube to 1050°C without losses. Attempts were made to determine tellurium in human whole blood and garlic, but the concentrations were found to be below the detection limits of 3 ng ml^-1 and 140 ng g^-1, respectively.     

Rapid determination of nanogram amounts of tellurium in silicate rocks

A hydride-generation flameless atomic-absorption technique is used to determine as little as 5 ng g^-1 tellurium in 0.25 g of silicate rock. After acid decomposition of the sample, tellurium hydride is generated with sodium borohydride and the vapor passed directly to a resistance-heated quartz cell mounted in an atomic-absorption spectrophotometer. Analyses of 11 U.S. Geological Survey standard rocks are presented.     

Determination of uranium by neutron activation and radiochemical separation of the tellurium fission product

After irradiation and dissolution of the samples (minerals, rocks etc.), elemental tellurium is precipitated, redissolved, extracted for its diethyldithiocarbamate, and finally reduced again for measurement of the ¹³²Te 228-keV γ-peak. The chemical yield is 75% and the lower limit of determination is 2 × 10^-7 g U.     

Tellurium Film Electrodes Deposited on Carbon and Mesoporous Carbon Screen‐printed Substrates for Anodic Stripping Voltammetric Determination of Copper

The performance of screen‐printed electrodes modified in situ with tellurium film for the anodic stripping voltammetric (ASV) determination of Cu(II) is reported. It was found that two types of screen‐printed substrates, namely carbon and mesoporous carbon, were optimal for this application. The selected in situ tellurium film modified electrodes were applied for the square wave ASV determination of copper at μg L⁻¹ concentration levels. Well‐defined and reproducible Cu oxidation stripping peaks were produced at a potential more negative than the anodic dissolution of tellurium. The highest sensitivity of Cu determination was achieved in 0.05 M HCl containing 50 μg L⁻¹ Te(IV) after 300 s of accumulation at −0.5 V. Using the optimized procedure, a linear range from 2 to 35 μg L⁻¹ of Cu(II) was obtained with a detection limit of 0.5 μg L⁻¹ Cu(II) (S/N=3) for 300 s of deposition time. Both sensors, carbon TeF‐SPE and mesoporous carbon TeF‐SPE, were successfully applied for the quantification of Cu in a certified reference surface water sample.     

Determination of cadmium,indium and zinc in nickel—base alloys by atomic absorption spectrometry with introduction of solid samples into furnaces

Atomic absorption spectrometry with an induction furnace is used for the determination of cadmium (0.002–2 μg g^-1), indium (0.6–350 μg g^-1) and zinc (0.05–26 μg g^-1) in 0.8–35 mg samples of nickel—base alloys dropped into the furnace. A resistively-heated furnace is employed for the determination of lower concentrations of indium (<0.6 μg g^-1). Standardised alloys were used for calibration. Accuracy, precision and detection limits are described for numerous nickel—base alloys. With alloys containing zinc, > 0.1 μg Cd g^-1 and >0.6 &,mu;g In g^-1, the relative standard deviations are 12%, 8% and 7%, respectively. Calculated detection limits for cadmium, indium and zinc are 2 ng g^-1, 10 ng g^-1 and 10 ng g^-1, respectively.     

Development and certification of a coal fly ash certified reference material for selected polycyclic aromatic hydrocarbons

The development and certification of a coal fly ash certified reference material (CRM) for polycyclic aromatic hydrocarbons (PAH) is described; this is the first natural matrix CRM for organic environmental analysis in China. The homogeneity and stability of this material have been tested by HPLC. The concentrations of several PAH were determined by use of two independent, different methods – solvent extraction–HPLC analysis with UV detection coupled with fluorescence detection (FLD) and solvent extraction, isolation with a silica column, and GC analysis with flame ionization detection (FID). Five certified values were determined: phenanthrene 7.1 ± 2.6 μg g^–1, anthracene 2.0 ± 0.8 μg g^–1, fluoranthene 7.4 ± 1.9 μg g^–1, pyrene 7 ± 2 μg g^–1, and benzo[a]pyrene 1.3 ± 0.3 μg g^–1. Reference values for several other PAH are also suggested.     

Differential pulse polarographic determination of traces of molybdenum in solar-grade silicon

After dissolution of silicon with hydrofluoric and nitric acids and matrix volatilization as hexafluorosilicic acid, 0.2 M nitric acid and 1.8 M ammonium nitrate are added to the residue. Molybdate is then determined by means of its catalytic wave in nitrate media. The limit of determination is ca. 0.1 μg g^-1 and calibration graphs are linear up to 0.2 μg Mo(VI) ml^-1.     

Microtitrimetric and photometric determination of sulphur in metals in the low μg g-1 range after wet or dry evolution of hydrogen sulphide

Wet and dry techniques have been optimized for the separation of sulphur traces from metals (e.g. Ag, Cu, Cu alloys, Pb, Sn, Fe) as hydrogen sulphide, in combination with a final microtitrimetric or spectrophotomefcric determination. The metal sample can be dissolved in a mixture of hydroiodic, formic and hypophosphorous acids, and the evolved hydrogen sulphide swept with nitrogen into an absorption vessel. Alternatively, in the hydrogenation technique, the metal sample is heated in a stream of pure hydrogen up to ?1150°C and the hydrogen sulphide produced is absorbed in sodium hydroxide solution or cadmium hydroxide suspension. The sulphide is determined in the absorption vessel by microtitration with cadmium(II) titrant and dithizone as indicator. The methylene blue colour reaction is applied for the speetrophotometric determination. Precautions are taken to avoid systematic errors (losses by absorption, contamination by laboratory air) and to lower reagent blanks, so that concentrations as low as ?0.2 μg g^-1 (sample weight ?1 g) can be determined. The coefficients of variations are ?10% and 2.5% at concentration ranges of 1–10 μg g^-1 and > 10 μg g^-1, respectively.     

Effect of six triorganotin(IV) compounds on nitrification and ammonification in soil

The effects of six triorganotin(IV) compounds and of Thiram on nitrification and ammonification in soil were investigated. Low concentrations of up to 50 μg g^?1 of the triorganotin(IV) compounds enhanced nitrate-nitrogen (NO₃^?-N) production in soil. Except for diphenylbutyltin bromide, which inhibited nitrification at 250 μg g^?1, the other triorganotin(IV) compounds were inhibitory at concentrations of 100 μg g^?1 to less than 250 μg g^?1. At 10 μg g^?1, only triphenyltin acetate was less inhibitory towards nitrification compared with Thiram. At 250 μg g^?1, Thiram exerted a strongly persistent inhibitory effect towards nitrification. The NO₃^?-N level recorded 28 days after application was only 0.10 μg g^?1 soil. With the triorganotin compounds NO₃^?-N levels of 7.05–12.06 μg g^?1 soil were recorded 28 days following their application. The deleterious effects of the triorganotin(IV) compounds were less persistent and recovery of nitrification was evident seven days after application. Low concentrations of Thiram and triorganotin(IV) compounds inhibited ammonification, whereas higher concentrations enhanced ammonification. Complete inhibition of ammonification was attained 21–28 days after application of Thiram at 50 μg g^?1. On the other hand, with the triorganotin(IV) compounds, except for diphenylbutyltin bromide at 10–50 μg g^?1, ammonification persisted at all concentrations 28 days after application.     

Etude thermoanalytique et lyodisponibilite de dispersions solides du tolbutamide

We have established the phase diagram tolbutamide (TBM)-PEG 6000 and determined the eutectic composition 1/9 (w/w) in tolbutamide and melting temperature 56.2°C±0.3; no solid solution has been found. Negative mixing enthalpies of physical mixture (?2.5 J·g^?1) and solid dispersions coprecipitate (?3.9 J·g^?1) melt (?9.9 J·g^?1) for eutectic composition involve the existence of interactions between drug and carrier. We have determined the dissolution kinetics: amount % dissolved (10 min) 65.87±0.55 (physical mixture), 78.02±0.02 (coprecipitate), 99.90±0.10 (melt). We have observed a good agreement between dissolution kinetics and mixing enthalpies data.     

Adsorption and colloidal behaviour of traces of tellurium(IV) in aqueous solutions

Various NaCl solutions containing traces of tellurium(IV) have been prepared. The effects of tellurium(IV) concentration and pH on the adsorption of tellurium(IV) on filter paper have been studied by filtration method. The effects of NaCl concentration, tellurium(IV) concentration and pH on the formation of a colloid have been also studied by ultracentrifugation and ultrafiltration methods. It has been found that tellurium(IV), at concentrations below about 10^–10M, in neutral NaCl solutions is adsorbed on filter paper and shows colloidal behaviour.     

The determination of copper in silicon by anodic stripping and differential pulse voltammetry

A critical comparison of the application of differential pulse voltammetry and anodic stripping voltammetry to the determination of micro amounts of copper in silicon is described. The anodic stripping technique offers advantages when a dropping mercury capillary with a long drop time is used. The method recommended allows the determination of copper in silicon with a precision of ± 5 %; the limit of determination is about 1μg g^-1. Calibration graphs are linear in the range 0–0.2 μg Cu ml^-1. Methods for the dissolution of silicon are also compared.     

The determination of boron in zirconium and zircaloy by proton activation analysis based on the 10B(p, α)7Be reaction

The determination of boron in zirconium and zircaloy based on the ¹⁰B(p, α)⁷Be reaction is described. At the 100 and 20 μg g^-1 concentration level (doped samples), instrumental analysis is feasible. At lower concentrations, ⁷Be is separated from the activities formed from zirconium and its alloying elements or impurities, by anion-exchange in hydrofluoric acid medium followed by precipitation of YF₃ and of BaBeF₄. The chemical yield of the separation was determined in several ways. The sensitivity of the method was 15 ng g^-1. For concentrations ranging from 100 to 0.15 μg g^-1, the precision ranged from 3.5 to 10.7%. The results are compared with results obtained by other methods.     

Ion-chromatographic measurements of ammonium,fluoride, acetate,formate and methanesulphonate ions at very low levels in antarctic ice

Ion chromatography is used to determine the concentrations of organic (formate, acetate and methanesulphonate) and inorganic (fluoride and ammonium) ions present in Antarctic ice at less than 10⁻⁹ g g⁻¹ levels. With suitable columns, the simultaneous measurement of these ions requires only 6 min. A sample volume of 5 ml is sufficient to reach the 10⁻¹⁰ g g⁻¹ level. The determination of such low concentrations requires stringent contamination-free techniques. For formate and acetate, the samples should never come into contact with plastics. Except for methanesulphonate, all the ions studied can be produced by dissolution of the various gaseous compounds present in a polluted atmosphere. Therefore a glass device with pure nitrogen circulation was designed for air-free melting of samples. To prevent possible biological activity on organic matter, samples were analysed immediately after melting. Measurements of ammonium ion in these Antarctic ice samples demonstrate that the problem of contamination by surrounding ammonia was not completely eliminated in previous studies. The serious contamination problems encountered, particularly for carboxylic acids, cast doubt on some earlier results for remote areas.     

A New Polarographic Adsorptive Catalytic Wave for the Determination of Trace Tellurium in Smog Dust and Wheat Flour

Linear-sweep polarography of tellurium in sulfuric acid solution containing methylene blue produces a wave at −0.82 V (vs SCE). In a cathodic sweep, the derivative peak current is directly proportional to the concentration of tellurium over the range 4 × 10⁻⁹to 1 × 10⁻⁷g/ml, and the detection limit is 2 × 10⁻⁹g/ml. The polarographic wave is an adsorptive catalytic hydrogen wave. This method has been applied to the determination of trace amounts of tellurium in smog dust and wheat flour, with satisfactory results.     

Pressurized fluid extraction of polycyclic aromatic hydrocarbons using silanized extraction vessels

We have investigated the extraction efficiency of a pressurized fluid extraction system using an Ottawa sand matrix, soils and a certified reference material (HS-6) spiked with the 16 polycyclic aromatic hydrocarbon (PAHs) associated with method EPA 8100. Acceptable recoveries were achieved for all PAHs using a nominal sand concentration of 2.0 μg.g^-1. However, similar experiments that were conducted at a concentration of 0.20 μg.g^-1 afforded poor recoveries and poor reproducibility for the six-ring PAHs indeno(1,2,3-cd)pyrene, dibenz(a)anthracene, and benzo(ghi)perylene. These were not adequately addressed by the use of indeno(1,2,3-cd)pyrene-d12 and benzo(g,h,i)perylene-d12 surrogates. Silanization of vessels using dichlorodimethylsilane adequately passivates the system but is only required for the high surface area retention frits. Replicate analyses at concentrations of 200 and 20 ng.g^-1 demonstrated that detection limits in the low ppb range (ng.g^-1) are achieved for Ottawa sand, dry soil and soil with moisture contents up to a mass fraction of 30 %. Such performance is consistent with the analytical requirements of the Canadian Sediment Quality Guidelines. Improved analyte recoveries were also observed for the certified reference material HS-6 which were further improved by increasing extraction temperatures from 100 to 150 °C.