The determination of antimony in natural waters with particular reference to sea water

A procedure is described for the determination of antimony in natural waters at concentrations down to 0.1 μg/l or less. The element is concentrated by coprecipitation with hydrous manganese dioxide (produced by the reaction of permanganate with ethanol). It is separated from manganese, iron and interfering elements by extraction from 5 M sulphuric acid, 0.01 M with respect to iodide, using methyl isobutyl ketone. After back-extraction with 0.4 M hydrochloric acid, it is determined photometrically using rhodamine B. The overall chemical yield of the process is measured radiochemically and amounts to ca. 80%. Sea water samples from the Irish Sea were found to contain 0.13–0.40 μg Sb/l.     

The determination of selenium in sea water,silicates and marine organisms

Spectrophotometric procedures are described for the determination of selenium in sea water, silicates (especially marine sediments) and marine organisms. Coprecipitation with iron(III) hydroxide at pH 4–6 is used to concentrate selenium and to separate it from many of the commoner elements. Separation from iron and other cations is achieved by ion exchange. Selenium is determined photometrically with diaminobenzidine. Isotope dilution with selenium-75 is used to correct results for the small losses occurring during the analysis. Silicates can be decomposed without loss of selenium by means of a mixture of hydrofluoric and nitric acids. The method of Cummins et al., with sulphuric and perchloric acids in presence of molybdate ion, is highly satisfactory for the decomposition of bio-materials. For sea water, which contains ca. 0.4–0.5 <mg Se/l, a standard deviation of 0.03 μg/l was obtained. A silicate sediment and a sea weed containing ca. 1.5 μg Se/g and 0.8 μg Se/g respectively gave coefficients of variation of 8.0% and 4.7%. The U.S. Geological Survey standard granite G1 was found to contain 2.5 ± 0.1 μg Se/g.     

The determination of vanadium in sea and natural waters,biological materials and silicate sediments and rocks

Vanadium was concentrated from sea and natural waters by coprecipitation with iron (III) hydroxide, and separated from iron and other elements by ion exchange, using hydrogen peroxide as a very selective eluting agent. The element was determined photometrically with diaminobenzidine. The ion-exchange process was also used to separate vanadium from other elements in the analysis of silicate rocks and marine plants. Coefficients of variation of 2.8%, 1.3% and 2.5% were found for the determination of the element in sea water, marine sediments and marine plants at levels of 1.8 μg/l, 57 μg/g and 2.2 μg/g, respectively. The U.S. Geological Survey standard granite GI was found to contain 17.2±0.9μg V/g.     

The rapid colorimetric determination of molybdenum with dithiol in biological, geochemical and steel samples.

A rapid method for the determination of molybdenum in botanical, biological, geochemical and steel samples with dithiol, is described. Botanical and biological samples are ashed at 550 °C before leaching with 4 M hydrochloric acid, while geochemical samples are fused with potassium hydrogensulphate, and steels are decomposed with nitric and hydrochloric acids. The dithiol complex of molybdenum is formed by the addition of an alkaline solution of dithiol to the sample solution, and then extracted into isoamyl acetate. Ascorbic acid and citric acid are used to eliminate interferences from iron and tungsten, and the addition of potassium iodide gives the procedure very high tolerance to copper. Up to 150 geochemical samples or ashed botanical or biological samples can be analysed per man-day. Sensitivity of the method is 0.05, 0.5 and 10 p.p.m. for biological, geochemical and steel samples, respectively. The relative standard deviation is better than ±7% over the standard range used, and recovery of added molybdenum is complete.     

Determination of arsenic in sea water,marine plants and silicate and carbonate sediments

Cocrystallization with thionalide in a 0.05 N sulphuric acid medium is proposed for the recovery of microgram amounts of arsenic from sea water and from solutions prepared by the decomposition of silicates and marino plants. After destruction of the organic precipitant, arsenic is determined photomotrically by means of a single-solution molybdenum blue method. The overall recovery for the whole process is 97-98%. Arsenic was determined in sea water with a coefficient of variation of 1.3% at a level of 2 μg As/l. Coefficients of variation of 2.6% and 1.7% were found, for the determination of the element in marine sediments and plants at levels of 6.6 μg/g and 1.7 μg/g respectively. The U. S. Geological survey standard granite G 1 was found to contain 1.2 μg As/g     

Trägerfreie Abtrennung von Rhenium-Isotopen aus einer deuteronenbestrahlten Wolfram-Matrix

A method is described for the carrier-free separation of rheniumisotopes from deuteron-irradiated tungsten. After being irradiated, metallic tungsten is first treated with a mixture of hydrofluoric acid and nitric acid, and the residue is then dissolved in ammonia and hydrogen peroxide. Ammonium nitrate is added to the solution, and thepH is adjusted to 4.5–5. The separation is performed on a column of hydrous zirconium dioxide using 2% ammonium nitrate solution; ≥99.9 of the tungsten is retained on the ion exchanger. The solution containing the rheniumisotopes is evaporated to dryness, and the ammonium nitrate removed by heating to about 160°C.      

The spectrophotometric determination of chromium in sea water

The coprecipitation of chromium from sea water by several precipitates was examined. With hydrous iron(III) oxide a recovery of chromium of >99% was obtained within the pH range 7.0–9.0 at a chromium level of ca. 0.4 μg/l. Chromium was separated from iron by anion exchange and determined spectrophotometrically using diphenylcarbazide. The method showed a precision of ±0.02 μg Cr/1. Chromium occurs in sea water in the 3+ oxidation state.     

The determination of bismuth in sea and natural waters

A spectrophotometric method is described for the determination of bismuth in natural waters, particularly sea water at the level of ca. 0.02 μg/l. The element is concentrated from the acidified sample, by sorption onto De-Acidite FF anion exchanger, eluted with nitric acid and determined photometrically with dithizone. The overall efficiency of the separation process was determined radiochemically and amounted to ca. 85%. The interference of elements also taken up in the ion-exchange process was negligible at their normal levels in natural waters. A deep water sample from the North Atlantic was found to contain 0.015μg Bi/l.     

Determination of lead in blood by tungsten coil electrothermal atomic absorption spectrometry

A method for the determination of lead in blood using a tungsten coil atomizer is described. A 100 μl volume of the whole blood sample is transferred to a sampler cup containing 100 μl of water plus 300 μl of 0.25% v/v Triton X-100. After lysis of blood cells, 500 μl of 10% w/v trichloroacetic acid is added for protein precipitation and 10 μl of the supernatant solution is automatically delivered into the tungsten coil. The furnace heating program is implemented in 41 s. It is shown by the paired t-test that there is no significant difference at the 5% probability level between results obtained by the proposed method and by using a transversely heated graphite atomizer with a longitudinal Zeeman background correction. Accuracy is also assessed by employing reference materials. The proposed tungsten coil procedure presents a characteristic mass of 15 pg Pb and a detection limit of 1.9 μg Pb dl⁻¹.     

Analysis of mixtures of citric and oxalic acids based on their oxidation with potassium permanganate and manganese(III) sulfate

A determination of mixtures of citric and oxalic acids has been developed based on quantitative oxidation of the two substances with excess potassium permanganate to carbon dioxide and water and on quantitative oxidation of oxalic acid to carbon dioxide and water and of citric acid to carbon dioxide and formic acid with excess manganese(III) sulfate. The content of the two substances in mixtures can be calculated from the different consumption in these two oxidimetric determinations; a single standard solution of potassium permanganate can also be used for the preparation of manganese(III) sulfate.     

A routine method for the determination of arsenic in plants, sediments and natural waters

Coprecipitation with molybdenum sulphide in 2 M hydrochloric acid solution is proposed for the recovery of microgram amounts of arsenic from solutions prepared by ashing plants and sediments, and from natural waters. After dissolution of the sulphide precipitate, arsenic is determined photometrically by a molybdenum blue method. The overall recovery for the procedure is 99%. Arsenic was determined in solutions of plant ash at the 2-μg As level with a coefficient of variation of 0.6%.     

Simultaneous spectrophotometric determination of Tungsten and Molybdenum with Thiocyanate after α-Benzoinoxime extraction

The extractability of tungsten α-benzoinoximate by chloroform as a function of the reagent concentration and acidity has been studied. In 0.5 M hydrochloric acid solution the extraction coefficient for tungsten (~ l p.p.m.) is given by the relation

An acidity range of 0.01–1 M provides favorable extraction coefficients. Tungsten can be separated by α-benzoinoxime extraction from much iron and most other metals. Molybdenum accompanies tungsten quantitatively and the two elements can be determined simultaneously by the familiar thiocyanate method if the absorbance of the isopropyl ether extract is measured at 405 mμ and 490 (or 475) mμ. As little as 1 μg W can thus be determined in the presence of 10 μg Mo without separation.     

Determination of Cu, Zn and Cd in water by FAAS after preconcentration by baker’s yeast (Saccharomyces cerevisiae) immobilized on sepiolite

By using the adsorbent Saccharomyces cerevisiae immobilized on sepiolite an adsorption-elution method was developed for the preconcentration of Cu, Zn, and Cd followed by flame atomic absorption spectrometry (FAAS). Recoveries were 98.3 ± 0.4% for Cu, 94.2 ± 0.3% for Zn, and 99.04 ± 0.04% for Cd at 95% confidence level obtained by the column method. The influence of sea water matrix elements on the separation of the trace elements was also assessed by using the column procedure. The breakthrough capacities were found to be 74 μmol/g for copper, 128 μmol/g for zinc and 97 μmol/g for cadmium. After optimization the proposed method was applied to the trace metal determination in sea and river water.     

Thermochemical Properties of the Lattice Oxygen in W,Mn-Containing Mixed Oxide Catalysts for the Oxidative Coupling of Methane

Mixed NaWMn/SiO₂ oxide, samples containing individual components (Na, W, Mn) and their double combinations (Na–W, Na–Mn, W–Mn) supported on silica were studied by temperature programmed reduction (TPR) and desorption (TPD), and heat flow calorimetry during their reoxidation with molecular oxygen in pulse mode. The NaWMn/SiO₂ mixed oxide was shown to contain two different types of reactive lattice oxygen. The weakly-bonded oxygen can be reversibly released from the oxide in a flow of inert gas in the temperature range of 575?900°C, while the strongly-bonded oxygen can be removed during the reduction of the sample with hydrogen at 700–900°C. The measured thermal effect of oxygen consumption for these two oxygen forms are 185 and 350 kJ/mol, respectively. The amount of oxygen removed at reduction (~443 μmol/g) considerably exceeded the amount desorbed in an inert gas flow (~56 μmol/g). The obtained results suggest that the reversible oxygen desorption is due to the redox process in which manganese ions are involved, while during the temperature programmed reduction, mainly oxygen bonded with tungsten is removed.     

Na-W-Mn/SiO2催化剂活化甲烷的研究Ⅱ.活性氧物种

制备了不同Ｎａ、Ｗ、Ｍｎ组分的Ｎａ－Ｗ－Ｍｎ／ＳｉＯ２催化剂,并进行了Ｏ２程序升温脱附（Ｏ２－ＴＰＤ）和不同温度下Ｎａ－Ｗ－Ｍｎ／ＳｉＯ２催化剂的ＣＨ４脉冲反应（ＣＨ４－ＰＲ）。研究结果表明,Ｎａ－Ｗ－Ｍｎ／ＳｉＯ２催化剂活化甲烷的活笥氧物种是Ｗ和Ｍｎ提供的、高温下易于流动的表面晶格氧（Ｏ＾２－）。Ｎａ和Ｏ＾２－的活泼性具有重要的促进作用,它可以极化Ｗ、Ｍn的金属一氧键,促进Ｏ＾２－的流动性。Ｎａ     

Anion-exchange separation and spectrophotometric determination of molybdenum and tungsten in silicate rocks

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum and tungsten in silicate rocks. After the decomposition of samples with a mixture of sulphuric, nitric and hydrofluoric acids, traces of molybdenum and tungsten are separated from other elements by anion-exchange in acid sulphate media containing hydrogen peroxide. The adsorbed molybdenum and tungsten can easily be stripped from the column by elution with sodium hydroxide-sodium chloride solution. The adsorption and desorption steps provide selective concentration of molybdenum and tungsten, allowing the simultaneous spectrophotometric determination of the two metals with dithiol. Results on the quantitative determination of molybdenum and tungsten in the U.S. Geological Survey standard samples are included.     

Influence of citric acid as chemical modifier for lead determination in dietary calcium supplement samples by graphite furnace atomic absorption spectrometry

Citric acid was used as a chemical modifier for Pb determination by graphite furnace atomic absorption spectrometry in dietary supplement samples (calcium carbonate, dolomite and oyster shell samples) and its efficiency was compared to the use of palladium. Pyrolysis and atomization curves were established without use of chemical modifier, with the addition of 20, 100 and 200 μg of citric acid, and with 3 μg of palladium. The citric acid modifier made possible the interference-free Pb determination in the presence of high concentrations of Ca and Mg nitrates. Acid sample digestion involving closed vessels (microwave-assisted and conventional heating) and acid attack using polypropylene vessels at room temperature were compared. All digestion procedures presented similar results for calcium carbonate and dolomite samples. However, for oyster shell samples accurate results were obtained only with the use of closed vessel systems. Analyte addition and matrix-matched standards were used for calibration. The characteristic mass for Pb using citric acid and palladium were 16 and 25 pg, respectively. The relative standard deviation (RSD) was always less than 5% when citric acid was used. The relative and absolute limits of detection were 0.02 μg g^− 1 and 8 pg with citric acid and 0.1 μg g^− 1 and 44 pg with the Pd modifier, respectively (n = 10, 3σ). The recovery of Pb in spiked calcium supplement samples (10 μg l^− 1) was between 98% and 105%. With the use of 100 μg of citric acid as chemical modifier, problems such as high background absorption and high RSD values were minimized in comparison to the addition of 3 μg of palladium.     

The spectrophotometric determination of antimony in water,effluents, marine plants and silicates

A spectrophotometric procedure is described for the determination of antimony in natural waters (including sea water and effluents), algae and silicates. After a preliminary oxidative digestion for waters, or acid attack for algae and silicates, the element is quantitatively coprecipitated at pH 5.0 with hydrous zirconium oxide. The precipitate is dissolved in acid, and, after reduction with titanium(III) chloride, antimony is oxidized to antimony(V) with sodium nitrite. The ion pair of the SbCl₆^- ion with crystal violet is extracted with benzene and its absorbance is measured at 610 nm (molar absorptivity 74,000 l mol^-1 cm^-1). Extraction with toluene causes some loss of sensitivity. The detection limit is 0.005 μg l^-1; relative standard deviations are 0.5% and 1.1% for spiked distilled water (0.5 μg l^-1) and sea water (0.26 μg l^-1), respectively. A wide range of anions and cations cause no interference at levels many times those in natural waters. The technique can be adapted for application to marine algae and silicates; relative standard deviations are 1.8% and 2% for samples of Pelvetia canaliculata (0.19 μg Sb g^-1) and a Pacific Ocean red clay (1.08 μg Sb g^-1), respectively. Results for the U.S. Geological Survey Standard rocks GSP1 (2.7 ppm) and DTS1 (0.53 ppm) are in good agreement with those of earlier workers.     

Determination of trace elements in manganese metal and compounds by ion-exchange chromatography and atomic absorption spectrometry : part 2. Determination of Bi,Cd, In,Zn, Pb,Fe(III), Ga,Cu(II), Co and U(VI)

Traces of the specified elements are separated from 1 g of manganese (II), using a 30- g column of AG50W-X8 cation-exchange resin and mixtures of hydrochloric acid and acetone as eluents. The trace elements are separated into three groups and are determined by atomic absorption spectrometry, except uranium for which spectrophotometry is used. Recoveries for 10 μg amounts (20 μg for gallium) vary between 94% (for gallium) and 103% (for uranium). A combined elution curve, results for the analysis of synthetic mixtures and for the determination of ten trace elements in samples of manganese metal, chloride and dioxide are presented.     

Determination of antimony in rocks and sulphide ores by flame and electrothermal atomic-absorption spectrometry

Atomic-absorption methods for determination of antimony at mug/g levels in rocks and sulphide ores by flame atomization (FAA) and electrothermal atomization (ETAA) have been described. The FAA method involves the separation of antimony from matrix elements by extraction as the iodide into methyl isobutyl ketone containing tri-n-octylphosphine oxide, from dilute hydrochloric acid solution, followed by direct aspiration of the extract into an air-acetylene flame. If necessary, antimony is first separated from copper and lead by co-precipitation with hydrous ferric oxide from ammoniacal medium and by precipitation of lead as lead sulphate. The ETAA method involves co-precipitation of antimony with hydrous ferric oxide followed by dissolution of the precipitate in dilute nitric acid, mixing with nickel solution as releasing agent, and ETAA measurement by use of a tungsten strip atomizer.