Determination of tungsten in silicates and natural waters

Coprecipitation with hydrous manganese dioxide is used for the concentration of tungsten from natural waters (including sea water) and from solutions prepared from silicate rocks and sediments by hydrofluoric acid attack. After dissolution of the hydrous manganese dioxide precipitate in acidified sulphur dioxide solution, cation excliange is used to separate tungsten and molybdenum from other coprecipitated elements, hydrogen peroxide being used as eluant. Molybdenum is separated from tungsten by extraction of its dithiol complex from 24 N hydrochloric acid medium containing citric acid and can be determined photometrically. After destruction of citric acid, tungsten is determined photometrically with dithiol. The overall cliemical yield of th analytical process is 94±1%. The standard deviation of the method is ±0.010 μg for sea water (0.116 μg W/l) and ca 0.05 μg/g for siliceous sediments containing 0.5–1.0 μg W/g.     

Spektrofotometrische bestimmung von calciumspuren nach ihrer abtrennung aus konzentrierten Lithiumchlorid-Lösungen mittels kationenaustausch

Calcium was separated from 1–2 M solutions of lithium chloride by means of Wofatit CP cation exchanger. Calcium was quantitatively separated from lithium by elution with 1 M ammonium chloride. Calcium, was eluted with hydrochloric acid and, eventually, measured spectrophotometrically at 567 mμ after addition of buffer and cresolphthalexone. The sensitivity was found to be 0.002 μg Ca/cm2 and Beer's law was obeved up to 15 μg Ca. With l g of lithium, the limit of determination was 10^-4% Ca.     

Determination of manganese in uranium by ion exchange and square-wave polarography

Traces of manganese in uranium and its compounds can be determined by ion-exchange separation and square-wave polarography. When a 9 M hydrochloric acid solution of the sample is introduced into a column of strongly basic anion-exchange resin, manganese can be quantitatively separated from uranium by cluting with 9 M hydrochloric acid. The determination of the separated manganese by square-wave polarography is performed in 1 M potassium hydroxide-0.4 M triethanolamine solution with an excellent sensitivity. The lower limit of the method is 0.5 p.p.m. of manganese.     

Determination of seven trace elements in natural waters after separation by solvent extraction and anion-exchange chromatography

A method is described for the determination of cadmium, cobalt, copper, manganese, lead, uranium, and zinc in samples of natural waters. After acidification with hydrochloric acid the water sample is filtered and the diethyldithiocarbamates of the trace elements are isolated by extraction with acetone—chloroform (2:5) at pH 5. Following this preconcentration step the metal ions are adsorbed on a column of the strongly basic anion-exchange resin Dowex 1-X8 (chloride form) using as sorption solution a mixture (5:4:1, $\text{v}\text{v}$) of tetrahydrofuran, methyl glycol and 6 M hydrochloric acid. Successive elution is effected with 6 M hydrochloric acid (Co, Cu, Mn and Pb), 1 M hydrochloric acid (U) and 2 M nitric acid (Cd and Zn); the metal ions in the eluates are determined by atomic absorption spectrophotometry (except uranium, which is determined fluorimetrically). The procedure was used to determine the trace-metals in water and snow samples collected in Austria and to analyse a sample of sea water from the Adriatic Sea.     

Differential pulse cathodic stripping voltammetric speciation of trace level inorganic arsenic compounds in natural water samples

A simple, fast and sensitive speciation method is described for inorganic arsenic in water at the μg/l level, applicable in the laboratory and in the field, based on differential pulse cathodic stripping voltammetry (DPCSV). Only As(III) is deposited on a Hg electrode in the presence of Cu and Se in HCl medium. Determination of total As is performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference. The detection limit (S/N>3) was 0.5 μg/l with a linear range from 4.5 to 180 μg/l. The relative standard deviation (n=6) was 2.4, 2.5, 4.2% for As(III) and 8.0, 6.8, 9.0% for As(V) at levels of 45, 10, and 5 μg/l, respectively. Analysis of the NIST 1640 natural water standard yielded total arsenic concentration 26.5±3.4 μg/l (n=3) compared to the certified value of 26.7 μg/l. Results obtained on several natural water samples analyzed both in the laboratory and on-site compared well with those obtained by HR ICP-MS, GFAAS and IC-AFS. Ions (phosphate, iron, manganese) commonly found in groundwater containing arsenic were found to have negligible interference.     

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.     

Oxidation of organic substances with compounds of trivalent manganese: XXIII. Preparation,stability, and determination of the titer of standard solutions of the fluoride complex of trivalent manganese

A method of preparation of 10^?2 ?10^?3M standard solutions of the fluoride complex of manganese(III) by the reaction of manganese(II) with permanganate in a medium of potassium fluoride acidified with sulfuric acid has been developed. It has been found that in a medium of 1 M sulfuric acid, 0.5 M manganese(II) sulfate, and 0.1 M potassium fluoride these solutions are sufficiently stable for both direct and indirect titrimetric determinations. The titer was determined using potassium iodide as a primary standard and potentiometric, bipotentiometric, or biamperometric titration.     

Semiautomatic indirect titration of alkaline-earth ions with catalytic endpoint indication

A semiautomatic spectrophotometric method of endpoint indication for indirect catalytic titrations of microamounts of alkaline-earth ions is described. The manganese(II)-catalyzed autoxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone is used as indicator reaction. Calcium and magnesium (10–150 μg), strontium (20–250 μg), and barium (20–450 μg) can be determined by adding a known excess of EDTA to the sample solution and back-titrating the unconsumed inhibitor agent with standard manganese(II) solution. This catalytic method was applied to determine the total concentration in calcium and magnesium (total hardness) in natural waters and milk. The method is fast, accurate (1–3%), precise (0.2–0.8%, relative standard deviation), and specially useful for the determination of microamounts where metallochromic indicator are ineffective (for concentrations ranges below 10^?4M).     

Selective spectrophotometric determination of uranium

Uranium(VI) (10–100 μg) is extracted with 2% dibenzoylmethane in benzene at pH 6–7 while other cations are masked with CDTA (maximum of 8 μg/100 ml). Shaking with 6 M hydrochloric acid reintroduces uranium(VI) into the aqueous phase, where after evaporation and complexation with Arsenazo III in 0.02 M hydrochloric acid the final measurement of absorbance at 650 nm is performed. Iron(III), copper(II), aluminum, and zinc do not interfere even if present in amounts of 15–19 mmol.     

Spectrophotometric determination of vanadium(V) and its application to vanadium steel containing chromium,molybdenum, manganese,and nickel

Promethazine hydrochloride forms a red colored species with vanadium(V) in 6.0–7.5 M phosphoric acid. A 16-fold molar excess of the reagent is necessary for full development of color intensity. Beer's law is valid over the concentration range of 0.1–7.0 ppm. The optimum concentration range as evaluated by Ringbom's method is 0.5–7.0 ppm. The sensitivity of the reaction is 0.005 μg cm^?2 and the molar absorptivity is 9.60 × 10³ liter mol^?1 cm^?1 at 517 nm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions were reported. Vanadium in vanadium steel containing chromium, molybdenum, manganese, and nickel was determined.     

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.     

A contribution to the use of tetravalent manganese in solutions of sulfuric acid as an oxidimetric reagent

The preparation of solutions of manganese(IV) sulfate in 9 M sulfuric acid as well as the stability of these solutions was studied for 0.00501 M concentration of manganese(IV) ions. Potentiometric titration of solutions of primary standard substances, potassium iodide and sodium hexacyanoferrate, was recommended for determining the titer of 0.005 M reagent solutions. It was verified that manganese(IV) sulfate can be used for determining low concentrations of organic substances by direct titration determination of hydroquinone, p-aminophenol, and metol and by indirect determination of oxalic acid.     

Semi-micro ion chromatography of iodide in seawater

Large sample volume injections including both on-column analyte focusing and on-column matrix elimination techniques were examined for semi-micro ion chromatography of trace iodide (I⁻) in seawater. A semi-microcolumn (35×1 mm I.D.) packed with styrene–divinylbenzene copolymer with high anion-exchange capacity and a mobile phase of 0.03 M NaClO₄+0.5 M NaCl+5 mM sodium phosphate buffer, pH 6.0, was used. Iodide in seawater was effectively concentrated on the column by both electrostatic and hydrophobic interactions and was eluted without peak broadening. ClO₄⁻ (NaClO₄) in the mobile phase was effective for the elution of iodide and Cl⁻ (NaCl) for both the concentration of iodide (I⁻) with hydrophobicity and the removal of interference by the major anions. An excess of major anions in seawater did not disturb the detection of iodide at UV 226 nm. The relative standard deviations for successive injections of 5 and 1 μg/l I⁻ (2 ml of 35‰ artificial seawater) were 1.5 and 5.8% (n=5, each), respectively. The slope of calibration curve (by peak area) using the semi-microcolumn was ∼2.8-times higher than that for a conventional column with the same resin (150×4.6 mm I.D.) The present method had a detection limit of 0.2 μg/l I⁻ for 2 ml of 35‰ artificial seawater and was successfully applied to seawater samples.     

Determination of chromium in sea water by atomic absorption spectrometry

A method for the determination of chromium in sea water is described which requires minimal sample preparation. The chromium from filtered samples is oxidized with permanganate, extracted with ammonium pyrrolidine dithiocarbamate into MIBK, and analyzed by atomic absorption spectrometry in a fuel-rich air-acetylene flame. Non-filterable solids are extracted with 12 M hydrochloric acid and analyzed. Detection limits for the methods are 0.05 μg 1^-1 in the soluble phase and 0.06 μg 1^-1 in the particulate phase.     

Direct determination of bismuth and antimony in sea water by anodic stripping voltammetry

A method based on anodic stripping voltammetry at the mercury-coated graphite electrode has been developed for the direct determination of bismuth and antimony at their natural levels in sea water. Bismuth plated at -0.4 V from sea water made 1 M in hydrochloric acid gives a stripping peak proportional to concentration at -0.2 V without interference from antimony or other metals normally present. Antimony may be plated from sea water made 4 M in hydrochloric acid and gives a stripping peak at -0.2 V proportional to the sum of bismuth and antimony. By use of the standard addition technique, satisfactory results were obtained for sea water samples with concentration ranges of 0.02–0.09 μg kg^?1 for bismuth and 0.2–0.5 μg kg^?1 for antimony.     

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 manganese with triethanolamine and o-tolidine by conventional and long-path photometry

A very sensitive method for the spectrophotometric determination of manganese is reported. To the sample is added triethanolamine (TEA) and sodium hydroxide to give a pH above 11; after atmospheric oxidation of manganese(II) to the green manganese(III)—TEA complex, sodium pyrophosphate is added and the solution is acidified. Manganese(III) thus forms a complex with pyrophosphate. Then o-tolidine is added and is oxidized in a 2e step to the intensely yellow quinonediimine, while manganese(III) is reduced to manganese(II). The absorbance is measured at 440 nm. The calibration curve is linear up to 1.6 μg Mn ml^-1 in the final solution; the limit of determination is 0.2 μg Mn ml^-1. For the 20-cm path cell, the respective data are 45 ng Mn ml^-1 and 2 ng Mn ml^-1. The only severe interferences are strong oxidants like dichromate or cerium(IV), which are readily reduced with sulfurous acid. Vanadium in amounts up to 2–3 times that of manganese can be dealt with by an appropriate blank solution; larger amounts of vanadium must be removed e.g. by a cupferron extraction.     

Semi-automatic catalytic titration of ethylenediaminetetraacetic acid and metal ions with the 1,4-dihydroxyphthalimide dithiosemicarbazone— aerial oxygen system as indicator reaction

A semi-automatic spectrophotometric method is described for the catalytic titration of ethylenediaminetetraacetic acid, based on its inhibitory effect on the manganese (II)catalyzed aerial oxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone. Amounts of EDTA in the 750–4000-μg range can be determined with a relative standard deviation of ca 0. 6% (n = 11). Methods are also described for the indirect catalytic titrations of manganese(II) and nickel(II)in the ranges 20–450 μg and 40–1000 μg, respectively, with relative standard deviations (n = 11) of ca. 1%.     

The determination of chromium(VI) in natural waters by differential pulse polarography.

A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml^-1 to 2.0 μg ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml^-1.     

Separation of rhenium(vii) from molybdenum(vi) and many other elements by anion exchange

A method is described for the selective separation of μg and mg amounts of rhenium(VII) from molybdenum (VI) and many other metal ions by means of the strongly basic anion-exchange resin Dowex 1-X8. The separation is based on the preferential elution of molybdenum by a 90% (v/v) methanol-10% 6 M nitric acid mixture; rhenium and a few other elements are retained while molybdenum and most other metal ions including Fe(III), Ca, Mg, Mn, U, Cu, V, etc., are practically unadsorbed. After elution of the adsorbed rhenium with 70% (v/v) tetrahydrofuran-30% 9 M hydrochloric acid, the rhenium is determined spectrophotometrically by a modified thiocyanate method.