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Results for “Analytica Chimica Acta”

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At least 37 records · Page 2Linked to original sources
USGS1975

Spectrofluorimetric determination of thallium in silicate rocks with rhodamine b in the presence of aluminum chloride

A sensitive spectrofluorimetric procedure with rhodamine B in the presence of aluminum chloride is given for determining submicrogram and microgram quantities of thallium in silicate rocks. Samples are decomposed with a mixture of hydrofluoric and nitric acids and then treated with hydrochloric acid. Thallium is extracted as its dithizonate with chloroform from an alkaline medium containing ascorbate, citrate, and cyanide and then back-extracted with dilute nitric acid.

Analytica Chimica Acta↗
USGS1970

Determination of niobium in rocks by an isotope dilution spectrophotometric method

Rocks and minerals are fused with sodium peroxide in the presence of carrierfree 95 Nb. The fusion cake is leached with water and the precipitate dissolved in hydrofluoric-sulfuric acid mixture. Niobium is extracted into methyl isobutyl ketone and further purified by ion exchange. The amount of niobium is determined spectrophotometrically with 4-(2-pyridylazo)-resorcinol, and the chemical yield of the separations determined by counting 95 Nb. This procedure is faster and less sensitive to interferences than previously proposed methods for determining niobium in rocks. The high purity of the separated niobium makes the method applicable to nearly all matrices.

Analytica Chimica Acta↗
USGS1973

Determination of indium in rocks by substoichiometric radioisotope dilution analysis

Rocks containing 10–140 ng of indium per g are decomposed with hydrofluoric and nitric acids in the presence of 114 In. Indium is separated from other constituents by sequential extractions of the bromide, cupferronate, and acetylacetonate, and is then reacted with a substoichiometric amont of EDTA. Excess of indium is removed by acetylacetone extraction and the specific activity of the complexed fraction is determined by counting 114 In. Analyses of the U.S.G.S. standard rocks are reported. These show good agreement with previous neutron activation analyses. Repetitive rock analyses indicated an analytical precision of ±4–7%.

Analytica Chimica Acta↗
USGS1974

Spectrophotometric determination of molybdenum in rocks with thiocyanate

A rapid procedure for the determination of microgram amounts of molybdenum in rocks is described. After acid decomposition, molybdenum is extracted from a hydrochloric acid solution into xylene with tributyl phosphate. After back-extraction with water, molybdenum is extracted as the α-benzoinoximate into chloroform, stripped into hydrochloric acid extracted as the thiocyanate into amyl alcohol, and determined spectrophotometrically. The molybdenum thiocyanate color produced is stable, sensitive, and reproducible. Results of analyses of several of the U.S. Geological Survey standard rocks are given.

Analytica Chimica Acta↗
USGS1974

A solvent extraction study of molybdenum chloride and molybdenum thiocyanate complexes

The effect of reducing agents on molybdenum(VI) solutions in hydrochloric acid was studied by a solvent extraction technique to elucidate the composition of the colored molybdenum thiocyanate complex. Neither copper(I) chloride nor ascorbic acid have any effect on the extraction of MoO 2 Cl 2 ; it is inferred that tin(II) chloride reduces Mo(VI) stepwise to a polynuclear Mo(V)·Mo(VI) complex and then to Mo(V). The colored thiocyanate complex produced by copper(I) and by ascorbic acid differs only slightly in extraction characteristics from the uncolored Mo(VI) complex. It is suggested that the color may be produced by an isomerization reaction of MoO 2 (SCN) 2 , and thus that the colored species may be a hexavalent rather than pentavalent molybdenum complex.

Analytica Chimica Acta↗
USGS1970

The determination of low levels of cobalt-60 in environmental waters by liquid scintillation counting

A method for determination of cobalt-60 in waters at levels greater than 0.5 pCi per sample is presented. A modification of the method may be used to analyze fluvial sediments and soils. After the cobalt has been separated, first as the hydroxide and then as the thiocyanate complex in methyl isobutyl ketone, it is counted in a liquid scintillation system at 80% efficiency. Separation factors achieved for six isotopes are generally greater than 2,000. The time for a single analysis, exclusive of the counting and evaporation operations, is about 2 h.

Analytica Chimica Acta↗
USGS1970

Lithium metaborate flux in silicate analysis

Lithium metaborate is an effective flux for silicates and other rock-forming minerals. The glass resulting from fusion is mechanically strong, reasonably nonhygroscopic, and is readily soluble in dilute acids. These characteristics lead to its use in X-ray spectrography and in methods which require whole-rock solutions, such as atomic absorption and emission spectrometry. Difficulties have been encountered in the use of such techniques : a high-quality reagent has been difficult to obtain ; fusion conditions must be rather closely controlled; graphite crucibles used in the fusions need special treatment. Methods for overcoming these difficulties are outlined. Selected procedures for various instrumental methods of analysis are described.

Analytica Chimica Acta↗
USGS1971

Determination of silver in soils, sediments, and rocks by organic-chelate extraction and atomic absorption spectrophotometry

A useful method for the determination of silver in soil, sediment, and rock samples in geochemical exploration has been developed. The sample is digested with concentrated nitric acid, and the silver extracted with triisooctyl thiophosphate (TOTP) in methyl isobutyl ketone (MIBK) after dilution of the acid digest to approximately 6 M . The extraction of silver into the organic extractant is quantitative and not affected by the nitric acid concentration from 4 M to 8 M , or by different volumes of TOTP-MIBK. The extracted silver is stable and remains in the organic phase up to several days. The silver concentration is determined by atomic absorption spectrophotometry.

Analytica Chimica Acta↗
USGS1972

Determination of nanogram amounts of bismuth in rocks by substoichiometric isotope dilution analysis

A rapid procedure suitable for the routine determination of 1–10 ng of bismuth in a silicate rock matrix is described. Results for the U.S. Geological Survey standard rocks are presented. Rocks and minerals are dissolved in hydrofluoric-perchloric acid in the presence of 207 Bi tracer and the silica is removed by evaporation. The perchloric acid residue is taken up in water and bismuth iodide is extracted into methyl isobutyl ketone. After three acid-iodide washes, the bismuth is stripped into water and reacted with a substoichiometric amount of EDTA. Excess of bismuth is extracted as the iodide and the specific activity of the bismuth-EDTA complex is determined.

Analytica Chimica Acta↗
USGS1972

Microcoulometric measurement of water in minerals

A DuPont Moisture Analyzer is used in a microcoulometric method for determining water in minerals. Certain modifications, which include the heating of the sample outside the instrument, protect the system from acid gases and insure the conversion of all hydrogen to water vapor. Moisture analyzer data are compared to concurrent data obtained by a modified Penfield method. In general, there is a positive bias of from 0.1 to 0.2% in the moisture analyzer results and a similarity of bias in minerals of the same kind. Inhomogeneity, sample size, and moisture pick-up are invoked to explain deviations. The method is particularly applicable to small samples.

Analytica Chimica Acta↗
USGS1971

The determination of vanadium in brines by atomic absorption spectroscopy

A standard addition method is described for the determination of vanadium in brines by atomic absorption spectroscopy with a nitrous oxide-acetylene flame. Sample pH is adjusted to 1.0 with concentrated hydrochloric acid and the vanadium is directly extracted with 5% cupferron in methyl isobutyl ketone (MIBK). The ketone layer is then aspirated into the flame and the recorded absorption values are plotted as a function of the concentration of the added metal. As little as 2.5 μg l −1 of vanadium can be detected under the conditions of the procedure. Tungsten and tin interfere when present in excess of 5 and 10 μg ml −1 , respectively. The concentrations of the two interfering ions normally found in brines are well below interference levels.

Analytica Chimica Acta↗
USGS1978

Determination of dissolved boron in fresh, estuarine, and geothermal waters by d.c. argon-plasma emission spectrometry

A d.c. argon-plasma emission spectrometer is used to determine dissolved boron in natural (fresh and estuarine) water samples. Concentrations ranged from 0.02 to 250 mg l -1 . The emission—concentration function is linear from 0.02 to 1000 mg l -1 . Achievement of a relative standard deviation of ⩽ 3% requires frequent restandardization to offset sensitivity changes. Dilution may be necessary to overcome high and variable electron density caused by differences in alkali-metal content and to avoid quenching of the plasma by high solute concentrations of sodium and other easily ionized elements. The proposed method was tested against a reference method and found to be more sensitive, equally or more precise and accurate, less subject to interferences, with a wider linear analytical range than the carmine method. Analyses of standard reference samples yielded results in all cases within one standard deviation of the means.

Analytica Chimica Acta↗
USGS1978

Flame and flameless atomic-absorption determination of tellurium in geological materials

The sample is digested with a solution of hydrobromic acid and bromine and the excess of bromine is expelled. After dilution of the solution to approximately 3 M in hydrobromic acid, ascorbic acid is added to reduce iron(III) before extraction of tellurium into methyl isobutyl ketone (MIBK). An oxidizing air-acetylene flame is used to determine tellurium in the 0.1–20 ppm range. For samples containing 4–200 ppb of tellurium, a carbon-rod atomizer is used after the MIBK extract has been washed with 0.5 M hydrobromic acid to remove the residual iron. The flame procedure is useful for rapid preliminary monitoring, and the flameless procedure can determine tellurium at very low concentrations.

Analytica Chimica Acta↗
USGS1981

Matrix modification with silver for the electrothermal atomization of arsenic and selenium

Silver as a matrix modifier is shown to improve the carbon-rod atomization of both arsenic and selenium for atomic absorption spectrometry. Compared to nickel, the efficiency of silver is greater for arsenic and about the same for selenium. Silver fulfils two functions in its reaction, namely stabilization during the ashing stage and enhancement of absorbance in the final atomization.

Analytica Chimica Acta↗
USGS1981

Application of capillary gas chromatography mass spectrometry/computer techniques to synoptic survey of organic material in bed sediment

A bed sediment sample taken from an area impacted by heavy industrial activity was analyzed for organic compounds of environmental significance. Extraction was effected on a Soxhlet apparatus using a freeze-dried sample. The Soxhlet extract was fractionated by silica gel micro-column adsorption chromatography. Separation and identification of the organic compounds was accomplished by capillary gas chromatography/mass spectrometry techniques. More than 50 compounds were identified; these include saturated hydrocarbons, olefins, aromatic hydrocarbons, alkylated polycyclic aromatic hydrocarbons, and oxygenated compounds such as aldehydes and ketones. The role of bed sediments as a source or sink for organic pollutants is discussed.

Analytica Chimica Acta↗