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At least 37 records · Page 2Linked to original sources
USGS1983

Determination of chloride in geological samples by ion chromatography

Samples of silicate rocks are prepared by sodium carbonate fusion and then treated by ion chromatography. The method was tested for geological standards with chloride concentration between 0.003 and 3%. Observed chloride concentrations comparedd favorably with literature values. The relative standard deviation and detection limit for the method were 8% and 7 ppm, respectively. Up to 30 determination per 24-hour period were possible. ?? 1983.

Analytica Chimica Acta↗
USGS1984

Determination of indium in geological materials by electrothermal-atomization atomic absorption spectrometry with a tungsten-impregnated graphite furance

The sample is fused with lithium metaborate and the melt is dissolved in 15% (v/v) hydrobromic acid. Iron(III) is reduced with ascorbic acid to avoid its coextraction with indium as the bromide into methyl isobutyl ketone. Impregnation of the graphite furnace with sodium tungstate, and the presence of lithium metaborate and ascorbic acid in the reaction medium improve the sensitivity and precision. The limits of determination are 0.025–16 mg kg −1 indium in the sample. For 22 geological reference samples containing more than 0.1 mg kg −1 indium, relative standard deviations ranged from 3.0 to 8.5% (average 5.7%). Recoveries of indium added to various samples ranged from 96.7 to 105.6% (average 100.2%).

Analytica Chimica Acta↗
USGS1968

Nuclear magnetic resonance studies of the phosphorus(v) pesticides: A rapid determination of the isomer ratio of systox

The integration circuit of the Varian A-60 nuclear magnetic resonance spectrometer is used in conjunction with vapor phase chromatography, to develop a rapid analysis technique for the determination of isomer ratios in technical Systox-Sulfotepp mixtures. The complete analysis requires less than 0.1 g of sample and only 15 min. The isomer ratio in the sample may be determined to an accuracy of ±1.5% and the undamaged sample may be recovered.

Analytica Chimica Acta↗
USGS1970

Radiochemical separation of gold by amalgam exchange

A rapid and simple method for the radiochemical separation of gold after neutron activation. The technique is based on treatment with a dilute indium-gold amalgam, both chemical reduction and isotopic exchange being involved. The counting efficiency for 198 Au in small volumes of the amalgam is good. Few interferences occur and the method is applicable to clays, rocks, salts and metals. The possibility of determining silver, platinum and palladium by a similar method is mentioned.

Analytica Chimica Acta↗
USGS1972

Determination of total iodine and iodate in sea water and in various evaporites

Iodine in sea water and evaporites is determined spectrophotometrically as the starch-iodine complex without prior separation or concentration of the iodine. In slightly alkaline solution, iodide is first oxidized to iodate with permanganate. Oxidized states of manganese are destroyed with iron(II) in phosphate medium without affecting the iodate. After acidification, iodide is added to react with the iodate in the presence of starch. The iodate content is determined by the same procedure, but without the addition of permanganate. As little as 0.1μg of iodine is determinable in the presence of 500 mg of chloride and 5 mg of bromide. The total iodine concentration in seven samples of sea water was found to vary from 50 ±3 to 84 ±6 μg l -1 with 50–100% present as the iodate.

Analytica Chimica Acta↗
USGS1969

The determination of nanogram amounts of Chromium in urine by x-ray fluorescence spectroscopy

Nanogram amounts of chromium can be extracted as oxinate into chloform. By treatment of the chloroform layer 3 M hydrochloric acid, oxinates of other elements and excess of reagent are removed, leaving a chloroform solution of the chromium chelate only. This solution is concentrated and transferred to the top of a small brass rod acting as sample holder. The intensity of the X-ray fluorescence of the Cr Kα line is measured with curved crystal optics. Chromium amounts greater than 5 ng can be detected. The application of the procedure to the analysis of the chromium content of urine is demonstrated.

Analytica Chimica Acta↗
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↗
USGS1968

Simultaneous determination of tantalum and hafnium in silicates by neutron activation analysis

A neutron activation procedure suitable for the routine determination of tantalum and hafnium in silicates is described. The irradiated sample is fused with sodium peroxide and leached, and the insoluble hydroxides are dissolved in dilute hydrofluoric acid-hydrochloric acid. After LaF 3 and AgCl scavenges, tantalum and hafnium are separated by anion exchange. Tantalum is obtained radiochemically pure; 233 Pa and 95 Zr contaminants in the hafnium fraction are resolved by γ-ray spectrometry. The chemical yield of the procedure is detemined after counting by re-irradiation. Values for the 8 U.S. Geological Survey standard rocks are reported.

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↗