Determination of lanthanides and yttrium in rocks and minerals by atomic-absorption and flame-emission spectrometry

The sensitivity of atomic-absorption and flame-emission determination of lanthanides and yttrium is improved by a factor of 2-5 when an absolute ethanol solution of the perchlorate of the metal (instead of an aqueous solution) is aspirated into a nitrous oxide-acetylene flame. Based on this, a method has been developed for accurate determination of small amounts of certain rare earths and yttrium. Lanthanum (1%) is used as a spectroscopic buffer to eliminate interferences and to enhance the sensitivities in certain determinations. Where the use of lanthanum is not practicable because of interferences (such as in the determination of praseodymium and samarium by flame emission), sodium (2000 ppm) is used as the spectroscopic buffer. Studies with synthetic solutions indicate that yttrium and most lanthanides can be directly determined in minerals without any chemical separation. With rock samples it is necessary to preconcentrate the traces of the rare earths by fluoride or oxalate precipitation with calcium as the carrier, followed by removal of calcium by hydroxide precipitation using mg amounts of iron as the carrier. The method developed has been applied to the determination of certain lanthanides and yttrium in a variety of rocks, including the Canadian reference rocks, syenites SY-1, SY-2 and SY-3, and some minerals such as britholite, cenosite, chevkinite, allanite, apatite and sphene.     

Determination of the rare earths, yttrium and scandium in silicate rocks and four new geological reference materials by electrothermal atomization from graphite and tantalum surfaces

An improved graphite furnace atomic-absorption method has been developed for the determination of Sc, Y and the rare-earth elements in silicate rocks and related materials. The method, which involves the separation of the lanthanides by ion-exchange followed by their determination by electrothermal atomization, with use of an automatic sampling device, is more rapid than a previous method based on separation by co-precipitation with calcium oxalate and hydrous ferric oxide followed by normal injection of the solution into the furnace. Greater sensitivity (~ 10-40-fold) for La, Ce, Pr, Gd, Tb and Lu is also achieved by using a tantalum foil-lined graphite furnace instead of a pyrolytically-coated furnace. Results obtained for five international reference rock samples, NIM-G, SCo-1, MAG-1, SDC-1 and BHVO-1, are compared with those obtained previously by the oxalate-hydrous oxide co-precipitation method and with other published values. Results are given for four new Canadian iron-formation reference materials, FeR-1 to FeR-4.     

Determination of yttrium and rare-earth elements in rocks by graphite-furnace atomic-absorption spectrometry

With use of synthetic solutions and several international standard reference materials a method has been developed for determining traces of Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in rocks by electrothermal atomization in a pyrolytically-coated graphite furnace. Depending on the element, the sensitivity is of the order of 10(-9)-10(-12) g at 2500 degrees . To avoid matrix interferences the lanthanides are separated from the common elements by co-precipitation with calcium and iron as carriers. The data for Canadian reference rock SY-2 (syenite), U.S.G.S. reference rocks W-2 (diabase), DNC-1 (diabase) and BIR-1 (basalt), and South African reference rock NIM-18/69 (carbonatite) obtained by graphite-furnace atomization are compared with the values obtained by flame atomic-absorption. The results are in good agreement with literature values.     

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.     

Determination of rare-earth elements and yttrium in silicate rocks by sequential inductively-coupled plasma emission spectrometry

An ICP—AES method for determination of rare-earth elements (REE) and yttrium at trace levels in silicate rocks is described. The method involves decomposition of the rock sample by heating with a mixture of hydrofluoric and perchloric acid, followed by precipitation of the REE and Y as oxalates, with calcium as carrier. The oxalate precipitate is ignited to the oxide, which is then dissolved in dilute nitric acid and the solution is used for ICP—AES measurements, with use of pure REE solutions as calibration standards. The method has been applied to the determination of REE in a number of standard reference materials and the results have been compared with the reported values. Three other silicate rock samples have also been analysed for REE and Y by this method.     

Determination of chromium in steel by atomic-absorption spectrometry with an air-acetylene flame

A new atomic-absorption procedure is described for the determination of chromium, at levels up to 1%, in steel. The method involves the use of the air-acetylene flame and incorporates 8-hydroxyquinoline as a releasing agent to suppress metallic interferences. Chemical operations have been reduced to a minimum in order to provide a simple, rapid and accurate procedure.     

Determination of indium in aluminium alloys by flame atomic-absorption spectroscopy and flame atomic-emission spectrometry

The use of flame atomic-absorption and atomic-emission spectrometry for the determination of indium in aluminium alloys is described. Two types of flame are used: air—acetylene and nitrous oxide—acetylene. The efrect of other ions, especially aluminium, has been studied, and the use of lanthanum as a releasing agent is proposed for both techniques, the amount used depending on the amount of aluminium present.     

Determination of aluminium, scandium and rare earth elements by emission flame spectrometry

Summary Emission spectrometry in nitrous oxide-acetylene flames in combination with a highly resolving double monochromator and sensitive detecting system enables simple, sensitive and selective determinations of aluminium, scandium and all rare earth elements with exception of cerium in complicated matrices. Calibration plots are linear for a large concentration interval ( 100 g·ml^–1), detection limits are in ng · ml^–1 level and RSD does not exceed 3% on the optimal concentration level of the particular element. The determination of Al, Sc, Eu and Yb showed particular advantages as to methods using ICP-spectrometry.

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Bestimmung von Aluminium, Scandium und Seltenen Erden durch Emissions-Flammenspektrometrie

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Determination of scandium in sea-water by atomic-absorption spectroscopy

A method for the determination of scandium in sea-water at the sub-microgram level has been developed. Scandium is coprecipitated with iron(III) hydroxide at pH 8-9, and then separated from the iron by ion-exchange. The final concentration is achieved by extracting the scandium into a solution of oxine in butanol. A nitrous oxide-acetylene flame is used for the determination by atomic-absorption spectroscopy. Recoveries of 99-100% are obtained. The storage of the solutions before analysis has been investigated by radiometric techniques with (46)Sc. The scandium concentration in surface waters of the South China Sea was found to be 0.01 +/- 0.005 microg/l .     

Determination of scandium and lanthanum in silicate rocks and coal with a simplified separation procedure and atomic absorption spectrometry

Simplified procedures for the quantitative separation and enrichment of scandium and lanthanum in igneous rocks are described. Co-precipitation with calcium oxalate is followed by co-precipitation with hydrated iron(III) oxide. Electrothermal and flame atomic absorption spectrometry are applied. The procedures are verified with synthetic sample solutions and the eighteen international reference samples of rocks and coal compare favourably with previously reported data and with data obtained by emission spectrography.     

Determination of gallium in geological materials by graphite-furnace atomic-absorption spectrometry

A graphite-furnace atomic-absorption spectrometric method has been worked out for the determination of traces of gallium in silicate rocks and minerals. The samples are opened up by fusion with a lithium carbonate-boric acid mixture and the cake is taken up with 2M nitric acid. Addition of nickel nitrate to this solution elminates the severe matrix effects allowing gallium solutions in nitric acid to be used as calibration standards. No separations are necessary. Results are quoted for 14 standard silicate rocks and two minerals. The RSD is 2.9%, and the sensitivity is 27 pg of gallium for 1% absorption.     

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L^–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L^–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g^–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g^–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g^–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.     

Determination of rare-earth elements,yttrium and scandium in manganese nodules by inductively-coupled argon-plastma emission spectrometry

A sequential-scanning, inductively-coupled argon plasma emission spectrometer is used for the determination of the rare-earth elements, plus yttrium and scandium, in manganese nodules. Wavelength selection is optimized to minimize spectral interferences from manganese nodule components. Samples are decomposed with mixed acids in a sealed polycarbonate vessel, and elements are quantified without further treatment. Results for U.S. Geological Survey manganese nodule standards A-1 and P-1 had average relative standard deviations of 6.8% and 8.1%, respectively, and results were in good agreement with those obtained by other methods.     

Determination of tungsten in rocks and minerals by chelate extraction and atomic-absorption spectrometry

An atomic-absorption method for determination of tungsten in rocks and minerals is proposed. The method involves sample decomposition by acid digestion or by pyrosulphate fusion, followed by chelate extraction of tungsten by N-benzoylphenylhydroxylamine in toluene. Atomic-absorption measurements are made on the organic phase aspirated into a nitrous oxide-acetylene flame. Quantitative extraction with efficient separation from other elements is achieved in a single extraction from strong acid media. The method is rapid and reliable in terms of precision and accuracy and is applicable to rocks and minerals containing tungsten in the range from 100 ppm to 15%.     

Determination of yttrium, scandium and other rare earth elements in uranium-rich geological materials by ICP-AES

A rapid method is described for the determination of yttrium, scandium, and other rare earth elements (REEs) in uranium-rich geological samples (containing more than 0.1% U) and in pitch blende type of samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) after separation of uranium by selective precipitation of the analytes as hydroxides using H(2)O(2)/NaOH in the presence of iron as carrier. Uranium goes into solution as soluble peruranate complex. The precipitated rare earth hydroxides (including Y and Sc) are filtered and dissolved in hydrochloric acid prior to their aspiration into plasma for their individual estimation after selecting interference free REE emission lines. The method has also been applied to some international reference standards like SY-2 and SY-3 (by doping a known amount of uranium) along with one in-house pitch blende sample and the REE values were found to be in agreement with the most usable values, offering an R.S.D. of 1-8.8% for all the REEs', Y and Sc. The method compared well, with the well- established cation exchange separation procedure.     

Determination of barium in sulphide ores, concentrates and other geological samples by flame atomic-absorption spectrometry

A rapid, precise and selective analytical method has been developed for estimation of barium in geological samples by flame atomic-absorption spectrometry. The method consists of precipitation of barium sulphate with ammonium sulphate, followed by dissolution of the sulphates in EDTA at pH 10. The barium in this solution is measured by AAS with a nitrous oxide-acetylene flame. Appreciable amounts of lead, calcium and strontium can be tolerated in the method, which has been applied for estimation of barium in sulphide ores and concentrates of lead, zinc and copper, and is feasible for estimation of barium from 20.0 ppm to the per cent level in such geological samples.     

Determination of trace quantities of scandium in silicate rocks by a combined ion exchange-spectrophotometric method

A spectrophotometric determination of scandium in silicate rocks has been developed with arsenazo as the color reagent. After the decomposition of samples with a hydrofluoric-perchloric acid mixture, traces of scandium are separated from interferences by cation- and anion-exchange in acid sulfate media and anion exchange in hydrochloric acid solution. The successive 3 steps, with an intermediate concentration step, yield scandium in a sufficiently pure state for spectrophotometric determination.     

Determination of trace amounts of barium in silicate rocks and minerals by ion-exchange Chromatography and atomic-absorption spectrophotometry

Trace amounts of barium are determined in the standard silicate rocks and minerals, W-1, AGV-1, BCR-1, DTS-1, GSP-1, G-2 of the U.S. Geological Survey and BR, GA, GH, GR, UB-N, DR-N, BX-N, DT-N, VS-N, FK-N, GS-N of the Centre de Recherche Petrographique et Geochimique de Nancy and the Association Nationale de la Recherche Technique. After an ion-exchange separation, the analyses are carried out by atomic-absorption spectrophotometry. The separation is performed to eliminate interferences due to matrix effects.     

Determination of ten rare-earth elements and yttrium in silicate rocks by ICP-AES without separation and preconcentration

Lanthanum, cerium, neodymium, samarium, europium, gadolinium, dysprosium, erbium, ytterbium, lutetium and yttrium have been determined in 8 international rock standards by inductively coupled plasma atomic emission spectrometry (ICP-AES) without prior ion-exchange separation and preconcentration. The results for La, Ce, Nd, Eu, Dy, Yb and Y were in good agreement with the reported values, whereas those for Sm, Gd, Er and Lu were less accurate. However, the results for Sm, Gd, Er and Lu can also be used for studies of petrogenesis.