Determination of beryllium in Pt-Be alloy by atomic-absorption spectrometry after ion-exchange separation

Traces of beryllium in platinum have been determined by graphite-furnace atomic-absorption spectrometry, the graphite furnace being coated with lanthanum or titanium carbide. The coating improves the reproducibility, sensitivity and detection limit. Platinum interferes in the beryllium determination, and an ion-exchange separation is used in the determination of beryllium in Pt-Be alloy.     

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 arsenic in geological materials by electrothermal atomic-absorption spectrometry after hydride generation

Rock and soil samples are decomposed with HClO₄—HNO₃; after further treatment, arsine is generated and absorbed in a dilute silver nitrate solution. Aliquots of this solution are injected into a carbon rod atomizer. Down to 1 ppm As in samples can be determined and there are no significant interferences, even from chromium in soils. Good results were obtained for geochemical reference samples.     

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.     

Determination of antimony in ores and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A continuous hydride-generation atomic-absorption spectrometric method for determining approximately 0.02 mug/g or more of antimony in ores, concentrates, rocks, soils and sediments is described. The method involves the reduction of antimony(V) to antimony(III) by heating with hypophosphorous acid in a 4.5M hydrochloric acid-tartaric acid medium and its separation by filtration, if necessary, from any elemental arsenic, selenium and tellurium produced during the reduction step. Antimony is subsequently separated from iron, lead, zinc, tin and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 4.5M hydrochloric acid/0.2M sulphuric acid in the presence of ascorbic acid as a reluctant for iron(III). After the extract is washed, if necessary, with 10% hydrochloric acid-2% thiourea solution to remove co-extracted copper, followed by 4.5M hydrochloric acid to remove residual iron and other elements, antimony(III) in the extract is oxidized to antimony(V) with bromine solution in carbon tetrachloride and stripped into dilute sulphuric acid containing tartaric acid. Following the removal of bromine by evaporation of the solution, antimony(V) is reduced to antimony(III) with potassium iodide in approximately 3M hydrochloric acid and finally determined by hydride-generation atomic-absorption spectrometry at 217.8 nm with sodium borohydride as reluctant. Interference from platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide during the iodide reduction step. Interference from gold is avoided by using a 3M hydrochloric acid medium for the hydride-generation step. Under these conditions gold forms a stable iodide complex.     

Automated wet ashing and multi-metal determination in biological materials by atomic-absorption spectrometry

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Automated wet ashing and multi-metal determination in biological materials by atomic-absorption spectrometry

     

Determination of trace and ultra-trace amounts of noble metals in geological and related materials by graphite-furnace atomic-absorption spectrometry after separation by ion-exchange or co-precipitation with tellurium

Two methods for determining mug/g and ng/g levels of the noble metals, except for osmium, in ores, concentrates, mattes, and silicate and iron-formation rocks are described. After sample decomposition with hydrofluoric acid and aqua regia, followed by fusion of any insoluble residue with sodium peroxide, the noble metals are separated from the matrix elements by either cation-exchange or co-precipitation with tellurium. The resulting eluate, or the solution obtained after dissolution of the tellurium precipitate, is evaporated to dryness and the noble metals are ultimately determined in a 1M hydrochloric acid medium by graphite-furnace atomic-absorption spectrometry. The ion-exchange method is recommended for the determination of mug/g levels of gold, silver and platinum-group elements, whilst the tellurium co-precipitation method is recommended for ng/g levels of platinum-group elements. The latter method is not recommended for the determination of ng/g levels of silver and gold in rocks, because of interference from tellurium during atomization in the furnace. Results obtained by these methods for 15 international reference samples, including four Canadian iron-formation rocks, are compared with other published data.     

Atomic-absorption determination of beryllium in geological materials by use of electrothermal atomization

A method is described for the atomic-absorption determination of beryllium in geological materials, that utilizes electrothermal atomization after a separation by solvent extraction. Samples are decomposed with hydrofluoric acid and nitric acid in Teflon-lined pressure decomposition vessels. Beryllium is isolated by its extraction as beryllium acetylacetonate at pH 8 into xylene and back-extraction in 3M hydrochloric acid. The method has been successfully applied to the determination of beryllium in 14 U.S. Geological Survey standard rocks. Four subsamples from four bottles of each standard sample were analysed in random order. The mean beryllium contents (ppm) are: AGV-1, 1.98; PCC-1, 0.024; MAG-1, 2.84; BHVO-1, 0.90; DTS-1, 0.026; SCo-1, 1.74; SDC-1, 2.52; BCR-1, 1.44; GSP-1, 1.22; SGR-1, 0.86; QLO-1, 1.83; RGM-1, 2.21; STM-1, 8.75; G-2, 2.29. An analysis of variance shows that all the samples may be considered homogeneous at F(0.95) except AGV-1 and DTS-1 which may be considered homogeneous at F(0.99).     

Direct determination of beryllium, copper and zinc in AlU matrices by electrothermal atomization atomic-absorption spectrometry

An atomic-absorption spectrometric method with electrothermal mode of atomization has been developed for the direct determination of Be, Cu and Zn in AlU (3:1) matrix samples without prior chemical separation of the major matrix. The studies carried out include the effect of the matrix on the analyte absorbance, optimization of sample aliquot and other experimental parameters, and analysis of a number of synthetic samples. Nanogram amounts of the analytes can be determined with a solution aliquot of 5 microlitres containing 25 micrograms of the sample with a precision of 6% or better. The analytical range obtained for these analytes is Be: 2-20 mug/l., Cu: 20-200mug/l. and Zn: 1-40mug/ml in the AlU matrix. The analysis of synthetic samples has shown good agreement with their added contents.     

Americium and samarium determination in aqueous solutions after separation by cation-exchange

The concentration of trivalent americium and samarium in aqueous samples has been determined by means of alpha-radiometry and UV–Vis photometry, respectively, after chemical separation and pre-concentration of the elements by cation-exchange using Chelex-100 resin. Method calibration was performed using americium (²⁴¹Am) and samarium standard solutions and resulted in a high chemical recovery for cation-exchange. Regarding, the effect of physicochemical parameters (e.g. pH, salinity, competitive cations and colloidal species) on the separation recovery of the trivalent elements from aqueous solutions by cation-exchange has also been investigated. The investigation was performed to evaluate the applicability of cation-exchange as separation and pre-concentration method prior to the quantitative analysis of trivalent f-elements in water samples, and has shown that the method could be successfully applied to waters with relatively low dissolved solid content.     

Determination of arsenic in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separation by xanthate extraction

A method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates and related materials is described. After sample decomposition arsenic(V) is reduced to arsenic(III) with titanium(III) and separated from iron, lead, zinc, copper, uranium, tin, antimony, bismuth and other elements by cyclohexane extraction of its xanthate complex from approximately 8-10M hydrochloric acid. After washing with 10M hydrochloric acid-2% thiourea solution to remove residual iron and co-extracted copper, followed by water to remove chloride, arsenic is stripped from the extract with 16M nitric acid and ultimately determined in a 2% nitric acid medium by graphite-furnace atomic-absorption spectrometry, at 193.7 nm, in the presence of thiourea (which eliminates interference from sulphate) and palladium as matrix modifiers. Small amounts of gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, do not interfere.     

Determination of arsenic in ores, concentrates and related materials by continuous hydride-generation atomic-absorption spectrometry after separation by xanthate extraction

A recent graphite-furnace atomic-absorption method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates, rocks, soils and sediments, after separation from matrix elements by cyclohexane extraction of arsenic(III) xanthate from approximately 8-10M hydrochloric acid, has been modified to include an alternative hydride-generation atomic-absorption finish. After the extract has been washed with 10M hydrochloric acid-2% thiourea solution to remove co-extracted copper and residual iron, arsenic(III) in the extract is oxidized to arsenic(V) with bromine solution in carbon tetrachloride and stripped into water. Following the removal of bromine by evaporation of the solution, arsenic is reduced to arsenic(III) with potassium iodide in approximately 4M hydrochloric acid and ultimately determined to hydride-generation atomic-absorption spectrometry at 193.7 nm, with sodium borohydride as reductant. Interference from gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, is eliminated by complexing them with thiosemicarbazide before the iodide reduction step. The detection limits for ores and related materials is approximately 0.1 mug of arsenic per g. Results obtained by this method are compared with those obtained previously by the graphite-furnace method.     

The determination of cadmium in geological materials by flameless atomic absorption spectrometry

The use of graphite-furnace atomic absorption spectrometry for the determination of cadmium in rocks and sediments by direct atomization from the solid state is described. At the 10–1000 p.p.b. level, the relative standard deviation is ± 10–20 %. Samples were ground to 100 mesh and, if necessary, 325 mesh before analysis. Two resonance lines were employed: 228.8 nm for less than 5 p.p.m. cadmium and 326.1 nm for levels above 5 p.p.m. Instrumental parameters were optimized to produce maximum peak heights. Results are given for a series of standard rocks and for stream sediment samples.     

Matrix modification for determination of selenium in geological samples by graphite-furnace atomic-absorption spectrometry after preseparation with thiol cotton fibre

A graphite-furnace atomic-absorption method has been developed for the determination of selenium in geological samples at or below the mug g level after decomposition of the sample with a mixture of perchloric, hydrofluoric and nitric acids and separation of selenium from the sample matrix with thiol cotton fibre. A few micrograms of palladium are added as a matrix modifier for the atomic-absorption determination. In the presence of palladium the charring temperature for selenium can be raised to 1100 degrees , and the signal enhancement is greater than with other matrix modifiers reported in the literature.     

The determination of vanadium in geological materials by activation analysis with pre-irradiation separation

Vanadium is determined in silicate rocks by neutron activation after dissolution of the samples with HF/HNO₃ and separation by solvent extraction. The chemical yield of the pre-irradiation separation is determined by means of ⁴⁸V tracer. Results for 15 U.S. Geological Survey standard rocks are presented and discussed in relation to literature data. The method is especially useful at vanadium concentrations below 10 ppm, where purely instrumental neutron activation as well as other techniques commonly used for vanadium determinations in rocks, have inadequate sensitivity.     

Determination of rare earth elements in geological samples by inductively-coupled plasma atomic emission spectrometry after oxalate coprecipitation and cation-exchange column separation

A method for separation and determination of traces of 14 rare earth elements (REEs) in geological samples is described. Determination by inductively-coupled plasma atomic emission spectrometry follows oxalate coprecipitation of the REEs with calcium as carrier and cation- exchange column separation in nitric acid. The combination of the two separation techniques improved the low recoveries found for Sm, Eu, and Gd when only ion-exchange was used, especially for iron- and aluminum-rich samples. The method was applied to the analysis of geological standard materials NBS SRM 688 (basalt), NBS SRM 278 (obsidian), GSJ JB-1 (basalt), GSJ JA- 2 (andesite), and CCRMP SY-3 (syenite). The results were evaluated on the basis of chondrite- normalized rare earth element distribution patterns.     

The determination of selenium by atomic-absorption spectrometry: A review

A comprehensive review is given of the determination of selenium by the various atomic-absorption spectrometry methods that have been developed, covering the use of various flame and electrothermal ionization methods, hydride techniques, preconcentration and separation, and giving an appraisal of the results.     

Ion-exchange separation and spectrophotometric determination of boron in geological materials

Various dissolution techniques were investigated for total rocks and minerals and the best approach found was alkaline fusion. Boron in silicates was rendered chemically reactive by fusion with potassium carbonate, the fusion cake was extracted with water and borate was isolated by Amberlite XE-243 boron-selective resin. The Amberlite XE-243 resin was utilized to separate microgram amounts of boron from natural waters (fresh to hypersaline) and salt cores. Borate was eluted with 2 M hydrochloric acid and determined by spectrophotometry of the carminic acid complex at 620 nm in either 94% sulphuric acid or sulphuric/acetic acid (20:80) medium, or preferably, as the azomethine-H ion-association complex at pH 5.2 (415 nm), depending on the sensitivity required. Good precision and accuracy were obtained on several international standard rocks with an average relative standard deviation of 1.37%.     

Determination of selenium in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separation by extraction of the 4-nitro-o-phenylenediamine complex

A method for determining approximately 0.01 mug/g or more of selenium in ores, concentrates, rocks, soils, sediments and related materials is described. After sample decomposition selenium is reduced to selenium(IV) by heating in 4M hydrochloric acid and separated from the matrix elements by toluene extraction of its 5-nitropiazselenol complex from approximately 4.2M hydrochloric acid. After the extract has been washed with 2% nitric acid to remove residual iron, copper and chloride, the selenium in the extract is oxidized to selenium(VI) with 20% bromine solution in cyclohexane and stripped into water. This solution is evaporated to dryness in the presence of nickel, and selenium is ultimately determined in a 2% v/v nitric acid medium by graphite-furnace atomic-absorption spectrometry at 196.0 nm with the nickel functioning as matrix modifier. Common ions, including large amounts of iron, copper and lead, do not interfere. More than 1 mg of vanadium(V) and 0.25 mg each of platinum(IV), palladium(II), and gold(III) causes high results for selenium, and more than 1 mg of tungsten(VI) and 2 mg of molybdenum(VI) causes low results. Interference from chromium(VI) is eliminated by reducing it to chromium(III) with hydroxylamine hydrochloride before the formation of the selenium complex.     

The determination of trace amounts of tin by flow-injection hydride generation atomic-absorption spectrometry with on-line ion-exchange separation and preconcentration

A hydride generation atomic-absorption spectrometric (AAS) method with flow-injection (FI), aimed at developing a practical routine assay for the determination of tin in food digests, is described. In order to modify the sample matrix and to achieve optimized and reproducible conditions for the hydride generation reaction, the analyte is initially converted into its chlorostannate-complex thereby allowing it to be separated and preconcentrated on-line on an incorporated micro-column packed with a strongly basic anion exchanger and subsequently to be eluted by diluted nitric acid under strictly controlled conditions. Optimum acidic conditions for the FI hydride generation AAS system was found to be 0.01-0.05M nitric acid. At a consumption of 2.7-ml sample volume, aspirated by time-based injection, the procedure resulted in an enrichment factor of 3.5 and yielded a detection limit of 0.08 microg/l. (3sigma) at a sampling frequency of 72/hr. The precision was 2.5% rsd at the 10 microg/l. level. Potential interferents, such as Ni(II), Co(II), Zn(II) and Fe(III) could, at a Sn level of 10 microg/l., be tolerated at an excess of 1000 times without impairing the assay, while a 100-1000-fold excess of Cu(II) decreased the signal by 10-15%. Recoveries in the range 94-102% were obtained for canned food sample digests spiked with 10 microg/l. Sn.