Chemical separation and inductively coupled plasma–atomic emission spectrometric determination of seventeen trace metals in thorium oxide matrix using a novel extractant – Cyanex-923

Comprehensive studies have been carried out on the extraction behaviour of thorium matrix vis-a-vis 17 trace metallic elements using a novel extractant viz. Cyanex-923. The near total extraction of thorium and quantitative separation of these metals has been established using inductively coupled argon plasma–atomic emission spectrometry (ICP–AES). The recovery of few representative elements has been confirmed by radio-active tracer studies. The studies carried out here have enabled determination of μg/l amounts of all analyte elements with a precision of better than 1% RSD with prior chemical separation from as low as 1 g thorium sample in just five chemical extractions.     

Determination of the REE and Y in silicate materials with ICP-AES

Summary An ICP-AES method for the determination of 12 rare earth elements and Y is described. Following a Na₂O₂-sinter dissolution of silicate materials the REE and Y were separated and concentrated using ion-exchange chromatography. The dissolution and separation procedures are described in detail. Numerous tests show good recovery of the REE. Spectral interferences were quantified and discussed. The precision is better than 5% (r.s.d.) for all measured REE, except Pr. The accuracy was tested by analyzing more than 30 international reference samples, the results are in good agreement with published data. In this paper we present our latest data from 6 new reference samples.

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Bestimmung der Seltenen Erden und Yttrium in silikatischem Material mit ICP-AES

     

Determination of rare-earth elements by high-performance liquid chromatography/inductively-coupled plasma/atomic emission spectrometry

Liquid chromatography coupled on-line to a sequential ICP/AES system is applied for the determination of 14 rare-earth elements (REEs) in samples with widely different concentrations of REEs and matrix elements. The REEs are separated on a cation-exchanger by applying an α- hydroxyisobutyric acid gradient. The determination limits were the same as those obtained by continuous nebulization of single-element standard solutions. The chromatographic separation precludes mutual spectral interferences between the REEs. The practical value of the method developed is demonstrated by the determination of REE impurities in Specpure rare-earth oxides, by its demonstrated potential to evaluate real spectral interferences, and by the analysis of geological samples (natural phosphates) with relatively low total REE contents. The detection limits of REEs in these natural phosphates ranged between 0.005 and 0.4 μg g^?1.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Precise determination of rare earth elements in rocks by neutron activation analysis

A pre-irradiation group separation method has been developed for the neutron activation analysis of rare earth elements (REE) and Ba in silicate rocks. REE and Ba were quantitatively separated from other elements by cation exchange column method. The chemical yield of each separation was monitored with Pr added to the sample powder before decomposition. The accuracy and precision were tested by repeated analyses of JB-1 and one analysis of BCR-1. In addition, it was found that REE distribution in a granitic rock powder was inhomogeneous and therefore special care must be taken for the sampling of granitic rock powders.     

Dimensional and elemental characterization of suspended particulate matter in natural waters: quantitative aspects in the integrated ultrafiltration, splitt-flow thin cell and inductively coupled plasma–atomic emission spectrometry approach

The present study investigates the quantitative aspects of an analytical procedure for the trace element characterization of suspended particulate matter (SPM) in natural waters. The procedure consists of the following steps: (1) ultrafiltration (UF) concentration; (2) splitt-flow thin (SPLITT) cell fractionation (SF) into different micronic–submicronic dimensional ranges; and (3) inductively coupled plasma–atomic emission spectrometry (ICP–AES) elemental determination on both the separated fractions and the bulk phase. One specific feature of the UF/SF steps is that they are gentle and thus preserve the complexity of the colloidal features of SPM samples as far as possible. The investigation was performed on a real SPM sample (Po River, Italy). Two SF modes were considered: the so called conventional SPLITT fractionation (CSF) mode and the full feed depletion SPLITT fractionation (FFDSF) mode. These differ in terms of resolution, time (both better in CSF as compared to FFDSF) and operating mode (FFDSF does not require a diluting carrier). Quantitative aspects of the UF step recovery and of the CSF and FFDSF modes were investigated in terms of total mass balance proving that only the FFDSF mode is currently satisfactory for quantitative purposes. Mass balance versus the following elements: Cd, Cr, Cu, Mn, Ni and Pb, was performed using ICP–AES over the 0.2–1.5 and 1.5–20 μm FFDSF SPM fractions, proving that the analytical procedure based on UF/FFDSF/ICP–AES is consistent and useful in the investigation of trace element distribution in different SPM dimensional ranges versus that of the bulk phase. The relevance of aggregation–solubility equilibria concerning colloids of SPM phase is emphasized and further improvement of the procedure is discussed.     

Extraction Chromatographic Separation of Ree and Y By P507 Containing Resin and Their Icp-Aes Determination In Chinese Soil Standard Samples

Abstract

This paper describes a procedure for the determination of REE and Y in soils by ICP-AES, the optimum conditions for separation of REE and Y from major elements have been investigated by precipitation with sodium hydroxide-triethanolamine and by extraction-chroroatography with P507 containing resin. Results are given for eight Chinese soil standard samples GSS-1 to GSS 8 and compared with recommended values.     

Determination of Hf, Sc and Y in geological samples together with the rare-earth elements

 A method is described for the determination of Hf, Sc and Y simultaneously with the REE in geological materials. An earlier method for REE separation from major elements was studied with the aim to apply it also to the determination of Hf, Sc and Y. Sample decomposition was carried out by melting with LiBO₂. The method involves separation and concentration stages, using the cation-exchange resin DOWEX AG 50W-X8. Matrix elements were eluted with 2 mol/l HCl, whereas 6 mol/l HNO₃ with oxalic acid and 8 mol/l HNO₃ were used to elute the elements to be determined. Some of the matrix elements could not be completely removed. This effect as well as the recovery rates of the determined elements were investigated. The measurements were performed by ICP-AES. Spectral interferences were also tested. Received: 8 November 1995/Revised: 12 March 1996/Accepted: 14 March 1996     

Separation and preconcentration of the rare-earth elements and yttrium from geological materials by ion-exchange and sequential acid elution

The abundance of rare-earth elements (REE) and yttrium in geological materials is generally low, and most samples contain elements that interfere in the determination of the REE and Y, so a separation and/or preconcentration step is often necessary. This is often achieved by ion-exchange chromatography with either nitric or hydrochloric acid. It is advantageous, however, to use both acids sequentially. The final solution thus obtained contains only the REE and Y, with minor amounts of Al, Ba, Ca, Sc, Sr and Ti. Elements that potentially interfere, such as Be, Co, Cr, Fe, Mn, Th, U, V and Zr, are virtually eliminated. Inductively-coupled argon plasma atomic-emission spectroscopy can then be used for a final precise and accurate measurement. The method can also be used with other instrumental methods of analysis.     

Simultaneous spectrophotometric determination of phosphate and silicate by using principal component artificial neural network

A very sensitive, simple and selective spectrophotometric method for simultaneous determination of phosphate and silicate based on formation of phospho- and silicomolybdenum blue complexes in the presence of ascorbic acid is described. Although the complexes of phosphate and silicate with reagent in the presence of ascorbic acid show a spectral overlap, they have been simultaneously determined by principal component artificial neural network (PC-ANN). The PC-ANN architectures were different for phosphate and silicate. The output of phosphate PC-ANN architecture was used as an input for silicate PC-ANN architecture. This modification improves the capability of silicate PC-ANN model for prediction of silicate concentrations. The linear range was 0.01-3.00 microg mL(-1) for phosphate and 0.01-5.00 microg mL(-1) for silicate. Interference effects of common anions and cations were studied and the proposed method was also applied satisfactorily to the determination of phosphate and silicate in detergents.     

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.     

A simple decomposition and chelating resin separation for the determination of heavy metals in silicates by atomic absorption spectrometry

A simple method for the determination of copper, nickel, zinc, and cadmium in silicate rock samples is reported. Silicates are decomposed with hydrofluoric acid and aqua regia in a sealed Teflon vessel. After centrifugation and addition of malonic acid, the supernatant liquid is passed through a small column of Chelex 100. The metals are eluted with 2 M nitric acid, and determined by atomic absorption spectrometry. The method is rapid, simple, and free from contamination. The results obtained for 14 standard reference rock samples (USGS, GSJ, and CSRM) agree with literature data; the recovery, reproducibility, and accuracy of the proposed method are satisfactory.     

On-line preconcentration of some rare earth elements in water samples using C18-cartridge modified with l-(2-pyridylazo) 2-naphtol (PAN) prior to simultaneous determination by inductively coupled plasma optical emission spectrometry (ICP–OES)

The on-line column preconcentration technique with inductively coupled plasma optical emission spectroscopy (ICP–OES) has been developed using a cartridge filled with octadecyl silica modified by l-(2-pyridylazo) 2-naphtol (PAN). The aim of this method was to determine some rare earth elements (REEs) (Ce, Dy, La, Sm, and Y) and uranium in water samples. Sample solutions were passed through the C₁₈-modified column. The adsorbed cations were subsequently eluted from the column and transferred into the plasma with nitric acid solution for simultaneous determination of them. Sample pH, amount of PAN as a complexing agent, sampling and eluting flowrates and concentration of the eluent were optimized. Detection limits based on three times of standard deviations of blank by 10 replicates were in the range of 11 ng l⁻¹ for Dy to 69 ng l⁻¹ for U. Sample throughput was 10 samples h⁻¹. The proposed method was applied to determine REEs in natural water samples. Recoveries of the REEs from natural water samples were between 95 and 106% with percent relative standard deviation (%R.S.D.) of 1.0–7.9%.     

Rapid spectrophotometric method (aqueous and extractive) for the determination of titanium in silicate rocks

A sensitive and highly selective aqueous as well as extractive spectrophotometric method has been developed for the determination of titanium(IV) using 2,3-dihydroxynaphthalene (H(2)ND) as a chromogenic agent. The reagent (H(2)ND) forms a 1:3 (TiOH(3+):ligand) complex at pH 4-9. The molar absorptivity and Sandell's sensitivity are 3.2 x 10(4) l . mol(-1)mol . cm(-1) and 0.001 microg/cm(2), respectively at lambda(max) 375 nm. The method has been found highly selective for Ti(IV) determination in rock samples. Solvent extraction of Ti(IV) in ethylacetate greatly improves the detection limit of the method. The method has been successfully applied to diverse silicate rock samples and results obtained are favourably comparable with those obtained from the tiron method. The reagent (H(2)ND) used in the present investigation is a much better variant than tiron for titanium(IV) determination in silicate rock samples in terms of sensitivity, selectivity, operational simplicity and economy.     

Rapid and sensitive determination of total vanadium inairborne particulates by an extraction—spectrometric method with N-benzoyl-N-phenylhydroxylamine

A method is described for the rapid and sensitive determination of 0.06 μg of total vanadium in airborne particulates collected in the filter bag of an air-cleaner or on a membrane filter attached to an air sampler. The method is based on decomposition of organic matter in the sample and membrane filter by successive use of nitric, sulfuric and perchloric acids, and decomposition of the suspended silicate residue in a sulfuric—hydrofluoric acid mixture, followed by the extraction of a vanadium—N-benzoyl-N-phenylhydroxylamine complex into chloroform for spectrophotometric measurement. A comparison with the troublesome fusion method for the residue is included.     

Kinetic spectrophotometric determination of iron oxidation states in geological materials

Summary A kinetic spectrophotometric approach is applied to the determination of iron oxidation states in geological materials. Silicate rock samples were sealed in a Teflon vial under argon atmosphere and were decomposed with a mixture of hydrofluoric acid and sulphuric acid by the microwave digestion technique. The absorbance of iron(III)-Tiron complex was followed at 560 nm and the absorbance/time relation was analyzed by non-linear least squares fitting. The FeO and Fe₂O₃ determinations in silicate rocks by the proposed kinetic method agree with those done by the static o-phenanthroline method. The analytical results for standard igneous rock samples are compared with published data.     

Preconcentration of rare earths in geological materials with ascorbic acid for their neutron activation analysis

The potential use of ascorbic acid as a complexing reagent in the separation and preconcentration of rare earth elements (REE) in geological materials in a suitable solid matrix has been demonstrated. Traces of REE from some USGS standard rock samples, viz., GSP-1, G-2, AGV-1 and PCC-1, have been separated after acid dissolution in two ways: (1) by ion exchange chromatography on Dowex 50×8 column and Na-ascorbate as eluent and (2) by direct complexation with ascorbic acid under specific experimental conditions. The separated REE were coprecipitated with the non isotopic diluent, calcium fluoride, before neutron activation analysis. Radiometric determinations showed that the overall recovery of REE in both cases was practically quantitative.     

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 the four major surfactant classes in cleaning products by reversed-phase liquid chromatography using serially connected UV and evaporative light-scattering detection

A method for the simultaneous determination of the most frequently used surfactant families –linear alkyl benzenesulphonates (LAS), alkyl ether sulphates (AES), fatty alcohol ethoxylates (FAE) and oleins (soaps, fatty acid salts) – in cleaning products, has been developed. The common reversed phase octyl (C8), pentafluorophenyl and biphenyl columns were not capable of separating the anionic LAS and AES classes; however, since only LAS absorbs in the UV, these two classes were independently quantified using a C8 column and serially connected UV and ELSD detection. The best compromise to resolve the four surfactant classes and the oligomers within the classes was achieved with a C8 column and an ACN/water gradient. To enhance retention of the anionic surfactants, ammonium acetate, as an ion-pairing agent compatible with ELSD detection, was used. Also, to shift the olein peaks with respect to that of the FAE oligomers, acetic acid was used. In the optimized method, modulation of the mobile phase, using ammonium acetate during elution of LAS and AES, and acetic acid after elution of LAS and AES, was provided. Quantitation of the overlapped LAS and AES classes was achieved by using the UV detector to quantitate LAS and the ELSD to determine AES by difference. Accuracy in the determination of AES was achieved by using a quadratic model, and by correcting the predicted AES concentration according to the LAS concentration previously established using the UV chromatogram. Another approach also leading to accurate predictions of the AES concentration was to increase the AES concentrations in the samples by adding a standard solution. In the samples reinforced with AES, correction of the predicted AES concentration was not required. FAE and olein were quantified using also quadratic calibration.