The utilization of modified BCR three-step sequential extraction procedure for the fractionation of Cd, Cr, Cu, Ni, Pb and Zn in soil reference materials of different origins

A modified three-step sequential extraction procedure for the fractionation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR) has been applied to the Slovak reference materials of soils (soil orthic luvisols, soil rendzina and soil eutric cambisol), which represent pedologically different types of soils in Slovakia. Analyses were carried out by flame or electrothermal atomic absorption spectrometry (FAAS or ETAAS). The fractions extracted were: exchangeable (extraction step 1), reducible-iron/manganese oxides (extraction step 2), oxidizable-organic matter and sulfides (extraction step 3). The sum of the element contents in the three fractions plus aqua-regia extractable content of the residue was compared to the aqua-regia extractable content of the elements in the origin soils. The accuracy obtained by comparing the determined contents of the elements with certified values, using BCR CRM 701, certified for the extractable contents (mass fractions) of Cd, Cr, Cu, Ni, Pb and Zn in sediment following a modified BCR-three step sequential extraction procedure, was found to be satisfactory.     

Electrothermal atomic absorption spectrometric determination of vanadium in extracts of soil and sewage sludge certified reference materials after fractionation by means of the Communities Bureau of Reference modified sequential extraction procedure

A modified three-step sequential extraction procedure proposed by the Commission of European Communities Bureau of Reference (BCR) was applied to certified reference materials of three different soil groups (rendzina, luvisol, cambisol) and sewage sludge of different composition originating from a municipal water treatment plant in order to assess potential mobility and the distribution of vanadium in the resulting fractions. Analysis of the extracts was carried out by electrothermal atomic absorption spectrometry with Zeeman background correction using transversely heated graphite atomizers. Extracts showed significant matrix interferences which were overcome by the standard addition technique. The original soil and sludge certified reference materials (CRMs) and the extraction residue from the sequential extraction were decomposed by a mixture of HNO₃–HClO₄–HF in an open system. The content of V determined after decomposition of the samples was in very good agreement with the certified total values. The accuracy of the sequential extraction procedure was checked by comparing the sum of the vanadium contents in the three fractions and in the extraction residue with the certified total content of V. The amounts of vanadium leached were in good correlation with the certified total contents of V in the CRMs of soils and sewage sludge. In the soils examined, vanadium was present almost entirely in the mineral lattice, while in the sewage sludge samples 9–14% was found in the oxidizable and almost 25% in the reducible fractions. The recovery ranged from 93–106% and the precision (RSD) was below 10%.     

Operationally defined extraction procedures for soil and sediment analysis: II. Certified reference materials

Single or sequential extraction procedures are often used for soil and sediment studies to determine forms or phases of elements (e.g. `bioavailable' forms of elements). The significance of the analytical results is highly dependent on the extraction procedures used, owing to the `operationally defined' character of these schemes which requires the adoption of standardized protocols. The first part of the present review discusses the aspects of standardization of leaching and extraction schemes as applied to environmental analysis. This second part focuses on the validation aspects of such procedures and describes the preparation and certification of soil and sediment reference materials certified for their extractable trace element contents, following standardized single and sequential extraction procedures.     

Operationally defined extraction procedures for soil and sediment analysis: II. Certified reference materials

Single or sequential extraction procedures are often used for soil and sediment studies to determine forms or phases of elements (e.g. ‘bioavailable' forms of elements). The significance of the analytical results is highly dependent on the extraction procedures used, owing to the ‘operationally defined' character of these schemes which requires the adoption of standardized protocols. The first part of the present review discusses the aspects of standardization of leaching and extraction schemes as applied to environmental analysis. This second part focuses on the validation aspects of such procedures and describes the preparation and certification of soil and sediment reference materials certified for their extractable trace element contents, following standardized single and sequential extraction procedures.     

Extraction and determination of hexavalent chromium in soil samples

A procedure for the extraction of Cr(VI) from solid soil-like samples was presented in which the complexing properties of diethylenetriaminepentaacetic acid (DTPA) were exploited to extract insoluble compounds of Cr(VI). A concentration of DTPA in an ammonium sulphate/ammonium hydroxide buffer equal to 0.02 mol l⁻¹ was chosen. The conditions of extraction of insoluble Cr(VI) from solid samples were optimised using soil certified reference material spiked with known concentration of insoluble Cr(VI) added as PbCrO₄. The extracts were analysed by adsorptive stripping voltammetry. Validation of the proposed procedure of extraction was carried out by analysis of certified reference material (CRM) 545 and comparison of the results obtained using the proposed and other methods of extraction in the course of analysis of natural soil samples.     

Determination of cadmium and lead in mussels by electrothermal atomic absorption spectrometry using an ultrasound-assisted extraction method optimized by factorial design

A simple and rapid method is described for the quantitative extraction and determination of Cd and Pb in mussel tissue (Mytilus edulis). The method is based on the quantitative ultrasound-assisted extraction (i.e. sample mass at mg level) of the two metals using diluted nitric acid as extractant. The extraction procedure is carried out in autosampler cups of the graphite furnace (typically, less than 20 mg). A two-level full factorial design (2⁴) was applied to optimize the variables influencing the ultrasound extraction process. These variables were: extraction time, ultrasound amplitude, nitric acid concentration and particle size. Optimization results showed that acid concentration and particle size were the more significant variables. Determination of Cd and Pb in extracts obtained after ultrasound treatment was carried out by Electrothermal Atomic Absorption Spectrometry. The method was validated by statistically comparing the metal contents found with the certified ones corresponding to the BCR 278 mussel tissue. No significant differences were observed for P = 0.05. LODs for Cd and Pb in mussel tissue were 0.019 and 0.37 μg g^–1. RSDs values (corresponding to between-batch precision for n = 5) were 2.2 and 6.7% for Cd and Pb, respectively. The method was applied to measure the contents of Cd and Pb in mussels used as pollution bioindicators from the Galician coast (Ria de Vigo, Spain).     

Accurate determination of trace amounts of phosphorus in geological samples by inductively coupled plasma atomic emission spectrometry with ion-exchange separation

In order to determine trace amounts of phosphorus in geological and cosmochemical rock samples, simple as well as reliable analytical schemes using an ICP-AES instrument were investigated. A (conventional) ICP-AES procedure could determine phosphorus contents at the level of several 100 μg g⁻¹ with a reasonable reproducibility (<10% for 200 μg g⁻¹; 1σ). An ICP-AES procedure coupled with matrix-separation using cation and anion exchange resins could lower the quantification level down to 1 μg g⁻¹ or even lower under the present experimental conditions. The matrix-separation ICP-AES procedure developed in this study was applied to twenty-one geological reference samples issued by Geological Survey of Japan. Obtained values vary from 1250 μg g⁻¹ for JB-3 (basalt) to 2.07 μg g⁻¹ for JCt-1 (carbonate). Matrix-separation ICP-AES yielded reasonable reproducibility (less than 8.3%; 1σ) of three replicate analyses for all the samples analyzed. In comparison of our data with certificate values as well as literature or reported values, there appear to be an apparent (and large) discrepancy between our values and certificate/reported values regardless of phosphorus contents. Based on the reproducibility of our data and the analytical capability of the matrix-separation ICP-AES procedure developed in this study (in terms of quantification limit, recovery, selectivity of an analyte through pre-concentration process, etc.), it is concluded that certified values for several reference standard rocks should be reevaluated and revised accordingly. It may be further pointed that some phosphorus data reported in literatures should be critically evaluated when they are to be referred in later publications.     

Producing SI-traceable reference values for Cd, Cr and Pb amount contents in polyethylene samples from the Polymer Elemental Reference Material (PERM) project using isotope dilution mass spectrometry

 The present paper describes the certification of the amount content of Cd, Cr and Pb in two different polyethylene materials within the third phase of the Polyethylene Elemental Reference Material (PERM) project. The analytical procedure to establish the reference values for Cd, Cr and Pb amount contents in these materials is based on isotope dilution mass spectrometry used as a primary method of measurement. Cd and Pb were measured with inductively coupled plasma-mass spectrometry and Cr with positive thermal ionization-mass spectrometry. The decomposition of the polymer matrix was carried out using a high pressure asher. Reference values for amount content, traceable to the SI-system, have been obtained for these three elements in both of the polyethylene samples of PERM. For each of the certified amount content values an uncertainty budget was calculated using the method of propagation of uncertainties according to ISO and EURACHEM guidelines. The measurement procedures, as well as the uncertainty calculations, are described for all three elements. In order to keep the whole certification process as transparent as possible, the preparations of various reagents and materials as well as the sample treatment and blending are described in detail. The mass spectrometry measurements and the data treatment are also explained carefully. The various sources of uncertainty present in the procedure are displayed in the uncertainty budgets. The obtained combined uncertainties for the amount content values were less than 2% relative (k=1) for all investigated elements. The amount contents were in the μmol/kg range, corresponding to mg/kg levels. Received: 21 October 1999 / Accepted: 29 January 2000     

Determination of cadmium and lead in mussels by electrothermal atomic absorption spectrometry using an ultrasound-assisted extraction method optimized by factorial design

A simple and rapid method is described for the quantitative extraction and determination of Cd and Pb in mussel tissue (Mytilus edulis). The method is based on the quantitative ultrasound-assisted extraction (i.e. sample mass at mg level) of the two metals using diluted nitric acid as extractant. The extraction procedure is carried out in autosampler cups of the graphite furnace (typically, less than 20 mg). A two-level full factorial design (2⁴) was applied to optimize the variables influencing the ultrasound extraction process. These variables were: extraction time, ultrasound amplitude, nitric acid concentration and particle size. Optimization results showed that acid concentration and particle size were the more significant variables. Determination of Cd and Pb in extracts obtained after ultrasound treatment was carried out by Electrothermal Atomic Absorption Spectrometry. The method was validated by statistically comparing the metal contents found with the certified ones corresponding to the BCR 278 mussel tissue. No significant differences were observed for P = 0.05. LODs for Cd and Pb in mussel tissue were 0.019 and 0.37 μg g^–1. RSDs values (corresponding to between-batch precision for n = 5) were 2.2 and 6.7% for Cd and Pb, respectively. The method was applied to measure the contents of Cd and Pb in mussels used as pollution bioindicators from the Galician coast (Ria de Vigo, Spain). Received: 30 June 1998 / Revised: 17 September 1998 / Accepted: 22 September 1998     

Determination of benzene, toluene, ethylbenzene and xylenes in soils by multiple headspace solid-phase microextraction

Multiple headspace-solid phase microextraction (MHS-SPME) is a recently developed technique for the quantification of analytes in solid samples that avoids the matrix effect. This method implies several consecutive extractions from the same sample. In this way, the total area corresponding to complete extraction can be directly calculated as the sum of the areas of each individual extraction when the extraction is exhaustive, or through a mathematical equation when it is not exhaustive. In this paper, the quantitative determination of benzene, toluene, ethylbenzene and xylene isomers (BTEX) in a certified soil (RTC-CRM304, LGC Promochem) and in a contaminated soil by multiple HS-SPME coupled to a gas chromatography-flame ionisation detector (GC-FID) is presented. BTEX extraction was carried out using soil suspensions in water at 30 degrees C with a 75 microm carboxen-polydimethylsiloxane (CAR-PDMS) fibre and calibration was carried out using aqueous BTEX solutions at 30 degrees C for 30 min with the same fibre. BTEX concentration was calculated by interpolating the total peak area found for the soils in the calibration graphs obtained from aqueous solutions. The toluene, ethylbenzene, o-xylene and m,p-xylene concentrations obtained were statistically equal to the certified values.     

Extraction procedures for the determination of heavy metals in contaminated soil and sediment

Extraction tests are commonly used to study the mobility of metals in soils and sediments by mimicking different environmental conditions or dramatic changes on them. The results obtained by determining the extractable elements are dependent on the extraction procedure applied. The paper summarises state of the art extraction procedures used for heavy metal determination in contaminated soil and sediments. Two types of extraction are considered: single and sequential. Special attention is paid to the Standard, Measurement and Testing projects from the European Commission which focused on the harmonisation of the extraction procedures and on preparing soil and sediment certified reference materials for extractable heavy metal contents.     

Application of Leaching Tests for the Assessment of Available Heavy Metals from Domestic and Industrial Sludges

Various sludge samples from different domestic and industrial wastewater treatment plants were analyzed by Flame Atomic Absorption Spectrometry to evaluate their total and available contents of heavy metals (Cu, Cr, Ni, Pb, Zn and Fe). The EDTA and acetic acid single extraction procedures were applied to these samples with the aim to study the leaching behaviour of the metals in the different sludges and also to predict their possible mobility when these wastes are disposed on the environment and landfills. In acidic medium, a higher extraction efficiency was observed for the major part of the elements studied in the industrial sludges, except for Ni and Zn, which were also considerably released from domestic sludges. In contrast, in the presence of the EDTA complexing ligand, a more elevated mobility of metals was found in the domestic sludges and little or no metals were released from the industrial sludges. Moreover, the results of the microwave total digestions were compared, for all metals, with those obtained using a more simplified pseudototal digestion procedure (based on the EPA Method 3051, named microwave assisted acid digestion of sediments, sludges, soils and oils) and a good agreement was found between them, except for Cr and Ni in some particular samples. The between-batch precision (expressed as RSD) of both compared digestion methods was very similar and values lower than 7.7% were obtained in both cases. A certified domestic sludge material (SRM 2781) was employed to validate the two digestion procedures and no significant differences were found between the certified and experimental values for all the elements studied.     

Extraction of soil organic phosphorus

Organic phosphorus is an important component of soil biogeochemical cycles, but must be extracted from soil prior to analysis. Here we critically review the extraction of soil organic phosphorus, including procedures for quantification, speciation, and assessment of biological availability. Quantitative extraction conventionally requires strong acids and bases, which inevitably alter chemical structure. However, a single-step procedure involving sodium hydroxide and EDTA (ethylenediaminetetraacetate) is suitable for most soils and facilitates subsequent speciation by nuclear magnetic resonance spectroscopy. Analysis of extracts by molybdate colorimetry is a potential source of error in all procedures, because organic phosphorus is overestimated in the presence of inorganic polyphosphates or complexes between inorganic phosphate and humic substances. Sequential extraction schemes fractionate organic phosphorus based on chemical solubility, but the link to potential bioavailability is misleading. Research should be directed urgently towards establishing extractable pools of soil organic phosphorus with ecological relevance.     

Metal fractionation in olive oil and urban sewage sludges using the three-stage BCR sequential extraction method and microwave single extractions

The conventional three-stage BCR sequential extraction method was employed for the fractionation of heavy metals in sewage sludge samples from an urban wastewater treatment plant and from an olive oil factory. The results obtained for Cu, Cr, Ni, Pb and Zn in these samples were compared with those attained by a simplified extraction procedure based on microwave single extractions and using the same reagents as employed in each individual BCR fraction. The microwave operating conditions in the single extractions (heating time and power) were optimized for all the metals studied in order to achieve an extraction efficiency similar to that of the conventional BCR procedure. The measurement of metals in the extracts was carried out by flame atomic absorption spectrometry. The results obtained in the first and third fractions by the proposed procedure were, for all metals, in good agreement with those obtained using the BCR sequential method. Although in the reducible fraction the extraction efficiency of the accelerated procedure was inferior to that of the conventional method, the overall metals leached by both microwave single and sequential extractions were basically the same (recoveries between 90.09 and 103.7%), except for Zn in urban sewage sludges where an extraction efficiency of 87% was achieved. Chemometric analysis showed a good correlation between the results given by the two extraction methodologies compared. The application of the proposed approach to a certified reference material (CRM-601) also provided satisfactory results in the first and third fractions, as it was observed for the sludge samples analysed.     

微波等离子体原子发射光谱法(MP-AES)测定米粉中的常量、微量和痕量元素

采用4200型微波等离子体原子发射光谱法(MP-AES)分析米粉中的镉和其它常量、微量以及痕量元素。对标准样品(CRM)的测定值与标准值十分吻合,检出限(MDL)足以满足分析需求,并且具有出色的长期稳定性。实验中无需使用改性剂或离子抑制剂,从而简化了样品前处理过程。4200 MPAES具有出色的分析性能,可分析火焰原子吸收法(FAAS)无法分析的磷元素、能够进行多元素无人值守操作、拥有更高的安全性和易用性,是期望获得新技术的FAAS用户的理想选择     

Tartaric acid extraction of organotin compounds from sediment samples

A new extraction method for the determination of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) in sediments based on extraction with tartaric acid and methanol has been developed. Tin species were extracted from sediment samples using focused microwave technology, then ethylated with sodium tetraethylborate (NaBEt₄) and analyzed by isotope dilution (ID) gas chromatography-mass spectrometry (GC-MS). The advantages of such methodology in comparison with other established extraction methods for the routine speciation analysis of organotin compounds are discussed with respect to sulfur interferences co-extracted from complex matrices.Interferences from elemental sulfur are normally found with acetic acid extraction, but with tartaric acid extraction these interferences were eliminated, demonstrating selective extraction.The accuracy of the analytical procedure was established by analyzing a certified reference material (CRM) (PACS-2, marine sediment) and comparing the results to the certified values. Good agreement between determined and certified values for butyltin compounds was obtained. Finally, some complex sediment samples collected from San Vicente's Bay, Chile, were analyzed with the proposed methodology, demonstrating its potential value for monitoring butyltins in environmental samples with high concentrations of sulfur compounds.     

Ultrasound and microwave-assisted extraction of metals from sediment: a comparison with the BCR procedure

In this paper we investigate alternatives to mechanical stirring for the extraction of the mobile fraction of metals from sediment, and analyze whether these techniques can reduce extraction time and improve reproducibility. We compare the quantities of metal extracted from BCR601 and BCR701 certified sediments using ultrasound bath, microwave-assisted extraction and the first step in the certified BCR sequential extraction procedure. Some environmentally important not-certified metals such as As, Mn, Co, Fe and Al have been included in this study. In the case of microwave-assisted extraction, we compare tests in which samples are exposed to constant, low power irradiation with tests using pulsed high power.

In the tests using the ultrasound bath, less metal was extracted than with the other extractive techniques and standard deviations were comparable to those obtained with the BCR procedure; in assays using microwaves at constant power, extraction efficiencies were different for different metals and for different reference materials and, in some cases, standard deviations were higher than those for the reference method. In contrast, tests with microwaves and constant temperature produced encouraging results: R.S.D.s lay in the 2–4% range, both for certified and not-certified metals; these values are very low compared to those for the reference method. Extraction efficiencies for certified metals were close to 100% for Cd, Zn, Cu and Ni and around 80% for Pb and Cr.     

Methyl mercury determination in environmental and biological reference and other materials by quality control with certified reference materials (CRMs)

Summary Two concentration methods — HCl extraction and extraction followed by water vapour distillation — prior to anion exchange separation and cold-vapour atomic absorption spectrometry were used for the quantification of methyl mercury in a number of reference materials of biological and environmental origin with reference or certified total mercury contents. The applied methods were validated by the analysis of three marine reference materials, certified for methyl mercury. The results obtained in the materials with methyl mercury contents ranging from less than 1 g/kg to a few hundred g/kg showed good agreement between both methods for biological materials, whereas extraction/anion exchange resulted in somewhat too high values for a number of environmental materials. These findings, however, require further confirmation by additional methods and by other laboratories.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Cloud point extraction for the determination of cadmium and lead in biological samples by graphite furnace atomic absorption spectrometry

The phase-separation phenomenon of non-ionic surfactants occurring in aqueous solution was used for the extraction of Cd and Pb from digested biological samples. After complexation with O,O-diethyldithiophosphate (DDTP) in hydrochloric acid medium, the analytes are quantitatively extracted to the phase rich in the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) after centrifugation. Methanol acidified with 0.1 mol L⁻¹ HNO₃ was added to the surfactant-rich phase prior to its analysis by electrothermal atomic absorption spectrometry (ET AAS). The adopted concentrations for DDTP, Triton X-114 and hydrochloric acid were all optimized. Pyrolysis and atomization temperatures were optimized using the extracts and pyrolysis temperatures of 700 °C for both elements and atomization temperatures of 1400 and 1600 °C for cadmium and lead, respectively, were used without adding any modifier, which shows that considerable analyte stabilization is provided by the medium itself. A more detailed investigation was carried out to determine which components of the extract were responsible for the high thermal stability achieved and it revealed that the amount of DDTP added and the phosphorus content of the digested samples contributed significantly to this phenomenon. Detection limits (3σ_B) of 6 and 40 ng g⁻¹, along with enrichment factors of 129 and 18 for Cd and Pb, respectively, were achieved. The proposed procedure was applied to the analysis of five certified biological reference materials after microwave-assisted acid digestion in a mixture of H₂O₂ and HNO₃. Comparison with certified values was performed for accuracy evaluation, resulting in good agreement according to the t-test for a 95% confidence level. The high efficiency of cloud point extraction to carry out the determination of the studied analytes in complex matrices was, therefore, demonstrated.     

Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils, and sludges

Microwave-assisted EPA method 3051 for nitric acid leaching of environmentally key elements from sediments, soils, and sludges was tested, and the influence of leaching temperature and time on element recovery for an estuarine sediment (CRM 277) was investigated. The extraction efficiencies for four certified reference materials applying EPA method 3051, an optimized nitric acid procedure, and an aqua regia (HCl/HNO₃ 3:1) procedure were compared. Digestions were carried out in a high-pressure microwave system offering simultaneous temperature and pressure control for all digestion vessels employed. Eight elements (Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) were determined by ICP-AES and ICP-MS. Extraction efficiency strongly depended on the applied leaching parameters and varied for certain elements among different materials when a nitric acid procedure was applied. In general, element recoveries obtained from the aqua regia procedure were superior to those obtained from nitric acid procedures and showed good agreement with the 95% confidence interval of the certified value for most of the elements investigated. Received: 27 March 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998