Accuracy of a method based on atomic absorption spectrometry to determine inorganic arsenic in food: Outcome of the collaborative trial IMEP-41.

A collaborative trial was conducted to determine the performance characteristics of an analytical method for the quantification of inorganic arsenic (iAs) in food. The method is based on (i) solubilisation of the protein matrix with concentrated hydrochloric acid to denature proteins and allow the release of all arsenic species into solution, and (ii) subsequent extraction of the inorganic arsenic present in the acid medium using chloroform followed by back-extraction to acidic medium. The final detection and quantification is done by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS). The seven test items used in this exercise were reference materials covering a broad range of matrices: mussels, cabbage, seaweed (hijiki), fish protein, rice, wheat, mushrooms, with concentrations ranging from 0.074 to 7.55mgkg(-1). The relative standard deviation for repeatability (RSDr) ranged from 4.1 to 10.3%, while the relative standard deviation for reproducibility (RSDR) ranged from 6.1 to 22.8%.

Migration of antimony from polyethylene terephthalate used in mineral water bottles.

The influence of storage time and temperature on Sb migration from PET bottles into mineral water was studied in short-term tests lasting up to 15 days and long-term studies lasting up to 220 days. Samples purchased were stored in three different coloured bottles: clear (CL), light blue (LB) and dark blue (DB). Sb migration was assayed by HG-AFS for total determination and HPLC-ICP-MS for speciation analysis. Migration studies showed that waters stored at 4 and 20 °C were not subject to Sb migration. At 40 °C there was a significant increase in Sb concentration, although the maximum limit established by the European Union (5.0 µgL(-)(1)) was not exceeded, whereas at 60 °C samples were subject to considerable Sb migration after 30 days of storage. In this case, the maximum limit established by the European Union was exceeded and both Sb (V) and Sb (III) were detected.

Determination of total cadmium, lead, arsenic, mercury and inorganic arsenic in mushrooms: outcome of IMEP-116 and IMEP-39.

The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre (JRC), a Directorate General of the European Commission, operates the International Measurement Evaluation Program (IMEP). IMEP organises inter-laboratory comparisons in support of European Union policies. This paper presents the results of two proficiency tests (PTs): IMEP-116 and IMEP-39, organised for the determination of total Cd, Pb, As, Hg and inorganic As (iAs) in mushrooms. Participation in IMEP-116 was restricted to National Reference Laboratories (NRLs) officially appointed by national authorities in European Union member states. IMEP-39 was open to all other laboratories wishing to participate. Thirty-seven participants from 25 countries reported results in IMEP-116, and 62 laboratories from 36 countries reported for the IMEP-39 study. Both PTs were organised in support to Regulation (EC) No. 1881/2006, which sets the maximum levels for certain contaminants in food. The test item used in both PTs was a blend of mushrooms of the variety shiitake (Lentinula edodes). Five laboratories, with demonstrated measurement capability in the field, provided results to establish the assigned values (Xref). The standard uncertainties associated to the assigned values (uref) were calculated by combining the uncertainty of the characterisation (uchar) with a contribution for homogeneity (ubb) and for stability (ust), whilst uchar was calculated following ISO 13528. Laboratory results were rated with z- and zeta (ζ)-scores in accordance with ISO 13528. The standard deviation for proficiency assessment, σp, ranged from 10% to 20% depending on the analyte. The percentage of satisfactory z-scores ranged from 81% (iAs) to 97% (total Cd) in IMEP-116 and from 64% (iAs) to 84% (total Hg) in IMEP-39.

Use of the modified BCR three-step sequential extraction procedure for the study of trace element dynamics in contaminated soils.

The modified BCR three-step sequential extraction procedure was used to examine the temporal dynamics of trace elements in soils contaminated by an accidental spill from an opencast mine in south-west Spain. Soils were mainly contaminated with pyritic sludge and acidic wastewater, whereas some soils were affected only by acidic wastewater. The distributions obtained for both some major (Ca, Fe and Mn) and trace elements (As, Cd, Cu, Pb and Zn) in the sludge and soil samples taken at different times after the accident, 1-3 months and 21 months, were compared. Sequential extractions were useful in identifying different sources of contamination, and in obtaining additional information on the solubility of secondary minerals formed by pyrite oxidation. Thus, the effectiveness of the BCR procedure has proved to be a useful tool for predicting short- and long-term mobility of trace elements, even in complex environmental scenarios.

Speciation analysis of antimony in extracts of size-classified volcanic ash by HPLC-ICP-MS.

Although there is concern about the presence of toxic elements and their species in environmental matrices, for example water, sediment, and soil, speciation analysis of volcanic ash has received little attention. Antimony, in particular, an emerging element of environmental concern, has been less studied than other potentially toxic trace elements. In this context, a study was undertaken to assess the presence of inorganic Sb species in ash emitted from the Copahue volcano (Argentina). Antimony species were extracted from size-classified volcanic ash (<36 microm, 35-45 microm, 45-150 microm, and 150-300 microm) by use of 1 mol L(-1) citrate buffer at pH 5. Antimony(III) and (V) in the extracts were separated and quantified by high-performance liquid chromatography combined on-line with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Antimony species concentrations (microg g(-1)) in the four fractions varied from 0.14 to 0.67 for Sb(III) and from 0.02 to 0.03 for Sb(V). The results reveal, for the first time, the occurrence of both inorganic Sb species in the extractable portion of volcanic ash. Sb(III) was always the predominant species.

Analytical speciation as a tool to assess arsenic behaviour in soils polluted by mining.

A study is performed to evaluate the occurrence of arsenic in polluted soils using acidic extractions and liquid chromatography-hydride generation-atomic fluorescence spectrometry (LC-HG-AFS) for speciation analysis. Seven soil samples were collected in an abandoned area polluted by mining in the Eastern Pyrenees (Spain), and two uncontaminated soils were taken for reference purposes. Moreover, the total arsenic content is evaluated in two different sieved fractions in order to obtain information on the possible particle-size-dependent association of arsenic with soil components. Soil samples were extracted with both phosphoric and ascorbic acids and the stabilities of the extracted species were studied. The arsenic species were determined by LC-HG-AFS. In addition, the ability of soil grinding to effect species change is also assessed. Arsenite and arsenate were found in the polluted soils, but only arsenate was found in the unpolluted soils. The quality of the results was assessed through a mass balance calculation and by analysing two soil Certified Reference Materials. Valuable information regarding arsenic occurrence in the studied soils is obtained from the speciation results. The presence of arsenite in the extracts can be attributed to arsenopyrite residues, whereas the presence of arsenate indicates release from weathered material.

Comparison of three strategies to evaluate uncertainty from in-house validation data. A case study: mercury determination in sediments.

In the present paper, three approaches are compared for the evaluation of the combined uncertainty in the determination of mercury in aquatic sediments by an aqua regia extraction procedure. For this, the data obtained in validation studies from five certified reference materials (CRMs), covering a range of concentrations from 0.8 to 130 mg kg(-1) of mercury and analysed by three atomic spectroscopic techniques (cold vapour generation atomic fluorescence spectrometry, CV-AFS, cold vapour generation atomic absorption spectroscopy, and inductively coupled plasma mass spectroscopy), were considered. The combined uncertainty was firstly assessed by considering separately the data obtained for each CRM analysed (approach A). Moreover, this assessment was also performed with two other calculation approaches (B and C) based on the pooled data obtained from the validation step. The comparison of the results obtained for the different techniques showed a clear bias effect when using CV-AFS with nitric acid as a diluent. In relation to the strategies tested for the combined uncertainty assessment, approach C proved to be the easiest and friendliest method for uncertainty assessment.

Comparison of chemical modifiers for selenium determination in soil aqua regia extracts by ZETAAS.

The effect of various chemical modifiers 0.5 g l(-1) Pd, 1% (w/v) Ni, 0.5 g l(-1) Pd+1% (w/v) Ni and 1.0 g l(-1) Pd on the measurement of selenium in soil aqua regia extracts, by ZETAAS, is described. Two Certified Reference Materials (CRMs) RTC-CRM 023-050 and RTC-CRM 025-050 were used for this study. Pyrolysis and atomization curves were obtained for each chemical modifier and their optimal values were assessed. By using standard addition as calibration method, accurate results were obtained for all the chemical modifiers studied. The precision was similar for both CRMs, with a maximum value of 7.5% R.S.D. The limits of detection and quantification for selenium in the soil extracts (n=10) were 3.0 and 6.0 microg l(-1), respectively. The characteristic mass of selenium is assessed as 10 pg. The use of aqua regia as extractant gave quantitative results for selenium in the CRMs assayed.

Antimony speciation in terrestrial plants. Comparative studies on extraction methods.

A suitable method for the extraction of antimony species from plant materials prior to IC-HG-AFS analysis is presented. The extraction efficiency with different extraction systems using various aqueous and aqueous/solvent mixtures was initially evaluated by analysing the Virginia Tobacco Leaves Certified Reference Material. The concentration of antimony extracted was compared with the total antimony content in the plant material measured by HG-AFS after focused microwave-acidic digestion using HNO3 and H2O2. The proposed extraction procedures were applied to antimony speciation in several plants from a natural terrestrial environment impacted by mining activities. End-over-end agitation (4 h) followed by sonication (1 h) extraction using 0.1 mol l(-1) citric acid was found to provide the best extraction efficiency while also giving reliable speciation information. Both inorganic and methylantimony species were found in the extractable portion of some terrestrial plants.

New considerations about the separation and quantification of antimony species by ion chromatography-hydride generation atomic fluorescence spectrometry.

A new method for the speciation of inorganic [Sb(III) and Sb(V)] and organic (Me3SbCl2) antimony species by using a polystyrene-divinylbenzene-based anion-exchange HPLC column (Hamilton PRP-X100) coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) is presented. Several mobile phases were tested for the baseline separation of these three antimony species, investigating in detail experimental parameters such as concentration and pH. The best efficiency and resolution was achieved by using a gradient elution between diammonium tartrate 250 mmol l(-1) pH 5.5 (A) and KOH 20 mmol l(-1) pH 12 (B). The gradient programme used was 100% B for 1.5 min, decreasing to 0% B in 0.1 min and maintained the elution with 100% A for 5.5 min. Analysis time was less than 7 min. Equilibration of the column with the complexing mobile phase was found to be critical in order to avoid Sb(III) double peak formation. Dilution in diammonium tartrate medium was necessary in order to avoid Sb(III) oxidation at microg l(-1) concentration level. Detection limits of 0.06 microg l(-1) for Sb(V), 0.09 microg l(-1) for Me3SbCl2 and 0.04 microg l(-1) for Sb(III) as well as repeatability and reproducibility better than 5% R.S.D. (n = 10) and 9% R.S.D. (n = 30) (for 1 and 5 microg l(-1) of Sb(V) and Sb(III) and 5 and 10 microg l(-1) of Me3SbCl2) were obtained. Accuracy and recovery studies were carried out by analysing one river freshwater sample and two water certified reference materials. The proposed methodology can be considered reliable and straightforward for antimony speciation in fresh water samples.

Prediction of trace element mobility in contaminated soils by sequential extraction.

The modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (or Bureau Communautaire de Reference, BCR) was used to predict trace element mobility in soils affected by an accidental spill comprising arsenopyrite- and heavy metal-enriched sludge particles and acid waste waters. The procedure was used to obtain the distribution of both the major (Al, Ca, Fe, Mg, and Mn) and trace elements (As, Bi, Cd, Cu, Pb, Tl, and Zn) in 13 soils of contrasting properties with various levels of contamination and in the sludge itself. The distributions of the major elements enabled us to confirm the main soil fractions solubilized in each of the three steps, and, in turn, to detect the presence of pyritic sludge particles by the high Fe extractability obtained in the third step. Cadmium was identified as being the most mobile of the elements, having the highest extractability in the first step, followed by Zn and Cu, Lead, Tl, Bi, and As were shown to be poorly mobile or nonmobile. In the case of some of the trace elements, the residual fractions decreased at higher levels of contamination, which was attributed to the anthropogenic contributions to the polluted samples. Comparison with soil-plant transfer factors, calculated in plants growing in the affected area, indicated that a relative sequence of trace element mobility was well predicted from data of the first step.

Analytical approaches to the determination of phosphorus partitioning patterns in sediments.

Three methods for phosphorus fractionation in sediments based on chemical extractions have been applied to fourteen aquatic sediment samples of different origin and characteristics. Two of the methods used different approaches to obtain the inorganic fractions. The Hieltjes and Lijklema procedure (HL) uses strong acids or bases, whereas the Golterman procedure (G) uses chelating reagents. The third one, the Standards, Measurements and Testing (SMT) protocol, was proposed in the frame of the SMT Programme (European Commission) which aimed to provide harmonisation and the validation of such methodologies. This harmonised procedure was also used for the certification of the extractable phosphorus contents in a sediment certified reference material (CRM BCR 684). Principal component analysis (PCA) was used to group sediments according to their composition and the three extraction methods were applied to the samples including CRM BCR 684. The data obtained show that there is some correlation between the results from the three methods when considering the organic and the residual fractions together. The SMT and the HL methods are the most comparable, whereas the G method, using a different type of reagent, yields different distribution patterns depending on sample composition. In relation to the inorganic phosphorus, the three methods give similar information, although the distribution between non-apatite and apatite fractions can be different.

Relationships between phosphorus fractionation and major components in sediments using the SMT harmonised extraction procedure.

Leaching procedures are one of the most widely used approaches to determine phosphorus fractionation in soils and sediments. Within the framework of the Standards, Measurements and Testing programme (SMT), an extraction protocol, based on the Williams procedure, was harmonised in order to improve reproducibility among laboratories. The so called SMT protocol was then used for the certification of a reference material (BCR 684) in five phosphorus fractions: non-apatite, apatite, inorganic, organic and total phosphorus. In the present paper, the SMT protocol has been applied to sediments of different composition (organic, calcareous and Fe-rich sediments). The P, Al, Ca, Fe and Mn contents extracted in each fraction were determined. The relations among these elements and the organic matter content in the samples were studied. The results obtained support the SMT protocol as a valuable tool for the study of phosphorus fractionation in sediments.

Harmonized protocol and certified reference material for the determination of extractable contents of phosphorus in freshwater sediments--a synthesis of recent works.

An analytical protocol for the determination of the extractable phosphorus contents in freshwater sediments has been harmonized through interlaboratory studies in the frame of the Standards Measurements and Testing Program of the European Commission. A homogeneous and stable sediment reference material has been prepared and certified on the basis of this protocol named SMT protocol, and will be available in spring of 2001. The SMT protocol, together with the reference material, are useful tools in the field of water management, especially at a time when quality assurance and data comparability are of paramount importance in laboratory analysis. The knowledge of the bioavailable forms of phosphorus is important not only for sediments but also for sludge and soils. Therefore, the SMT protocol could be extended to these materials and new CRMs could be prepared. The SMT protocol was used in a study of a reservoir, which allowed to calculate the P stock, therefore helping to predict the restoration delay of the lake. The paper describes the protocol and the CRM, and gives a brief outline of the case study.

Certification of the extractable contents of Cd, Cr, Cu, Ni, Pb and Zn in a freshwater sediment following a collaboratively tested and optimised three-step sequential extraction procedure.

Sequential extraction procedures have been used during the last decades to study and determine trace element mobility in aquatic sediments. However, the results obtained are operationally defined and, therefore, the significance of the analytical results is related to the extraction scheme used. So, there is a need for suitable reference materials for this type of study to enable the validation of the methodologies and to control the quality of the measurements. This paper describes the preparation of a sediment reference material, BCR-701, the homogeneity and stability studies and the analytical work performed for the certification of the extractable contents of some trace elements, following a collaboratively tested and optimised sequential (three-step) extraction procedure. The paper contains all the results and gives the methods used to certify the extractable contents (mass fractions expressed as mg kg-1 on a dry matter basis) of Cd, Cr, Cu, Ni, Pb and Zn in all steps. Moreover, indicative values are given for the aqua regia extractable contents of the six elements in the sediment and the residue obtained after sequential extraction.

A new organic-rich soil reference material certified for its EDTA- and acetic acid- extractable contents of Cd, Cr, Cu, Ni, Pb and Zn, following collaboratively tested and harmonised procedures.

There is an increasing requirement for assessment of the bioavailable metal fraction and the mobility of trace elements in soils upon disposal. One of the approaches is the use of leaching procedures, but the results obtained are operationally defined; therefore, their significance is highly dependent on the extraction protocol performed. So, for this type of study, there is a need for reference materials that allow the quality of measurements to be controlled. This paper describes the steps involved in the certification of an organic-rich soil reference material, BCR-700, for the EDTA- and acetic acid-extractable contents of some trace elements, following collaboratively tested and harmonised extraction procedures. Details are given for the preparation of the soil, homogeneity and stability testing, analytical procedures and the statistical selection of data to be included in the certification.

Development of a harmonised phosphorus extraction procedure and certification of a sediment reference material.

A harmonised procedure for the determination of the forms of phosphorus in freshwater sediments, developed in the frame of the European Programme, Standards, Measurements and Testing (SMT) has been used for a certification campaign for a reference material. This operationally defined scheme is a good compromise between method performance and reproducibility. Furthermore, the method is rather simple to implement and could be used by water managers on a routine basis. A homogeneous and stable sediment reference material has been prepared and will be available before mid 2001. The so-called SMT protocol, together with the reference material, are useful tools in the field of water management, especially at a time when quality assurance is of paramount importance in laboratory analyses. Knowledge of the bioavailable forms of phosphorus is important not only for analysis of sediments but also for sludge and soils. Therefore, the SMT protocol could be extended to these materials.

Application of a modified BCR sequential extraction (three-step) procedure for the determination of extractable trace metal contents in a sewage sludge amended soil reference material (CRM 483), complemented by a three-year stability study of acetic acid and EDTA extractable metal content.

This paper provides additional data on a sewage sludge amended soil certified reference material, CRM 483, which was certified in 1997 for its EDTA and acetic acid extractable contents of some trace metals, following standardised extraction procedures. The additional work aimed to test the long-term stability of the material and the applicability of an improved version of the BCR three-step sequential extraction procedure on the sewage sludge amended soil (CRM 483). The paper demonstrates the CRM 483 long-term stability for EDTA and acetic acid extractable contents of Cd, Cr, Cu, Ni, Pb and Zn and gives the results (obtained in the framework of an interlaboratory study) for the extractable contents of the same elements in the CRM 483, following the BCR three-step sequential extraction scheme. The aqua regia extractable contents following the ISO 11466 Standard are also given. The data are given as indicative (not certified) values.

Selection and evaluation of sequential extraction procedures for the determination of phosphorus forms in lake sediment.

In order to achieve comparable measurements in the determination of phosphate forms in freshwater sediments, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has launched a project the first step of which was to select and evaluate collaboratively existing extraction procedures. This was carried out through expert consultations and a literature survey, and was followed by the organisation of a first interlaboratory study for the evaluation of four sequential extraction schemes, one of which was selected as the most promising method for achieving comparability. This scheme, a modified version of the Williams protocol, was further tested in a second interlaboratory study. The so-called SMT extraction scheme seems promising and will provide, in the near future, a valuable tool for water managers in the field of lake restoration. It will be particularly helpful in estimating the stock of P potentially available, hence the risk of eutrophication due to internal P release.

Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials.

The Standards, Measurements and Testing Programme (formerly BCR) of the European Commission proposed a three-step sequential extraction procedure for sediment analysis, following extensive expert consultations and two interlaboratory studies. This scheme was recently used to certify the extractable trace element contents of a sediment reference material (CRM 601). Although this procedure offers a means to ensure the comparability of data in this field, some difficulties concerning the interlaboratory reproducibility still remain, and a new project is currently being conducted to determine the causes of poor reproducibility in the extraction scheme. The final objective of the project is the certification of new sediment and soil reference materials for their extractable contents of Cd, Cr, Cu, Ni, Pb and Zn. This paper presents the results of a small-scale interlaboratory study, which aimed to test a revised version of the extraction schemes by comparing the original and the modified protocols using the CRM 601 sample. This work offers an improvement to the BCR sequential extraction procedure through intercomparison exercises. This improved procedure will allow the obtaining of CRMs to validate analytical data in the analysis of soils and sediments, and it will also facilitate comparability of data in the European Union.