Certification of trace and major elements and methylmercury concentrations in a macroalgae (Fucus sp.) reference material, IAEA-140

A marine reference material, IAEA-140, prepared with a macroalgae (Fucus sp.) was recently produced by the International Atomic Energy Agency and certified for trace and major elements and for methylmercury (MeHg). Certification of this material was achieved as an outcome of an international analytical intercomparison study which resulted in 116 independent sets of results reported by participants from 54 countries. The statistical evaluation of the collected data and the criteria used for assignment of the mean and uncertainty values are described. The analysis of data allowed to certify concentration values for 24 elements and MeHg, and to provide information values for another 10 elements. Regarding the elements which could be given certified values, between two and eight different instrumental methods were used to measure metal concentrations, and four independent analytical procedures were used to measure MeHg concentrations. In order to assess the results of the certification procedure, a comparison was made between the certified values obtained from the world-wide intercomparison results and the values obtained from a small subgroup of well-qualified laboratories. The means and 95% confidence intervals for reference values obtained by the two methods are similar for most elements showing that the usual method of certification used by the IAEA, based on large groups of participants, is indeed pertinent.     

Certification of total mercury and methylmercury concentrations in mussel homogenate (Mytilus edulis) reference material, IAEA-142

Due to the increased demand for new reference materials certified for total and methylmercury (MeHg) a sample of mussel homogenate (IAEA-142) has been prepared. Thirteen experienced laboratories reported results for total Hg of which 9 laboratories also reported results for MeHg content. Laboratories reporting MeHg results used various isolation techniques (solvent extraction, saponification, acid leaching, ion-exchange separation, and distillation) and detection systems (cold vapour atomic absorption spectrometry (CV AAS), cold vapour atomic fluorescence spectrometry (CV AFS), gas chromatography with electron capture detector (GC/ECD) and HPLC with CV AAS detector). In the case of total Hg, most of the laboratories used acid digestion, only two used alkaline dissolution, followed either by CV AAS or CV AFS. One laboratory used neutron activation analyses with radiochemical separation. The data received were in good agreement. The value for total Hg was certified to be 126 ng/g, with a 95% confidence interval from 119 to 132 ng/g. For MeHg the certified value of 47 ng/g expressed as Hg was assigned, with a 95% confidence interval from 43 to 51 ng/g. Stability testing has shown that both total and MeHg are stable if samples are stored in a dry and dark place at room temperature. The sample is now available as a certified reference material and is, in particular, useful for quality control measurements of Hg and MeHg in mussel samples at low concentration levels. Received: 24 September 1996 / Revised: 20 November 1996 / Accepted: 8 December 1996     

Certification of total mercury and methylmercury concentrations in mussel homogenate (Mytilus edulis) reference material, IAEA-142

Due to the increased demand for new reference materials certified for total and methylmercury (MeHg) a sample of mussel homogenate (IAEA-142) has been prepared. Thirteen experienced laboratories reported results for total Hg of which 9 laboratories also reported results for MeHg content. Laboratories reporting MeHg results used various isolation techniques (solvent extraction, saponification, acid leaching, ion-exchange separation, and distillation) and detection systems (cold vapour atomic absorption spectrometry (CV AAS), cold vapour atomic fluorescence spectrometry (CV AFS), gas chromatography with electron capture detector (GC/ECD) and HPLC with CV AAS detector). In the case of total Hg, most of the laboratories used acid digestion, only two used alkaline dissolution, followed either by CV AAS or CV AFS. One laboratory used neutron activation analyses with radiochemical separation. The data received were in good agreement. The value for total Hg was certified to be 126 ng/g, with a 95% confidence interval from 119 to 132 ng/g. For MeHg the certified value of 47 ng/g expressed as Hg was assigned, with a 95% confidence interval from 43 to 51 ng/g. Stability testing has shown that both total and MeHg are stable if samples are stored in a dry and dark place at room temperature. The sample is now available as a certified reference material and is, in particular, useful for quality control measurements of Hg and MeHg in mussel samples at low concentration levels.     

Working Methods Paper: Certification of methylmercury compounds concentration in marine sediment reference material,IAEA-356

An intercomparison exercise was organized between seven laboratories using various isolation procedures (extraction, distillation, ion-exchange and alkaline digestion) and detection systems (CV AAS, cold vapour atomic absorption spectroscopy; CV AFS, cold vapour atomic fluorescence spectroscopy; GC, ECD, gas chromatography electron capture detector and HPLC with CV AFS detection) for determination of methylmercury compounds in sediment sample. All certification criteria were fulfilled and therefore the value for total concentration of methylmercury compounds was certified to be 5.46 ng g^?1, with a 95% confidence interval from 4.07–5.84 ng g^?1. The acceptable range, calculated as two times the confidence interval of the mean is therefore from 4.68–6.23 ng g^?1. This is the first sediment reference material ever to be certified for concentration of methylmercury compounds. Comparison of the data obtained by various methodologies has shown that the most critical step is the isolation of methylmercury compounds from binding sites. Acid leaching only cannot release methylmercury compounds quantitatively. Total release of methylmercury compounds could only be achieved by alkaline digestion or distillation. This simple intercomparison exercise has shown that since large numbers of laboratories world-wide are performing methylmercury compound analyses using various improved and specific separation methods and sensitive detection systems, certification of methylmercury compounds in different biological and environmental samples should not be a problem in the future.     

New human hair certified reference material for methylmercury and trace elements

 A new human hair certified reference material (NIES CRM No. 13) for mercury speciation and trace element analysis was prepared at the National Institute for Environmental Studies (NIES), Environmental Agency of Japan. Scalp hair from Japanese males, which is identical with the original material for the previous human hair CRM (NIES CRM No. 5), was used. Special attention was paid to reduce contamination from a grinding vessel during the preparation procedure. A newly-prepared ceramic/Teflon disc mill was used for cryogenic grinding of the hair. 1,000 bottles (3 g each) were produced after sieving and blending of the hair powder. Certified values for total mercury and methylmercury, as well as other trace elements of toxicological and nutritional significance (antimony, cadmium, copper, lead, selenium, and zinc), were determined based on analyses from extensive collaborations. Reference values for 12 elements (aluminium, arsenic, barium, calcium, cobalt, iron, magnesium, manganese, silver, sodium, sulfur and vanadium) were also given. Received: 8 February 1996/Accepted: 4 April 1996     

New human hair certified reference material for methylmercury and trace elements

A new human hair certified reference material (NIES CRM No. 13) for mercury speciation and trace element analysis was prepared at the National Institute for Environmental Studies (NIES), Environmental Agency of Japan. Scalp hair from Japanese males, which is identical with the original material for the previous human hair CRM (NIES CRM No. 5), was used. Special attention was paid to reduce contamination from a grinding vessel during the preparation procedure. A newly-prepared ceramic/Teflon disc mill was used for cryogenic grinding of the hair. 1, 000 bottles (3 g each) were produced after sieving and blending of the hair powder. Certified values for total mercury and methylmercury, as well as other trace elements of toxicological and nutritional significance (antimony, cadmium, copper, lead, selenium, and zinc), were determined based on analyses from extensive collaborations. Reference values for 12 elements (aluminium, arsenic, barium, calcium, cobalt, iron, magnesium, manganese, silver, sodium, sulfur and vanadium) were also given.     

Characterization of a potato reference material for major, minor and trace elements

Summary A potato reference material (RM) was prepared for the analytical quality control program to be employed by the Sub-network on Trace Elements in Food of the FAO European Co-operative Network on Trace Elements. Approximately 50 kg of commercially available potato granules prepared from baked, mashed and roller-dried potatoes, containing 2.8% ash and 3 mg/kg added butylhydroxyanisole was purchased. The granules were carefully homogenised in large glass cylinders followed by division into 50 g portions into numbered acid-washed bottles. The bottled material was tested for homogeneity by taking ten bottles throughout the bottling line and determining by validated atomic absorption spectrometric methods 1.0 g samples for seven mineral elements. Homogeneity for Mg, Ca, Zn, Fe, Mo, Ni and Cd was better than 5%. An international network on experienced, high-quality reference laboratories was established to conduct an interlaboratory comparison study on the determination of 14 mineral elements in the RM. A total of seven methods based on independent analytical principles were employed by the reference laboratories. After excluding outlying analytical results, the criteria defined by the IAEA were used for classification of the overall medians obtained through the interlaboratory comparison study. The relative standard deviations for the 95% confidence limits of the medians were as follows: P=4.2%, K=0.7%, Na=4.7%, Ca=5.5%, Mg=2.4%, Fe=9.3%, Mn=4.0%, Zn=3.6%, Cu=4.7%, Mo=23%, Ni=22%, Cr=19%, Pb=11% and Cd=4.6%. With the exception of Cr, all of the recommended concentration values obtained for the above indicated elements fell into category A, i.e. values recommended with a high degree of confidence according to the classification criteria of the IAEA. The present RM is the only certified potato RM currently available for mineral elements.

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Charakterisierung eines Kartoffel-Referenzmaterials für Haupt-, Neben- und Spurenelemente

     

Certification for trace elements and methyl mercury mass fractions in IAEA-456 marine sediment sample

Accreditation and Quality Assurance - Marine sediment certified reference material (CRM), IAEA-456 was recently produced by the Environment Laboratories of the International Atomic Energy Agency...     

A systematic study on the extractability of arsenic species from algal certified reference material IAEA-140/TM (Fucus sp., Sea Plant Homogenate) using methanol/water extractant mixtures

Using methanol/water mixtures (from pure water to pure methanol), with different desorption and solubility parameters, and varying extractant volume to algal mass (V/m) ratios, the extractability of arsenic species from CRM IAEA-140/TM was investigated. A linear sorption isotherm-based model was developed to process the data obtained with variable volume extraction, allowing the unambiguous deduction of the maximal extractable species concentrations under the specific extraction conditions, even for more stable species.The maximal extractable arsenic fraction ranged from 41 to 68% of the total arsenic concentration in CRM IAEA-140/TM, depending on the extractant composition, with pure methanol giving the lowest extraction yield and pure water giving erratic extractability (probably due to bad wettability). The main arsenic species quantified in the methanol/water extracts were arsenosugars, with arsenosugars 1 (glycerol arsenosugar), 3 (sulfonate arsenosugar) and 4 (sulfate arsenosugar) making up ca. 90% of the maximal extractable arsenic. The rest accounts for DMA (dimethylarsinate), arsenosugar 2 (phosphate arsenosugar) and As(V). There is no clear extraction pattern emerging from the data although it may be seen that extraction of more polar species (e.g. arsenosugar 1) is favoured in pure methanol and less polar more ionic species (e.g. arsenosugar 2 and As(V)) in methanol extractants with a higher water percentage.The precise and highly accurate data may be used for quality control purposes under strictly followed extraction conditions since the extraction is operationally defined. Additionally, the variable volume extraction methodology presented may be applied to other elemental species in other matrices using other extractants. Although this approach does not maximise the absolute extractability but only that which is extractant-specific, experimentators are forewarned that in most cases only a fingerprint of the extractant-specific species is produced unless a quantitative extraction of all species is obtained.     

Certification for trace elements and methyl mercury mass fractions in IAEA-452 scallop (Pecten Maximus) sample

A marine certified reference material (CRM), IAEA-452, prepared with scallop (Pecten maximus) sample was recently produced by the International Atomic Energy Agency (IAEA) and certified for trace elements and methyl mercury (MeHg). The Scallop (Pecten maximus) sample is commonly found and consumed seafood and is also used as bio-indicators for trace metal contamination in marine pollution studies. This paper presents the sample preparation methodology, material homogeneity and stability studies, evaluation of certification campaign results, the assignment of property values and their associated uncertainty. The reference values and associated expanded uncertainty for 9 trace elements (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb and Zn) and MeHg in scallop sample are established. The informative value for one more element (Ni) is also given. The new CRM can be used for the development and validation of analytical methods for determination of trace elements and methyl mercury in seafood and also for quality assurance/quality control purposes.     

Certification of the mass fractions of trace elements and pentachlorophenol in an impregnated wood reference material

The resource-saving utilisation of recovered waste wood is a matter of growing concern. In several European countries, this utilisation is governed by regulations and is dependent on the contents of certain trace elements and organic compounds. Thus, for decision-making with respect to waste wood management (recycling or combustion), reliable analytical data are needed and, due to their great economic and environmental impact, must be assured by appropriate quality control. To support the improvement in quality assurance in waste wood analysis, for the first time, a wood reference material was certified for its mass fractions of arsenic, cadmium, chromium, copper, lead, mercury, and pentachlorophenol (PCP). These analytes were selected because they represent typical constituents of wood preservatives most widely used in the past. Material preparation and testing of homogeneity and stability were carried out by BAM Federal Institute for Materials Research and Testing. The certification measurements were performed involving selected laboratories with documented expertise in the field of waste wood analysis. The certified values and their corresponding uncertainties were assigned in full compliance with the requirements of ISO Guide 35. The certified mass fractions and their expanded uncertainties (k = 2) are as follows: (3.1 ± 0.5) mg/kg for As, (3.02 ± 0.24) mg/kg for Cd, (36.4 ± 2.6) mg/kg for Cr, (22.9 ± 1.7) mg/kg for Cu, (0.60 ± 0.14) mg/kg for Hg, (39 ± 4) mg/kg for Pb, and (7.9 ± 0.6) mg/kg for PCP. The certified material is available as European Reference Material ERM^®-CD100.     

Certification of a second-generation biological reference material (freeze-dried human serum) for trace element determinations

The certification of a second-generation biological reference material (freeze-dried human serum) for trace element determinations is described. The material was prepared under rigorously controlled conditions to avoid extraneous additions. Analytical data were obtained by the authors as well as by numerous other intra- and extra-mural investigators, solicited on the basis of established experience in determining selected elements. For 14 trace elements (aluminium, chromium, manganese, iron, cobalt, copper, zinc, arsenic, selenium, bromine, rubidium, molybdenum, cadmium and caesium) certified values (in ng g^?1 or μg g^?1 dry weight) are listed; for an additional element (nickel) a best estimate (in ng g^? dry weight) is added. Trace element concentrations in the material, which is available to the scientific community, closely approximate those in normal, lyophilized blood plasma or serum samples. The material thus provides the means to check the accuracy and precision of analytical procedures for quantifying low-level trace elements in the best possible conditions and to detect errors that can easily be overlooked when reference materials with higher levels of trace elements are used. In addition, and in contrast to already existing biological reference materials with high levels of trace elements, it offers the possibility of identifying unsuspected errors at the sample preparation stage.     

Distribution of major and trace elements concentrations in gold processing using EDXRF

Studies have been carried out on the distribution of major and trace elements concentrations in oxide and sulphide feed ores at various stages of milling and processing of gold in a goldmine at Bogoso in the western region of Ghana. The studies evaluated concentration enhancements at various stages of treatment with emphasis on understanding the typical processes leading to enhancement of concentration at each stage and ultimately the impact from discharges into the surrounding environment. The feed ore samples were analyzed using energy dispersive X-ray fluorescence spectrometry. The results show concentration enhancements of a significant number of elements at some stages of processing in the two processing plants with the highest number of elements with enhanced concentrations coming from chemically treated media of both plants. Though there are relatively high concentrations of V (max.: 284 ppm), Cr (max.: 149 ppm), Co (max.: 84 ppm), and U (max.: 26.8 ppm) at the discharge points, the concentrations of most of the toxic elements in the slurries discharged into the tailings dam are mostly within their respective world averages. The enrichment indices computed for the slurries being discharged into the tailings dam suggests that the dam is not enriched with the toxic elements Cr, Co, Ni, Zn, Cu and Pb. The enrichment index of the slurries discharged into the tailings dam decreases in the order of oxide plant > sulphide plant. Principal component analyses performed suggest that Al₂O₃, K₂O, Co, Zn, Cu, Y and Zr are geochemically associated. Results from the studies also suggest that the discharge of these elements into the tailings dam may contribute insignificant pollution of the surrounding area.     

Certification of methylmercury in cod fish tissue certified reference material by species-specific isotope dilution mass spectrometric analysis

A new cod fish tissue certified reference material, NMIJ CRM 7402-a, for methylmercury analysis was certified by the National Metrological Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Cod fish was collected from the sea close to Japan. The cod muscle was powdered by freeze-pulverization and was placed into 600 glass bottles (10 g each), which were sterilized with γ-ray irradiation. The certification was carried out using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), where ²⁰²Hg-enriched methylmercury (MeHg) was used as the spike compound. In order to avoid any possible analytical biases caused by nonquantitative extraction, degradation and/or formation of MeHg in sample preparations, two different extraction methods (KOH/methanol and HCl/methanol extractions) were performed, and one of these extraction methods utilized two different derivatization methods (ethylation and phenylation). A double ID method was adopted to minimize the uncertainty arising from the analyses. In order to ensure not only the reliability of the analytical results but also traceability to SI units, the standard solution of MeHg used for the reverse-ID was prepared from high-purity MeHg chloride and was carefully assayed as follows: the total mercury was determined by ID–ICPMS following aqua regia digestion, and the ratio of Hg as MeHg to the total Hg content was estimated by GC–ICPMS. The certified value given for MeHg is 0.58 ± 0.02 mg kg⁻¹ as Hg. Figure NMIJ CRM 7402-a: cod fish tissue for MeHg analysis     

Certification of standard reference material (SRM) 1941a, organics in marine sediment

SRM 1941a, Organics in Marine Sediment, has been recently issued with certified concentrations for 23 polycyclic aromatic hydrocarbons, 21 polychlorinated biphenyl congeners, 6 chlorinated pesticides, and sulfur. Noncertified concentrations have been also reported for additional PAHs, PCB congeners, and chlorinated pesticides and for percent total organic carbon (TOC), aliphatic hydrocarbons, and trace elements. SRM 1941a is the most extensively characterized natural matrix SRM issued by the National Institute of Standards and Technology (NIST).     

Certification of the methylmercury content in SRM 2977 mussel tissue (organic contaminants and trace elements) and SRM 1566b oyster tissue

The methylmercury content in two new marine bivalve mollusk tissue Standard Reference Materials (SRMs) has been certified using results of analyses from the National Institute of Standards and Technology (NIST) and two other laboratories. The certified concentrations of methylmercury were established based on the results from four and six different (independent) analytical methods, respectively, for SRM 1566b Oyster Tissue (13.2 +/- 0.7 microg/kg) and SRM 2977 Mussel Tissue (organic contaminants and trace elements) (36.2 +/- 1.7 microg/kg). The certified concentration of methylmercury in SRM 1566b is among the lowest in any certified reference material (CRM).     

Certification of the methylmercury content in SRM 2977 Mussel Tissue (organic contaminants and trace elements) and SRM 1566b Oyster Tissue

The methylmercury content in two new marine bivalve mollusk tissue Standard Reference Materials (SRMs) has been certified using results of analyses from the National Institute of Standards and Technology (NIST) and two other laboratories. The certified concentrations of methylmercury were established based on the results from four and six different (independent) analytical methods, respectively, for SRM 1566b Oyster Tissue (13.2 ± 0.7 μg/kg) and SRM 2977 Mussel Tissue (organic contaminants and trace elements) (36.2 ± 1.7 μg/kg). The certified concentration of methylmercury in SRM 1566b is among the lowest in any certified reference material (CRM).