Determination of ultra-trace level 241Am in marine sediment and seawater by combining TK200-TK221 tandem-column extraction chromatography and SF ICP-MS.

Sound strategies for marine chemical monitoring call for measurement systems capable of producing comparable analytical results with demonstrated quality. This work presents the development and validation of a new analytical procedure for the determination of the 241Am mass fraction in marine sediment and seawater samples at low levels. The procedure includes a tandem-column extraction chromatography for separation of 241Am and sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) for its determination. The separation is based on the application of two new extraction resins, TK200 and TK221. The acid leaching method was employed for the pre-treatment of marine sediments, while Fe(OH)3 co-precipitation was used for Am pre-concentration in seawater samples. The extraction behaviors of Am on TK221 resins in the different acidic mediums were investigated. The removal capabilities of the tandem TK200-TK221 columns for the 241Am in the presence of interfering elements including Pu, Pb, Hg, Bi, Tl, Pt, Hf, U, and Th were carefully investigated and the corresponding decontamination factors (DFs) estimated to be in the range from 104 to 106. The main interfering element Pu was efficiently removed with a DF of about 6 × 105. Matrix rare earth elements (REEs) in marine sediments were further removed by the application of TEVA resins. 241Am mass fraction was quantified by the application of external calibration and SF ICP-MS. Following the recommendations of the ISO/IEC 17025 guidelines, the validation of the analytical procedure was accomplished by executing it on the certified reference material (CRM) IAEA-385 (marine sediment) and the seawater IAEA-443 reference materials (RM). The obtained results showed that 241Am mass fractions were accurately determined in both reference samples, with excellent reproducibility (2.1 % and 7.6 %) and low LODs (0.4 fg g-1 and 0.2 fg g-1). The relative expanded uncertainties (k = 2) obtained were 17.1 % and 29.0 %, respectively. The overall analytical times for the application of the proposed procedure on the marine sediment and seawater samples were evaluated to be only about 9 h and 6.5 h, respectively. It shows great advantages for its potential applications for emergency monitoring of 241Am contamination in the marine environment.

Determination of uranium isotopes in marine sediments and seawaters by SF ICP-MS after rapid chemical separation using TK200 resin.

This work provided a novel analytical procedure for rapid and precise uranium isotopic determination in marine sediment and seawater, using a new type of extraction resin, TK200 resin, in combination with microwave digestion (for marine sediments), Fe(OH)3 co-precipitation (for seawater), and single collector sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) measurement. The removal ability of TK200 extraction chromatography for the interfering elements (IEs) Hg, Pb, Th, Pt, Tl, and the matrix rare earth elements (REEs) was carefully investigated. High decontamination factors (DFs) were obtained for IEs and REEs. Accurate quantification of uranium isotope ratios was accomplished based on a "double-cycle" ICP-MS measurement method. The analytical method was optimized and validated with isotopic standards (IRMM-187), matrix-containing certified reference marine sediments (IAEA-384, IAEA-385, and IAEA-412), and seawater reference material (IAEA-443). A stable chemical recovery of ~ 90% was obtained for both types of marine environmental samples, and the method showed great efficiency with a total analytical time of less than 6 h. The proposed procedure was validated following ISO/IEC 17025 guidelines. The important factors affecting the isotope ratio results (instrument background, procedural blank, memory effects, peak tailing, mass discrimination, dead time, and hydride interferences) were considered in the estimation of combined uncertainties. This work provides an alternative way for the determination of trace uranium isotope ratios and can be applied in the emergency monitoring of nuclear accidents and marine environmental analysis.

Application of SS-CS-HR-AAS measurements for the detection of Ag nanoparticles in marine invertebrates.

The present study describes the development of a fit-for-purpose analytical procedure for the detection of Ag NPs in different marine organisms by Solid Sampling Continuous Source High Resolution Atomic Absorption Spectrometry (SS-CS-HR-AAS). The detection is based on the observation of the Ag absorption peak and its atomization delay tad which is different for ionic Ag and Ag NPs. The temperature program was optimized in order to achieve the maximum difference between the t ad (Δtad ). The method was first developed using biota CRMs spiked with different Ag NPs standard solutions or Ag+ , at the same concentration. Then, laboratory exposure experiments were performed on mussels and marine sponges. The results showed that the developed methodology is suitable for the detection of Ag NPs for both groups of organisms, showing Δtad up to 3.1 s. The developed method is therefore a promising tool to assess the presence of AgNPs in marine invertebrates.

Marine sponges as coastal bioindicators of rare earth elements bioaccumulation in the French Mediterranean Sea.

In recent years, the widespread use of rare earth elements (REEs) has raised the issue of their harmful effects on the aquatic environment. REEs are now considered as contaminants of emerging concern. Despite the increasing interest of REEs in modern industry, there is still a lack of knowledge on their potential impact on the environment and especially in the marine environment. In this context, the need for monitoring tools to assess REEs pollution status in marine ecosystems is considered as the first step towards their risk assessment. Similar to mussels, filter-feeder sponges have emerged as a key bio-monitor species for marine chemical pollution. Their key position at a low level of the trophic chain makes them suitable model organisms for the study of REEs potential transfer through the aquatic food web. We therefore undertook a comparative study on seven marine sponge species, assessing their capability to bioaccumulate REEs and to potentially transfer these contaminants to higher positions in the trophic chain. A spike experiment under controlled conditions was carried out and the intra- and inter-species variability of REEs was monitored in the sponge bodies by ICP-MS. Concentrations were found to be up to 170 times higher than the corresponding control specimens. The tubular species Aplysina cavernicola showed the highest concentrations among the studied species. This study shows, for the first time, the potential of marine sponges as bio-monitor of REEs as well as their possible application in the bioremediation of polluted sites.

Rapid determination of femtomolar methylmercury in seawater using automated GC-AFS method: Optimisation of the extraction step and method validation.

Among ionic mercury species methyl mercury (MMHg) is the most toxic form present in the environment, which is known to be bio-accumulative neurotoxin in the aquatic food chain and could provide the major route of exposure for humans to mercury through consumption of marine food products. The availability of reliable analytical methods for evaluating spatial and temporal contamination trends of MMHg in the ocean is an important prerequisite for marine monitoring. Sound strategies for marine monitoring call also for measurement systems capable of producing comparable analytical results with demonstrated quality. A sensitive analytical procedure for environmental monitoring of MMHg content in seawater, based on specific extraction and Gas Chromatography Atomic Fluorescence Spectrometry validated according to the requirements of international guidelines and standards, ISO 17025 and Eurachem guidelines, is presented in this study. The entire measurement process was described by mathematical equations and all factors influencing the results were systematically investigated. Selectivity, working range, linearity, recovery (94 ± 4%), repeatability (3.3%-4.5%), intermediate precision (2.9%), limits of detection (0.0004 ng kg-1as Hg) were systematically assessed. The relative expanded uncertainties obtained were in the range from 16% to 25%, (k = 2). Modelling of the entire measurement process related obtained values for MMHg in seawater to the International System of units (Kg). The potential of this analytical procedure was tested and additionally validated via inter laboratory comparison exercise organised under the Geotraces programme. Obtained results were in excellent agreement with the assigned values. The proposed analytical procedure from the sample preparation to the measurement step combined with the high efficiency of the new generation of the automated MMHg analyzers is fit for purpose for routine monitoring studies on the dissolved MMHg in the costal and open ocean seawaters.

Comparative study on Hg bioaccumulation and biotransformation in Mediterranean and Atlantic sponge species.

In this work we present an assessment of mercury (Hg) and methyl mercury (MeHg) bioaccumulation in different species of marine sponges collected off the Northwestern Mediterranean and Northeastern Atlantic coasts. Overall the results showed significant accumulation of Hg in sponges, with the Mediterranean sponge Chondrilla nucula exhibiting the highest total Hg content (up to 0.5 mg kg-1) and bio-concentration factor (BCF) up to 23. A significant inter-species variability of Hg bioaccumulation was observed among species collected at the same site. The sponges, collected in marine environment contaminated with Hg show consistently higher Hg accumulation, meaning that the bioaccumulation is proportional to the Hg availability in the surrounding environment. Different extraction protocols were tested for MeHg analysis and, generally, a low MeHg ratio in Hg species (4% and 17% average for Mediterranean and Irish sponges respectively) was detected suggesting a possible demethylation process and therefore a promising role of sponges for Hg bioremediation Additionally, the Hg isotopic composition in these organisms was determined and it showed that MDF (mass dependent fractionation) is the main process in sponges, with the absence of significant MIF. This result suggests a dominant role of associated microbial population in the methylation and/or demethylation processes.

Simultaneous speciation analysis of mercury in marine origin samples by high performance liquid chromatography and species - specific isotope dilution inductively coupled plasma mass spectrometry.

Species-specific isotope dilution inductively coupled plasma quadrupole mass spectrometry reference method and high-performance liquid chromatography were applied for simultaneous determination of mercury species in marine samples. Different extraction protocols for mercury species were tested and evaluated. It was found that after exposure to microwave energy the inorganic mercury (iHg) and methyl mercury (MeHg) can be completely extracted from marine biota sample by 4.5 mol L-1 HCl as well as by 3.0 mol L-1 HNO3 and further separated with HPLC. The obtained results for iHg and MeHg in the IAEA-461 certified reference material (CRM) clam Gafrarium tumidum biota sample were as follow: (341 ± 21) µg kg-1 or (338 ± 15) µg kg-1 and (61.3 ± 2.2) µg kg-1 (recovery of (98.4 ± 3.6) %) or (61.1 ± 2.8) µg kg-1 (recovery of (98.1 ± 4.6) %), respectively when diluted HCl or HNO3 were applied in the extraction step. However, these protocols are not applicable to marine sediment samples, where the iHg is the predominant form. Therefore, one selective extraction procedure for MeHg from sediment was applied to make possible its separation and quantification. This procedure consisted of series of subsequent extraction steps at room temperature: first with a mixture of H2SO4/KBr/CuSO4, next with organic solvent dichloromethane and as a final step one back-extraction with Na2S2O3 solution. The combination of the selective extraction with the ID calibration approach was found to be an efficient way for the simultaneous determination and separation of both MeHg and iHg species in one chromatographic run. The proposed procedure was successfully used for the determination of mercury species in the IAEA-405 sediment CRM and further applied for the simultaneous measurements of iHg and MeHg in a candidate CRM - the IAEA-475 sediment sample. The determined mass fractions were (30.1 ± 1.6) µg kg-1 and (196 ± 8) ng kg-1 for iHg and MeHg, respectively. The difference between obtained in this study results and those from the reference IAEA-475 values was 1.5% and further validated the developed in this study analytical methodology. To the best of our knowledge, this selective procedure for MeHg extraction was never used before for the simultaneous quantification of mercury species in marine sediment.

Trace elements contamination assessment in marine sediments from different regions of the Caribbean Sea.

Trace elements (TEs), rare earth elements (REEs), and methylmercury (MeHg) concentrations as well as mercury (Hg) and lead (Pb) isotope compositions in sediment samples collected from strategic locations along the Caribbean Sea were determined. The analyzed sediment samples were collected at different core depths from localities in Colombia, Cuba, Haiti, and the Dominican Republic. The evaluation of pollution assessment indices i.e. enrichment factors and geoaccumulation index revealed significant enrichment of several priority substances, such as Pb, Cd and Hg, in most of the sampling sites. Hg was found in extremely high concentrations (up to 22 ± 3 mg kg-1) in bottom samples of Colombian core, which led the authors to further investigate this area with respect to the source for Hg contamination. The analysis of Hg isotope ratios in Colombian sediments and the Pb isotope ratios in all studied cores, helped in the identification of likely pollution sources and represents a critically important record of anthropogenic influence in the region. Finally, the REEs patterns determined in all samples, also provide a needed baseline for these contaminants in the Caribbean region.

Cold vapour matrix-independent generation and isotope dilution inductively coupled plasma mass spectrometry for reference measurements of Hg in marine environmental samples.

The analytical procedure for reference measurements of Hg in marine environmental samples based on cold vapour generation (CVG) inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and isotope dilution calibration strategy (ID) is described in the present study. The procedure was applied on different matrices and varying mass fractions for mercury in oyster, marine sediment and costal seawater samples. The use of CVG for sample introduction resulted in sensitivity enhancement, reduction of blank levels, minimization of matrix interferences and the elimination of memory effects. The entire measurement process was described by mathematical equations, and all factors influencing the final results were systematically investigated. The expanded uncertainty on results was estimated following the ISO/Guide to the Expression of Uncertainty in Measurement guidelines, and all major contributions were identified. Modelling of the entire measurement process and the use of primary method of measurements ID ICP-MS related obtained values for total mercury in different types of marine matrices to the international system of units SI. Obtained results for mercury mass fractions in biota and marine sediments were used as the International Atomic Energy Agency's  contribution in the certification campaigns for marine reference materials and were in excellent agreement with the assigned reference values.

First assessment on trace elements in sediment cores from Namibian coast and pollution sources evaluation.

Trace elements (TEs), Rare Earth Elements (REEs) and Pb isotope ratios were determined in six small cores sampled along the Namibian coast and different indices, such as Enrichment Factor, Geo-accumulation Index and Pollution load index, were calculated to evaluate possible metal contamination in the area. Concentrations of Pb, Cu, As and Cd were strongly enhanced at the upper 7 cm of core C5, which is located at Walvis Bay, at the major harbor and urban/industrial center of Namibia, indicating the impact from the recent anthropogenic activities. Principal Component Analysis was applied to the data set indicating possible common sources of the contaminants. Pb stable isotope ratios, combined with the dating of core C5 at Walvis Bay, further confirmed the anthropogenic provenance of Pb sources in the recent sediment deposits, which occurred after 1945, when the anthropogenic activities in the area began to increase. REEs profiles were also determined, showing enrichment in REEs for some of the samples, typical for the minerals present in the area. Ce anomaly was detected in one of the cores but the REEs profile did not reveal anomalies ascribable to anthropogenic influence.

Baseline study on trace and rare earth elements in marine sediments collected along the Namibian coast.

Namibia is a fast-growing country with extensive mineral extraction activities used in diamond, fluorspar, uranium, and metals production. To assess the impact of land based human activities on the Namibian coastal marine environment, 25 elements were analyzed in 22 surface sediments samples collected along the coast. After applying a variety of pollution assessment indices (Enrichment Factor, Igeo and Pollution Load Indexes) was concluded that As, Cd and Sb were considerably enriched in the sediments from several sites, while Cu, Pb and Zn showed very high enrichment near the Walvis Bay harbor. Pearson's correlation and Principal Component Analysis were used to investigate common metal sources. Additionally, the determination of Pb isotope ratios confirmed the contribution of land based human activities at Walvis Bay and Lüderitz as sources of pollution. The analysis of REEs did not reveal any important enrichment due to anthropogenic activities, but provides a needed baseline for further investigations.

Marine sponges as a powerful tool for trace elements biomonitoring studies in coastal environment.

In this work, we performed a comparative study on six marine sponge species collected along the French Mediterranean and Irish coasts for their TEs accumulation. Intra and inter-species variabilities were examined. Among the Mediterranean species, Cymbaxinella damicornis accumulates significantly more As and Cu than others sponge species; Chondrilla nucula more Ni and Mo and Acanthella acuta more Ag. Among Irish samples, Hymeniacidon perlevis showed higher accumulation properties for most of TEs in comparison to Halichondria panicea. Bioconcentration Factors were > 1 in all species for most of TEs. This study suggests that TEs bioaccumulation is most likely associated to differences in morphological features and/or to specific bacterial communities associated to different species. The determination of Pb isotope ratios revealed mainly natural Pb sources for Mediterranean and Kilkieran Bay's samples, and rather anthropogenic influence for Belfast samples. This study confirms that sponges represent a powerful tool for biomonitoring studies.

Determination of ultra-trace level of 232Th in seawater by ICP-SFMS after matrix separation and preconcentration.

This article describes the development and validation of an analytical procedure for the matrix separation, preconcentration and determination of sub-ng kg-1 levels 232Th in a small volume (20 mL) of seawater samples. The matrix separation and Th preconcentration was carried out using a commercially available ion-chelation system seaFAST-pico. The acidified to pH < 2 seawater samples were mixed on-line with the ammonium acetate buffer (pH of 6.0 ± 0.2) before loading on the column containing resin with iminodiacetic and ethylenediaminetriacetic functional groups. At this pH, 232Th was quantitatively retained on the resin, demonstrating a good affinity (selectivity) for Th in seawater matrix. The element retained on the resin was eluted using only 0.2 mL of 1.8 M HNO3 enabling to achieve high preconcentration factor. The pretreatment procedure, with two sample loading cycles (each one 10 mL), was accomplished in about 25 min. Determining 232Th mass fraction in seawater samples was based on isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS) method, which was considered as the most accurate calibration strategy for precise quantification of 232Th mass fraction in seawater samples. ISO/IEC17025 and Eurachem guidelines were followed to perform the validation of the developed in this study procedure. In the case of seawater samples with natural level of thorium the major contributions to the expanded uncertainty arose from the uncertainty associated with isotopic ratio measurements in the isotopically spiked sample, followed by the correction for procedural blank and the correction for mass discrimination effect. The estimated method detection limit for 232Th was 0.005 ng kg-1. The developed method was successfully applied to the determination of 232Th mass fraction in seawater reference samples: IAEA-443, SLEW-3, NASS-4, NASS-6, and CASS-5. Although 232Th is not certified in any of the seawater reference materials, a good agreement was obtained between the results in this study and data published elsewhere.

Determination of low-level plutonium in seawater by sector field inductively coupled plasma mass spectrometry: method validation.

Sources of plutonium isotopes to the marine environment are well defined, both spatially and temporally which makes plutonium (Pu) a potential tracer for oceanic processes. This paper presents the optimisation and validation of an analytical procedure for ultra-trace determination of Pu isotopes (239Pu and 240Pu) in seawater based on the external calibration and sector field inductively coupled plasma mass spectrometry (SF ICP-MS) determination. Additionally, method for Pu isotope ratio (240Pu/239Pu) in marine samples is also discussed. A combination of two-step anion exchange (AG1-X8) and one-step extraction chromatography (TEVA) was very efficient resulting in uranium (U) decontamination factor of 5 × 106-1 × 108. A full validation approach in line with ISO 17025 standard and Eurachem guidelines was followed. With this in mind, blanks, recovery (87 ± 8 %, k = 2), within-laboratory repeatability (5.6 %), limits of detection (0.12 and 0.08 fg mL-1 for 239Pu and 240Pu, respectively) and expanded uncertainty (13 %, k = 2) were systematically assessed. The procedure was applied for the determination of 239Pu and Pu in seawater sample coming from Mediterranean Sea. Obtained results were in good agreement with results obtained with alpha spectrometry, applied on the same seawater sample. Pu/239Pu atom ratio in seawater sample from the Mediterranean Sea was also determined. The precision and accuracy of 240Pu/239Pu isotopic ratio analysis were carefully examined using NBS-947 isotopic standard. 240Pu/239Pu ratio was found to be 0.187 ± 0.006 and is in agreement with accepted ratios for the global fallout of Pu.

Reference measurements for total mercury and methyl mercury content in marine biota samples using direct or species-specific isotope dilution inductively coupled plasma mass spectrometry.

The analytical procedures for reference measurements of the total Hg and methyl mercury (MeHg) mass fractions at various concentration levels in marine biota samples, candidates for certified reference materials (oyster and clam Gafrarium tumidum), were evaluated. Two modes of application of isotope dilution inductively coupled plasma mass spectrometry method (ID ICP-MS), namely direct isotope dilution and species-specific isotope dilution analysis with the use of two different quantification mass spectrometry techniques were compared. The entire ID ICP-MS measurement procedure was described by mathematical modelling and the combined uncertainty of measurement results was estimated. All factors influencing the final results as well as isotopic equilibrium were systematically investigated. This included the procedural blank, the moisture content in the biota samples and all factors affecting the blend ratio measurements (instrumental background, spectral interferences, dead time and mass discrimination effects as well as the repeatability of measured isotopic ratios). Modelling of the entire measurement procedures and the use of appropriate certified reference materials enable to assure the traceability of obtained values to the International System of Units (SI): the mole or the kilogram. The total mass fraction of mercury in oyster and clam biota samples, after correction for moisture contents, was found to be: 21.1 (1.1) 10(-9) kg kg(-1) (U =5.1% relative, k=2) and 390.0 (9.4) 10(-9) kg kg(-1) (U=2.4% relative, k=2), respectively. For the determination of mercury being present as methyl mercury, the non-chromatographic separation on anion-exchange resin AG1-X8 of the blended samples was applied. The content of MeHg (as Hg) in oyster sample was found: 4.81 (24) 10(-9)kgkg(-1) (U=5.0%, k=2) and 4.84 (21) 10(-9)kgkg(-1) (U=4.3%, k=2) with the use of quadrupole (ICP QMS) or sector field (ICP SFMS) inductively coupled plasma mass spectrometers, respectively. In the case of clam sample, the concentration of MeHg (as Hg) was found to be: 61.0 (2.3) 10(-)(9)kgkg(-1) (U=3.8%, k=2) and 61.3 (2.2) 10(-)(9)kgkg(-1) (U=3.6%, k=2), respectively. The mass fractions for total Hg and MeHg determined in this study were used as a contribution of the International Atomic Energy Agency (IAEA) Environment Laboratories in the characterisation of the IAEA 461 and IAEA 470 certified reference materials. The obtained good agreement with the reference values further validated the methods developed in this study.

Determination of methylmercury in marine biota samples with advanced mercury analyzer: method validation.

In this paper, we present a simple, fast and cost-effective method for determination of methyl mercury (MeHg) in marine samples. All important parameters influencing the sample preparation process were investigated and optimized. Full validation of the method was performed in accordance to the ISO-17025 (ISO/IEC, 2005) and Eurachem guidelines. Blanks, selectivity, working range (0.09-3.0ng), recovery (92-108%), intermediate precision (1.7-4.5%), traceability, limit of detection (0.009ng), limit of quantification (0.045ng) and expanded uncertainty (15%, k=2) were assessed. Estimation of the uncertainty contribution of each parameter and the demonstration of traceability of measurement results was provided as well. Furthermore, the selectivity of the method was studied by analyzing the same sample extracts by advanced mercury analyzer (AMA) and gas chromatography-atomic fluorescence spectrometry (GC-AFS). Additional validation of the proposed procedure was effectuated by participation in the IAEA-461 worldwide inter-laboratory comparison exercises.

Determination of methylmercury in marine sediment samples: method validation and occurrence data.

The determination of methylmercury (MeHg) in sediment samples is a difficult task due to the extremely low MeHg/THg (total mercury) ratio and species interconversion. Here, we present the method validation of a cost-effective fit-for-purpose analytical procedure for the measurement of MeHg in sediments, which is based on aqueous phase ethylation, followed by purge and trap and hyphenated gas chromatography-pyrolysis-atomic fluorescence spectrometry (GC-Py-AFS) separation and detection. Four different extraction techniques, namely acid and alkaline leaching followed by solvent extraction and evaporation, microwave-assisted extraction with 2-mercaptoethanol, and acid leaching, solvent extraction and back extraction into sodium thiosulfate, were examined regarding their potential to selectively extract MeHg from estuarine sediment IAEA-405 certified reference material (CRM). The procedure based on acid leaching with HNO3/CuSO4, solvent extraction and back extraction into Na2S2O3 yielded the highest extraction recovery, i.e., 94±3% and offered the possibility to perform the extraction of a large number of samples in a short time, by eliminating the evaporation step. The artifact formation of MeHg was evaluated by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS), using isotopically enriched Me(201)Hg and (202)Hg and it was found to be nonexistent. A full validation approach in line with ISO 17025 and Eurachem guidelines was followed. With this in mind, blanks, selectivity, working range (1-800 pg), linearity (0.9995), recovery (94-96%), repeatability (3%), intermediate precision (4%), limit of detection (0.45 pg) and limit of quantification (0.85 pg) were systematically assessed with CRM IAEA-405. The uncertainty budget was calculated and the major contribution to the combined uncertainty (16.24%, k=2) was found to arise from the uncertainty associated with recovery (74.1%). Demonstration of traceability of measurement results is also presented. The validated measurement procedure was applied to the determination of MeHg incurred in sediments from a highly polluted and scarcely studied area in the Caribbean region.

Determination of methylmercury in marine biota samples: method validation.

Regulatory authorities are expected to measure concentration of contaminants in foodstuffs, but the simple determination of total amount cannot be sufficient for fully judging its impact on the human health. In particular, the methylation of metals generally increases their toxicity; therefore validated analytical methods producing reliable results for the assessment of methylated species are highly needed. Nowadays, there is no legal limit for methylmercury (MeHg) in food matrices. Hence, no standardized method for the determination of MeHg exists within the international jurisdiction. Contemplating the possibility of a future legislative limit, a method for low level determination of MeHg in marine biota matrixes, based on aqueous-phase ethylation followed by purge and trap and gas chromatography (GC) coupled to pyrolysis-atomic fluorescence spectrometry (Py-AFS) detection, has been developed and validated. Five different extraction procedures, namely acid and alkaline leaching assisted by microwave and conventional oven heating, as well as enzymatic digestion, were evaluated in terms of their efficiency to extract MeHg from Scallop soft tissue IAEA-452 Certified Reference Material. Alkaline extraction with 25% (w/w) KOH in methanol, microwave-assisted extraction (MAE) with 5M HCl and enzymatic digestion with protease XIV yielded the highest extraction recoveries. Standard addition or the introduction of a dilution step were successfully applied to overcome the matrix effects observed when microwave-assisted extraction using 25% (w/w) KOH in methanol or 25% (w/v) aqueous TMAH were used. ISO 17025 and Eurachem guidelines were followed to perform the validation of the methodology. Accordingly, blanks, selectivity, calibration curve, linearity (0.9995), working range (1-800pg), recovery (97%), precision, traceability, limit of detection (0.45pg), limit of quantification (0.85pg) and expanded uncertainty (15.86%, k=2) were assessed with Fish protein Dorm-3 Certified Reference Material. The major contributions to the expanded uncertainty, i.e. 86.1%, arose from the uncertainty associated with recovery, followed by the contribution from fluorescence signal. Additional validation of the methodology developed was effectuated by the comparison with the values reported for MeHg in the IAEA-452 inter-laboratory comparison exercise.

Cadmium determination in natural waters at the limit imposed by European legislation by isotope dilution and TiO2 solid-phase extraction.

The cadmium content in surface water is regulated by the last European Water Framework Directive to a maximum between 0.08 and 0.25 µg L(-1) depending on the water type and hardness. Direct measurement of cadmium at this low level is not straightforward in real samples, and we hereby propose a validated method capable of addressing cadmium content below µg L(-1) level in natural water. It is based on solid-phase extraction using TiO(2) nanoparticles as solid sorbent (0.05 g packed in mini-columns) to allow the separation and preconcentration of cadmium from the sample, combined to direct isotope dilution and detection by inductively coupled plasma mass spectrometry (ID-ICP-MS). The extraction setup is miniaturised and semi-automated to reduce risks of sample contamination and improve reproducibility. Procedural blanks for the whole measurement process were 5.3 ± 2.8 ng kg(-1) (1 s) for 50 g of ultrapure water preconcentrated ten times. Experimental conditions influencing the separation (including loading pH, sample flow rates, and acid concentration in the eluent) were evaluated. With isotope dilution the Cd recovery rate does not have to be evaluated carefully. Moreover, the mathematical model associated to IDMS is known, and provides transparency for the uncertainty propagation. Our validation protocol was in agreement with guidelines of the ISO/IEC 17025 standard (chapter 5.4.5). Firstly, we assessed the experimental factors influencing the final result. Secondly, we compared the isotope ratios measured after our separation procedure to the reference values obtained with a different protocol for the digested test material IMEP-111 (mineral feed). Thirdly, we analysed the certified reference material BCR-609 (groundwater). Finally, combined uncertainties associated to our results were estimated according to ISO-GUM guidelines (typically, 3-4% k = 2 for a cadmium content of around 100 ng kg(-1)). We applied the developed method to the groundwater and wastewater samples ERM-CA615 and BCR-713, respectively, and results agreed with certificate values within uncertainty statements.

Determination of the total and extractable mass fractions of cadmium and lead in mineral feed by using isotope dilution inductively coupled plasma mass spectrometry.

This paper describes the determination of the total and extractable mass fractions of Cd and Pb in mineral feed test sample distributed by the Community Reference Laboratory for Heavy Metals in Feed and Food (CRL-HM), in the frame of the fifth interlaboratory comparison for the European Union National Reference Laboratories (NRL). The developed in this study protocol for the total and extractable mass fractions of Pb and Cd in mineral feed sample is based on isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The applied dual spiking approach reduced by 50% the number of analytical steps. The addition of hydrofluoric acid in the digestion step was found necessary to ensure a full decomposition and complete isotope equilibration. Quadrupole inductively coupled plasma mass spectrometer equipped with collision reaction interface (CRI) was employed for the measurements of Cd and Pb. Two methods for the determination of Cd were applied and compared. In the first one the high molybdenum content was reduced by introduction of matrix separation step followed by standard ICP-MS mode measurement, whereas in the second one CRI mode was used for the determination of Cd without preliminary matrix separation. The estimation of the combined uncertainty was performed according to the ISO guidelines. Uncertainty propagation was used as a tool for validation of proposed analytical procedure. Contributions from the correction for moisture content, sample homogeneity, procedural blank, instrumental background and dead time effects were evaluated in both cases. The largest uncertainty contributors for Cd and Pb is due to the within bottle homogeneity of the mineral feed sample - 50.3% and 90% respectively. The IUPAC data for isotope composition are the second major contributor to the combined uncertainty of the result for the total mass fraction of Cd in mineral feed - 43.3%. However, the ID ICP-MS results achieved from the two series of samples (partial and total extraction) were in excellent agreement within uncertainty, irrespective of the method used for extraction. The ID ICP-MS results for the total and extractable mass fractions of Cd and Pb in feed sample were compared with the results obtained with external calibration approach and routinely applied in the daily analytical practice of the Belgium National Reference Laboratory for trace elements in food and feed.