Biomedical subjects

H Emons

Publications and source records attributed to H Emons.

At least 19 recordsLinked to original sources

PubMed2006

Towards the certification of the purity of calibrant reference materials for thyroid hormones: a chicken and egg dilemma.

The certification of the purity of CRMs intended for calibration, where no other certified material already exists for comparison, raises principle questions on how to determine the purity of a "first" calibrant in the calibration hierarchy. We developed and certified two calibration CRMs for their purity in thyroid hormones taking into consideration inorganic residues, residual solvents and organic impurities detectable by HPLC-UV and HPLC-MS. IRMM-468 was certified for a thyroxine (T(4)) mass fraction of 98.6+/-0.7% and IRMM-469 was certified for a 3,3',5-triiodothyronine (T(3)) mass fraction of 97.1+/-0.7%. The approach we used aims to determine the purity of these two CRMs to the best of our knowledge and taking all scientific aspects properly into account for the estimation of an uncertainty related to the stated purity.

Calibration↗

PubMed2005

Homogeneity and stability study of the candidate reference material Adamussium colbecki for trace elements.

The preparation of a new candidate certified reference material (CRM) for trace elements based on the antarctic bivalve Adamussium colbecki(IRMM 813) was carried out by the Istituto Superiore di Sanità(ISS, Rome, Italy) in cooperation with the Institute for Reference Materials and Measurements, Joint Research Centre of the European Commission (EC-JRC-IRMM), in the frame of the Italian National Programme of Research in Antarctica (Programma Nazionale di Ricerca in Antartide, PNRA). Samples were collected at Terra Nova Bay (Ross Sea) during the 2000-2001 expedition in Antarctica. The preparation of a material suitable for certification was performed by the EC-JRC-IRMM. Measurements for homogeneity and short-term stability tests were carried out by ISS. The elements selected for the certification project were As, Cd, Cu, Cr, Fe, Mn, Ni and Zn. For the above-mentioned tests, the determination of the elements of interest was performed on samples mineralised by microwave-assisted acid digestion. The analytical techniques employed to this end were inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry (ICP-DRC-Q-MS). The candidate material was shown to be fit for purpose with regard to homogeneity and short-term stability, thus allowing the following phases of the certification project to be undertaken, in the first place the selection of expert laboratories for the accomplishment of the certification campaign.

Animals↗

PubMed2005

Aflatoxin M1 in milk powders: processing, homogeneity and stability testing of certified reference materials.

As part of the certification campaign of three candidate reference materials for the determination of aflatoxin M1 (AfM1) in whole milk powders, homogeneity, short- and long-term stability tests of naturally contaminated milk powders have been performed. The homogeneity of two AfM1-contaminated milk powders was studied by taking samples at regular intervals of the filling sequences and analysing in triplicate for their AfM1 contents by liquid chromatography with fluorescence detection (LC-FLD) using random stratified sampling schemes. The homogeneity testing of an AfM1 'blank' milk powder material was performed by determining the nitrogen content because AfM1 levels were below the limit of detection of the most sensitive determination method. The short-term stability of AfM1-contaminated milk powders was evaluated at three different storage temperatures (4, 18 and 40 degrees C). After storage times of 0, 1, 2 and 4 weeks, samples were investigated using LC-FLD. The long-term stability study comprised of measurements after 0, 6, 12 and 18 months after storage at -20 and 4 degrees C. Analyses were done by LC-FLD. Based on the homogeneity tests, the materials were sufficiently homogenous to serve as certified reference materials. Corresponding uncertainty contributions of 0.23-0.89% were calculated for the homogeneity. The stability measurements showed no significant trends for both short- and long-term stability studies. The long-term stability uncertainties of the AfM1-contaminated milk powders were 7.4 and 6.3%, respectively, for a shelf-life of 6 years and storage at -20 degrees C. Supplementary stability monitoring schemes over a long period of several years are currently ongoing.

Aflatoxin M1↗

PubMed2004

Trichothecenes: reference materials and method validation.

The frequent contamination of food and feed with trichothecene mycotoxins, the high consumption of these products, and the potential risk associated herewith, has led to an increasing public awareness and therefore to the establishment of measures to control trichothecene contamination. The analytical difficulty and the economic importance of controlling trichothecenes in food and feed support the need for certified reference materials (CRMs) and validated methods. They form invaluable tools to ensure comparability and traceability in analytical measurements and are very useful for the implementation of written standards, legislation/regulations and laboratory accreditation. The present paper provides an overview of previous work, current strategies and prospectives for the production of CRMs and validation of analytical methods in the field of trichothecene analysis. Additional information is given on methodological demands, normative frameworks and commonly accepted procedures.

Chemistry Techniques, Analytical↗

PubMed2004

Development of an ombrotrophic peat bog (low ash) reference material for the determination of elemental concentrations.

Given the increasing interest in using peat bogs as archives of atmospheric metal deposition, the lack of validated sample preparation methods and suitable certified reference materials has hindered not only the quality assurance of the generated analytical data but also the interpretation and comparison of peat core metal profiles from different laboratories in the international community. Reference materials play an important role in the evaluation of the accuracy of analytical results and are essential parts of good laboratory practice. An ombrotrophic peat bog reference material has been developed by 14 laboratories from nine countries in an inter-laboratory comparison between February and October 2002. The material has been characterised for both acid-extractable and total concentrations of a range of elements, including Al, As, Ca, Cd, Cr, Cu, Fe, Hg, Mg, Mn, Na, Ni, P, Pb, Ti, V and Zn. The steps involved in the production of the reference material (i.e. collection and preparation, homogeneity and stability studies, and certification) are described in detail.

Environmental Monitoring↗

PubMed2003

Preservation of sensitive CRMs and monitoring their stability at IRMM.

Over the years, the nature of CRMs has changed considerably. Recently, more and more CRMs have been certified in their "natural" form, that is processed as little as possible, with analytes at their natural concentration level. This and the trend towards certified properties other than the concentrations of clearly defined molecules/elements have made guaranteeing stability of CRMs and estimating a shelf life an even more important issue for reference material producers than it has been before. One way to meet this challenge is to take more care in processing, storage and dispatch of CRMs. At IRMM, approximately 20 % of the RMs are stored at -20 degrees C or below and about 10% require cooled transportation. In addition, increased efforts for assessing stability are needed. Shelf lives are estimated using addition of an uncertainty component based on real-temperature stability studies rather than by accelerated stability studies. These pre-certification efforts are complemented by a stability-monitoring program, which at IRMM includes 80 % of the non-nuclear and non-isotopic materials. Although the costs for these efforts are high in absolute terms, they are only a minor and indispensable contribution to the total costs of CRM production.

Journal Article↗

PubMed2002

Methyl mercury uptake and associations with the induction of chromosomal aberrations in Chinese hamster ovary (CHO) cells.

In order to evaluate possible health effects of environmental exposure of humans towards methyl mercury species, relevant exposure experiments using methyl mercury chloride in aqueous solution and Chinese hamster ovary (CHO) cells were performed. The solution was monitored for the presence of monomethyl, dimethyl and elemental mercury by several analytical techniques including chromatographic as well as atomic absorption and mass spectrometric methods. Methyl mercury induces structural chromosomal aberrations (CA) and sister chromatid exchanges (SCE) in CHO cells. At a concentration of methyl mercury in the culture medium of 1.0 x 10(-6) M where the frequencies of CA and SCE are significantly elevated, the intracellular concentration was 1.99 x 10(-16) mol/cell. Possible biochemical processes leading to the cytogenetic effects are discussed together with toxicological consequences, when humans (e.g. workers at waste deposits) are exposed to environmental concentrations of methyl mercury.

Animals↗

PubMed2001

Detection of metal ions in aqueous solution by voltohmmetry.

A new electrochemical detection principle is described for the trace analysis of dissolved species which can be deposited at polycrystalline thin-film metal electrodes and which change the surface resistance of the electrode. Because the latter parameter is measured in dependence on the applied electrode potential this method is called voltohmmetry. The preparation of the required thin-film electrodes and the experimental set-up is introduced and discussed. Typical voltohmmetric experiments are illustrated by measurements of Tl+/Tl at polycrystalline gold electrodes with a thickness of 15 nm. The analytical capabilities of this new approach are discussed. It is already possible to determine heavy metals such as Tl+, Pb2+ or Cd2+ in the range of a few microgram/L by surface resistance-potential measurements at thin-film electrodes with a simple cyclic technique. Further developments of voltohmmetry are envisaged.

Journal Article↗

PubMed2001

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).

Animals↗

PubMed2001

Challenges from speciation analysis for the development of biological reference materials.

Starting with explanations for the increasing demand for speciation analysis the need of appropriate certified reference materials is justified. Specific aspects of biological reference materials for speciation QA/QC are discussed from the point of view of the total analytical process. Examples of unwanted species transformations during analysis are given and critical analytical steps are highlighted. Unchanged biological materials as CRMs and appropriate pure standard compounds are indispensable for the further development of this analytical field.

Animals↗

PubMed2001

Selective leaching of elements associated with Mn-Fe oxides in forest soil, and comparison of two sequential extraction methods.

For selective dissolution of Mn oxides as components of soil (easily reducible oxides) 0.05 mol L(-1) and 0.1 mol L(-1) NH2OH.HCl acidified to pH 2 and for dissolution of Fe oxides (crystalline form of the oxides) 0.25 mol L(-1) NH2OH.HCl in 25% acetic acid, 0.2 mol L(-1) oxalate buffer and 0.1 mol L(-1) ascorbic acid in oxalate buffer were tested. Dissolved elements were determined by ICP-MS and ICP-OES. The studies indicate that the use of 0.05 mol L(-1) NH2OH.HCl in nitric acid solution (pH 2) and 0.1 mol L(-1) ascorbic acid in 0.2 mol L(-1) oxalate buffer led to selective leaching of trace metals bound by Mn and Fe oxide phases in soil. Comparison of different extraction schemes indicates that the trace elements investigated are mainly bound to minerals consisting of crystalline Fe oxides and insoluble minerals (under the extraction conditions used). The studies also indicate that Mn oxides and organic matter retain a major mobile fraction of the elements investigated in the soil.

Chemistry Techniques, Analytical↗

PubMed2001

Representative sampling and sample preparation in biological environmental monitoring using spruce shoots.

The design of sampling and sample processing has a tremendous effect on the analytical results from which conclusions are drawn with respect to the quality of the environment and any possible impact on human health. Large scale environmental surveys need rigorous planning and extensive screening experiments to evaluate their boundary conditions. Representativeness and sample homogeneity are highlighted here in the context of a long-term biological monitoring survey for trace elements using spruce shoots. Several aspects concerning the selection of samples, amount of material, material processing and sample preparation prior to chemical characterisation are illustrated by selected examples.

Environmental Monitoring↗

PubMed2000

Extraction of antimony and arsenic from fresh and freeze-dried plant samples as determined by HG-AAS.

Six extraction media (acetic acid, EDTA, tetrabutylammonium hydroxide, NaOH, MeOH/H2O, acetonitrile/H2O) were tested for their ability to extract antimony (Sb) and arsenic (As) from freeze-dried poplar leaves, pine shoots and spruce shoots, as well as from a peat matrix. Additionally, the extraction efficiency of Sb and As in fresh and freeze-dried elder leaves and poplar leaves was compared. Total concentrations of Sb and As of aliquots (approximately 220 mg) of the freeze-dried samples were analysed by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) after open vessel digestion with adequate mixtures of nitric, sulfuric, hydrochloric, and perchloric acid. Three reference materials GBW 07602 Bush Branches and Leaves, GBW 07604 Poplar Leaves, and SRM 1575 Pine Needles were analysed with every batch of samples to ensure the accuracy and precision of the applied analytical procedures. The use of hydrofluoric acid in the digestion mixture leads to distinctly lower As values (down to 40%) than actual concentrations in the investigated plant materials. Extraction efficiencies were generally low and lower for Sb than for As. Solutions of 0.66 mol L(-1) NaOH liberated highest amounts of Sb with approximately 10% for poplar leaves, and approximately 19% each for pine shoots and spruce shoots. Distinctly higher concentrations of As in NaOH extracts of poplar leaves (22%), pine shoots (32%), and spruce shoots (36%) were quantified. Extraction experiments resulted in yields of 7-9% from fresh elder and poplar leaves, respectively, and 8-13% for freeze-dried samples for Sb. The corresponding values for As were 10-35% for the fresh material and 7-37% for the freeze-dried samples.

Antimony↗

PubMed1999

Quality assurance in measuring the elemental composition of the alga Fucus vesiculosus.

Algae are increasingly used for the purpose of environmental biomonitoring, for instance in the long-term program of the Federal Environmental Specimen Bank of Germany. Therefore, for the studies presented here, freeze-dried samples of Fucus vesiculosus collected from the North Sea shores were analyzed for a broad range of elements by instrumental neutron activation analysis (INAA), while inductively coupled plasma atomic emission spectrometry (ICP-AES) and mass spectrometry (ICP-MS) were carried out on digests. The entire analytical procedures, including field sampling, cleaning of material, sample handling, determination of blanks and instrumental parameters, are described. Certified reference materials analyzed in parallel with real samples and intermethod comparisons were used for assuring the accuracy of the analytical data. Reproducibility of INAA measurements was between 4 and 6% depending on the element considered. Possible sources of uncertainty and variation of the contaminant origins are discussed. Boundary conditions for the performance of algae sampling within environmental monitoring programs and the application of this marine bioindicator for the purpose of controlling time-dependent and local differences in element patterns are presented.

Cryopreservation↗

PubMed1999

Optimized procedure for the determination of antimony in lipid-rich environmental matrices by flow injection hydride generation atomic absorption spectrometry.

An analytical procedure for the reliable determination of Sb in digests of lipid-rich environmental matrices in the low ng l-1-range based on flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) has been developed. Prior to HG-AAS, aliquots (250 to 320 mg) of dry samples were mineralized with 3 ml nitric acid and 0.5 ml of each sulfuric and perchloric acids in open digestion vessels made of glassy carbon in a heating block. Procedure detection and quantification limits of a previously developed procedure for the determination of Sb in plant materials by FI-HG-AAS were decreased with respect to the lower Sb concentrations in animal tissues, the sensitivity of the instrumental response was increased, and the composition of the acid digestion mixture was re-optimized for lipid-rich samples. The accuracy and precision of the developed procedure was evaluated by the analysis of the two reference materials Bovine Liver 1577a and Pig Kidney CRM 186. These reference materials have been additionally spiked with appropriate amounts of Sb to obtain recovery data. The solution detection limit (3 sigma) in digested samples was 0.021 microgram l-1, the detection limit for the whole procedure based on the dry powders was 7 pg g-1, the method quantification limit for a reliable determination of Sb was 23 pg g-1. The reproducibility of repetitive measurements was 6.0% at 0.1 microgram Sb l-1 and 2.2% at 0.5 microgram Sb l-1. Calibration curves were linear from 0.05 to 3 micrograms Sb l-1. To demonstrate the suitability of the developed method, concentrations of Sb have been determined in pigeon eggs (approximately 2 ng Sb g-1), as well as in bream livers (approximately 4 ng g-1) and in deer livers (approximately 5 to 8 ng g-1) from animals living in remote and urban-industrialized areas of Germany, respectively.

Animals↗

PubMed1999

Biomonitoring of antimony in environmental matrices from terrestrial and limnic ecosystems.

Elder and poplar leaves from various sampling sites were studied with respect to their antimony content. Moreover, a retrospective determination of Sb was performed in representative limnic and terrestrial samples of the Federal Environmental Specimen Bank of Germany which have been collected over 14 years. The analytical procedure is based on an open vessel acid digestion of freeze-dried biological samples and the subsequent quantification of Sb in the digests by flow injection hydride generation atomic absorption spectrometry. Strict quality control schemes were applied to the entire procedure to guarantee accurate and precise results. No long-term changes of the Sb concentrations were found in spruce shoots or poplar leaves from different sampling sites. However, spruce shoots from a semi-natural region showed concentrations of Sb (approximately 22 ng g-1; range: 17-29 ng g-1) that were approximately four times lower than in corresponding samples from an urban-industrialized area. The analysis of virgin and washed elder leaves revealed that approximately 20-30% of the Sb is present on the leaf surface. Sb levels in elder leaves ranged from 5.2 +/- 0.3 ng g-1 in samples from Argentina to 589 +/- 30 ng g-1 in leaves collected directly beside a motorway in Germany. Similarly, poplar leaves from Argentina and Chile showed about 4 ng Sb g-1, whereas 150 ng Sb g-1 was found in poplar leaves from Germany. The lowest concentrations of Sb were determined in digests of pigeon eggs (approximately 2 ng g-1), bream liver (approximately 4 ng g-1) and deer liver (approximately 6 ng g-1). A similar pattern of Sb concentrations in spruce shoots, leaves or liver samples from an industrialized area and an agrarian ecosystem in Germany was established. Concentrations of Sb in elder leaves were closely associated with car traffic, giving maximum concentrations of 589 ng g-1 directly beside a motorway, 207 ng g-1 50 m from the motorway and 153 ng g-1 in a close residential area.

Agriculture↗

PubMed1998

Distribution pattern of organotin compounds at different trophic levels of aquatic ecosystems.

Organotin compounds including methyl- and butyltin species were determined in selected aquatic specimens (fish muscles, fish liver, mussels, algae) as well as in sediment and water from the mud flats of the German North Sea and the River Elbe. The concentration of tributyltin (TBT) ranged between 27-202 ng/g (fresh mass) in fish muscles, 54-223 ng/g (fresh mass) in fish liver, 10-25 ng/g (fresh mass) in common mussels and 42-97 ng/g (fresh mass) in bladderwrack. The concentration of total organotin compounds (mono-, di-, and trimethyltin + mono-, di-, and tributyltin) in water samples along the River Elbe up to the Elbe estuary ranged between 30-96 ng/l. Retrospective investigation of butylin compounds in mussel samples from the North Sea was performed by the analysis of cryogenically stored samples from 1985. A comparison of the results with that in muscles from 1993 shows that the total tin content and the TBT content decreased from 1985-1993 by a factor of 3.5 and 6.5, respectively. In addition estimated bioconcentration factors (BCF) for organotin compounds in samples from different trophic levels are presented.

Animals↗

PubMed1997

Statistical evaluation of ecosystem properties influencing the uptake of As, Cd, Co, Cu, Hg, Mn, Ni, Pb and Zn in seaweed (Eucus vesiculosus) and common mussel (Mytilus edulis).

In order to evaluate the influence of geographically varying marine ecosystem properties on the uptake of trace elements in bioindicators, samples were taken of seaweed (Fucus vesiculosus) and common mussel (Mytilus edulis) along the North Sea and Baltic Sea coast. Seasonal variations of the bioindicator status were minimized by sampling within 1 month. Ecosystem properties considered were the geographical position, the salinity and the concentrations of the macroelements Ca, Fe, K, Mg, Na, P and S in the bioindicators. Trace elements studied were As, Cd, Co, Cu, Hg, Mn, Ni, Pb and Zn. Factor analysis of the concentration patterns in the bioindicators and of salinity as a function of location confirmed the influence of the geographically varying salinity on the biological uptake of macroelements and trace elements. This influence of salinity was higher in the case of seaweed than in the case of mussel. Comparison of the geographical courses of the macroelement and trace-element concentrations by cluster analysis revealed corresponding courses for As and Hg in both bioindicators. All other elements showed different courses in seaweed and mussel. Subsequent cluster analysis comparing locations with respect to the macroelement or trace-element concentration patterns in the bioindicators, indicated a clear separation of North and Baltic Sea locations. However, the trace-element concentration patterns provided a regionally less distinctive ecosystem arrangement than those of the macroelement ones. The results of the cluster analysis were verified by discriminant analysis forming groups of locations with respect to geographical position and salinity. Results of discriminant analysis demonstrated, both for seaweed and for mussel as bioindicators, that the location groups formed according to the macroelement concentration patterns corresponded well with the geographical regions in the order of salinity. On the other hand, location groups based on the trace-element concentration patterns again showed a modified less distinctive ecosystem arrangement than the location groups based on macroelement concentration patterns. This confirms modified conditions for the uptake of trace elements in seaweed or mussel in comparison to the uptake of macroelements.

Animals↗