Measurement of trace elements in murine liver tissue samples: Comparison between ICP-MS/MS and TXRF

BackgroundTrace elements exhibit essential functions in many physiological processes. Thus, for research focusing on trace element homeostasis and metabolism analytical methods allowing for multi-element analyses are fundamental. Small sample amounts may be a big challenge in trace element analyses especially if also other end points want to be addressed in the same sample. Therefore, the aim of the present study was to examine trace elements (iron, copper, zinc, and selenium) in murine liver tissue prepared by a RIPA buffer-based lyses method.Methods and resultsAfter centrifugation, lysates and pellets were obtained and trace elements were analyzed with TXRF in liver lysates. The results were compared to that obtained by a standard microwave-assisted acidic digestion with subsequent ICP-MS/MS analysis of the same liver tissue, liver lysates, and remaining pellets. In addition, trace element concentrations, determined in murine serum with both methods, were compared. For serum samples, both TXRF and ICP-MS/MS provide similar and highly correlating results. Furthermore, in liver lysate samples prepared with RIPA buffer, comparable trace element concentrations were measured by TXRF as with the standard digestion technique and ICP-MS/MS. Only marginal amounts of trace elements were detected in the pellets.ConclusionTaken together, the results obtained by the present study indicate that the RIPA buffer-based method is suitable for sample preparation for trace element analyses via TXRF, at least for the here investigated murine liver samples.     

Role of nuclear analytical probe techniques in biological trace-element research

Many biomedical experiments require the qualitative and quantitative localization of trace elements with high sensitivity and good spatial resolution. The feasibility of measuring the chemical form of the elements, the time course of trace element metabolism, and conducting experiments in living biological systems are also important requirements for biological trace element research. Nuclear analytical techniques that employ ion or photon beams have grown in importance in the past decade and have led to several new experimental approaches. Some of the important features of these methods are reviewed here along with their role in trace element research. Examples of their use are given to illustrate potential for new research directions. It is emphasized that the effective application of these methods necessitates a closely integrated multidisciplinary scientific team.     

Instrumental neutron activation analysis of Standard Reference Material 1941, Organics in Marine Sediment

The National Institute of Standards and Technology has developed a new Standard Reference Material 1941, “Organics in Marine Sediment.” In addition to the organic constituents, over 30 elements have been determined by instrumental neutron activation analysis and prompt-gamma activation analysis. The homogeneity of the material was investigated and relative standard deviations of single-element concentrations in 250-mg samples were found to be 1% or less with regard to major inorganic constituents and rare earth elements. A slightly higher relative SD was found for elements that may stem from biological or anthropogenic input. The element concentrations determined in this work are discussed in comparison to concentrations in other similar reference materials. Concentrations for 31 elements will be included for information on the certificate.

     

Matrix interferences in the analysis of digested biological tissues with inductively coupled plasma-mass spectrometry

To investigate the physiological roles or toxicity of trace or toxic elements, multielement analysis of limited quantities of samples in the biological tissues is required. Inductively coupled plasma mass spectrometry (ICP-MS) suits this requirement, but spectral and nonspectral interferences are inevitable. We examined correction methods for the nonspectral interferences by analyzing signals of 21 elements in various concentrations of HNO₃ as well as five major elements (Na, K, P, Ca, and Cl). Using internal standards, the interferences caused by the major elements were corrected, but the interferences caused by HNO₃ were impossible to correct for elements with high ionization potentials. The analytical results using the standard addition method on 14 elements in standard reference materials and fresh brain tissues confirmed the accuracy of this method. Thus, we concluded that the standard addition method is useful to correct for the nonspectral interferences.     

Multianalysis of trace elements in mosses with inductively coupled plasma-mass spectrometry

As a part of an air-pollution biomonitoring survey, a procedure using inductively coupled plasma-mass spectrometry (ICP-MS) and microwave digestion was developed to achieve a high sample throughput and guarantee the accuracy of the results. This article presents an analytical method to measure 22 trace elements. As, Ba, Cd, Ce, Co, Cr, Cs, Cu, Fe, Hg, La, Mo, Ni, Pb, Rb, Sb, Sr, Th, Tl, U, V, W were analyzed in 563 mosses collected in France. The digestion was performed in polytetrafluoroethylene (PTFE) vessel using the mixture HNO₃-H₂O₂-HF. The data were reprocessed taking into account the drift curve calculated for each element. The detection limits (DL) calculation was based on the standard deviations of the reagent blanks concentrations. The DL varied from one batch to another, because of the heterogeneity of the mosses’ elemental contents. The DL ranged between 0.001 μg/g (Cs, Tl) and 70 μg/g (Fe) and were mainly around 0.01 μg/g (As, Cd, Ce, Co, Hg, La, Mo, Sb, Sr, U, V, W). The detection limits obtained were in agreement with the concentrations observed in the samples, except for Hg and Ni. The reproducibility between duplicates and the analytical precision were near 10%. The procedure was tested with the mosses’ reference materials.     

Imaging and speciation of trace elements in biological environment

Mineral elements, often at the trace level, play a considerable role in physiology and pathology of biological systems. Metallogenomics, metalloproteomics, and metallomics are among the emerging disciplines which are critically dependent on spatially resolved concentration maps of trace elements in a cell or tissue, on information on chemical speciation, and on that on metal-binding coordination sites. The mini-review discusses recent progress in analytical techniques for element profiling on the genome scale, biological trace element imaging, and probing, identification and quantification of chemical species in the biological environment. Imaging of the element distribution in cells and tissue sections is becoming possible with sub-micrometer spatial resolution and picogram-level sensitivity owing to advances in laser ablation MS, ion beam and synchrotron radiation X-ray fluorescence microprobes. Progress in nanoflow chromatography and capillary electrophoresis coupled with element specific ICP MS and molecule-specific electrospray MS/MS and MALDI enables speciation of elements in microsamples in a complex biological environment. Laser ablation ICP MS, micro-SXRF, and micro-PIXE allow mapping of trace element distribution in 1D and 2D proteomics gels. The increasing sensitivity of EXAFS and XANES owing to the use of more intense synchrotron beams and efficient focusing optics provide information about oxidation state, fingerprint speciation of metal sites and metal-site structures.     

Trace elements in the atmosphere.

The distribution and behaviour of particulate trace elements in the atmosphere have been studied by continuous measurements for 5 years at seven non-urban sites in the United Kingdom. Samples have been taken regularly of airborne dust, rainwater and dry deposition: these have been analysed for up to 36 elements. Concentrations of trace elements vary considerably between sites but the relative concentrations are among uniform: this suggests similarity of origin or good atmospheric mixing. By comparing the relative concentrations with those in soil it is possible to differentiate between trace elements that are derived from soil and those that may be attributed to industrial activity. This classification is supported by estimates of the particle sizes in air. The deposition of trace elements can be related to the concentrations presnet in soil and to the annual removal by crops. Retrospective analyses of stored samples from one site describe the history of trace element concentrations in air since 1957. The sea surface is considered as a possible source of atmospheric trace elements.     

Concentrations of copper, zinc, manganese, rubidium, and magnesium in thoracic empyemata and corresponding sera

In this study, a number of selected trace elements and clinically relevant parameters were compared between thoracic empyemata and the corresponding sera for a better understanding of the trace element distribution between these two compartments. Serum-empyema pairs were obtained from 13 patients and quantified for selected and essential trace elements, namely copper (Cu), zinc (Zn), manganese (Mn), rubidium (Rb), and magnesium (Mg), by inductively coupled plasma-mass spectrometry (ICP-MS). In addition, the concentrations of the following clinical laboratory parameters were analyzed by standard methods: total protein, leukocyte count, lactate dehydrogenase, glucose, pH, and the C-reactive protein. Individual concentrations of the elements determined in the empyemata were frequently higher than in pleural effusions of any other benign or malignant condition except for Cu. Serum Cu exceeded the normal range (600–1400 μg/kg) in 6 out of 13 patients (median 1410 μg/kg). In the empyemata, Zn concentrations (median 2000 μg/kg) were characteristically higher than in the sera (median 450 μg/kg) and exceeded the upper limit for serum (1200 μg/kg) in 8 of the 13 patients. Manganese concentrations in the empyemata (median 2.7 μg/kg) were also higher compared to corresponding sera, although they stayed within the limits considered normal for serum of healthy adults (upper limit 2.9 μg/kg). Rubidium was also moderately higher in most empyemata (median 290 μg/kg) and exceeded the upper limit for serum (560 μg/kg) in two patients. The median concentration of the essential element magnesium was higher in the empyemata (23 mg/kg) than in the sera (21 mg/kg). However, all serum Mg concentrations except three remained within the normal range (17–22 mg/kg). Removal of large amounts of empyematous fluid may deprive the body of trace elements and can cause suboptimal or deficient trace element status and homeostasis. Recuperation will be accelerated by compensatory supplementation of trace elements. Therefore, selective medication with adequate trace element compounds in patients with thoracic empyema can be generally recommended for zinc. The other elements need not necessarily be monitored or substituted, because of their stable concentrations in the serum. Rb may have a biological impact, but deficiency symptoms in man are not clearly defined. Deceased.     

Human biomonitoring of 73 elements in blood,serum, erythrocytes and urine

BackgroundHuman biomonitoring studies of trace elements in biological fluids are mostly limited to a certain number of elements or biological materials. In this study, we describe the significant extension of a biomonitoring to 73 elements being present in concentration ranges from ng/L to g/L in clinically relevant specimens such as blood, serum, erythrocytes and urine.MethodsThe samples were collected from 102 occupationally non-exposed inhabitants of northern Germany. The elements were determined either by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) in the low concentration range or by inductively coupled plasma optical emission spectrometry (ICP-OES) for essential trace elements and electrolytes.ResultsMean values and selected percentiles of element concentrations are presented for all sample materials. From the results, we calculated the distribution of elements between plasma and blood cells. Application of ICP-MS/MS improves selectivity and accuracy in the determination of elements that are strongly spectrally interfered, such as Cr, Ge, Pd or Ti in blood samples.ConclusionsThis publication provides very valuable information for occupational or environmental hygienists, toxicologists and clinical chemists due to the particularly high number of determined elements and presented concentration ranges.     

Zirconium

Summary The action of Zirconium (Zr) on biological systems presents an enigma. It is ubiquitous, being present in nature in amounts higher than most trace elements. It is taken up by plants from soil and water and accumulated in certain tissues. The entry into animal systems in vivo is related to the mode of exposure and the concentration in the surrounding environment. Retention is initially in soft tissues and then slowly in the bone. The metal is able to cross the blood brain-barrier and is deposited in the brain and the placental barrier to enter milk. The daily human uptake has been known to be as high as 125 mg. The level of toxicity has been found to be moderately low, both in histological and cytological studies. The toxic effects induced by very high concentrations are nonspecific in nature. Despite the presence and retention in relatively high quantities in biological systems, Zr has not yet been associated with any specific metabolic function. Very little information is available about its interaction with the compounds of the genetical systems, such as nucleic acids. Apparently, the metal is neither an essential nor toxic element in the conventional sense. However, the increasing exposure to this element through its increasing use in new materials and following radioactive fallout, has increased the importance of the study of its effects on living organisms. The tetravalent nature of the ionic state and the high stability of the compounds formed are important factors that need to be considered, as also the accumulation of this element in the brain, reminiscent of the relationship between Al³⁺ and Alzheimer's disease.     

Trace-element analysis by charged-particle-induced reactions as a tool for physicians and chemists

The object of this article is to apprise physicians and chemists of nuclear analytical techniques and, in particular, of ion beam analysis (PIXE and PIGE) for the purpose of application to the clinical diagnostic method. The feasibility of the technique, sampling, and sample preparation for trace element analysis in biological and biomedical samples has been described previously (1–3). Analysis data from normal human blood samples and biomedical samples by ion beam reactions have been compared at the end. Emphasis will be placed on the use of the analytical technique on determination of the range of trace and toxic elements in human blood samples.     

TRACE METAL CYCLING IN THE U.S. COASTAL ZONE: A SYNTHESIS

This synthesis of trace element research in estuarine communities of the U.S. coastline and the Caribbean provides a summary applicable to the shoreline of the tropical and temperate regions of the world which have mangroves, kelp beds, riverine marshes and seagrass communities. An inventory of sediments and leaf tissues shows Mn and Fe to be the most highly concentrated elements with Hg and Cd present in lowest concentrations. Generally, trace element concentrations in roots are much higher than in leaves and other tissues above the sediment. Tissue to sediment concentration ratios show that Cd is most likely to be bioamplified and that Cu, Hg, Sr and Zn may have relatively high concentration ratios which can exceed unity. A conceptual model was constructed to integrate the forcing functions, compartmental couplings, and dynamics common to these estuarine systems. Seasonality is important for changes in some trace element concentrations in plants and litter. Trace element additions to water or sediment increased certain trace element concentrations in plants and dead organic matter. It is clear that estuarine plant communities serve as living filters of estuarine trace elements. However, increased knowledge of trace element cycling in estuarine systems and relationships between trace element concentrations in plants and the estuarine food chain is needed, particularly food chains to man. There is a need for structured long-term estuarine research to allow direct comparison of results among estuarine study sites, to identify the similarity of population and system processes among estuaries and to define the geographical scale over which estuarine research results may be generalized.     

Influence of ashing techniques on the analysis of trace elements in biological samples

Dry ashing and wet ashing are two commonly used methods for the preparation of biological materials for trace element analysis by atomic absorption spectrophotometry. In this paper, National Bureau of Standards (NBS) bovine liver was dry ashed at 450°C for 24 h in silica glass (Vycor) or procelain crucibles; the resulting ash was dissolved in either concentrated nitric or hydrochloric acid. Dry ashing efficiency was evaluated by comparing iron, copper, zinc, and manganese concentrations of the samples with the values certified by NBS. Highest recoveries were obtained by dry ashing in silica glass (Vycor) crucibles. Dissolving the resultant ash in either hydrochloric or nitric acids did not significantly alter the results. A comparison between dry and wet ashing shows the latter method to be superior for the preparation of biological tissues for analysis of iron, copper, zinc, and manganese.     

Selenium metabolism and function

Selenium like many other elements has a bimodal effect. At lower concentrations selenium is an essential trace element necessary for the growth of man and animals. However, at higher concentrations, selenium has toxic properties for man and animals. The biochemistry of selenium as a component of glutathione peroxidase and the analytical properties of selenium are also outlined.     

Comparison of the linear finite element prediction of deformation and strain of human cancellous bone to 3D digital volume correlation measurements

The mechanical properties of cancellous bone and the biological response of the tissue to mechanical loading are related to deformation and strain in the trabeculae during function. Due to the small size of trabeculae, their motion is difficult to measure. To avoid the need to measure trabecular motions during loading the finite element method has been used to estimate trabecular level mechanical deformation. This analytical approach has been empirically successful in that the analytical models are solvable and their results correlate with the macroscopically measured stiffness and strength of bones. The present work is a direct comparison of finite element predictions to measurements of the deformation and strain at near trabecular level. Using the method of digital volume correlation, we measured the deformation and calculated the strain at a resolution approaching the trabecular level for cancellous bone specimens loaded in uniaxial compression. Smoothed results from linearly elastic finite element models of the same mechanical tests were correlated to the empirical three-dimensional (3D) deformation in the direction of loading with a coefficient of determination as high as 97% and a slope of the prediction near one. However, real deformations in the directions perpendicular to the loading direction were not as well predicted by the analytical models. Our results show, that the finite element modeling of the internal deformation and strain in cancellous bone can be accurate in one direction but that this does not ensure accuracy for all deformations and strains.     

Assessment of the uncertainty of trace metal and nitrogen concentrations in mosses due to sampling,sample preparation and chemical analysis based on the French contribution to ICP-Vegetation

Moss bio-monitoring is a convenient tool for establishing specific or large-scale exposure to atmospheric trace metals and nitrogen pollution. However, the uncertainty associated with sampling, sample preparation and chemical analysis of bio-monitors has been poorly documented, with the exception of one study dealing with lichens; thus, the uncertainty associated with moss bio-monitoring has never been assessed. Here, we propose following the Eurachem guidelines to determine the uncertainties associated with the concentrations of elements measured in mosses during the sampling survey across France in 2011. In addition, we assess the analytical method used in four surveys from 1996 to 2011. Uncertainties were expressed as linear functions of the element concentrations, with minimum and maximum slopes of 14 and 61%, corresponding to nitrogen and chromium, and a median of 32%. Although the data reveal that some steps of the protocol should be performed carefully, they also indicate that the protocol was executed properly and is reproducible. The chemical analyses contribute to a small proportion of the uncertainty associated with the protocol, except for the analysis of chromium. The sampling period, and intra-site variability largely contribute to this uncertainty. The moss species did not introduce additional uncertainty. This integrative assessment of measurement uncertainty will help improve the protocol for future surveys. Such studies could be useful for developing a standard operating procedure and could be used to improve comparisons between countries and to identify temporal trends across Europe.     

The use of secondary ion mass spectrometry (SIMS) to evaluate internal contamination.

Secondary ion mass spectrometry (SIMS) permits the detection of stable and radioactive elements in microvolume. Based on the ablation of specimens by ion bombardment, this mass spectrometry method allows a rapid assessment of trace elements in biological samples and enables accurate isotopic ratio determination. In this work, an application of SIMS in studies involving element microdistribution is illustrated on the basis of analyses of duodenal tissue sections from rats contaminated with either cerium or thorium. For this purpose, tests are performed with SIMS to analyze tissue sections obtained 12, 24 and 48 hr after contamination. In this report, strengths and limitations of SIMS are pointed out as an important tool in biological research.     

Survey of chemical speciation of trace elements using synchrotron radiation

Information concerning the chemical state of trace elements in biological systems generally has not been available. Such information for toxic elements and metals in metalloproteins could prove extremely valuable in the elucidation of their metabolism and other biological processes. The shielding of core electrons by binding electrons affect the energy required for creating inner-shell holes. Furthermore, the molecular binding and symmetry of the local environment of an atom affect the absorption spectrum in the neighborhood of the absorption edge. X-ray absorption near-edge structure (XANES) using synchrotron radiation excitation can be used to provide chemical speciation information for trace elements at concentrations as low as 10 ppm. The structure and position of the absorption curve in the region of an edge can yield vital data about the local structure and oxidation state of the trace element in question. Data are most easily interpreted by comparing the observed edge structure and position with those of model compounds of the element covering the entire range of possible oxidation states. Examples of such analyses will be reviewed.     

The role of sulfur assimilation and sulfur-containing compounds in trace element homeostasis in plants

Sulfur assimilation and production of sulfur-containing compounds are essential biological activities that play critical roles in many biological processes, including the role of sulfur containing compounds such as glutathione and phytochelatin in trace element homeostasis in plants. This review will discuss the role of sulfur assimilation and the biosynthesis of sulfur containing compounds in both mechanisms of trace element hyperaccumulation and heavy metal stress responses in plants.