Selective detection and identification of Se containing compounds--review and recent developments

The complexity of selenium (Se) chemistry in the environment and in living organisms presents broad analytical challenges. The selective qualitative and quantitative determination of particular species of this element is vital in order to understand selenium's metabolism and significance in biology, toxicology, clinical chemistry and nutrition. This calls for state-of-the-art analytical techniques such as hyphenated methods that are reviewed with particular emphasis on interfaced separation with element-selective detection and identification of the detected selenium compounds. Atomic spectral element specific detection for monitoring chromatographic eluent enabled quantitative determination of selenium species in selenized yeast and qualitative measurement for breath samples. Gas chromatography with atomic emission detection (AED) of ethylated species and fluoroacid ion pair HPLC applied to the analysis of currently produced or archived selenized yeast and Brassica juncea have revealed the presence of a previously unrecognised Se-S amino acid, S-(methylseleno)cysteine.     

Analytical determination of selenium in medical samples,staple food and dietary supplements by means of total reflection X-ray fluorescence spectroscopy

Selenium is essential for many aspects of human health and, thus, the object of intensive medical research. This demands the use of analytical techniques capable of analysing selenium at low concentrations with high accuracy in widespread matrices and sometimes smallest sample amounts.In connection with the increasing importance of selenium, there is a need for rapid and simple on-site (or near-to-site) selenium analysis in food basics like wheat at processing and production sites, as well as for the analysis of this element in dietary supplements. Common analytical techniques like electrothermal atomic absorption spectroscopy (ETAAS) and inductively-coupled plasma mass spectrometry (ICP-MS) are capable of analysing selenium in medical samples with detection limits in the range from 0.02 to 0.7 μg/l. Since in many cases less complicated and expensive analytical techniques are required, TXRF has been tested regarding its suitability for selenium analysis in different medical, food basics and dietary supplement samples applying most simple sample preparation techniques.The reported results indicate that the accurate analysis of selenium in all sample types is possible. The detection limits of TXRF are in the range from 7 to 12 μg/l for medical samples and 0.1 to 0.2 mg/kg for food basics and dietary supplements. Although this sensitivity is low compared to established techniques, it is sufficient for the physiological concentrations of selenium in the investigated samples.     

生物样品中硒的测定方法及形态分析研究进展

硒的毒性和营养功能不仅与其总量有关,而且与其存在的化学形态有关。因此,硒的测定及形态分析对于了解不同形态的硒化物在生物体和环境中的迁移转化规律具有重要意义。文章综述了生物样品中硒的测定分析方法以及形态分析研究进展。     

The effect of the presence of volatile organoselenium compounds on the determination of inorganic selenium by hydride generation

As a result of microbiological activity it is possible to find dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in a wide type of environmental samples, such as soils, sediments, sewage sludges and plants where methylation can take place.Selenium determination by hydride-generation (HG) techniques requires its presence as Se(IV). Consequently, inorganic speciation by hydride generation techniques is done by first determining Se(IV) and then, after reduction of Se (VI) to Se(IV), the total selenium. Therefore, the concentration of Se (VI) is evaluated as the difference between total inorganic selenium and Se(IV). In the present work it could be demonstrated that DMSe and DMDSe are forming other volatile species by reaction with sodium borohydride, applying the same reduction condition as for inorganic selenium. These species are subsequently detected by several atomic techniques (atomic absorption AAS, atomic fluorescence AFS and inductively coupled plasma-mass spectrometry ICP-MS). The error that their presence can cause in determination of inorganic selenium has been evaluated. The magnitude of this error depends on the specific analytical detector used.The coupling of pervaporation-atomic fluorescence is proposed for the identification of these species and pervaporation-gas chromatography-atomic fluorescence for their individual quantification.     

硒酵母中硒含量测定方法的研究

报道了人工培养硒酵母中总硒、无机硒和有机硒的测定方法,建立了无机硒和有机硒的鉴别方法,并采用透析处理法使硒酵母中的无机硒和有机硒得以分离;还报道了不同培养条件下得到的5种硒酵母中总硒、无机硒和有机硒的定量分析数据,为硒酵母在医药和添加剂领域的应用提供了可靠的数据。     

Novel approaches for selenium speciation in foodstuffs and biological specimens: A review

Selenium is an essential element for human health. It has been recognized as an antioxidant and chemopreventive agent in cancer. Selenium is known to develop its biological activity via selenocysteine residue in the catalytically active centre of selenoproteins. The main source of selenium in human beings is the diet. However, in several regions of the world the content of selenium in diet has been estimated insufficient for a correct expression of the proteins. The beneficial effects of selenium on human health are strongly dependent on its chemical form and concentration. This review critically evaluated the state-of-the art of selenium speciation in biological matrices mainly focused in nutritional and food products. Besides the number of publications related to selenium speciation, isolation and accurate characterization and quantification of selenium species is still a challenge. Hyphenated techniques based on coupling chromatography separation with inductively coupled plasma spectrometry (ICP-MS) and its combination with molecular mass spectrometry (ESI-MS, ESI-MS-MS and MALDI-TOF) and isotopic dilution allow identification, quantification and structural characterization of selenium species. Particular attention is paid in the development of Se-enriched food and nutritional products and how the application of the techniques mentioned above is mandatory to get reliable results on selenium metabolisms in these particular matrices.     

Selenium speciation in anaerobic granular sludge

Chromatographic (IC-CD, GC-FID) and spectroscopic (XRD) techniques that allow the specific determination of several selenium species present or formed during bioremediation processes of selenate contaminated drinking, ground, or wastewaters have been established. The developed techniques are shown to be applicable in determining selenium species in the range of target concentrations for emissions and are thus appropriate to characterize bioremediation processes. The applied techniques offer advantages regarding short analytical times without loss of satisfactory accurateness towards more sophisticated methods. By means of IC-CD, selenate and selenite can be detected specifically to concentrations far below allowance levels for metal finishing industries (20?µg?L^?1 selenate, 40?µg?L^?1 selenite) within 16.0?min. Thus, the removal of selenate from the liquid phase by anaerobic granular sludge was quantified by IC-CD, and the concomitantly formed red precipitates were analysed by XRD. Hexagonal elemental selenium was found to be present in the XRD analysis. Even if the precipitate contained iron and zinc, as shown by ICP-OES, no iron- or zinc-containing selenium minerals were detected by XRD. The GC-FID method described determines dimethylselenide and dimethyldiselenide at a detection limit of 1?ng and 2?ng, respectively, without further chemical derivatization within 7.4?min. Thus, the GC-FID offers adequate detection of two major volatile organic selenium species potentially formed during bioremediation of selenium contaminated waters.     

Electroanalytical Techniques for the Detection of Selenium as a Biologically and Environmentally Significant Analyte—A Short Review

This short review deals with the properties and significance of the determination of selenium, which is in trace amounts an essential element for animals and humans, but toxic at high concentrations. It may cause oxidative stress in cells, which leads to the chronic disease called selenosis. Several analytical techniques have been developed for its detection, but electroanalytical methods are advantageous due to simple sample preparation, speed of analysis and high sensitivity of measurements, especially in the case of stripping voltammetry very low detection limits even in picomoles per liter can be reached. A variety of working electrodes based on mercury, carbon, silver, platinum and gold materials were applied to the analysis of selenium in various samples. Only selenium in oxidation state + IV is electroactive therefore the most of voltammetric determinations are devoted to it. However, it is possible to detect also other forms of selenium by indirect electrochemistry approach.     

硒的化学形态分析

对硒的化学形态分析的现状(1991-2006)进行了评述,主要涉及的分析方法有紫外-可见分光光度法、荧光光度法、氢化物发生(HG)原子荧光光谱法、HG原子吸收光谱法、电感耦合等离子体(ICP)原子发射光谱、气相色译原子吸收光谱联用、ICP-质谱与多种分析技术联用等(引用文献45篇).     

Purity control of aluminium metal

As a contribution to the neutron activation assay of the reactor grade aluminium, a number of elements have been investigated by a developed analytical scheme. With the performance of ion-exchange chromatography combined with the precipitation techniques, ppm concentration (or even less) of arsenic, antimony, calcium, copper, mercury, selenium and strontium contaminants were demonstrated with good reproducibility. Whenever possible, some of the elements analyzed by radioactivation and proved to be present in high concentration levels were assayed by other standard analytical methods.     

Elimination of Inteferences in Trace Element Determination by Graphite Furnace Atomic Absorption Spectrometry

Graphite furnace atomic absorption spectrometry has been recognized as one of the most sensitive and selective analytical techniques for trace element determination. It is especially suitable for the measurement of parts-per-billion levels of essential or toxic elements like selenium,arsenic, germanium or lead in environmental and biological samples.     

Differential pulse polarographic determination of arsenic, selenium and tellurium at mug levels

An analytical method, based on differential pulse polarography, for determination of arsenic, selenium and tellurium in solid matrices, is described. The method involves decomposition of the matrix with a mixture of nitric, perchloric and hydrofluoric acid, isolation of tellurium from the other analytes by liquid-liquid extraction (from 4M hydrochloric acid with methyl isobutyl ketone), and determination of the analytes. Tellurium is determined separately, and arsenic is determined in the same solution as selenium after determination and oxidation of the selenium and addition of catechol. Graphitized carbon black and chelating resin were used to eliminate the organic solvent in the aqueous solution and avoid interferences due to the other metals of the matrix. The decomposition, the influence of each analyte on the determination of the others, and the extraction process were given particular attention. The method is characterized by>96% recovery, with a relative standard deviation ranging from 2 to 10% at ppm levels.     

Inorganic chemical approaches to pharmacognosy. VIII. Determination of selenium in crude drugs by energy-dispersive X-ray fluorescence spectrometry

Energy-dispersive X-ray fluorescence spectrometry following sample decomposition and preconcentration was developed to determine selenium in crude drugs. Samples were decomposed with conc. HNO3 and conc. H2SO4 in a flask with a reflux condenser. Evaporation of HNO3 had to be avoided to prevent serious loss of this element. Selenium was preconcentrated from the digestion liquid by two-step reduction with 4M HCl and ascorbic acid, the elemental selenium formed was adsorbed on activated carbon and then collected on a Nuclepore membrane filter for direct irradiation in an X-ray spectrometer. This analytical method (detection limit, 0.03 ppm) was used to determine selenium in many kinds of crude drugs. The analytical results indicated vegetable drugs to be low in selenium content: more than 0.5 ppm in only a limited number of samples and less than detection limit (0.03 ppm) in nearly all the samples. Animal drugs contain selenium at higher levels, Lumbricus and Cantharis being 7.46 and 1.67 ppm, respectively.     

Trends in selenium determination/speciation by hyphenated techniques based on AAS or AFS

The field of selenium speciation has been studied for decades and the growing interest in this field seems never to reach a plateau. Although powerful techniques based on mass spectrometry are nowadays used for selenium determination/speciation, few laboratories can support the high cost of such techniques. The hyphenation of chromatography to atomic absorption or atomic fluorescence spectrometry (AAS or AFS) is still a reliable and low-cost alternative for routine laboratories. In this work we present the most important parameters dealing with selenium speciation along with the latest trends in this subject, namely in the items related with sample treatment and hyphenation techniques with AAS and AFS detection.     

Rapid determination of selenium in erythrocytes by neutron activation analysis

The use of ultrafiltration prior to the determination of selenium via the short-lived activation product,^77mSe, provided a simple and rapid method for the determination of this element in erythrocytes. An associated reduction in analytical error made this procedure acceptable for monitoring small changes in erythrocyte selenium concentrations.     

Complementary use of molecular and element-specific mass spectrometry for identification of selenium compounds related to human selenium metabolism

The aim of this paper is to give an overview of analytical data on the identification of selenium compounds in biological samples with relevance for selenium metabolism. Only studies applying the combination of element-specific inductively coupled plasma mass spectrometry as well as molecular electrospray mass spectrometry detection have been included. Hence, selenium compounds are only considered identified if molecular mass spectra obtained by analysis of the authentic biological sample have been provided. Selenium compounds identified in selenium-accumulating plants and yeast are included, as extracts from such plants and yeast have been widely used for examination of the cancer-preventive effect of selenium in cell lines, animal models and human intervention trials. Hence, these selenium compounds are available for absorption and further metabolism. Identification of selenium metabolites in simulated gastric and intestinal juice, intestinal epithelial tissue, liver and urine is described. Hence, selenium metabolites identified in relation to absorption, metabolism and excretion are included.     

Combined elemental analysis of ancient glass beads by means of ion beam,portable XRF,and EPMA techniques

Ion beam analysis (IBA)- and X-ray fluorescence (XRF)-based techniques have been well adopted in cultural-heritage-related analytical studies covering a wide range of diagnostic role, i.e., from screening purposes up to full quantitative characterization. In this work, a systematic research was carried out towards the identification and evaluation of the advantages and the limitations of laboratory-based (IBA, electron probe microanalyzer) and portable (milli-XRF and micro-XRF) techniques. The study focused on the analysis of an Archaic glass bead collection recently excavated from the city of Thebes (mainland, Greece), in order to suggest an optimized and synergistic analytical methodology for similar studies and to assess the reliability of the quantification procedure of analyses conducted in particular by portable XRF spectrometers. All the employed analytical techniques and methodologies proved efficient to provide in a consistent way characterization of the glass bead composition, with analytical range and sensitivity depending on the particular technique. The obtained compositional data suggest a solid basis for the understanding of the main technological features related to the raw major and minor materials utilized for the manufacture of the Thebian ancient glass bead collection.     

Utility of protein electrophoretic analysis in the characterization of malignant tissues

High-resolution electrophoresis of samples from malignant tissues and tumour cells has developed from a simple analytical tool to a high-tech system requiring a lot of satellite techniques. Though this developmental history now demands additional expensive instrumentation and a detailed knowledge of protein chemistry, the usefulness of this technique in tumour biology has been dramatically enhanced. Consequently, electrophoretic techniques combined with additional high-resolution and sensitive analytical tools can now be used to elucidate a particular phenotype of a cancer cell; moreover, the chemical nature of this phenotype can be revealed. The way from the protein backwards to the gene is now open!     

电化学分析法测定硒的研究进展

本文综述了国内外电化学分析(极谱和溶出伏安法)测定痕量硒的研究进展,主要包括极谱催化波、吸附波以及阴极溶出伏安法,阳极溶出伏安法,并从反应体系、催化波类型、检出限和电极反应机理等方面进行归纳与评述,展望了硒分析方法的研究方向和发展前景,对进一步研究硒的电化学性质和探索测定硒的新体系有重要参考价值。     

Surveying selenium speciation from soil to cell—forms and transformations

The aim of this review is to present and evaluate the present knowledge of which selenium species are available to the general population in the form of food and common supplements and how these species are metabolized in mammals. The overview of the selenium sources takes a horizontal approach, which encompasses identification of new metabolites in yeast and food of plant and animal origin, whereas the survey of the mammalian metabolism takes a horizontal as well as a vertical approach. The vertical approach encompasses studies on dynamic conversions of selenium compounds within cells, tissues or whole organisms. New and improved sample preparation, separation and detection methods are evaluated from an analytical chemical perspective to cover the progress in horizontal speciation, whereas the analytical methods for the vertical speciation and the interpretations of the results are evaluated from a biological angle as well.