Accurate determination of element species by on-line coupling of chromatographic systems with ICP-MS using isotope dilution technique

The instrumental design for coupling different liquid chromatographic systems such as ion, reversed phase, and size exclusion chromatography as well as capillary gas chromatography, with ICP-MS for the determination of element species is described. For accurate analyses obtaining ‘real time’ concentrations of chromatographic peaks, the isotope dilution mass spectrometric (IDMS) technique is applied. Two different spiking modes are possible, one using species-specific and another one using species-unspecific spike solutions of isotope-enriched labelled compounds. The species-specific mode is only possible for element species well defined in their structure and composition, for example iodate or selenite, whereas the species-unspecific mode must be applied in all cases where the structure and composition of the species is unknown, for example, for metal complexes with humic substances. For accurate determinations by the isotope dilution technique the mass discrimination effect must also be taken into account. Iodate, iodide and organoiodine species, including those of humic substances, have been analysed in mineral, drinking and environmental water samples by coupling different liquid chromatographic methods with ICP-IDMS. Heavy metal complexes with humic substances in water samples of different origin have been characterized by size exclusion/ICP-IDMS. The possibilities of determining different environmental selenium species are discussed and the results for the analysis of selenite and selenate, which has been carried out by GC/ICP-IDMS after converting these species into a volatile piazselenol compound, are presented.     

Determinations of humic substances and other dissolved organic matter and their effects on the increase of COD in Lake Biwa.

Humic substances and other dissolved organic matter (DOM) in Lake Biwa and the surrounding rivers were investigated to elucidate their origins and behavior. An annual increase in chemical oxygen demand (COD) has been observed in the northern basin of Lake Biwa since 1985. The concentrations of dissolved organic carbon (DOC) in the northern and southern basins of Lake Biwa were 1.7-2.4 mgC/l and 1.9-2.6 mgC/l, respectively. The DOC concentrations tended to be high in summer and low in winter, and the seasonal changes in the concentrations of humic substances were small. The humic substances content of DOM was considered to be comparatively small because the ratio of the concentration of humic substances to DOC was in the range of 0.14-0.32. From the results of the fractionation of DOM in lake waters, it was estimated that hydrophobic acids, such as humic substances and hydrophilic acids, were about 25% and 45%, respectively. The main origin of hydrophobic acids in Lake Biwa may be humic substances from soils around the rivers that flow into Lake Biwa, while hydrophilic acids may be due to the inner production by phytoplankton. Therefore, the increase of COD in the northern basin of Lake Biwa may be attributed to the contributions of not only humic substances but also hydrophilic acids.     

Synthesis of Selenium-Containing Humic Nano-Biocomposites from Sodium Bis(2-phenylethyl)phosphinodiselenoate

New water-soluble selenium-containing nano-biocomposites have been synthesized by oxidation of sodium bis(2-phenylethyl)phosphinodiselenoate with hydrogen peroxide using humic substances to stabilize selenium nanoparticles. As shown by a set of physicochemical methods, the obtained hybrid nanocomposites are formed as spherical hexagonal selenium particles with a size of 13–30 nm, dispersed in a humic matrix.     

Selenium Enrichment on <Emphasis Type="Italic">Cordyceps militaris</Emphasis> Link and Analysis on Its Main Active Components

To investigate the effects of selenium on the main active components of Cordyceps militaris fruit bodies, selenium-enriched cultivation of C. militaris and the main active components of the fruit bodies were studied. Superoxide dismutase (SOD) activity and contents of cordycepin, cordycepic acid, and organic selenium of fruit bodies were sodium selenite concentration dependent; contents of adenosine and cordycep polysaccharides were significantly enhanced by adding sodium selenite in the substrates, but not proportional to sodium selenite concentrations. In the cultivation of wheat substrate added with 18.0 ppm sodium selenite, SOD activity and contents of cordycepin, cordycepic acid, adenosine, cordycep polysaccharides, and total amino acids were enhanced by 121/145%, 124/74%, 325/520%, 130/284%, 121/145%, and 157/554%, respectively, compared to NS (non-selenium-cultivated) fruit bodies and wild Cordyceps sinensis; organic selenium contents of fruit bodies reached 6.49 mg/100 g. So selenium-enriched cultivation may be a potential way to produce more valuable medicinal food as a substitute for wild C. sinensis.     

Altlastsanierung mit Huminstoffsystemen. Prinzipien der Natur in der Umwelttechnologie

A former open‐cast pit was used as deposit for wastewater from lignite‐pyrolysis processes until 1990. The lake formed was filled with highly toxic and dark phenolic water. Traditional remediation methods were not applicable and it was therefore necessary to develop a new ecologically and economically acceptable remediation strategy. The full‐scale remediation of this lake was realized as the results of an interdisciplinary research by a team of chemists, microbiologists and hydrologists. The newly developed complex remediation strategy is mainly based on the knowledge of the chemistry of dissolved‐organic matter systems. We could show the similarity of dissolved natural humic substances to the industrially formed black phenolic macromolecules formed in the wastewater deposit lake. Transfer of the knowledge originating from research on humic substances, their chemical reactions and microbiological interactions and on the hydrological behaviour of natural lakes helped to create a successful mild remediation strategy. As a result of the full‐scale application, after 10 years now, a new ecosystem with clear water was formed without any danger for the environment.     

Qualitative detection of selenium in fortified soil and water samples by a paper chromatographic-carboxyl esterase enzyme inhibition technique.

Thevetia peruviana seed carboxyl esterase was employed as a biosensor for the detection of selenium compounds by an enzyme inhibition technique on paper chromatograms. The selenium compounds (sodium selenite and selenium dioxide) appeared as white spots on a magenta background due to the inhibition of Thevetia peruviana seed carboxyl esterase (substrate 1-naphthyl acetate, coupling reagent Fast blue B salt). The minimum detectable amounts were about 5 microg of sodium selenite and 5 microg of selenium dioxide. Many other animal and plant carboxyl esterases gave no inhibition spot under the same conditions. Soil and water samples were fortified with sodium selenite and selenium dioxide. A procedure for preparing test solutions and conditions for paper chromatography was established.     

富硒肝对大鼠GSH-Px、GSH和游离巯基含量的影响

为观察富硒肝和亚硒酸钠对大鼠抗氧化能力的影响。将6只大鼠分为两组:A组用亚硒酸钠[按Se元素计,6μg/(只.d)]灌胃,B组用富硒肝[按Se元素计,6μg/(只.d)]灌胃。于灌胃第0、4、8、12、16、20天内眦采血,测定血浆和血细胞内液中GSH-Px活力以及GSH、游离巯基的含量。结果表明:①给药20 d后A、B组血浆和血细胞内液GSH-Px活力和GSH含量均明显高于灌胃前(P0.05);②A、B组血浆中游离巯基的含量略有增加,而血细胞内含量则大幅降低(P0.05)。结论:经口给予富硒肝可诱导大鼠产生较多的抗氧化物质,增强大鼠的抗氧化能力。其作用可达同剂量亚硒酸钠水平。     

Interference from iodide in the determination of trace level selenium

The rate of the reaction between iodide and selenium(IV) at trace levels to form selenium and iodine has been determined in 1-6M hydrochloric acid. The reaction rate increases rapidly with acidity. When hydrochloric acid is added to reduce selenate to selenite prior to the determination of total selenium, some selenium may be lost by reduction to the element if iodide is present. A table of half-lives of the selenite-iodide reaction under various conditions is presented. A method for removal of iodide is suggested.     

On-line size-exclusion chromatography/electrospray ionisation mass spectrometry of aquatic humic and fulvic acids

Isolated aquatic humic and fulvic acids were analysed with on-line size exclusion chromatography/electrospray ionisation mass spectrometry (SEC/ESI-MS). An eluent composition which enabled electrospray ionisation was identified. The SEC separation improved interpretability of mass spectra and may open up new possibilities for molecular weight determination of humic substances. A linear dose-response relationship over a factor of 20 was obtained and the limit of detection was 50ng/uL for humic and fulvic acids. Spectral changes due to different ionisation conditions (pH and cone voltage) were investigated. A natural water sample from a Swedish lake was analysed. Copyright 2000 John Wiley & Sons, Ltd.     

亚硒酸钠在L-半胱氨酸自组装类生物膜修饰电极上的电化学行为

利用L-半胱氨酸自组装膜修饰金电极(L-Cys,Au/SAMs), 在0.05mol/L H_2SO_4 底液中研究了 Na_2SeO_3 的电化学特性.在0.00～1.30 V (vs. SCE) 电位范围内对微量Na_2SeO_3进行循环伏安扫描,发现L-Cys, Au/SAMs修饰电极在峰电位0.89 V处有灵敏的Se的氧化溶出峰.通过比较裸金电极和修饰电极在Na_2SeO_3 溶液中的电化学特性发现,修饰电极通过巯基中的S与Na_2SeO_3发生氧化还原作用生成Se,且修饰电极对沉积在电极表面的Se的氧化过程具有催化作用.根据Na_2SeO_3在单分子膜上的电化学行为,提出了单分子膜中硫(Au-S)与Se(Ⅳ)作用生成Se的反应机理、Se电化学催化氧化机理及巯基化合物通过生成纳米硒生物吸收Se的类生物膜模型.     

GC–ICP–MS determination of dimethylselenide in human breath after ingestion of <Superscript>77</Superscript>Se-enriched selenite: monitoring of in-vivo methylation of selenium

The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg ⁷⁷Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked ⁷⁷Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R ²=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L⁻¹, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of ⁷⁷Se-enriched selenite. Additional DM⁷⁷Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of ⁷⁷Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R ²=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L⁻¹ whereas the dietary background level was less than 0.4 ng Se L⁻¹. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.     

Utilization of two different chemical forms of selenium during lactation using stable isotope tracers: an example of speciation in nutrition.

The bioavailability and metabolism of different chemical species of mineral nutrients in the diet are receiving much attention from research nutritionists. In order to make scientifically based recommendations for mineral intakes, the chemical form of the mineral, with its specific absorption, utilization and retention, needs to be considered. Selenium is an example of an essential nutrient that is consumed in several different chemical forms, hence information is needed on the bioavailability and metabolism of each form before recommendations for dietary intakes can be made. A valuable tool for research on bioavailability and metabolism in humans is stable isotope tracers. When there are more than two stable isotopes available, as with selenium, stable isotope methodology allows the comparison of the utilization of different chemical forms of the nutrient simultaneously in in vivo studies. As an example of speciation questions addressed by nutritionists, a study is described that simultaneously evaluated utilization (absorption, retention and appearance in milk and blood) of two different chemical forms of selenium (selenite and selenomethionine) in lactating, non-lactating and never pregnant women using stable isotope tracers. All three groups of women had similar selenium status at the start of the study. Significantly more selenium from selenomethionine than from selenite was absorbed and appeared in the plasma in all groups. Milk contained more selenium from apparently absorbed selenomethionine than from selenite. All groups retained significantly more selenium from selenomethionine than from selenite; lactating women retained more selenium from selenite than did the other two groups, suggesting that milk losses may be partially compensated by enhanced retention of dietary selenium as selenite.(ABSTRACT TRUNCATED AT 250 WORDS)     

土壤胡敏酸的^13C核磁共振研究

胡敏酸(HA)是土壤有机质的重要组分,其结构性质与土壤形成和肥力特性有密切关系,长期以来一直是土壤化学研究的难点和重点之一。NMR是研究HA结构的有效手段。自Bar-ton和Schnitzer(1963)首次用~1H NMR研究土壤有机质以来,国外已先后应用~1H、~(13)C NMR和CP-MAS-~(13)C NMR等对土壤及其它来源的HA进行了许多研究,并取得引人注目的进展。但在国内,这方面研究还刚刚开始。本文应用~(13)C NMR方法对东北几种主要耕作土壤以及泥炭和猪粪的HA进行了结构表征,为土壤腐殖酸化学的基础研究提供了资料。     

Voltammetric Study of Reduction Processes in Rhodium(+3)–Selenium(+4) Acidic Mixtures

Using square‐wave voltammetry and linear scan voltammetry, some reduction processes, that take place on the hanging mercury drop electrode (HMDE) in rhodium(+3)–selenium(+4) mixtures, were studied in highly acidic sulfate, chloride and perchlorate solutions. The special attention was paid to the peak located at ?1.1 V, that reflects catalytic hydrogen evolution on the rhodium islets, and its changes under the influence of added selenium(+4), or selenium(?2) produced at the electrode. It can be concluded that addition of selenite to a dilute rhodium solution has the similar effect as the increase of rhodium(+3) concentration, making the catalytic hydrogen evolution more pronounced, probably by changing the properties of metal clusters on the mercury drop. If so, the effect could be of some practical importance in production of rhodium deposits on other surfaces, too.     

Investigation of the stability of selenoproteins during storage of human serum by size-exclusion LC-ICP-MS

The stability of selenium-containing proteins in human serum was investigated by size-exclusion chromatography-ICP-MS under non-denaturating conditions. The peak characteristic to glutathione peroxidase (GSHPx) (tetramer) was the most affected; peaks of the GSHPx monomer and of selenite were found to appear with time. No trace of selenite was present in fresh samples, which suggest that the presence of this species in serum may be an artifact of storage. The mass balance of selenium species indicates that some of selenium is lost as a function of the storage time.     

Capillary electrophoretic separation of humic substances using hydroxyethyl cellulose as a buffer additive and its application to characterization of humic substances in a river water sample

We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated. Figure Addition of Fe(III) ions or EDTA to a solution containing fulvic acid (FA) results in a distinct change in the electropherogram pattern, which reflects the conformational change of FA: this forms the basis for the characterization of humic substances in river water samples     

不同质量浓度亚硒酸钠对豌豆芽苗菜生长及硒含量的影响

调查了不同质量浓度亚硒酸钠喷施对豌豆芽苗菜生长的影响及植物体硒富集情况。结果 表明,对苗长2．5cm、5．0cm的豌豆芽苗菜两次喷施,处理质量浓度高于150mg／L,豌豆苗芽长、芽干质量和鲜质量、根长、根鲜质量及产量均有大幅度下降。豌豆芽苗菜中大分子结合硒和全硒含量均随外源硒的质量浓度升高而增加,但明显低于全硒的增加趋势;150mg/L处理的硒吸收利用率出现明显下降。     

Hydrophilic interaction liquid chromatography method for measuring the composition of aquatic humic substances

A hydrophilic interaction liquid chromatography (HILIC) method was developed to measure the composition of humic substances from river, reservoir, and treated wastewater based on their physicochemical properties. The current method fractionates the humic substances into four well-defined groups based on parallel analyses with a neutral and a cationic HILIC column, using mobile phases of varied compositions and pH. The results indicate that: (i) the proportion of carboxylic acids in the humic substances from terrestrial origins is less than half of that from treated wastewater (Jeddah, KSA), (ii) a higher content of basic compounds was observed in the humic substances from treated wastewater and Ribou Reservoir (Cholet, France) than in the sample from Loire River (France), (iii) a higher percentage of hydrophobic macromolecules were found in the humic substances from Loire River than in the other samples, and (iv) humic substances of treated wastewater contained less ionic neutral compounds (i.e., pK_a 5–9) than the waters from terrestrial origins. The physicochemical property disparity amongst the compounds in each humic substances sample was also evaluated. The humic substances from the lightly humic Loire river displayed the highest disparity, whereas the highly humic Suwannee river (Georgia, USA) showed the most homogeneous humic substances.     

Imaging translocation and transformation of bioavailable selenium by Stanleya pinnata with X-ray microscopy

Selenium hyperaccumulator Stanleya pinnata, Colorado ecotype, was supplied with water-soluble and biologically available selenate or selenite. Selenium distribution and tissue speciation were established using X-ray microscopy (micro-X-ray fluorescence and transmission X-ray microscopy) in two dimensions and three dimensions. The results indicate that S. pinnata tolerates, accumulates, and volatilizes significant concentrations of selenium when the inorganic form supplied is selenite and may possess novel metabolic capacity to differentiate, metabolize, and detoxify selenite concentrations surpassing field concentrations. The results also indicate that S. pinnata is a feasible candidate to detoxify selenium-polluted soil sites, especially locations with topsoil polluted with soluble and biologically available selenite.     

Negative Thermionen-Massenspektrometrie von Selen

Summary Selenite and selenate were determined in ground waters with isotope dilution mass spectrometry (IDMS). This species analysis was possible by the use of an⁸²Se enriched selenite and selenate spike and a Chromatographic separation of both species after the isotope dilution step. In a column filled with the DEAE cellulose anion exchanger selenite could be separated with 1 mol/l formic acid, whereas selenate was eluted with 0.1 mol/1 nitric acid. The mass spectrometric isotope ratio measurement was carried out in a thermal ionization instrument using the formation of negative Se^– thermal ions for detection. Selenite, selenate and total selenium in ground water samples were determined in the concentration range of 0.2–20 n/g with relative standard deviations of 0.5%–5%. The selenate concentration was approximately ten to eighty times higher than the corresponding selenite concentration. There was always a difference of about 8% between the sum of the selenite and selenate concentrations and the total selenium concentration which can possibly be attributed to water-soluble selenides and elementary selenium, respectively.

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Herrn Prof. Dr. R. Neeb zum 60. Geburtstag gewidmet