Nondispersive X-ray fluorescence in the study of rapid radiochemical separation of selenium from arsenic,germanium and zinc

A rapid radiochemical separation of selenium from arsenic, germanium and zinc based on the precipitation of elemental selenium by NaHSO₃ is discussed. Yields of 90% and greater are achieved for selenium in 1 to 2 min. The kinetics, separation characteristics of the process and chemical yield of Se and trace contaminants such as Zn, Ge and As were studied using nondispersive X-ray fluorescence techniques. Work supported by USAEC.     

A chemical concentration x-ray determination of selenium in copper-, nickel-and iron-base alloys

A method is described for the determination of selenium in various metals and alloys at concentrations of 3-100ppm. A chemical separation is made by filtration after reduction of the selenious acid to elemental selenium with hydroxylamine hydrochloride. The pure selenium product is readily analysed by X-ray fluorescence; the method is free from errors due to matrix effects. The relative standard deviation is 6 % for a copper-nickel alloy at the 60 ppm level.     

Separation and speciation of selenium in food and water samples by the combination of magnesium hydroxide coprecipitation-graphite furnace atomic absorption spectrometric determination

A simple and economic separation and speciation procedure for selenium in food and water samples have been presented prior to its graphite furnace atomic absorption spectrometry (GFAAS). Magnesium hydroxide coprecipitation system for selenium(IV) was applied to the separation and speciation of selenium ions. The influences of the various analytical parameters for the quantitative recoveries of selenium ions like pH, amounts of magnesium ions as carrier elements, etc. on were examined. The effects of the alkaline and earth alkaline metals, some transition metals and some anions on the recoveries of selenium(IV) were also investigated. The recoveries of analytes were found greater than 95%. No appreciable matrix effects were observed. The detection limit, defined as three times the blank standard deviation (3σ), was 0.030 μg l⁻¹. The preconcentration factor for the presented system was 25. The proposed method was applied to the speciation of selenium(IV), selenium(VI) and determination of total selenium in natural waters and microwave digested various food samples with satisfactory results. The procedure was validated with certified reference materials. The relative errors and relative standard deviations were below 6% and 10%, respectively.     

Bestimmung und abtrennung von sauerstoffverunreinigungen in reinst-selenThe determination and separation of oxygen impurities in high-purity selenium

(The determination and separation of oxygen impurities in high-purity selenium)By distillation in high vacuum, high-purity selenium is almost completely freed from impurities caused by metallic elements, oxides and water. If bulk vitreous selenium has a suitable thermal history, the oxygen content may be determined from the intensity of the oxide absorption band at 932 cm^?1 in the i.r. spectrum of the glass. In distilled selenium this content is < 1 × 10^?4 wt.< %.     

Speciation of selenium compounds with ion-pair reversed-phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection

For selenium speciation analysis, the hyphenation of chromatographic separation with element-specific detection has proved a useful technique. A powerful separation system, which is capable of resolving several biologically and environmentally important selenium compounds in a single column, is greatly needed. However, that has been difficult to achieve. In this paper eight selenium compounds, namely, selenite [Se(IV)], selenate [Se(VI)], selenocystine (SeCys), selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), selenocystamine (SeCM) and trimethylselenonium ion (TMSe+), were separated by using mixed ion-pair reagents containing 2.5 mM sodium 1-butanesulfonate and 8 mM tetramethylammonium hydroxide as a mobile phase. The separation of these anionic, cationic and neutral organic selenium compounds on a LiChrosorb RP18 reversed-phase column took only 18 min at a flow-rate of 1.0 ml/min with isocratic elution, and baseline separation among the six organic Se compounds was achieved. Inductively coupled plasma mass spectrometry (ICP-MS) was employed as element-specific detection. A comparison of ICP-MS signal intensity obtained with a Barbington-type nebulizer and with an ultrasonic nebulizer (USN) was made. Different signal enhancement factors were observed for the various selenium compounds when a USN was used. The speciation technique was successfully applied to the study on chemical forms of selenium in a selenium nutritional supplement. Selenomethionine was found to be the predominant constituent of selenium in the supplement.     

Determination of selenium in human diets by radiochemical neutron activation analysis.

A post-irradiation radiochemical separation technique was tested for the determination of selenium levels in diet samples, collected by using a duplicate portion technique, from both rural and urban population groups in Turkey. The technique involved sample irradiation, acid digestion, selective distillation, precipitation and filtration steps. During the separations it was possible to determine the yield of each sample using a stable selenium carrier. An average chemical yield of 71 +/- 3% was obtained for the radiochemical neutron activation analysis. For samples from urban and rural regions, the average selenium concentrations obtained were 0.14 +/- 0.04 and 0.07 +/- 0.02 mg kg-1, respectively. It was also possible to determine daily dietary selenium intakes, which were found to be 81 +/- 41 micrograms and 23 +/- 11 micrograms for the urban and rural groups, respectively. Although daily selenium intakes were found for a small number of subjects in this study, the separation technique developed can be used for determination of the selenium status in larger population groups.     

环境样品中砷、硒形态分析研究进展

综述了近年来环境样品中砷、硒形态分析的研究进展,主要内容包括样品的前处理技术、分离技术、检测技术。前处理技术主要是用各种提取液采用各种方式提取样品中的砷、硒形态,分离技术主要有高效液相色谱分离、气相色谱分离、毛细管电泳分离等,检测技术主要有原子吸收光谱法、原子发射光谱法、原子荧光光谱法、电感耦合等离子体质谱法等。最后对其研究前景进行了展望。     

Analytical selenoamino acid studies by chromatography with interfaced atomic mass spectrometry and atomic emission spectral detection

Consumption of selenium enriched plants or yeast-based nutritional supplements has been reported to provide anticarcinogenic benefits which are selenium compound dependent. Separation and identification of these selenium compounds is critical to understand the activity. Plants and yeast convert inorganic selenium in the soil or growth media into organoselenium compounds, probably following a route similar to the sulfur assimilatory pathway. Non-volatile selenium compounds produced include selenoamino acids, some of which have shown anticarcinogenic activity. Volatile compounds produced by chemical reaction of involatile precursors have also been found. An ion pair chromatographic method with ICP-MS detection for the separation of selenoamino acid standards potentially present in real samples is given. The method allows separation of selenoamino acids including such analytes as the cis-trans isomers of Se-1-propenyl-dl-selenocysteine. The method also provides the capability of determining the presence of selenoxides and possibly selenones, and tracking of other functionalities and reactions by selective derivatization. Alternatively, selenoamino acids are treated with ethylchloroformate to produce stable volatile derivatives which are amenable to GC separation with element specific atomic emission detection (GC-AED). Results of total selenium determination and speciation of selenium enriched yeast-based nutritional supplements, selenium enriched allium vegetables and bioremediation samples are presented.     

Determination of Selenium in Natural Waters Using the Centrifugal Photometric Analyzer

Abstract

A rapid ion exchange separation converts the methylene blue spot test for selenium into a selective and sensitive method for quantitative determination of trace quantities of selenium. Increased speed, accuracy, and reproducibility is achieved because of the parallel analysis technique of the centrifugal photometric analyzer (GeMSAEC Fast Analyzer). Natural water samples, spiked with 0.10 to 0.5 μg of selenium, were analyzed with an average accuracy of 4.2 % after removal of interferences by ion exchange.     

Analytical application of phenylbenzene sulphazide in separation and determination of selenium

In this paper the utility of phenylbenzene sulphazide is illustrated by its application to the determination of selenium and the separation of this element from tellurium, lead, copper, bismuth, nickel and iron. Selenious acid is reduced to black selenium in acid media at 100 degrees . To minimize interference by other elements but yet give rapid recoveries of selenium an acidity of 40% (v/v) formic/acetic acid is recommended. The co-precipitation of tellurium is prevented by adding tartaric acid. Oxalate, tartrate, citrate, EDTA and phosphate do not interfere.     

The separation of selenium from sea water by adsorption colloid flotation

Adsorption colloid flotation can be applied successfully to the separation of selenium as SeO₃^2- from sea water. Separation is achieved in 5 min. The modified catalytic method of West and Ramakrishna is used to determine the selenium. The recovery of selenium based on spiked sea-water samples is 100 ± 10%. Standard addition analysis of near-shore Oahu sea water showed a value of 0.40 ± 0.12 μg l^-1.     

Analytical selenoamino acid studies by chromatography with interfaced atomic mass spectrometry and atomic emission spectral detection

Consumption of selenium enriched plants or yeast-based nutritional supplements has been reported to provide anticarcinogenic benefits which are selenium compound dependent. Separation and identification of these selenium compounds is critical to understand the activity. Plants and yeast convert inorganic selenium in the soil or growth media into organoselenium compounds, probably following a route similar to the sulfur assimilatory pathway. Non-volatile selenium compounds produced include selenoamino acids, some of which have shown anticarcinogenic activity. Volatile compounds produced by chemical reaction of involatile precursors have also been found. An ion pair chromatographic method with ICP-MS detection for the separation of selenoamino acid standards potentially present in real samples is given. The method allows separation of selenoamino acids including such analytes as the cis-trans isomers of Se-1-propenyl-dl-selenocysteine. The method also provides the capability of determining the presence of selenoxides and possibly selenones, and tracking of other functionalities and reactions by selective derivatization. Alternatively, selenoamino acids are treated with ethylchloroformate to produce stable volatile derivatives which are amenable to GC separation with element specific atomic emission detection (GC-AED). Results of total selenium determination and speciation of selenium enriched yeast-based nutritional supplements, selenium enriched allium vegetables and bioremediation samples are presented. Received: 16 February 1998 / Revised: 4 June 1998 / Accepted: 9 June 1998     

Selenium speciation analysis using inductively coupled plasma-mass spectrometry

Selenium exists in several oxidation states and a variety of inorganic and organic compounds, and the chemistry of selenium is complex in both the environment and living systems. Selenium is an essential element at trace levels and toxic at greater levels. Interest in speciation analysis for selenium has grown rapidly in this last decade, especially in the use of chromatographic separation coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Complete characterization of selenium compounds is necessary to understand selenium's significance in metabolic processes, clinical chemistry, biology, toxicology, nutrition and the environment. This review describes some of the essential background of selenium, and more importantly, some of the currently used separation methodologies, both chromatographic and electrophoretic, with emphasis on applications of selenium speciation analysis using ICP-MS detection.     

Use of transition elements to enhance sensitivity for selenium determination by graphite-furnace atomic-absorption spectrophotometry combined with solvent extraction with the APDC-MIBK system

A microanalytical method for the measurement of selenium in waters and biological materials by a flameless atomic-absorption technique has been developed. The ammonium pyrrolidinedithiocarbamate-methyl isobutyl ketone extraction system is used for separation from interfering materials such as large amounts of alkali and alkaline earth metal salts and mineral acids. The atomic-absorption sensitivity for selenium is found to be enhanced to a large extent by co-extraction of some transition metal ions. Copper(II) has been used successfully as such an additive to diminish the volatility of selenium in the graphite furnace during the ashing step of the atomization cycle. When the aqueous phase/organic solvent volume ratio is 5 and the volume injected into the graphite furnace is 20 mul, the sensitivity for selenium is 0.3 ng/ml for 1% absorption. The relative standard deviation is ca. 2%. Interference by other metal ions is prevented by masking with EDTA. The method has been applied satisfactorily for the determination of minute amounts of selenium in waters and various biological materials.     

Activation analysis of Se in biological samples through75Se and77mSe

A method is described to separate trace amounts of selenium in biological samples without using a carrier. This method is based on the adsorption on active carbon of the complex ion formed with APDC /ammonium salt of l-pyrrolidine carbodithioic acid/ at pH 1. The efficiency of the radiochemical separation described is measured by using carrier-free⁷⁵Se labelled solutions of sodium selenite at selenium concentrations from 3.5×10^–8 to 3.5×10^–11 g ml^–1. The results were between 95% and 98% with statistical variations from 2% to 10%. The determination of selenium can be made following this separation either through⁷⁵Se in the traditional way, or through^77mSe if the separation is performed prior to irradiation. The detection limits on the available conditions were 0.01 ppm for⁷⁵Se and 0.1 ppm for^77mSe. When the analysis is performed through⁷⁵Se /t=120 d/, the statistical error is notably smaller because the counting time may be considerable, whereas through^77mSe/t=17.5 s/it is higher than 20%, depending on the concentration and the available neutron flux. However, the advantages of gaining time and the fact of performing the trace separation from a non radioactive material, make both procedures competitive as useful tools for the research on the function of Se in vertebrates.     

A critical study on the determination of selenium in gallium arsenide by polarographic techniques

A simple voltammetric method is described for the determination of traces of selenium in gallium arsenide. Differential-pulse cathodic stripping voltammetry permits a direct determination of selenium without preliminary enrichment or separation processes. Selenium can be determined down to levels of 1–2 μg g^?1, with relative standard deviations of about 10%, in ? 100-mg samples of gallium arsenide. Results for gallium arsenide doped with 7–75 μg g^?1 selenium agree in most cases with those obtained by spectrophotometry based on 4-chloro-o-phenylenediamine.     

Macro micro separation of selenium and tellurium: Application to NAA</p> </p>

Summary A simple pre-irradiation separation approach has been worked out for the determination of traces of tellurium in high purity selenium followed by neutron activation analysis (NAA) for the end determination of the analyte/s. The difference in volatilities of these elements has been utilized for the separation of the analyte from the matrix. The complete volatility of selenium at ~600 °C was established using neutron activation analysis and selenium radiotracer. Standard addition was used to validate the results. The proposed method of separation of selenium prior to irradiation could make the determination of tellurium possible and also improved the detection limit by several folds.</p> </p>     

Determination of inorganic selenium species by miniaturised isotachophoresis on a planar polymer chip

The use of miniaturised isotachophoresis to allow the simultaneous determination of two inorganic selenium species has been investigated using a poly(methyl methacrylate) chip with a 44-mm-long, 200-microm-wide, 300-microm-deep separation channel. The miniaturised device included an integrated on-column, dual-electrode conductivity detector and was used in conjunction with a hydrodynamic fluid transport system. A simple electrolyte system has been developed which allowed the separation of selenium(IV) and selenium(VI) species to be made in under 210 s. The limits of detection were calculated to be 0.52 mg L(-1) for selenium(IV) and 0.65 mg L(-1 )for selenium(VI). The method allowed the separation of the selenium species from a range of common anions including fluoride, nitrate, nitrite, phosphate, sulfate and sulfite.     

Retention study of inorganic and organic selenium compounds on a silica-based reversed phase column with mixed ion-pairing reagents

Summary Separation of seven inorganic and organic selenium compounds, namely selenic acid [Se(VI)], selenous acid [Se(IV)], trimethylselenonium iodide (TMSe⁺), selenocystine (SeCys), selenomethionine (SeMet), selenoethionine (Seet), and selenocystamine (SeCM), has been performed on a LiChrosorb C 18 column by using mixed ion-pair reagents; 1-butanesulfonic acid and tetramethylammonium hydroxide. Flame atomic absorption spectrometry (FAAS) was used as an element-specific detector. The retention behaviors of selenium compounds in terms of several chromatographic parameters, such as pH of the mobile phase, the concentrations of ion-pair reagents, and the content of organic modifier (methanol) were investigated. It was found that the separation of both inorganic and organic selenium compounds can be achieved within 12 min with a mobile phase of 10 mM 1-butanesulfonic acid −4 mM tetramethylammonium hydroxide −4 mM malonic acid −0.05% methanol adjusted to pH 4.5 at a flow rate of 1.0 mL min⁻¹. The results obtained in this study showed that the use of mixed ion-pair reagents is very useful to improve the separation of selenium compounds. The applicability of this technique for the speciation of selenium compounds in real samples was demonstrated by the determination of selenium compounds in a selenium nutritional supplement. The results were found to be in good agreement with those obtained by ion-exchange HPLC-ICP-MS.     

Radiochemical separation of selenium from hydrochloric or hydrobromic acid into toluene

A separation of selenium based on the extraction of different concentrations of Se(IV) from 12 M hydrochloric acid or 8 M hydrobromic acid into toluene is described. Recoveries of 92% and 97%, respectively, are achieved in 7 min. Oxidizing agents interfere.