Determination of selenium in freshwaters by cathodic stripping voltammetry after UV irradiation

An analytical method was developed for the determination of total dissolved selenium in fresh waters, using linear sweep cathodic stripping voltammetry (CSV) in combination with UV photolytic digestion. Both the CSV method, based on the electrodeposition and stripping of Cu(2)Se, and the UV irradiation procedure were investigated in detail. In the presence of dissolved organic substances, as in freshwaters, Se(VI) is reduced to Se(IV) by UV irradiation in 0.1M hydrochloric acid. Glucose can be used as the carbon source in samples low in natural dissolved organic carbon (DOC). The photolytic yields of Se(IV) were about 90% in both cases. Five freshwater samples were analysed for total selenium by CSV after UV photolysis, and by hydride generation atomic absorption spectrometry (HG-AAS) after oxidative digestion followed by reduction with hydrochloric acid. The results agreed well and the concentrations were in the range 70-190 ng/l., well above the detection limit of the CSV method at 2 ng/l.     

Preconcentration and separation of inorganic selenium on Dowex 1X8 prior to hydride generation-atomic absorption spectrometry

Exchange reactions between inorganic selenium species and chloride were studied on Dowex 1X8. The concentration exchange constants were determined with the batch technique at room temperature and used to predict the chromatographic enrichment and separation of tetra- and hexavalent selenium. A procedure for the determination of total selenium after digestion with permanganate and anion exchange preconcentration was also developed. The enrichment techniques were applied to the determination of Se(IV) and total dissolved selenium in drinking water and fresh water using flow injection hydride generation-atomic absorption spectrometry (HG-AAS). Results agreed with those obtained in a HG-AAS system where selenium was preconcentrated as hydrogen selenide in a trap at liquid nitrogen temperature.     

Radiochemical separation of7 5Se with o-phenylenediamine for instrumental neutron activation analysis of selenium in biological materials

A new method of radiochemical separation for determination of selenium in biological materials has been developed. The method is based on the reaction of tetravalent selenium with the amino groups of aromatic ortho-diamines resulting in selenodiazoles, which can be easily extracted with organic solvents. The biological samples were irradiated in a reactor, mineralized with nitric and perchloric acids and MgCl₂. Selenium was transformed to teravalent form with hydrochloric acid and the resulting bezoselenodiazole formed in the reaction with o-phenylenediamine was extracted with toluene. The radioactivity of selenium^{7 5}Se was measured with a well-type NaI(Tl) scientillation detector. The accuracy of the method was verified by determining selenium levels in SRM NBS. The detection limit of the method was found to be 0.5 ng Se. The comparison of selenium levels in human blood determined by HG-AAS. non-destructive NAA and the described method is presented.     

Selenium Determination in Biological Matrices

In this study, we discuss some relevant aspects concerning the determination of selenium in biological materials with special reference to fluorometry and hydride generation atomic absorption spectroscopy (HG-AAS) techniques. The two methods may be applied without modifications to the analysis of Se in a wide spectrum of specimen types, and we describe their reliability in serum and hair analyses. Thirty-six independent control serum samples, the concentrations of which were unknown to the analyst, were analyzed in duplicate using both techniques in the Italian External Quality Assessment Scheme (EQAS). Accuracy was assessed by comparing Se values with those previously assigned by the organizers of the scheme using graphite furnace atomic absorption spectrometry (GF-AAS), which is the most frequently used technique for selenium determination in serum among the participants in the Italian EQAS. The results confirmed that fluorometry has a higher degree of accuracy than HG-AAS: the mean differences between observed and expected values were 1.5 μg/liter (95% confidence interval, −1.06 to 3.97) for fluorometry and −1.1 μg/liter (95% confidence interval, −5.05 to 2.76) for Hg-AAS. We also report some results obtained for the determination of Se in hair. Since a critical step in hair preparation is the pretreatment for removal of external contamination, we compared six different washing procedures. In general, Se is poorly leached from hair, but the efficiency of removal differed with the substance used, ranging from 0 to 13% of the original content. A nonionic detergent like Triton X-100 offers the advantage of safe working conditions and a substantial reduction in costs compared with organic solvents. Lastly, in a consistent group (n= 131) of women, Se in hair was found to be strongly reduced by the use of dye (389.9 ng/g vs 498.7 ng/g,P< 0.001). We recommend recording information on cosmetic treatments when hair is collected to evaluate Se reference values in epidemiological studies.     

电感耦合等离子体质谱（ICP-MS）法与氢化物发生-原子吸收光谱（HG-AAS）法测定土壤中硒含量的对比研究

基于氢化物发生器与原子吸收光谱联用(HG-AAS),测定土壤样品中硒的含量,并与电感耦合等离子体质谱(ICP-MS)法测定值进行了对比。在两种仪器的最佳工作条件下,测定土壤硒的含量,实验结果表明:ICP-MS法和HG-AAS法对土壤硒含量测定的线性范围分别为0.85~100.00μg/L和0.08~16.00μg/L,检出限分别为0.25μg/L和0.02μg/L,精密度分别为1.3%和2.1%;用加标回收实验和测定国家标准土壤样品(GSS-7)对这两种方法的准确性进行了验证,ICP-MS法和HG-AAS法的加标回收率分别为96.7%~99.4%和94.9%~99.5%,GSS-7标准土样的结果均在标准值范围内,说明这两种测定土壤中硒含量的方法是准确可靠的。HG-AAS法测定线性范围窄,部分样品需要稀释,而且氢化物发生系统是手动进样,导致操作复杂,分析周期长;ICP-MS法仪器测定快速,但是仪器昂贵。     

Determination of dissolved selenium(VI) in freshwater

A procedure is proposed for the determination of selenate in freshwaters with a high content of dissolved organic material. After passage through an XAD-8 column, selenate is collected on a strong anion exchanger and subsequently eluted with hydrochloric acid. Following conversion into the tetravalent state, selenium is determined using atomic absorption spectrometry after hydride generation and preconcentration in a cold trap system. The two-column procedure effectively separates selenium(VI) from possible organic interferents and allows quantification at the low ng/l. level. Results from the investigation of waters from lakes and streams indicate that selenium(IV) and (VI) may constitute a very small part of total dissolved selenium.     

预富集-氢化物发生原子吸收光谱法测定饮料中的痕量铅

原子吸收光谱法测定水样中的痕量元素是应用得最广泛的方法之一[1]。有时需采用多种方法对水样中的痕量元素进行富集。其中一类方法是基于待测元素配合物可以最终定量富集于少量颗粒上,过滤收集这些颗粒,然后制成小体积的、可直接用原子吸收光谱法测定的悬浊液。特定的配位剂分     

Preconcentration of inorganic selenium species (Se (IV) and Se (VI)) in an alumina filled microcolumn and on-line determination by hydride generation atomic absorption spectrometry

A flow injection system has been developed consisting of on-line preconcentration of selenium species in a microcolumn filled with activated alumina, reduction of Se(VI) to Se(IV) and determination by HG-AAS. When 0.01 mol/L HNO₃ is used both as carrier and activation reagent for the alumina microcolumn, up to 150 ng of Se(IV) and Se(VI) can be preconcentrated and quantitatively eluted by 500 L of 2 mol/L NH₃. The preconcentration factor is 50 when 25 mL of sample is used. The detection limit is about 6 ng/L, the precision is 5% for low concentrations such as 150 ng/L and 3% at high concentrations such as 120 ng/mL. The proposed method is suitable for natural water samples and inorganic Se speciation can be performed by determining Se(IV) and total selenium [Se(VI) is evaluated from the difference].     

The gas chromatographic determination of selenium(IV) and total selenium in natural waters with 1,2-diamino-3,5-dibromobenzene

The total selenium and selenium(IV) contents in sea water and river water can be determined directly by a gas chromatographic method with l,2-diamino-3,5-dibromobenzene without preconcentration. The reagent reacts only with selenium(IV) to form a 4,6-dibromopiazselenol; other oxidation states of selenium must therefore be converted to the tetravalent state for total selenium determinations. The piazselenol formed can be extracted quantitatively into 1 ml of toluene from 500 ml of sample water. A method is proposed for the determination of selenium(IV) and total selenium in natural waters at levels as low as 2 ng l^-1. Coastal sea water and river water in Japan contain 8–30 ng of Se(IV) and 20–50 ng of total Se per liter.     

Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS

A procedure has been developed for determining the selenium in cows milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 g l^–1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 g l^–1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.     

Determination of total gaseous selenium in atmosphere by honeycomb denuder/differential pulse cathodic stripping voltammetry

A new analytical method has been developed for the determination of total gaseous selenium in the atmosphere by honeycomb denuder collection followed by differential pulse cathodic stripping voltammetry (DPCSV) measurement. Gaseous selenium was collected in a denuder coating solution containing 2% HNO(3) and 2% glycerine. The soluble product, selenious acid, was then extracted by water for DPCSV analysis. The collection efficiency for gaseous selenium was 99.1% at a flow rate of 1 l min(-1) for 3 h. Excellent linearity in DPCSV was maintained up to Se concentration of 40 ng ml(-1). This was equivalent to a working concentration of 220 ng m(-3) of selenium in the atmosphere. A precision of 1.26% RSD (n=5) for 5 ng Se was obtained, and the detection limit (3sigma) and the quantitative determination limit were estimated to be 0.96 and 3.19 ng m(-3). The average recovery of selenium in three standard samples prepared by independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 99.0%. The total content of gaseous selenium in the atmosphere of our laboratories was 3.2-4.4 ng m(-3).     

Optimisation of sample pre-treatment in the HG-AAS selenium analysis

A fast and accurate method of pre-treatment for biological materials in the hydride generation-atomic absorption spectroscopy (HG-AAS) selenium determination is described. All procedures of sample pre-treatment were performed in closed-vessels in a microwave oven. After sample decomposition using a HNO3/H2O2 mixture, the pre-reduction and a 'denitrification' step (reduction of interfering nitrogen intermediates) with amidosulfuric acid were combined. Hence, analysis time and the risk of element losses or the emergence of possible contamination are minimised.     

Determination of selenium in human serum by liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry after acid digestion and derivatization using 2,3-diaminonaphthalene

Analysis of selenium in biological samples is very important and numerous analytical methods for the element have been developed. One of the most convenient and widely used methods for routine determination of serum selenium is a fluorometric method using 2,3-diaminonaphthalene (DAN); however, this method lacks specificity. We observed that 4,5-benzopiazselenol (BPS), a selenium derivative of DAN, is ionized with electron capture in an atmospheric pressure chemical ionization (APCI) interface, and subsequently established a method for determining total human serum selenium by means of liquid chromatography/atmospheric pressure chemical ionization mass spectrometry. All pretreatment procedures were carried out in a single test tube to minimize selenium loss. The recovery of organic or inorganic selenium spiked to human serum was 97-103%.The detection limit of BPS was equivalent to 0.2 ng of selenium and the lower quantitative limit of serum selenium was 10 ng mL(-1). The coefficient of variation of standard concentrations in control serum samples was 4.5%. The purity of the observed peak obtained from serum samples was confirmed using the ion cluster technique.     

On-line electrochemically controlled in-tube solid phase microextraction of inorganic selenium followed by hydride generation atomic absorption spectrometry

In this work, for the first time, a rapid, simple and sensitive microextraction procedure is demonstrated for the matrix separation, preconcentration and determination of inorganic selenium species in water samples using an electrochemically controlled in-tube solid phase microextraction (EC-in-tube SPME) followed by hydride generation atomic absorption spectrometry (HG-AAS). In this approach, in which EC-in-tube SPME and HG-AAS system were combined, the total analysis time, was decreased and the accuracy, repeatability and sensitivity were increased. In addition, to increases extraction efficiency, a novel nanostructured composite coating consisting of polypyrrole (PPy) doped with ethyleneglycol dimethacrylate (EGDMA) was prepared on the inner surface of a stainless-steel tube by a facile electrodeposition method. To evaluate the offered setup and the new PPy-EGDMA coating, it was used to extract inorganic selenium species in water samples. Extraction of inorganic selenium species was carried out by applying a positive potential through the inner surface of coated in-tube under flow conditions. Under the optimized conditions, selenium was detected in amounts as small as 4.0 parts per trillion. The method showed good linearity in the range of 0.012–200 ng mL⁻¹, with coefficients of determination better than 0.9996. The intra- and inter-assay precisions (RSD%, n = 5) were in the range of 2.0–2.5% and 2.7–3.2%, respectively. The validated method was successfully applied for the analysis of inorganic selenium species in some water samples and satisfactory results were obtained.     

On-line focused microwave digestion-hydride generation of inorganic and organic selenium: Total determination and inorganic selenium speciation by atomic absorption spectrometry

An on-line FIA pretreatment with HBr/KBrO₃, assisted by on-line focused microwave-induced digestion, has been coupled with hydride generation-atomic absorption spectrometry (HG-AAS) for final detection for total selenium determination. This total selenium determination is virtually independent of the different Se species investigated (selenite, selenate, selenomethionine, selenoethionine and selenocystine). Detection limits of 0.8 μg l⁻¹ of Se can be achieved by AAS with precisions better than 5%. This continuous flow system for selenium determination allows a high sample throughput (about 30 samples h⁻¹ can be analyzed) in which high automation can be achieved and constitutes a convenient real-time continuous detector for the different selenocompounds tested. Direct non-chromatographic speciation of inorganic selenium (selenite and selenate in their mixtures) is demonstrated by simple on-off operation of the focused microwaves connected in the flow system.

Validation of this simple on-line FIA system has been carried out by analyzing total Se recovered from spiked tap waters and by speciating mixtures of Se(IV) and Se(VI) spiked to the same samples. The fast conversion of Se compounds into volatile selenium could be considered as a sort of specific “general” detector for Se compounds which can be extremely useful for Se speciation by hybrid chromatographic techniques.     

Organic and inorganic selenium speciation in environmental and biological samples by nanometer-sized materials packed dual-column separation/preconcentration on-line coupled with ICP-MS

A novel, fast, and cheap nonchromatographic method for direct speciation of dissolved inorganic and organic selenium species in environmental and biological samples was developed by flow injection (FI) dual-column preconcentration/separation on-line coupled with ICP-MS determination. In the developed technique, the first column packed with nanometer-sized Al(2)O(3) could selectively adsorb the inorganic selenium [Se(IV), Se(VI)], and the retained inorganic selenium could be eluted by 0.2 mol l(-1) NaOH, while the organic Se [selenocystine (SeCys(2)) and selenomethionine (Se-Met)] was not retained. On the other hand, the second column packed with mesoporous TiO(2) chemically modified by dimercaptosuccinic acid (DMSA) could selectively adsorb Se(IV) and SeCys(2) and barely adsorb Se(VI) and Se-Met. When the sample solution was passed through the column 1, separation of inorganic selenium and organic selenium could be achieved first. Then, the effluent from column 1 was successively introduced into the column 2 and the speciation of organic selenium could be attained due to the different adsorption behaviors of Se-Met and SeCys(2) on DMSA modified TiO(2). After that, the eluent from column 1 contained Se(IV), and Se(VI) was adjusted to desired pH and injected into column 2, and the speciation of Se(IV) and Se(VI) could also be realized thanks to their different retention on column 2. The parameters affecting the separation were investigated systematically and the optimal separation conditions were established. The detection limits obtained for Se(IV), Se(VI), Se-Met and SeCys(2) were 45-210 ng l(-1) with precisions of 3.6-9.7%. The proposed method has been successfully applied for the speciation of dissolved inorganic and organic selenium in environmental and biological samples. In order to validate the methodology, the developed method was also applied to the speciation of selenium in certified reference material of SELM-1 yeast, and the determined values were in good agreement with the certified values.     

Separation and determination of selenium in water samples by the combination of APDC coprecipitation: X-ray fluorescence spectrometry

A sensitive and non chromatographic analytical procedure for the separation of inorganic selenium species in natural water has been performed. A combination of APDC coprecipitation and determination by an absolute thin layer Energy dispersive X-ray fluorescence spectrometry method was used. The influence of various analytical parameters such as element concentration, oxidation states and pH on the recoveries of Se (IV) was examined. The presence of organic matter and bicarbonate anions, typical components in Cuban groundwater samples, was also tested. Negligible matrix effects were observed. At pH 4 a 100% recovery was found for Se (IV). The coprecipitation recovery of the oxidized selenium species (Se (VI)) was null for the selected concentration range (5–100 μg L⁻¹). When the Se (VI) was reduced by heating the solution with 4 mol L⁻¹ HCl, quantitative recovery was also obtained. The determination of total selenium was conducted by the application of the oxidation–reduction process and the analytical procedure for Se (IV). Se (VI) content was calculated as the difference between total selenium and Se (IV). The detection limit was 0.13 μg L⁻¹. The relative standard deviation was lower than 3.5% for 5 μg L⁻¹ of Se (IV). The trueness of the method was verified by using standardized hydride generation-atomic absorption spectrometry technique. The results obtained using the EDXRF technique were in good agreement with the ones determined by HG-AAS. The proposed method was applied to the determination of Se (IV) in surface water and groundwater samples.     

New Indicator Reactions Involving Sulfur-Containing Organic Compounds for the Kinetic Determination of Selenium

New indicator reactions were proposed for the determination of selenium by the kinetic method based on the reduction of Methylene Blue by some sulfur-containing organic compounds. It was demonstrated that a high sensitivity of the determination of selenium is attained using unithiol and thiomalic, 2,3-dithiomercaptopropionic, and rubeanic acids as reducing agents. In the presence of unithiol, down to 4 ng/mL selenium can be determined.     

Evaluation of a purge-and-trap injection system for capillary gas chromatography-microwave induced plasma-atomic emission spectrometry for the determination of volatile selenium compounds in water

A method is presented for the selective determination of the volatile selenium species dimethylselenide and dimethyldiselenide, using a commercially available purge-and-trap injection system coupled to capillary gas chromatography-microwave induced plasma-atomic emission spectrometry. The efficiency of the purging step was evaluated and the parameters affecting the purge and trap processes were optimized. The method was applied to the determination of volatile selenium compounds in lake water. Relative detection limits of 2ng/l for dimethylselenide and dimethyldiselenide, corresponding to an absolute detection limit of 10 pg, were achieved.