Selenium speciation in tea by dispersive liquid–liquid microextraction coupled to high‐performance liquid chromatography after derivatization with 2,3‐diaminonaphthalene

Selenium is an important element for human health, and it is present in many natural drinks and foods. Present study described a new method using dispersive liquid–liquid microextraction prior to high‐performance liquid chromatography with a UV variable wavelength detector for the determination of the total selenium, Se(IV), Se(VI), and total organoselenium in tea samples. In the procedure, 2,3‐diaminonaphthalene was used as the chelating reagent, 400 μL acetonitrile was used as the disperser solvent and 60 μL chlorobenzene was used as the extraction solvent. The complex of Se(IV) and 2,3‐diaminonaphthalene in the final extracted phase was analyzed by high‐performance liquid chromatography. The factors influencing the derivatization and microextraction were investigated. Under the optimal conditions, the limit of detection was 0.11 μg/L for Se(IV) and the linearity range was in the range of 0.5–40 μg/L. This method was successfully applied to the determination of selenium in four tea samples with spiked recoveries ranging from 91.3 to 100%.     

A cost‐effective shortcut to prepare organoselenium catalysts via decarboxylative coupling of phenylacetic acid with elemental selenium

An interesting decarboxylative coupling reaction of phenylacetic acid with elemental selenium was discovered and employed for the preparation efficient organoselenium catalysts for Baeyer–Villiger reaction and oxidative deoximation reaction. Compared with the traditionally used Grignard reagent method, the decarboxylative coupling reaction with selenium powders provides a shortcut for the preparation of organoselenium catalysts free of carcinogenic organohalide starting materials, toxic and odorous selenol intermediates and magnesium salt solid wastes. This may be helpful for reducing the cost of selenium catalysts to facilitate the application of organoselenium‐catalyzed green reactions in large‐scale production.     

Selective photometric determination of low conentrations of selenium(IV) and selenium(VI) in bottled drinking water

A procedure is developed for the selective photometric determination of selenium(IV) in bottled drinking water by the oxidation of Methylene Blue in 1 M HCl to colorless decomposition products and of selenium(VI) by its interaction with the specified reagent at pH 5–6 with the formation of a colored ion pair. The limits of detection are 1 and 0.8 µg/L, respectively. At the concentration of selenium(IV) 2 µg/L, the admissible weight ratios are: SeO₄^2-, Br₃^- (1: 20); Br^– (1: 60); I^–, IO₃^- and IO₄^- (1: 100). At equal concentration of selenium(VI), the following species: SeO₄^2-(1: 20); Br₃^-, Br^–, I^–, IO₃^-, and IO₄^- (1: 100) do not interfere with the determination. Other anions and cations present in highly mineralized waters do not interfere with the determination. The relative error of determination is 8–10% in the concentration range 2–10 µg/L of selenium(IV) and selenium(VI) and does not exceed 5% in their concentration range of 10–100 µg/L.     

Fabrics and papers modified with analytical reagents for the test determination of selenium(IV) and tellurium(IV)

It is shown that Malachite Green and Crystal Violet immobilized on viscose fabrics can be used as reagents for the rapid determination of selenium(IV) and tellurium(IV). Selenium is determine by the color intensity of ion associates formed by the reagents with the triiodide ion formed upon the reduction of selenium(IV) with potassium iodide and tellurium, by the color intensity of reagent ion associates with telluromolybdic heteropoly acid. The analytical ranges for selenium and tellurium(IV) were 0.005–0.5 and 0.01–0.1 mg/L upon passing 20 and 100 mL of a test solution through the indicator matrix, respectively. The duration of analysis does not exceed 15–20 min. The relative standard deviation is 50%. Test strips were proposed for determining 0.1–100 mg/L selenium(IV) and 1–1000 mg/L tellurium(IV) by the length of the colored zone. The determination of selenium(IV) is based on the oxidation of 4-nitrophenylgydrazine to its diazonium salt and salt interaction with naphthylamine chemically immobilized on paper with the formation of a red azo compound. The determination of tellurium(IV) is based on its reaction with Bismuthol II immobilized on a paper.     

Solid-phase spectrophotometric iodometric determination of nitrite and selenium(IV) using a polymethacrylate matrix

Procedures for the iodometric solid-phase spectrophotometric determination of nitrite and selenium( IV) using a polymethacrylate matrix are proposed. The procedures are based on the reaction of nitrite and selenium(IV) with iodine in an acidic medium with the release of free iodine in amounts equivalent to those of the substances to be determined, extraction of the iodine formed with a polymethacrylate matrix, and measurement of absorbance of the matrix at 370 nm. The developed procedures ensure the determination of 0.01–0.12 mg/L of nitrite and 0.05–0.40 mg/L of selenium(IV) with limits of detection of 0.005 and 0.03 mg/L, respectively. It was shown that the proposed procedures can be applied to the determination of selenium(IV) in mineral water and nitrites in vegetables and soil.     

Photometric determination of trace selenium in aqueous media

A new procedure is developed for the photometric determination of trace selenium in aqueous solutions. The selection of 2-(p-nitrophenyl)-3,5-diphenyltetrazolium chloride as a reagent for selenium is justified. The proposed sample preparation procedure involves gas extraction of selenium as hydrogen selenide followed by its liquid-adsorption extraction from the gas phase to an aqueous reagent solution with the formation of a water-insoluble formazan. Formazan formed upon the absorption of hydrogen selenide is extracted with isoamyl alcohol. The concentration of selenium is determined from the absorbance of the formazan extract in the isoamyl alcohol. The procedure allows the determination of 10–120 μg/L selenium.     

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     

Artificial and natural fiber fabrics with immobilized di-and triaminotriarylmethane reagents in chemical test methods

The potentials of fabrics made of artificial and natural fibers as supports for the di-and triaminotriarylmethane reagents were shown for their possible use in chemical test methods. Malachite Green, Brilliant Green, Methyl Violet, Crystal Violet, and Parafuchsine were immobilized on viscose, calico, coarse calico, and a mixed fabric. The reagent retention was 70–90%. The indicator fabrics are resistant to strong acids and alkalies and can be used for the test determination of 0.01–10 mg/L of phosphates, 1–80 mg/L of silicates, 0.01–8 mg/L of dissolved oxygen, biological oxygen demand for 5 days (BOD₅), 0.5–10 mg/L of formaldehyde, and 0.1–10 mg/L of anionic surfactants. The analysis time was 10–15 min. The relative standard deviation did not exceed 30%.     

Characterization of selenium species in extract from Niboshi (a processed Japanese anchovy)

Fish are selenium rich foodstuffs and a major selenium source for the Japanese population. Niboshi is processed from Japanese anchovy (Engraulis japonicus) and commonly used to prepare soup stock for Japanese dishes. In this study, we characterized selenium species in the Niboshi extract by ultrafiltration, ion-exchange chromatography and mass spectrometry. Selenium species in the Niboshi were more extractable by polar solvents (water and ethanol) than an apolar one (hexane) along with amino acids and proteinous species. Selenium in the water-extract from the Niboshi was mostly ascribed to organoselenium compounds with a molecular mass less than 5?kDa. Although selenoamino acids and selenoproteins and their fragments were involved in the extract, a large portion of the selenium species appeared to be low-molecular-mass organoselenium compounds other than selenoamino acids and their derivatives. Ion-exchange chromatographic separations revealed that most of the selenium species in the extract possess anionic and/or amphoteric characteristics. One of these selenium species from the Niboshi extract was detected at m/z 577 for 80Se by mass spectrometry subsequent to ion-pair extraction.     

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.     

Selenium redox cycling in the protective effects of organoselenides against oxidant-induced DNA damage

The biological role of selenium is a subject of intense current interest, and the antioxidant activity of selenoenzymes is now known to be dependent upon redox cycling of selenium within their active sites. Exogenously supplied or metabolically generated organoselenium compounds, capable of propagating a selenium redox cycle, might therefore supplement natural cellular defenses against the oxidizing agents generated during metabolism. We now report evidence that selenium redox cycling can enhance the protective effects of organoselenium compounds against oxidant-induced DNA damage. Phenylaminoethyl selenides were found to protect plasmid DNA from peroxynitrite-mediated damage by scavenging this powerful cellular oxidant and forming phenylaminoethyl selenoxides as the sole selenium-containing products. The redox properties of these organoselenoxide compounds were investigated, and the first redox potentials of selenoxides in the literature are reported here. Rate constants were determined for the reactions of the selenoxides with cellular reductants such as glutathione (GSH). These kinetic data were then used in a MatLab simulation, which showed the feasibility of selenium redox cycling by GSH in the presence of the cellular oxidant, peroxynitrite. Experiments were then carried out in which peroxynitrite-mediated plasmid DNA nick formation in the presence or absence of organoselenium compounds and GSH was monitored. The results demonstrate that GSH-mediated redox cycling of selenium enhances the protective effects of phenylaminoethyl selenides against peroxynitrite-induced DNA damage.     

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.     

微波辅助萃取-衍生气相色谱-电子捕获检测器法测定电子电气产品中的四溴双酚A

以N,O-双(三甲基硅烷基)三氟乙酰胺(BSTFA)作衍生化试剂,采用微波辅助萃取-衍生气相色谱-电子捕获检测器法(GC-ECD)测定电子电气产品中的四溴双酚A。使用V(甲苯)∶V(甲醇)=10∶1微波辅助萃取电子电气样品,用正己烷沉淀萃取液中的高聚物,净化后,将萃取液进行衍生化反应,采用ECD检测器进行定量测定。对衍生化时间、衍生化温度、衍生化试剂用量、沉淀试剂用量等前处理条件进行了优化,并进行了线性、回收率、精密度等试验。结果表明,方法线性范围为0.005~5 mg/L,相关系数为0.9985,方法的检测下限为0.02 mg/kg。采用样品加标的方式进行四溴双酚A的精密度及回收率实验,回收率在81.7%~110%之间,相对标准偏差RSD(n=7)小于7.2%。所建方法能很好的应用于电子电气产品中四溴双酚A的检测。     

The determination of trace levels of selenium contained in Chinese herbal drugs by differential pulse polarography

A differential pulse polarographic method for the determination of trace amounts of selenium contained in Chinese herbal drugs is described. In the Na(2) SO(3)KIO(3)NH(3)NH(4)Cl Medium (pH > 9) the selenium complex Se(O)SO(2-)(3) gives a catalytic wave, the peak potential of the wave is -0.76 V vs. Ag/AgClKCl (1M), and the peak current is directly proportional to selenium in the range 0.01-1.0 mug per 0.5 g of sample (0.08-8 ng/ml). The recoveries of selenium added to the samples tested are between 95 and 105%. The method is simple, sensitive, accurate and rapid. The results are in good agreement with those found by a DAN (2,3-diamino-naphthalene) spectrofluorimetric method.     

分子荧光光谱法测定富硒大米中的痕量硒

硒(Ⅳ)与DAN(2,3-二氨基萘)生成具有荧光特性的4,5-苯并苤硒脑,可用分子荧光光谱法测定,优化测定的实验条件,建立了快速准确测定大米中痕量硒的方法.结果表明,其最佳测定条件为:pH=2.0,反应温度为80℃,1.0×10-5 mol/L十六烷基溴化吡啶用作表面活性剂,环己烷萃取条件下,增敏效果明显,在0～0.0...     

Critical study of fluorimetric determination of selenium in urine

Different steps for the fluorimetric determination of Se in urine have been investigated. A HNO₃---HClO₄ (4:1) mixture is useful for urine digestion, and reduction of Se(VI) to Se(IV) is effectively carried out with HCl (6M). Selenium(VI) present after the digestion process constitutes 14.5–36.6% of total Se. An optimum pH of 1.80±0.05 and the addition of 1 ml of 2,3-diaminonaphthalene (DAN) (0.1%, w/v) are established in the formation of Se—DAN complex. Heating to 60°C, a time of incubation of 15 min is recommended to assure the complete formation of Se—DAN complex. A volume of 5 ml of cyclohexane and vigorous shaking for 45 sec is necessary for the extraction process. With this optimized method, the detection limit of selenium was 0.82 μg/l., within-day precision for a 50.0 μg/l. standard solution and urine (27.3 μg/l.) were 2.4 and 2.7% and between-day for the urine was 3.9% (33.9 μg/l.). Analytical recovery of 0.5 ml of Se standard (250 μg/l.) added to 1 ml of urine was 99.9±2.9% (95.8–104.4, n = 12). Normal levels of selenium excretion in urine obtained from healthy people were 27.9±8.7 μg/day (13.2–44.1), not observing significant differences (P < 0.05) between sexes.     

A New Turbidimetric Method for Determination of Melamine Based on its Reaction with Mercury(II)

A turbidimetric technique based on a reaction between Hg(II) and melamine is described for the measurement of melamine content of wastewater of a petrochemical company. The present technique is rapid and simple, uses a small amount of reagent and is set up with low‐cost equipment, making this system economically viable. The experimental conditions such as volume of reagent, pH of buffer, stirring time, stirring speed, ionic strength, etc. were optimized and used in plotting the calibration curve. The linear dynamic range was 1–70 mg/L with a limit of detection of 0.3 mg/L. Repeatability of the proposed method is good, and the relative standard deviation (RSD%) is less than 1.5%. Interferences studies showed that the common compounds existing in wastewater have no negative effect on the efficiency of the method at relatively high concentrations. Finally, the proposed method has been successfully used in determination of melamine in wastewater of Urmia Petrochemical Company.     

Glutathione peroxidase (GPx)-like antioxidant activity of the organoselenium drug ebselen: unexpected complications with thiol exchange reactions

The factors that are responsible for the relatively low glutathione peroxidase (GPx)-like antioxidant activity of organoselenium compounds such as ebselen (1, 2-phenyl-1,2-benzisoselenazol-3(2H)-one) in the reduction of hydroperoxides with aromatic thiols such as benzenethiol and 4-methylbenzenethiol as cosubstrates are described. Experimental and theoretical investigations reveal that the relatively poor GPx-like catalytic activity of organoselenium compounds is due to the undesired thiol exchange reactions that take place at the selenium center in the selenenyl sulfide intermediate. This study suggests that any substituent that is capable of enhancing the nucleophilic attack of thiol at sulfur in the selenenyl sulfide state would enhance the antioxidant potency of organoselenium compounds such as ebselen. It is proved that the use of thiol having an intramolecularly coordinating group would enhance the biological activity of ebselen and other organoselenium compounds. The presence of strong S...N or S...O interactions in the selenenyl sulfide state can modulate the attack of an incoming nucleophile (thiol) at the sulfur atom of the -Se-S- bridge and enhance the GPx activity by reducing the barrier for the formation of the active species selenol.     

Determination of Selenium(IV) by Stripping Voltammetry at a Mercury-Film Electrode

A procedure was proposed for the determination of selenium(IV) by stripping voltammetry on a mercury-film electrode at an electrolysis potential of +0.4 V versus the saturated silver–silver chloride reference electrode in a 1 M H₂SO₄ solution. The current of the cathodic peak is a linear function of the selenium(IV) concentration in the range from 5 × 10^–3 to 3 × 10^–1 mg/L (6.3 × 10^–8 to 3.8 × 10^–6 M) at a time of electrolysis of 30 s (t _el). The detection limit for selenium is 1 × 10^–4 mg/L (1.3 × 10^–9 M) at t _el = 300 s. It was shown that selenium(IV) can be determined in the presence of 10 mg/L Zn(II), 1 mg/L Cd(II), 0.5 mg/L Pb(II), and 0.2 mg/L Cu(II). A procedure for the determination of selenium in natural, mineral, and potable water was proposed.     

催化柴油中氮化物分布的气相色谱-原子发射光谱分析方法的研究

建立了催化柴油馏分中各种氮化物类型分布的气相色谱-原子发射光谱(GC-AED)分析方法,考察了色谱条件和不同的试剂气压力对各种氮化物分离和检测灵敏度的影响,定性(或归类)了某典型催化柴油中的73个氮化物,计算了程升条件下各种氮化物的保留指数,为不同实验室的定性比较提供了依据。以峰面积对质量浓度作图,氮化物在2.0~600 mg/L浓度范围内,AED检测器对不同氮化物有良好的线性响应,线性相关系数达0.998。几种氮化物(吲哚、1-甲基吲哚、C2-吲哚、咔唑、1-甲基咔唑、1,8-二甲基咔唑)峰面积的相对标