Article

Simultaneous analysis of selenate and selenite in bacterial suspensions by capillary electrophoresis

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Abstract

The use of capillary electrophoresis allows simultaneous determination of selenate and selenite during reduction by whole bacteria or their lysates. Optimal separation was achieved with 20 mM sodium borate and 1.0 mM tetradecyltrimethylammonium bromide, pH 9.5, −25 kV, at 28°C in an open, uncoated 44 cm×75 μm silica column. This method eliminates many steps in sample preparation and reduces necessary sample size. Application of this CE method in studying the depletion of both selenate and selenite in bacterial suspensions is reported.

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... Modification of the capillary surface with a cationic surfactant, which leads to the appearance of the positive fixed charges, is commonly used for reverse EOF. A range of longchain alkyltrimethylammonium salts, including cetyltrimethylammonium bromide (CTAB) [35,37], trimethyltetradecyloammonium bromide (TTAB) [39,40] or hydroxide (TTAOH) [41,42] and hexadecyltriethylammonium phosphate (HDTA) [43] or bromide (HDTAB) [36] could be utilised fairly well for this purpose. The combination of both negative applied potential and cationic surfactant added to the electrolyte solution appeared to be especially convenient for resolving selenium oxoanions and selenoamino acids, such as selenomethionine and selenocystine [35,39,41,43]. ...
... UV/VIS absorption detectors are still the most popular due to their simplicity and availability with most commercial instruments. Direct UV detection could be applied for speciation analysis of selenium, because its inorganic compounds absorb in the low wavelength range of 195-210 nm [35,[37][38][39][40][43][44][45]. However, they cannot be detected at low concentrations, which is especially pronounced for Se(IV), due to low absorption coefficients [43]. ...
... Whatever the detection method employed, sample introduction by the electrokinetic mode lowers the limits of detection by a factor of at least 10 in comparison with hydrodynamic injection [19,40,43]. But the increase in sensitivity is at the expense of calibration linearity and precision. ...
Article
The presence of selenium in the form of different species in environmental and biological samples receives an increasing attention due to better understanding of its bioavailability, toxicity and transport mechanism. For many years, gas and liquid chromatography have been extensively explored in speciation analysis of this element. Recently, capillary electrophoresis (CE) has made much progress in this field. This review presents the developments in the application of CE for simultaneous separation and determination of different selenium compounds. Various separation approaches and detection methods as well as pre-concentration techniques are discussed. The speciation performance of CE is illustrated by a number of practically relevant applications.
... Capillary zone electrophoresis (CZE) is a powerful separation technique that has been also applied successfully. Several published papers are devoted to ultraviolet (UV; [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], conductivity (8), and ICP-mass spectrometry (20)(21)(22) identification and determination of arsenic (2-11, 16, 17, 20-22) and selenium (6-8, 14, 15, 18, 19, 21) species. Different separation modes have been used including counterelectroosmotic capillary electrophoresis (CE) in uncoated fused silica capillaries (2-8, 13, 15, 16) and coelectroosmotic CE in capillaries in which the electroosmotic flow (EOF) is modified dynamically with cationic surfactants (7-12, 14, 18, 21) or by applying hydrodynamic pressure in a direction opposite to the EOF (22). ...
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A capillary zone electrophoresis method was de-veloped for the determination of 8 arsenic and se-lenium species in a polymer-coated capillary. Large-volume stacking with matrix removal was used for sensitivity enhancement. The entire analy-sis time was only a few minutes. The experimental sensitivity enhancement for 7 species was found to be near its theoretical value. Coating capillaries for long-term stability in alkaline buffer electrolytes was also investigated.
Chapter
Während für den Bereich der Kationenanalytik schon seit geraumer Zeit relativ schnelle und empfindliche Analysenmethoden wie AAS, ICP oder Voltammetrie zur Verfügung stehen, konnte der Mangel am hochempfindlichen Methoden auf dem Gebiet der Anionenanalytik erst durch Einführung der Ionenchromatographie (IC) durch Small, Stevens und Bauman im Jahr 1975 beseitigt werden. Seit dieser Zeit hat sich die Ionenchromatographie durch Entwicklung hocheffizienter Trennsäulen und spezifischer Detektions-verfahren zu einer vielseitigen Analysentechnik für ionische Spezies aller Art entwickelt [1].
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A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.
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The chemical mechanisms responsible for the immobilization of selenate (SeO4(2-) from aqueous solutions on cuprite (Cu2O) particles were determined from batch experiments. This was achieved by performing both solution-phase analyses and characterization of solid particles by X-ray photoelectron spectroscopy and transmission electron microscopy techniques, after equilibration of cuprite particles with selenate-containing solutions at various pH values, solid-to-solution ratios, and ionic strengths. Two distinct mechanisms have been pointed out. In the acidic medium, where the acid-catalyzed dissolution of cuprite into CuI species occurs, the immobilization of selenate implies a redox reaction with transient CuI leading to the precipitation of copper(II) selenite, CuSeO3. In the absence of protons added in the medium, Cu2O is chemically stable and immobilization of SeO4(2-) is essentially due to adsorption in the form of an outer-sphere surface complex. The uptake level of selenate by Cu2O is markedly lower than that observed for selenite species in the same conditions.
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A review of the general principles of ion analysis by capillary electrophoresis (CE) as well as its applications in biological and clinical analysis is presented. The separation modes, sample introduction and sample preparation and detection techniques are discussed in some detail. Method validation parameters are also highlighted. (152 references).
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In capillary electrophoresis, electrokinetic injection is a highly controversial sampling technique. It is a simple mode of sample introduction which is suitable for on-line preconcentration of the analytes, but its precision and accuracy are more strongly affected by experimental conditions compared to hydrodynamic injection. In the first part of this paper the features of electrokinetic and hydrodynamic injections are compared, followed by a detailed discussion on the different biases of electrokinetic injection and on how to reduce them. Finally, applications of the electrokinetic injection are reviewed with special emphasis on the analysis of inorganic compounds.
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This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.
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Most studies on the microbial transformations of elements have emphasized nutrient cycling within the biosphere or the economics of agricultural or industrial processes. Cyclic transformations within the biosphere between soluble, insoluble, and gaseous forms of carbon, nitrogen, hydrogen, oxygen, and sulfur are well known. Recently, attention has been focused on the role of microorganisms in the production and degradation of chemicals containing toxic elements (Alexander, 1973; Wood, 1974). Measures to increase animal and food crop production or disposal of waste materials can result in the introduction of elements in amounts harmful to terrestrial and aquatic ecosystems. Many elements and their compounds vary widely in both toxicity and mobility. Consequently, their safe disposal or effective recycling requires an understanding of their potential toxicities and possible transformations in the environment.
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The disposition of selenium (Se) was investigated in Wistar rats of various Se status after an intravenous injection of 82Se-selenite. Various fractions of plasma, urine, and cytosols from liver and kidney were separated by high performance liquid chromatography (HPLC), coupled with an inductively coupled argon plasma-mass spectrometry (ICP-MS). The technique allowed simultaneous differentiation of the fate of injected and endogenous Se, and if it was influenced by the previous Se burden in the tissues. A broad Se-peak from plasma was resolved in two fractions by assessing the m/z 82/78 ratios. Urinary profiles indicated that the metabolism of Se was dose-dependent; monomethylselenol being the primary metabolite of Se in untreated animals, whereas noticeable amount of trimethylselenonium ion was detected after the injection of 82Se. Liver and kidney cytosols contained complex Se-enriched fractions, a positive identification of which was not done in this study. In most cases, the enrichment of tissue fractions with the stable isotope was altered by the dietary Se levels, the isotope nevertheless was exchanged with the endogenous Se in various macromolecules to a varying degree.
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A Pseudomonas stutzeri isolate rapidly reduced both selenite and selenate ions to elemental selenium at initial concentrations of both anions of up to 48.1 mM. Optimal selenium reduction occurred under aerobic conditions between pH 7.0 and 9.0 and at temperatures of 25 to 35 degrees C. Reduction of both selenite and selenate was unaffected by a number of anions except for sulfite, chromate, and tungstate ions, which inhibited both growth and reduction.
Biotechnology in Minerals and Metal Processing
  • Larsen