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Simultaneous analysis of selenate and selenite in bacterial suspensions by capillary electrophoresis
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.
... 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. ...
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). ...
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.
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].
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.
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.
Capillary electrophoresis (CE) with indirect fluorescence detection was used to analyze selenium (selenite, selenate, selenomethionine, and selenocystine) and antimony (antimonite and antimonate) compounds. The separation was achieved by CE in 6 min with a 1.2 mM fluorescein solution at pH 9.5. Fluorescein also functioned as a background fluorophore for the indirect detection of these nonfluorescent species. Linearity of more than two orders of magnitude was generally obtained. Precision of migration times and peak areas was less than 1.0% and 7.2%, respectively. The concentration limits of detection (CLODs) was in the microM range. The detection sensitivity was generally dependent upon the transfer ratio (TR, defined as the number of moles of fluorescein ions displaced by one mole of analyte ions) of each species.
One of the major problems facing the development of capillary electrophoresis (CE) is the relatively high limits of detection when compared to traditional high-performance liquid chromatographic (HPLC) methods. While the use of an alternative detector can offer better sensitivity, a more universal approach is sample preconcentration. Numerous on-line methods have been developed to improve the sensitivity of CE, and are based on electrophoretic principles, chromatographic principles, or a combination of both. This review will discuss all forms of on-line preconcentration methods for CE, with emphasis given to those that have shown particular merit when applied to inorganic and small organic anions.
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).
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.
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.
An overview of recent developments in the application of capillary electrophoresis to simultaneous separation and determination of different chemical forms of an inorganic element is presented, with particular emphasis placed on metal speciation analysis. Examples of species analysis are addressed, covering metal ions in different oxidation states, metal complexes with inorganic and organic ligands, metalloid oxoanions, organometallic compounds, ionic non-metal species, etc. The speciation performance of capillary electrophoresis is illustrated by a number of practically relevant applications. The method's strengths and current limitations with regard to chemical speciation studies are critically discussed.
A new and very simple technique has been developed in capillary zone electrophoresis for the separation of organic acids. In this new method, capillaries were simply treated with 0.1 M NaOH via high pressure for 3 min, then flushed with running buffer solutions via high pressure for 10 s before performing separation. After this treatment, electroosmotic flow (EOF) is higher than electrophoretic mobilities (EPM) of all analytes in weak acidic conditions. Thus, eight organic acids are well separated in less than 7 min at an applied voltage of 22 kV. In addition to significant differences of EPM among analytes in weak acidic conditions, dynamic changes in EOF and pH account for the good separation results. Capillary dimensions, ionic strength and type of buffer solution all show dramatic effects on the separations of organic acids. The results also support the existence of dynamic changes in the system during a run. This new method provides the advantages of reproducibility, speed and simplicity for the separation of organic acids which cannot be easily separated in the range of pH 4–6 by any conventional means.
While capillary electrophoresis (CE) is growing in importance as a versatile assay for providing element speciation information, there still exist major challenges that limit the technique’s practical acceptance. The potential problems in CE applied to speciation analysis are due to certain “noes”: no special attention on sample preparation procedures ensuring species stability and avoiding matrix effects, no sufficient care on possible changes in speciation during electrophoresis, no appropriate treatment on method validation and system suitability aspects, no sample enrichment methodologies and detection systems refined for routine use, etc. Approaches to help address these problems are brought into focus and critically evaluated. Recommendations are given how to advance reliable speciation measurements by CE.
AIM: To determine the dissociation constant of panaxatriol 3,6- disuccinic acid by thin-layer pH-chromatography. METHOD: The dissociation constant of panaxatriol 3,6- disuccinic acid is calculated from the data of Rf-pH curves. The accuracy of this way is validated by tartaric acid. RESULT: The dissociation constant of panaxatriol 3,6- disuccinic acid were determined for the first time. CONCLUSION: It needs only simple instruments. The compound can be present in the sample only in small amount and cannot be isolated in pure solid state.
A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25samples per hour using a background electrolyte solution containing 8.75mM l-histidine (His) adjusted to pH4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190gL–1 and 7.5gL–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.
Progress made in the last five years in the application of capillary electrophoresis methods to chemical speciation of elements is reported on the basis of over 100 literature references. The main trends observed include development of new on- and off-capillary derivatization methods, application of new detection methods, and especially coupling of CE separation systems to powerful atomic spectroscopy and mass spectrometry instruments with various ionization techniques, providing either a sensitive element-specific detection method or a third dimension for high performance separation. Besides numerous CZE and MEKC capillary electrophoresis methods only very few examples of CE speciation with capillary electrochromatography can be found. Concerning the chemical forms of elements determined, the new procedures developed are mostly focused on redox speciation of various oxidation states of elements, metal-bound high molecular compounds, and organometallic species.
An overview of the state-of-the-art of capillary electrophoresis (CE) for metal speciation analysis is presented. Various CE separation approaches and detection modes applied are discussed. A comprehensive description of reported methods to date in CE speciation studies of individual metals in different oxidation states, metal complexes with inorganic and organic ligands, oxoanions and organometallic compounds is demonstrated. The potential of CE for characterisation of metal interactions with large molecules like humic substances and proteins is also described. Several examples are presented to demonstrate CE's ability to solve real-world speciation problems. Further, the current strengths and limitations of CE with regard to speciation studies are discussed. The performance of CE is also critically evaluated in relationship to conventional chromatographic techniques used in metal speciation determination.
A new hydride generation system, ‘movable reduction bed hydride generator’ has been developed which accomplishes hydride generation at microliter sample volume without the need for an external addition of acid, or the use of a gas–liquid separator. Interferences among hydride forming elements have been greatly reduced. The technique may offer a possibility for automatic operation, and could be used as an interface for LC, CE and other chromatographic techniques. The recoveries of As, Se and Sb by standard addition from a Chinese tea are 81.1 (±2.7%), 102.6 (±3.4%) and 94.1% (±4.1%), respectively.
Ultraviolet and ultrasound irradiation-induced redox reactions have been assessed for the determination of Se(IV), Se(VI), selenomethionine and selenocystine in model waters, enriched natural waters and soil/fly ash extracts by the hydride-generation technique with atomic absorption and fluorescence detection. Photooxidation of Se-methionine and Se-cystine into Se(IV) by UV irradiation in HCl medium (pH 0.4) can be achieved within 10 min, whilst Se(IV), the only Se species reactive towards NaBH4, leading to SeH2 formation, remains unaffected. Photoreduction of Se(VI) to Se(IV) required at least 45 min under the same conditions. Higher pH values yielded incomplete conversions of the Se species into Se(IV). Se(VI) photoreduction was completely inhibited by the presence of 10000 mg L−1 nitrate as KNO3. Ultrasonic oxidation of Se-cystine to Se(IV) is seen to occur, the remaining Se species remaining unaffected. According to the above redox reactions, a four-stage model for speciation of Se is proposed. The combination of these reactions could be the basis for a new speciation approach that is advantageous in terms of sensitivity and simplicity over methods involving chromatographic separations. The LOD of each Se species was 40 pg mL−1 and 2 pg mL−1 with detection by atomic absorption and fluorescence, respectively. The repeatability expressed as relative standard deviation was in the range 2–5% for natural waters and 4–10% for phosphate extracts.
Capillary electrophoresis (CE) encompasses a number of characteristics quite suitable for the simultaneous analysis of small ions such as high efficiency and resolving power, directly associated to its impressively high peak capacity, and short analysis time. In appropriate conditions, it is possible to perform the separation of approximately 36 anions in less than 3 minutes. In this work, the mechanisms by which anion analysis is performed was criteriously discussed, and a thorough review of the literature in the past 5 years, focusing mostly in applications of CE to anion analysis in real matrices, was presented.
This chapter discusses gas chromatography (GC), liquid chromatography (LC), and electroseparation methods used for inorganic species. It examines developments and applications in inorganic GC for the period 1992–2002. The chapter discusses elements, binary compounds, coordination compounds, anions, and organometallics. Prior to 1980, the development of LC methods for the separation and determination of inorganic species was much less rapid than for the application of these techniques to organic species. The LC methods include only modern, high-performance techniques, such as ion chromatography (IC), high-performance liquid chromatography (HPLC) (both normal and reversed phases), ion-pair chromatography, and ion-exclusion chromatography. The chapter discusses some special features that apply to the electroseparation methods, especially capillary zone electrophoresis (CZE) and capillary electrochromatography (CEC).
The common selenium oxoanions selenite (SeO32-) and selenate (SeO42-) are toxic at intake levels slightly below 1 mg day-1. These anions are currently monitored by a variety of traditional analytical techniques that are time consuming, expensive, require large sample volumes, and/or lack portability. To address the need for a fast and inexpensive analysis of selenium oxoanions, we present the first microchip capillary zone electrophoresis (MCE) separation targeting these species in the presence of chloride, sulfate, nitrate, nitrite, chlorate, sulfamate, methanesulfonate, and fluoride, which can be simultaneously monitored. The chemistry was designed to give high selectivity in non-ideal matrices. Interference from common weak acids is avoided by operating near pH 4. Separation resolution from chloride was enhanced to improve tolerance of high-salinity matrices. As a result, selenate can be quantified in the presence of up to 1.5 mM NaCl, and selenite analysis is even more robust against chloride. Using contact conductivity detection, detection limits for samples with conductivity equal to the background electrolyte (BGE) are 53 nM (4.2 ppb Se) and 380 nM (30 ppb) for selenate and selenite, respectively. Analysis time, including injection, is ~2 min. The MCE method was validated against ion chromatography (IC) using spiked samples of dilute BBL™ broth and slightly outperformed the IC in accuracy while requiring <10% of the analysis time. The applicability of the technique to real samples was shown by monitoring the consumption of selenite by bacteria incubated in LB broth.
A simple capillary zone electrophoretic method for the determination of biospherically important oxyanions of selenium (Se) and tellurium and another Se-containing anion, selenocyanate, has been developed. The method uses direct UV absorption detection. Time course experiments with time slices as short as 6 min are possible. This method's detection limits and linear range compare well with other methods involving samples containing complex biological matrices. The metalloid-containing anions examined were selenocyanate, selenite, selenate, tellurite, and tellurate. We applied this method to live cultures of two different bacteria in two different growth media in time course experiments following the changes in metalloid-containing anion concentrations. The results show that this method is a useful means of following the biological processing of these analytes in bacterial cultures.
Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h-1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14.38, and 155 mumol m-2 day-1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively.
Samples collected from Kesterson Reservoir were screened for bacterial presence and selenate reduction capability. Selenate concentrations of 100 mg/liter were not toxic to indigenous bacteria. Of the 44 samples collected, 20 possessed microbial populations capable of reducing selenate. Reduction was observed in 4% of the water samples, 92% of the sediment samples, and 100% of the soil samples. Microbial reduction of 100 mg of selenate per liter was complete within 1 week of incubation. Up to 75 mg of selenate per liter was reduced beyond selenite to an insoluble red precipitate. Data collected indicate that indigenous bacteria have a significant role in the biogeochemical cycling of selenium.
Resting cell suspensions of a strain of Corynebacterium isolated from soil formed dimethyl selenide from selenate, selenite, elemental selenium, selenomethionine, selenocystine, and methaneseleninate. Extracts of the bacterium catalyzed the production of dimethyl selenide from selenite, elemental selenium, and methaneseleninate, and methylation of the inorganic Se compounds was enhanced by S-adenosylmethionine. Neither trimethylselenonium nor methaneselenonate was metabolized by the Corynebacterium. Resting cell suspensions of a methionine-utilizing pseudomonad converted selenomethionine to dimethyl diselenide. Six of 10 microorganisms able to grow on cystine used selenocystine as a sole source of carbon and formed elemental selenium, and one of the isolates, a pseudomonad, was found also to produce selenide. Soil enrichments converted trimethylselenonium to dimethyl selenide. Bacteria capable of utilizing trimethylselenonium, dimethyl selenide, and dimethyl diselenide as carbon sources were isolated from soil.
Interstitial water profiles of SeO(4), SeO(3), SO(4), and Cl in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO(4) occurred under anaerobic conditions, was more rapid with H(2) or acetate, and was inhibited by O(2), NO(3), MnO(2), or autoclaving but not by SO(4) or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO(2). A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters.
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.
Direct current plasma atomic emission spectrometry (DCPAES) was evaluated as an element selective method of detection (ESD) for ion chromatography (IC). By use of DCPAES, different species of a given element can be determined with identical measurement sensitivity. Those species that are separated in the chromatographic analytical column but are not detectable by conductivity detection, such as As(III), are easily detected by monitoring the atomic emission of a targeted element (in this case arsenic) in the chromatographic effluent. With the use of DCPAES, interference and other matrix effects are eliminated. Thus, a wide range of eluent composition can be employed without experiencing detector limitations. Reduction in detection capability as a result of dilution of the analyte during the chromatographic process can be offset by employing large (up to 1000..mu..L) sample injection loops or by using a concentrator column. With a concentrator column, the measurable concentration of arsenic was found to be 10 ppb with a detection limit of 2.5 ppb. These values are 3 orders of magnitude smaller than those determined when dc plasma is used in the uninterfaced mode. With the use of element selective detectors, element speciation can be facilitated considerably.
Tetraalkylammonium salts [R3RN]+X– (R=R, XCH3, Cl; C2H5, Br; C3H7, Br; C4H9, H2PO4; C5H11 Br; R, R, XCH3, C16H33, Br) were investigated as ion-pairing reagents for the reversed-phase ion-pair chromatographic separation of selenite and selenate. Other chromatographic parameters such as composition and pH of the mobile phase and concentration of the ion-pairing reagent were also investigated. The compatibility of the proposed chromatographic procedures with various selenium-specific detectors is discussed. The absolute detection limits were found to be 31 ng Se for selenite and 51 ng Se for selenate (100 l injection) with a solution of 5 mM tetrabutylammonium dihydrogen phosphate in 5050 (v/v) methanol/water as mobile phase at a flow rate of 1 ml/min when a flame atomic absorption spectrometer was used as detector. The HPLC/FAAS system was employed for the determination of selenite in solutions serving as selenium supplement for animals.
The general abilities of capillary electrophoretic methods [capillary zone electrophoresis (CZE), isotachophoresis and isoelectric focusing] to perform species analysis are described. Several examples of the speciation of heavy metal complexes (e.g., complexes of gadolinium, platinum and iron) and metal oxoanions (arsenic and selenium) using CZE are demonstrated and the applicability to separation problems in the fields of medicine, pharmacology and ecology is discussed.
Inorganic capillary electrophoresis (ICE) is a new separations technology which melds the technique of classical electrophoresis with the separations approach of ion chromatography. Matrices which have been difficult to deal with using ion chromatography have proven amenable to analysis by ICE. The simultaneous analysis of weak acid anions, oxalate and citrate and inorganic anions, chloride, sulfate, nitrate, phosphate and carbonate in diluted urine was achieved using ICE. The determination of the oxyanions of arsenic (i.e. arsenite and arsenate) in urine was also performed.
The high levels of selenium (selenate, selenite) in agricultural drainage water in the San Joaquin Valley of California, which have led to environmental problems, might be lowered if the selenate/selenite could be reduced to elemental insoluble selenium. Two organisms have been newly isolated which do this in anaerobic coculture. One, a strictly anaerobic, Gram-positive rod, reduces selenite to elemental selenium. The other, a Pseudomonas species, was shown to respire selenate to selenite. Cells grown anaerobically in Minimal Medium on acetate plus selenate oxidized 14C-acetate to 14CO2 with concomitant reduction of selenate to selenite and small amounts of elemental selenium.
When Salmonella Heidelberg is grown in 0.1% w/v Na2SeO3 and examined microscopically during growth, two morphological changes can be seen. Red intracellular granules are seen in most of the population within 10 to 12 hours, and organisms containing granules elongate without cell division. The intracellular granules produced by S. heidelberg in selenite broth have been identified by X-ray analysis as amorphous red selenium. The intermediate in the conversion of selenite to elemental selenium has been trapped and identified as divalent selenium ion. Growth studies have shown that selenite toxicity is primarily associated with the lag phase of growth, and also that the divalent intermediate is more toxic than the tetravalent precursor.
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.
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