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Natural Water Samples (natural + water_sample)
Selected AbstractsA New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon NanotubesELECTROANALYSIS, Issue 9 2009Cruz Moraes, Fernando Abstract The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700,mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12,,mol L,1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection. [source] Study of Factors Affecting the Performance of Voltammetric Copper Sensors Based on Gly-Gly-His Modified Glassy Carbon and Gold ElectrodesELECTROANALYSIS, Issue 12 2006Guozhen Liu Abstract This paper reports a study of the factors affecting the analytical performance of gold and glassy carbon electrodes modified with the tripeptide Gly-Gly-His for the detection of copper ions. Gly-Gly-His is attached to a glassy carbon (GC) surface modified with 4-carboxyphenyl moieties or a gold surface modified with 3-mercaptopropionic acid by the reaction of the N-terminal amine group of the peptide with the carboxylic acid groups of the monolayer via carbodiimide activation. X-ray photoelectron spectroscopy was used to characterize the steps in the biosensor fabrication. It was found that the analytical performance of a sensor prepared with Gly-Gly-His on a GC electrode was similar to that on a gold electrode under the same conditions. The performance was greatly enhanced at higher temperature, no added salt during copper accumulation and longer accumulation time within a pH range of 7,9. Interference studies and investigations of stability of the Gly-Gly-His sensor are reported. Analysis of natural water samples show that the sensors measure only copper ions that can complex at the sensor surface. Strongly complexed copper in natural water is not measured. Despite greater stability of diazonium salt derived monolayers on carbon surfaces compared with alkanethiols self-assembled monolayers on gold, the stability of the sensors was essentially the same regardless of the modification procedure. [source] Utilization of a Copper Solid Amalgam Electrode for the Analytical Determination of AtrazineELECTROANALYSIS, Issue 22 2005Djenaine De, Souza Abstract A copper solid amalgam electrode was prepared and used for the voltammetric determination of atrazine in natural water samples by square wave voltammetry. This electrode is a convenient substitute for the hanging mercury electrode since it is selective, sensitive, reliable and inexpensive and presents low toxicity characteristic. The detection limit of atrazine obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency. The relative standard deviation for 10 different measurements was found to be only 3.98% in solutions containing 8.16×10,6,mol L,1 of atrazine. In polluted stream water samples, the recovery measurements were approximately 70.00%, sustaining the applicability of the proposed methodology to the analysis of atrazine in such matrices. [source] Integrated Microanalytical System Coupling Permeation Liquid Membrane and Voltammetry for Trace Metal Speciation.ELECTROANALYSIS, Issue 10 2004Optimization, Technical Description Abstract A new minicell coupling the liquid-liquid extraction technique called permeation liquid membrane (PLM) with an integrated Ir-based Hg-plated microelectrode array for voltammetric detection has been developed for the speciation of heavy metals in natural waters. Lead and cadmium have been used as model compounds. The PLM consists of a carrier (0.1,M 22DD+0.1,M lauric acid) dissolved in 1,:,1 mixture of toluene/phenylhexane held in the small pores (30,nm) of a hydrophobic polypropylene membrane (Celgard 2500). One side of this membrane is in contact with a flowing source solution, containing the metal ions of interest. An acceptor or strip solution (pyrophosphate) is placed on the other side of the PLM with the microelectrode array placed at 480,,m of the PLM. The analyte is transported by the carrier from the source solution to the strip solution. The originality of the new minicell is that accumulation in the strip solution is voltammetrically followed by the integrated microelectrode array in real time, and at low concentration level, using square-wave anodic stripping voltammetry (SWASV). In order to protect the Hg microelectrodes from the adsorption of the hydrophobic carrier, the microelectrodes are embedded in a thin gel layer (280,,m) of 1.5% LGL agarose gel containing 10% of hydrophobic silica particles C18. The choice of optimum conditions is discussed in details in this article. Due to the very small effective strip volume of the new cell (less than 1,,L), high enrichment factor can be obtained (e.g., 330 for Pb) after 2,hours of accumulation. No deaeration of the solutions is required for SWASV measurements. Detection limits under these conditions are 2,pM and 75,pM for Pb and Cd, respectively, using a voltammetric deposition time of 5,min. In addition, no fouling effects were observed with natural water samples. [source] Simultaneous determination of Zr(IV) and Hf(IV) by CE using precolumn complexation with a [PW11O39]7, ligandELECTROPHORESIS, Issue 10 2007Sadayuki Himeno Professor Abstract A CE method was developed for the simultaneous determination of Zr(IV) and Hf(IV) at trace levels. A lacunary Keggin-type [PW11O39]7, ligand reacted quantitatively with a mixture of trace amounts of Zr(IV) and Hf(IV) to form the so-called ternary Keggin-type anions [P(ZrIVW11)O40]5, and [P(HfIVW11)O40]5, in 0.010,M monochloroacetate buffer (pH,2.2). Since both ternary anions possessed different electrophoretic mobilities and high molar absorptivities in the UV region, Zr(IV) and Hf(IV) were determined simultaneously with direct UV detection at 258,nm. Each peak height was linearly dependent on the concentration of Zr(IV) or Hf(IV) in the range of 5.0×10,7,1.0×10,5,M; a detection limit of 2×10,7,M was achieved. The utility of the proposed CE method was demonstrated for the simultaneous determination of Zr(IV) and Hf(IV) in natural water samples with satisfactory results. [source] Development and field validation of a biotic ligand model predicting chronic copper toxicity to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2004Karel A.C. De Schamphelaere Abstract In this study, we developed a toxicity model predicting the long-term effects of copper on the reproduction of the cladoceran Daphnia magna that is based on previously reported toxicity tests in 35 exposure media with different water chemistries. First, it was demonstrated that the acute copper biotic ligand model (BLM) for D. magna could not serve as a reliable basis for predicting chronic copper toxicity. Consequently, BLM constants for chronic exposures were derived by multiple regression analysis of 21-d median effective concentrations (EC50s; expressed as Cu2+ activity) versus physicochemistry from a large toxicity dataset and the results of an additional experiment in which the individual effect of sodium on copper toxicity was investigated. The effect of sodium on chronic toxicity (log KNaBL = 2.91) seemed to be similar to its effect on acute toxicity (log KNaBL = 3.19). However, in contrast to the acute BLM, no significant calcium, magnesium, or combined competition effect was observed, and an increase in proton competition and bioavailability of CuOH+ and CuCO3 complexes was noted. Some indirect evidence was also found for some limited toxicity of complexes of copper with two of three tested types of dissolved organic matter. Because the latter was only a minor effect, this factor was not included in the chronic Cu BLM. The newly developed model performed well in predicting 21-d EC50s and no-observed-effect concentrations in natural water samples: 79% of the toxicity threshold values were predicted within a factor of two of the observed values. It is clear, however, that more research is needed to provide information on the exact mechanisms that have resulted in different BLM constants for chronic exposures (as opposed to acute exposures). It is suggested that the developed model can contribute to the improvement of risk assessment procedures of copper by incorporating bioavailability of copper in these regulatory exercises. [source] Degradation products of a phenylurea herbicide, diuron: Synthesis, ecotoxicity, and biotransformationENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2001Céline Tixier Abstract The degradation products of diuron (photoproducts and metabolites), already described in the literature, were synthesized in order to carry out further investigations. Their ecotoxicity was determined using the standardized Microtox® test, and most of the derivatives presented a nontarget toxicity higher than that of diuron. Therefore, the biotransformation of these compounds was tested with four fungal strains and a bacterial strain, which were known to be efficient for diuron transformation. With the exception of the 3,4-dichlorophenylurea, all the degradation products underwent other transformations with most of the strains tested, but no mineralization was observed. For many of them, the biodegradation compound for which the toxicity was important was 3,4-dichlorophenylurea. This study underlines the importance of knowing the nature of the degradation products, which has to be kept in mind while analyzing natural water samples or soil samples. [source] OLIGONUCLEOTIDE PRIMERS FOR THE DETECTION OF BIOLUMINESCENT DINOFLAGELLATES REVEAL NOVEL LUCIFERASE SEQUENCES AND INFORMATION ON THE MOLECULAR EVOLUTION OF THIS GENE,JOURNAL OF PHYCOLOGY, Issue 2 2008Andrea Baker Bioluminescence is reported in members of 18 dinoflagellate genera. Species of dinoflagellates are known to have different bioluminescent signatures, making it difficult to assess the presence of particular species in the water column using optical tools, particularly when bioluminescent populations are in nonbloom conditions. A "universal" oligonucleotide primer set, along with species and genus-specific primers specific to the luciferase gene were developed for the detection of bioluminescent dinoflagellates. These primers amplified luciferase sequences from bioluminescent dinoflagellate cultures and from environmental samples containing bioluminescent dinoflagellate populations. Novel luciferase sequences were obtained for strains of Alexandrium cf. catenella (Whedon et Kof.) Balech and Alexandrium fundyense Balech, and also from a strain of Gonyaulax spinifera (Clap. et Whitting) Diesing, which produces bioluminescence undetectable to the naked eye. The phylogeny of partial luciferase sequences revealed five significant clades of the dinoflagellate luciferase gene, suggesting divergence among some species and providing clues on their molecular evolution. We propose that the primers developed in this study will allow further detection of low-light-emitting bioluminescent dinoflagellate species and will have applications as robust indicators of dinoflagellate bioluminescence in natural water samples. [source] Selective enrichment of trace copper(II) from biological and natural water samples by SPE using ion-imprinted polymerJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Yunhui Zhai Abstract A novel Cu(II)-imprinted polymer sorbent was prepared by an ion-imprinted polymer (IIP) technique using (2Z)- N,N,-bis(2-aminoethylic)but-2-enediamide as the functional monomer and pentaerythritol triacylate as a crosslinker. IR, XPS, and elemental analysis techniques were used to confirm the obtained product. Subsequently, when this polymer was used as sorbent in SPE, it exhibited excellent selectivity for template ion from an aqueous solution. Quantitative extraction of Cu(II) was achieved in the pH range of 4,7. The time needed to extract each sample was less than 30 min by the batch method. The distribution ratio (D) values of IIP for Cu(II) were greatly larger than that for other ions. At optimal pH value, the maximum extraction capacity of IIP and nonimprinted polymer (NIP) was found to be 29.8 and 7.0 mg/g, respectively. The adsorption behavior of Cu(II) on the sorbents could be described by Langmuir adsorption isotherm equation. The feasible flow rate of Cu(II)-containing solution for quantitative extraction onto the column packed with IIP was 1,4 mL/min, whereas for elution it was less than 1 mL/min. The developed method was successfully applied to the separation and enrichment of trace Cu(II) in biological and natural water samples with satisfactory results. [source] Evaluation and applicability of a purification method coupled with nested PCR for the detection of Toxoplasma oocysts in waterLETTERS IN APPLIED MICROBIOLOGY, Issue 5 2006C. Kourenti Abstract Aims:, To describe the development, evaluation and applicability of a complete method for the detection of Toxoplasma gondii in water. Methods and Results:, The method incorporated concentration of water samples by Al2(SO4)3 -flocculation, purification by discontinuous sucrose gradients and detection of toxoplasmic DNA by 18S-rRNA nested PCR. Tap water replicates and natural water samples were seeded with defined numbers of Toxoplasma oocysts and processed for evaluation studies. When applied to environmental samples, the method gave highest detection sensitivities of 100 oocysts in river water and 10 oocysts in well- and sea water. The method was finally applied in 60 water samples of different quality and origin collected over a 14-month period. Toxoplasmic DNA was detected in four samples. Conclusions:, The method offers an alternative towards improving current methods that can be used for the detection of Toxoplasma oocysts in environmental water samples. Significance and Impact of the Study:, The method in its current form will be helpful for assessment of Toxoplasma contamination in water resources, particularly after outbreak events. [source] A fluorimetric method for the determination of trace pentachlorophenol, based on its inhibitory effect on the redox reaction between the improved Fenton reagent and rhodamine BLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 5 2007Huiqin Guo Abstract A sensitive fluorimetric method is presented and discussed for the determination of pentachlorophenol in aqueous solutions. This method is based on the inhibitory effect of pentachlorophenol on the reaction of conventional Fenton [Fe(III) + H2O2] reagent with rhodamine B in the medium of perchloric acid, which results in the fluorescence quenching of rhodamine B. It was further found that the sensitivity for the determination was improved significantly when the molecular ligand EDTA was added. This improved system was therefore presented for the determination of pentachlorophenol. The characteristics of the excitation and emission spectra, optimization of the experimental conditions, the stability of the system and the influence of foreign matter have all been investigated. Under optimal conditions, the linear range for the determination of pentachlorophenol is 12,480 ng/mL with a 3, limit of detection of 0.96 ng/mL. Compared with the conventional Fenton system, the improved system shows obvious advantages in both sensitivity and selectivity. By combination with the pretreatment of samples using ion exchange resins and XDA-1 absorption resin, the improved Fenton method was used for the first time for the determination of pentachlorophenol in synthetic samples and natural water samples, and satisfactory results, in agreement with those of the HPLC method, were achieved. The possible mechanism of the reactions has also been discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Improved method for isotopic and quantitative analysis of dissolved inorganic carbon in natural water samplesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2006Nelly Assayag We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (,13CDIC) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO2(g),CO2(aq) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H3PO4 -loaded and He-flushed 12,mL glass tube. The H3PO4 reacts with the water and converts the DIC into aqueous and gaseous CO2. After a CO2(g),CO2(aq) equilibration time of between 15 and 24,h, a portion of the headspace gas (mainly CO2+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO2(g), from which the ,13CDIC is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25,mmol,·,L,1 and solution volume of 1,mL (high DIC concentration samples) or 5,mL (low DIC concentration samples), ,13CDIC values are determined with a precision (1,) better than 0.1,. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO2(g),CO2(aq) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same ,gas/liquid' and ,H3PO4/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||