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1.
A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidic medium and the reaction mechanism was investigated. The reaction was followed spectrofluorimetrically by measuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λex=356 nm, λem=439 nm) at a fixed time of 5 min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0 ng ml−1 with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088 ng ml−1 and the catalytic reaction activation energy was found to be 43.92 kJ mol−1. The proposed method was tested for the determination of vanadium(V) in rice and natural water samples.  相似文献   

2.
The electronic tongue (ET) multisensor system has been employed for the detection of metal-oxygen cluster anions (polyoxometalates) containing vanadium (IV/V) atoms. Sensitivity of a variety of potentiometric chemical sensors with plasticized polyvinyl chloride and chalcogenide glass membranes was evaluated with respect to vanadyl/vanadate ions, decavanadate and a series of Keggin-type polyoxometalates (POM) such as α-[SiW11VIVO40]6−, α-[SiW11VVO40]5−, α-[BW11VIVO40]7−, α-[BW11VVO40]6−, α-[PW11VIVO40]5− and α-[PW12−nVnVO40](3+n)− (n = 1, 2, 3). Sensor's responses to vanadium complexes were evaluated in the pH range of 2.4-6.5 and a set of sensors appropriate for detecting a variety of vanadium species was selected. Such sensor array was able to distinguish different vanadium complexes allowing their simultaneous quantification in binary (V(IV)/V(V)) mixtures. The vanillyl alcohol oxidation with α-[SiW11VVO40]5− was monitored using ET to evaluate the capacity of proposed analytic system to detect simultaneously V(IV)/V(V) in POM under dynamic equilibrium. ET was demonstrated to be a promising tool for the discrimination and quantification of vanadium-containing POMs at different oxidation states. In particular, such a system could represent a significant interest for the mechanistic studies of redox reactions with POMs.  相似文献   

3.
A novel flow injection analysis (FIA) system based on liquid-liquid microextraction and fluorimetric determination was developed for the determination of traces of the Zn2+ ion using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a sensitive and selective fluorimetric sensor, with λex = 373 nm and λem = 530 nm, and hexanol as the extracting organic solvent. In the designed FIA system, the phase separation takes place via gravitation forces in the absence of any segmenter. The influence of pH and ionic strength of the solution, amount of ligand, nature of counter ion, volume of organic solvent, extraction time and coil length was investigated. Under optimized experimental conditions, the calibration curve found to be liner over a concentration range of 0.025-4.53 μg mL−1 (R2 = 0.9951) with a limit of detection of 2.3 ng mL−1. The enrichment factor was 45 and relative standard deviation for 7 replicate determinations was 2.43%. The method is very fast and uses low levels of organic solvents. The proposed method was applied successfully to the determination of zinc(II) in human hair, human serum and two inorganic sludge samples.  相似文献   

4.
The development of more efficient anti-tuberculosis drugs is of interest. Three oxovanadium(IV) and three cis-dioxovanadium(V) complexes with thiosemicarbazone derivatives bearing moieties with different lipophilicity have been prepared and had their inhibitory activity against Mycobacteriumtuberculosis H37Rv ATCC 27294 evaluated. The analytical methods used by the complexes’ characterization included IR, EPR, 1H, 13C and 51V NMR spectroscopies, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. [VO(acac)(aptsc)], [VO(acac)(apmtsc)] and [VO(acac)(apptsc)] (acac = acetylacetonate; Haptsc = 2-acetylpyridinethiosemicarbazone; Hapmtsc = 2-acetylpyridine-N(4)-methyl-thiosemicarbazone and Happtsc = 2-acetylpyridine-N(4)-phenyl-thiosemicarbazone) are paramagnetic and their EPR spectra are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral structures of rhombic symmetry and with the oxidation state +IV for the vanadium atom. As result of oxidation of the vanadium(IV) complexes above, the diamagnetic cis-dioxovanadium(V) complexes [VO2(aptsc)], [VO2(apmtsc)] and [VO2(apptsc)] are formed. Their 1H, 13C and 51V NMR spectra were acquired and support a distorted square pyramidal geometry for them, in accord with the solid state X-ray structures determined for [VO2(aptsc)] and [VO2(apmtsc)]. In general, the vanadium compounds show comparable or larger anti-M. tuberculosis activities than the free thiosemicarbazone ligands, with MIC values within 62.5–1.56 (μg/mL).  相似文献   

5.
Wu Y  Jiang Z  Hu B 《Talanta》2005,67(4):854-861
A simple and selective method of flow injection (FI) using a micro-column packed with quinine modified resin as solid phase extractant has been developed for preconcentration and separation of trace amount of vanadium(V) and vanadium(IV) in water samples, followed by determination with fluorination assisted electrothermal vaporization (FETV)-inductively coupled plasma optical emission spectrometry (ICP-OES). At pH 3 ∼ 3.8, the modified resin is selective towards V(V) and almost not towards V(IV), while, V(IV) could be quantitatively adsorbed by the modified resin at pH 5 ∼ 7. The two vanadium species adsorbed by modified resin could be readily desorbed quantitatively with 0.3 ml of 0.5 mol l−1 HCl. Both vanadium species in elution were then determined by ETV-ICP-OES with the use of polytetrafluoroethylene (PTFE) as chemical modifier. Effects of acidity, sample flow rate, concentration of elution solution and interfering ions on the recovery of the analytes have been systematically investigated. Under the optimal conditions, the adsorption capacities of the quinine modified resin for V(V) and V(IV) are 7.6 and 8.0 mg g−1, respectively. The detection limit (3σ) of V is 0.072 ng ml−1 for FETV-ICP-OES and 0.56 pg ml−1 for FETV-ICP-MS with enrichment factor of 62.5, and the relative standard deviation (R.S.D.) is 4.9% (n = 9, C = 0.2 μg ml−1) and 3.8% (n = 9, C = 1.0 ng ml−1), respectively. The proposed method has been applied to the determination of trace V(V) and V(IV) in different water samples, and the recoveries of V(V) and V(IV) are 100 ± 10%. In order to further verify the accuracy of the developed method, FETV-ICP-MS was employed to analyze the vanadium species in water samples after separation/preconcentration, and analytical results are in good agreement with that obtained by the proposed method. The developed method was also applied to the analysis of the total V in GBW07401 soil certified reference material and in GBW07605 tea leaves certified reference material, and the determined values coincided with the certified values very well.  相似文献   

6.
Two series of complexes of the types trans-[CoIII(Mebpb)(amine)2]ClO4 {Mebpb2− = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[CoIII(cbpb)(amine)2]X {cbpb2− = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF6 (1b), piperidine (pprdn), X = PF6 (2b), morpholine (mrpln), X = ClO4 (3b), benzylamine (bzlan), X = PF6 (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and 1H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of CoIII, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.  相似文献   

7.
A novel dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) for separation/preconcentration of ultra trace amount of vanadium and its determination with the electrothermal atomic absorption spectrometry (ETAAS) was developed. The DLLME-SFO behavior of vanadium (V) using N-benzoyl-N-phenylhydroxylamine (BPHA) as complexing agent was systematically investigated. The factors influencing the complex formation and extraction by DLLME-SFO method were optimized. Under the optimized conditions: 100 μL, 200 μL and 25 mL of extraction solvent (1-undecanol), disperser solvent (acetone) and sample volume, respectively, an enrichment factor of 184, a detection limit (based on 3Sb/m) of 7 ng L−1 and a relative standard deviation of 4.6% (at 500 ng L−1) were obtained. The calibration graph using the preconcentration system for vanadium was linear from 20 to 1000 ng L−1 with a correlation coefficient of 0.9996. The method was successfully applied for the determination of vanadium in water and parsley.  相似文献   

8.
The reaction of M(η6-1,3,5-Me3C6H3)2, M = Cr, Mo, with the tetrahalides of Groups 4 and 5 elements proceeds with the monoelectronic oxidation of the metal bis-arene to the [M(η6-Me3C6H3)2]+ cation. In the case of MX4, M = Ti, X = Cl, Br, M = V, X = Cl, and of Nb2Cl10 the reduction products are the titanium(III), vanadium(III) halides and the niobium(IV) chloride, isolated as the solvate anions [MCl4(THF)2] and [NbCl4(CH3CN)]. The reaction of the tetrachloro complexes MCl4(THF)2, M = Zr, Hf, with Cr(η6-1,3,5-Me3C6H3)2 in THF produces the ionic [Cr(η6-1,3,5-Me3C6H3)2][MCl5(THF)], which has been characterized by single-crystal X-ray diffraction in the case of hafnium.  相似文献   

9.
A variety of fluorinated surfactants soluble in organic solvent were prepared, including C8F17SO2NHCnH2n+1 (n = 2, 4, 6, 8, 10), C8F17SO2NHR (R = C6H11, C6H5), C8F17SO2N(CnH2n+1)2 (n = 1, 2, 3, 4) and C8F17SO2NH(CH2)nNHO2SC8F17 (n = 6, 10). Their surface activities in various organic solvents were determined by surface tension measurement. The results showed that these fluorinated surfactants can reduce the surface tension of both polar and non-polar organic solvents. In general, organic solvents with strong polarity or long alkyl chain are beneficial to increase the surface activity of these polar fluorinated surfactants. By comparing fluorinated surfactants with the same fluorocarbon segment and connecting group, C8F17SO2N(CnH2n+1)2 (n = 1, 2, 3, 4) showed lower surface activity in organic solvents than C8F17SO2NHCnH2n+1 (n = 2, 4, 6, 8) with an equal carbon number of the solvophilic group. Through surface tension vs. concentration curves given for N-octyl perfluorooctanesulfonamide in various organic solvents, a break point like the critical micelle concentration of ordinary surfactants in aqueous solutions was observed, and the effect of the different types of organic solvents on adsorption and aggregation behavior was also studied.  相似文献   

10.
The new ramsdellite series LiTi2−yVyO4 (0≤y≤1) has been prepared by conventional solid state chemistry techniques and was characterized by X-ray powder diffraction and electron diffraction. To our knowledge, this is the first report on ramsdellites containing vanadium. The magnetic behaviour of these ramsdellites is strongly influenced by its vanadium content. In this sense, LiTi2O4 (y=0) exhibits metallic-like temperature independent paramagnetism, but d electrons tend to localize with increasing V content. LiTiVO4, though also paramagnetic, follows then the Curie-Weiss law. The crossover from delocalized to localized electrons is observed between compositions y=0.6 and 0.8. For y≥0.8 the magnetic results evidence an isovalent substitution mechanism of trivalent Ti by V. The electrochemical lithium intercalation and deintercalation chemistry of LiTi2−yVyO4 is grouped into two different operating voltage regions. Reversible lithium deintercalation of vanadium-substituted ramsdellite titanates LiTi2−yVyO4 in the high voltage range 2-3 V vs. Li occurs in two main steps, one at about 2 V and the other at about 3 V. The 3 V process capacity increases with the vanadium content, while the 2 V capacity decreases at the same time. The vanadium to titanium substitution rate in LiTi2O4 was found to be beneficial to the specific energy in as much as a 50% increase (1 V) of the working voltage is observed. On the other hand, reversible lithium intercalation in vanadium-substituted ramsdellite titanates LiTi2−yVyO4 in the low voltage range 1-2 V vs. Li occurs in one main single step, in which the capacity is not affected by the vanadium content, although vanadium-doping produces an improved capacity retention with an excellent cycling behaviour observed for y≤0.6.  相似文献   

11.
The reactivity of M(η6-arene)2 derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC6H5; M = V, Nb, arene = 1,3,5-Me3C6H3) has been investigated and the syntheses of new and known compounds are described. The derivatives M(CH3COO)3, M = Ti, V, Nb, Cr; M(CF3COO)3, M = Ti, Nb, Cr; M(acac)3, M = Ti, V, Mo, acac = acetylacetonato, and M(F6acac)3, F6acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives with the appropriate Lewis acid. The crystal and molecular structure of V(F6acac)3 has been determined. Hydrogen halides or halogens react with M(η6-arene)2 with formation of metal halides, a highly reactive form of VCl3 being obtained from V(η6-1,3,5-Me3C6H3)2 and hydrogen chloride in heptane. TiCl4 oxidizes Ti(η6-arene)2 with complete loss of the arene ligands. An electron transfer process affording ionic derivatives of formula [M(η6-MeC6H5)2][TiCl4(THF)2], M = Cr (structurally characterized), Mo, has been observed between the THF-adduct of TiCl4 and the appropriate metal-arene derivative of Group 6.  相似文献   

12.
A flow injection analysis (FIA) method for the determination of peroxide value (PV) in edible oils is described. Oil sample (undiluted) and KI reagent were aspirated into a homemade reaction chamber where the redox reaction between iodide in the aqueous phase and hydroperoxides in the oil was effected by applying a short (typically 30 s) vortex action. After allowing for the emulsified oil phase to be separated from the aqueous phase (bottom layer), an aliquot of the aqueous phase containing triiodide was next aspirated to the surface of a triiodide-selective membrane for detection. The optimized FIA procedure is linear over 0.35-28.0 PV (mequiv. O2/kg) with a detection limit of 0.32 PV. Exhibiting good reproducibility (R.S.D. of 2.7% (n = 8) for the determination of 1.1 PV) and sampling rate of 80 samples h−1, the proposed method, unlike previous FIA procedures, completely eliminated the use of organic solvents (except the use of 2-propanol for cleaning of reaction chamber). Excellent correlation (R2 = 0.9949) between the proposed method and the manual official AOCS method was found when applied to the determination of PV in diverse type of edible oils (n = 20).  相似文献   

13.
In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min−1, sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L−1 in HCl 0.5 mol L−1 (elution volume = 1 mL, elution flow rate = 0.5 mL min−1). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 μg L−1, linear range: 2-100 μg L−1 (both analytes), sensitivity: 0.015 and 0.013 μg−1 L and sample throughput: 6 h−1 (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water.  相似文献   

14.
Reaction of the dimeric rhodium complex [{(η5-C5Me5)Rh(μ-Cl)Cl}2] with an excess of 1-(4-cyanophenyl)-imidazole in dichloromethane afforded neutral mononuclear complex [(η5-C5Me5)RhCl2(CPI)] (CPI = 1-(4-cyanophenyl)-imidazole) 1. The complex 1 reacted with EPh3 (E = P, As, Sb) and N-N donor bases 2,2′-bipyridine and 1,10-phenanthroline in different solvents to give substitution products wherein, nature of the product was governed by polarity of the solvents employed in the reaction. Resulting complexes have been characterized by elemental analyses, spectral (FAB-MS, IR, 1H,13C, 31P NMR, UV-Vis, Emission) and electrochemical studies. Coordination of CPI through imidazole nitrogen and the presence of pendant nitrile group have been supported by spectral studies.  相似文献   

15.
The rate-surfactant concentration profiles for the reaction of the insecticide paraoxon with hydroxamate ions (R(CO)·NHO, R = CH3, R = C6H5, R = 2-HOC6H4) in aqueous solutions of cetyltrimethylammonium salts, CTAX (X = Br, Cl, SO3H) have been measured at pH 11.0 at 30 °C. All these profiles are typical of micelle-assisted bimolecular reactions involving interfacial ion exchanges. The salicylhydroxymic acid-CTACl combination is most reactive.  相似文献   

16.
Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH2+ group in the protonated form of H2SeO4 by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k1[H+][Br]1.15[Se(IV)] the rate constant 1 × 10−3 L2 mol−2 s−1 was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.  相似文献   

17.
The synthesis and hyperpolarizabilities of a series of push-pull chromophores containing bis-(4-methoxyphenyl)-amine donor and efficient acceptors bridged with ring locked polyene are presented. The chromophores are readily soluble in common organic solvents and exhibit high thermal decomposition temperatures (highest Td = 330 °C). Molecular hyperpolarizabilities (β) of the chromophores were measured by Hyper Rayleigh Scattering (HRS) at 1604 nm (highest β = 20,000 × 10−30 esu). These chromophores can be used to develop electro-optic (EO) materials due to their large optical nonlinearities, good absorption characteristics, high thermal decomposition temperatures, and excellent solubility with organic solvents and polymeric materials.  相似文献   

18.
Capillary zone electrophoresis (CZE) with UV detection was used to determine vanadium species. Nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) and 2,6-pyridinedicarboxylic acid (PDCA) were investigated to determine whether these ligands formed stable anionic complexes with vanadium. Of all the ligands studied HEDTA was the most suitable ligand because it gave the largest UV response with reasonable migration time. Electrospray mass spectrometry (ES-MS) was used to confirm the formation of [VO2(HEDTA)]2− and [VO(HEDTA)]1− in solution. An electrolyte containing 25 mM phosphate, 0.25 mM tetradecyltrimethylammonium bromide (TTAB) at pH 5.5 was optimum for the separation of these anionic vanadium complexes. Sample stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were tested to improve the sensitivity. Best sensitivity was obtained using FASI, with detection limits of 0.001 μM, equivalent to 0.4 μg L−1, for [VO2(HEDTA)]2− and 0.01 μM, equivalent to 3.4 μg L−1 for [VO(HEDTA)]1−. The utility of the method for the speciation of V(IV) and V(V) was demonstrated using ground water samples.  相似文献   

19.
The tetradendate macrocyclic ligands, [H2L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H2L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R2Sn(L-1)/R2Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R2SnCl2 (R = Me or Ph) or n-Bu2SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state 13C NMR, 119mSn Mössbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO2 confirmed by XRD analysis.  相似文献   

20.
A simple and robust on-line sequential insertion system coupled with hydride generation atomic absorption spectrometry (HG-AAS) was developed, for selective As(III) and total inorganic arsenic determination without pre-reduction step. The proposed manifold, which is employing an integrated reaction chamber/gas-liquid separator (RC-GLS), is characterized by the ability of the successful managing of variable sample volumes (up to 25 ml), in order to achieve high sensitivity. Arsine is able to be selectively generated either from inorganic As(III) or from total arsenic, using different concentrations of HCl and NaBH4 solutions. For 8 ml sample volume consumption, the sampling frequency is 40 h−1. The detection limit is cL = 0.1 and 0.06 μg l−1 for As(III) and total arsenic, respectively. The precision (relative standard deviation) at 2.0 μg l−1 (n = 10) level is sr = 2.9 and 3.1% for As(III) and total arsenic, respectively. The performance of the proposed method was evaluated by analyzing the certified reference material NIST CRM 1643d and spiked water samples with various concentration ratios of As(III) to As(V). The method was applied for arsenic speciation in natural waters samples.  相似文献   

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