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1.
Samples of fulvic acids obtained from cultivated calcareous soils are analyzed using acid-base titrations with spectrofluorimetric detection. Observed changes in both synchronous and emission spectra of fulvic acids when pH is changed are explained in terms of a limited number of fluorescent contributions each defined by its specific fluorescent spectrum and a concentration profile (species distribution) recovered from the multivariate curve resolution analysis of experimental data. Information on equilibrium is estimated from concentrations of the acid-base species. 相似文献
2.
Atomic force microscopy of soil and stream fulvic acids 总被引:4,自引:0,他引:4
Ksenija Namjesnik-Dejanovic Patricia A. Maurice 《Colloids and surfaces. A, Physicochemical and engineering aspects》1997,120(1-3):77-86
Atomic force microscopy (AFM) was used to image fulvic acid (FA) deposited from aqueous solution on to the basal-plane surfaces of freshly cleaved muscovite, and allowed to air dry. Two fulvic acid samples were used: a soil fulvic acid (SFA) prepared by NaOH extraction from a muck soil underlying a freshwater fen in the New Jersey Pinelands and the IHSS standard Suwannee River fulvic acid (SRFA). The use of tapping-mode AFM (TMAFM), a relatively new technique which reduces the lateral frictional forces generally associated with contact-mode AFM, allowed excellent images of delicate FA structures to be obtained with minimal sample disturbance. Four main structures were observed on SFA. At low concentrations, sponge-like structures consisting of rings ( 15 nm in diameter) appeared, along with small spheres (10–50 nm). At higher concentrations, aggregates of spheres formed branches and chain-like assemblies. At very high surface coverage, perforated sheets were observed. On some samples, all of these structures were apparent, perhaps owing to concentration gradients on drying. SRFA samples were only imagined at higher concentrations. Spheres, aggregated branches, and perforated sheets were apparent. The results agree with previous work by Stevenson and Schnitzer [Soil Sci., 133(1992) 179], who applied TEM to soil FAs freeze-dried on muscovite. However, the TEM images did not detect the smaller spheres and sponge-like structures observed by AFM at low concentrations. The relevance of imaging dried samples remains questionable; hence, it is hoped in the future to use new in situ TMAFM to image FAs sorbed to surfaces in solution. Although TMAFM provided excellent images, a variety of artifacts and potential problems were encountered, as discussed. 相似文献
3.
The interaction of fulvic acids with Cd(II) ions has been studied by differential pulse anodic stripping voltammetry (ASV), at pH 7.0 and 0.1 M KNO3. Voltammetric data obtained during the titration of mixtures of Cd(II) and fulvic acids at different concentrations have been analyzed using multivariate curve resolution (MCR). The application of this method allowed the resolution of the major contributions involved in the titration experiments. Apart from free Cd(II), two more contributions related with the complexation process were detected and resolved, and their corresponding pure voltammograms and concentration profiles were estimated. Simultaneous analysis of independent voltammetric titrations using the proposed MCR methods is shown extremely recommended because it overcame some of the limitations observed in the analysis of individual titrations. 相似文献
4.
Fulvic acids (FAs) were extracted by alkali extraction from different soil samples in China, then purified using resins and characterized by Fourier transform infrared spectroscopy. The complexing ability of FAs was investigated by measuring the stability constants of rare earth elements (REEs) (La3+, Ce3+, Sm3+, Gd3+, Y3+) with FAs by the ion exchange technique. The results indicated that maximum binding ability forY3+ (4.414.44) was higher than other REEs (La3+, Ce3+, Sm3+, Gd3+) (0.721.03). There were two types of binding sites in the functional groups of fulvic acids. The complexing reaction followed two steps. The stability constants (K1 and K2) of REEs with FAs were calculated from experimental data by division of Scatchard plots into two straight-line segments. Y3+ (log K1=5.72±0.05, log K2=4.83±0.01) also has higher stability constants than the other four REEs (log K1=4.37±0.16, log K2=3.62±0.28). 相似文献
5.
The aim of this work was to characterize the fulvic acids (FA) extracted from peat by use of capillary electrophoresis (CE). Two FA extracts have been obtained using two different extractants (0.1 M NaOH and 0.1 M NaOH plus 0.1 M Na4P2O7, Na+PP). The CE runs wre performed using a coated silica capillary, and several buffer solutions at different PH values. The results obtained show that the Fa extracts may be well characterized by CE even if the isolelectric point of the fulvic compounds is very low. The best fractionation has been obtained using a buffer borate at PH 8.9 as funning buffer. The charcterization of the two extracts also showed some important differences between the NaOH extract and the Na+PP extract. 相似文献
6.
A selective procedure for the determination of Al3+ in drinking and natural waters is proposed. The analytical procedure is based both on the complex formation between Al3+ and 8-hydroxyquinoline-5-sulfonic acid (HQS) and on a fluorimetric detection of the complex. The reaction was carried out in presence of thioglycolic acid as a masking agent. This procedure has been adapted to a sequential injection analysis (SIA) system. Operative conditions both for batch and SIA procedures were investigated including reagent concentration, volumes, pH and wavelengths used for the fluorimetric detection. Batch procedure allows determination of Al3+ at ppb level (LOQ: 2.8 μg l−1) within a working range of 2.2-300 μg l−1. The SIA procedure was successfully employed for the determination of Al3+ in several commercial drinking and tap waters. 相似文献
7.
Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment 总被引:2,自引:0,他引:2
Bertoncini EI D'Orazio V Senesi N Mattiazzo ME 《Analytical and bioanalytical chemistry》2005,381(6):1281-1288
Conventional monodimensional fluorescence spectroscopy in the emission, excitation, and synchronous-scan modes and total luminescence spectroscopy have proven to be sensitive techniques for characterization and differentiation of humic acid (HA) and fulvic acid (FA) fractions isolated from an aerobically and anaerobically digested and limed biosolid, two layers of a sandy and a clayey Brazilian oxisol, and the corresponding biosolid-amended soils. The spectral patterns and the relative fluorescence intensities suggest greater molecular heterogeneity, less aromatic polycondensation, and less humification of biosolid HA and FA compared with soil HA and FA. However, the differences are smaller for the FA fractions than for the HA fractions. Fluorescence properties of soil HA and FA differ slightly as a function of soil type and soil layer. Biosolid application causes a shift to shorter wavelengths of the main fluorescence peaks and marked variation of the relative fluorescence intensities of HA and FA isolated from amended soils. These results suggest that molecular components of relatively small molecular size, with a low level of aromatic polycondensation, and low degree of humification present in biosolid HA and FA are partially and variously incorporated into amended soil HA and FA. In general, these modifications seem to be smaller in HA and FA from the clayey soil layers than in those from the sandy soil layers, possibly because of protective effects exerted by clay minerals of native soil HA and FA against disturbances caused by biosolid application. 相似文献
8.
Spatial structures of complexes [DyAc]2+, [DyBz]2+, [DyAc2]+ and [DyBz2]+ in aqueous solutions (Ac– and Bz–, acetate and benzoate anions, respectively) are studied using the paramagnetic double refraction method. The polyhedra of [DyAc(H2O)6]2+ and [DyBz(H2O)6]2+ are dodecahedra with ligands coordinated at one of the edges. In the complexes [DyAc2(H2O)4]+ and [DyBz2(H2O)4]+ the ligands are coordinated at the edges of a square antiprism at an angle of 50 (55)° to the local symmetry axis of higher symmetry.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1038–1040, June, 1993. 相似文献
9.
John P. Sanders Patrick K. Gallagher 《Journal of Thermal Analysis and Calorimetry》2009,96(3):805-811
For complex decomposition reactions, traditional methods, such as TG and DSC cannot fully resolve all of the steps in the
reaction. Evolved gas analysis (EGA) offers another tool to provide more information about the decomposition mechanism. The
decomposition of sodium bicarbonate was studied by TG, DSC and EGA using a simultaneous thermal analysis unit coupled to a
FTIR. The decomposition of sodium bicarbonate involves two reaction products H2O and CO2, which are not evident from either TG or DSC measurements alone. A comparison of the reaction kinetics from TG, DTG and EGA
data were compared. 相似文献
10.
The kinetic method has been extended to enantiomeric excess (ee) determinations on amino acids present in mixtures. Singly charged trimeric clusters [Cu(II)(ref*)(2)(A(m)) - H](+) are readily generated by electrospraying solutions containing Cu(II), a chiral reference ligand (ref*), and the amino acids (analytes A(m), m = 1-3). A trimeric cluster ion for each amino acid is individually mass-selected and then collisionally activated to cause dissociation by competitive loss of either the reference ligand or the analyte. For each analyte in the mixture, as shown from separate experiments, the logarithm of the ratio of the fragment abundances for the complex containing one enantiomer of this analyte expressed relative to that for the fragments of the corresponding complex containing the other enantiomer is linearly related to the enantiomeric composition of the amino acid. Formation and dissociation of each trimeric complex ion are shown to occur independently of the presence of other analytes. Chiral selectivity appears to be an intrinsic property and the chiral selectivity R(chiral(m)) measured from the mixture of analytes is equal to R(chiral) measured for the pure analyte. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, characteristic of the kinetic method, allow the determination of chiral impurities of less than 2% ee in individual compounds present in mixtures by simply recording the ratios of fragment ion abundances in a tandem mass spectrum. 相似文献
11.
Kelly M ElkinsDonald J Nelson 《Coordination chemistry reviews》2002,228(2):205-225
Aluminum ion (Al3+) in the ‘free’ (aquo) state is becoming increasingly prevalent in environmental waters, especially fresh waters, as a consequence of acid rain and other environmental processes. As Al3+ ion is known to affect markedly a wide range of biological systems, and since the presence of Al3+ in humans has been linked to a number of human diseases, it is important to understand the speciation of Al3+ ion in natural waters. Since some of the most important complexation agents for Al3+ in both fresh and sea waters are members of the complex humic substances group, it is important to understand the manner in which Al3+ interacts with this class of molecules, especially since binding of Al3+ to these molecules can effectively increase the bioavailability of this toxic metal ion to biological systems. The objective of this review is to present the current state of our understanding of aqueous aluminum complexation with the most acidic members (and therefore the most likely candidates for serving as Al3+ complexing agents) of the humic substances group, the fulvic acids. Much of the current knowledge has been revealed by comprehensive fluorescence titration analyses. Some additional information has come from other experimental approaches, including infrared spectroscopy, nuclear magnetic resonance spectroscopy, and a variety of electrochemical approaches. In this review, we also report on the results of our recent fluorescence and IR spectroscopy survey of the interaction of metals from of all three Nieboer and Richardson categories of environmental metals (Class A, Class B and Intermediate Class) with the fulvic acid sub-group of the humic substances. This has proven helpful in understanding some of the unique spectral behaviors of the Al3+-fulvic acid complex vis-a-vis fulvic acid complexes with many other metal ions. The results of our fluorescence and IR experiments with the model compounds, such as salicylic and phthalic acids, have allowed confirmation of the important roles played by both salicylic acid-like sites and phthalic acid-like sites in the unique complexation of Al3+ to humic substances, and help to explain some of the observed spectroscopic changes associated with Al3+ ion complexation to humic material. From the current work, it seems clear that major sources of the deviation in spectral properties between Al3+ and many other metal ions (across all three Nieboer and Richardson categories) are the unusually high value of its charge density and relatively low propensity for involvement in covalent bonding interactions (i.e. a very high ionic index combined with a relatively low covalent index in the Nieboer and Richardson classification of environmental metals), as well as affinity for certain functional groups. 相似文献
12.
Effect of fulvic acid on neodymium uptake by goethite 总被引:1,自引:0,他引:1
Christopher R. Armstrong 《Journal of colloid and interface science》2012,387(1):228-233
Experimental studies of the interaction of aqueous neodymium (Nd), Suwannee River fulvic acid (FA), and solid phase goethite were conducted. Results from blank systems (individual Nd and FA), binary systems (Nd-goethite, FA-goethite, and Nd-FA), and ternary systems (Nd-FA-goethite) at 0.1 mol/kg and 25 °C are reported.In the binary Nd-goethite system a classic sorption edge is observed, whereby virtually all Nd is removed from solution above the goethite point of zero charge (PZC). Similarly, the binary FA-goethite system exhibits strong FA sorption; However in this system near complete removal of FA from solution is observed below the goethite PZC. In the binary Nd-FA system, both aqueous Nd and FA feature a sharp decrease in concentration at ca. pH 9.Various experiments in the ternary system were conducted. For all concentrations, FA enhanced Nd sorption below the goethite PZC, attributed to the formation of a Type B ternary surface complex (mineral-ligand-metal ion). Notably, the 100 ppm FA ternary system showed anomalously high dissolved Nd in solution above the PZC (i.e., Nd sorption suppression) and a concomitant increase in goethite dissolution (∼9 ppm total Fe3+ observed above circa pH 9.5).Our results suggest that Nd-FA complexation plays a key role in Nd uptake by goethite, and that this process is largely governed by pH: Whereas at pHs below the goethite PZC, Nd-FA complexation facilitates Nd sorption, above the PZC, and particularly at elevated FA concentrations, the formation of aqueous Nd-FA complexes suppresses Nd removal. Moreover, under these conditions, goethite dissolution may also play a role in mitigating Nd uptake by goethite. 相似文献
13.
三元配合物停流—动力学分析法测定铝的研究 总被引:8,自引:0,他引:8
利用自动化动力学分析装置研究了铝与3,5-二溴水杨基荧光酮及表面活性剂形成三元配合物的动力学性质,测定了质子、显色剂及表面活性剂的反应级数及反应活化能。提出了一种简便、快速、精密和准确的分析方法,并用于人发中痕量铝的测定。方法灵敏度较高(ε=1.11×10~5L/mol·cm),大多数元素的干扰均可用动力学方法消除,优于其它测定铝的多元配合物体系。 相似文献
14.
Edwin Palacio-Barco 《Analytica chimica acta》2010,668(1):74-9100
In this paper, an on-line spectrofluorimetric system is proposed for a simple, rapid and accurate measurement of volatile fatty acids (VFA) in anaerobic treatment processes. The determination method is based on the derivatization of VFA with N-(1-naphthyl)ethylenediamine (EDAN) followed by a spectrofluorimetric detection of the corresponding amide. The analytical procedure is automated with a flow analysis technique, coupling multisyringe (MSFIA) and multi-pumping (MPFS) methods. Operative conditions have been investigated with a special attention paid to the activation and amidation steps and to the liquid-liquid extraction of the derivatized final product. Fluorescence intensities (λem = 335 nm, λex = 395 nm) were found to be proportional to the concentration of VFA, expressed as acetic equivalent, in the range 19-1000 mg L−1, with a detection limit (3σ) of 5.1 mg L−1. Our results showed a good selectivity for VFA as compared to other organic and inorganic compounds usually found in sewage sludges. Validation of the on-line system developed has been assessed by application of the procedure to aqueous samples originating from sewage sludge treatment plants. The results were in good agreement with ion chromatography measurements. 相似文献
15.
We describe a novel solution-based method for the determination of dissolved organic matter (DOM) relying on the formation of silver nanoparticles (AgNPs) via photo-stimulated reduction of silver ions by humic and fulvic acids. The method is based on natural driven formation of nanoscale materials yielding a direct relationship between DOM concentration and AgNPs formation. The aqueous dispersion of the formed AgNPs show strong and uniform UV–Vis absorption bands between 450 and 550 nm irrespectively of DOM nature and properties (i.e. humic or fulvic acids). The ensuing chromatic shift accompanying the appearance of the new absorption bands is easily conceivable by a simple spectrophotometer and the bare eye, holding great promise for the on-site, instrumental-free screening of DOM levels. Under the optimum experimental conditions the determination of DOM was successfully demonstrated to various water samples with high sensitivity (<1.0 mg L−1), satisfactory recoveries (87.5–123.5%) and reproducibility (5.87–6.73%). 相似文献
16.
Yu. I. Tarasevich V. V. Luk’yanova G. M. Tel’biz 《Theoretical and Experimental Chemistry》2005,41(1):48-52
We chemically modified the surface of kaolinite with nanoclusters of aluminum hydroxo cations. We have determined their composition and sizes. We have used IR spectroscopy to establish the interaction between the carbonyl and -diketone groups of fulvic and humic acids with the Lewis acid sites: coordination unsaturated Al3+ cations of the Al13 nanoclusters. We have obtained spectral evidence for hydrogen bond formation between the carboxyl groups of fulvic acid and the hydroxyl groups of the aluminum hydroxo cations.__________Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 41, No. 1, pp. 45–49, January–February, 2005. 相似文献
17.
The estimation of adsorption parameters for chromatographic systems is a very important step for column characterization used in the design of continuous separation equipments. The turbulent hydrodynamics aspect of batch procedures makes the kinetic modeling an interesting tool for the process modeling used for the determination of the main parameters that will be considered in the equipment design. The implemented irreversible kinetic model, which depends on both solute and site concentrations, was found to be very effective in the experimental correlation of two different enzyme adsorption systems: adsorption of Inulinases and beta-Galactosidase using two different adsorbents, the CM-Sepharose CL-6B and Accell plus QMA, respectively. The implementation of an error analysis methodology associated with an inverse problem approach was successful in determining the kinetic parameters with high accuracy. The simulations indicated a decrease in the kinetic constants with an increase in the solute concentration, which can be related to the increase in the competition by sites of adsorption. 相似文献
18.
Raewyn M. Town 《Electroanalysis》1997,9(5):407-415
The utility of potentiometric stripping analysis (PSA) for studying the interaction of fulvic acid with CuII and PbII at pH 1.8 and 4.8 was assessed. The impact of fulvic acid on both the deposition and stripping steps was considered. In contrast to results obtained by anodic stripping voltammetry, fulvic acid influenced both these steps in PSA, and to different degrees. Surface active substances have been claimed to have self-compensatory effects in PSA; this work shows that this is not valid for heterogenous natural complexants such as fulvic acid. 相似文献
19.
Summary Although the binding of pesticides to organic carbon in soil, especially to humic acid (HA), is well recognized, the mechanisms
have not been completely explained. This publication deals with adsorption of atrazine and terbuthylazine by humic acid under
different experimental conditions, including adsorption times longer than those used hitherto. Direct HPLC analysis of HA
suspensions is assessed as an alternative to more complicated techniques for estimation of free triazines, and compared with
combined solid-phase extraction and HPLC. Experimental conditions such as time of exposure, addition of neutral salt, pH of
the suspension, and HA concentration have a significant impact on the extent of triazine adsorption. At alkaline pH, triazines
become partitioned in the HA fraction because of its hydrophobicity, whereas at acidic pH hydrogen-bonding probably occurs
between triazine molecules and humic acid polymers.
Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999 相似文献
20.