Chemical and physicochemical characteristics of humic acids extracted from compost, soil and amended soil

In order to gain understanding about how “HA-like substances” from organic amendments may change some properties in the soil solution, the knowledge of chemical and physicochemical characteristics (charge development, acid–base behavior and heterogeneity) should be known.

The aim of this research were (i) to study the elemental and functional composition, (ii) to determine charge behavior, acid–base properties (apparent dissociation constant and buffer capacity) and (iii) to evaluate heterogeneity of humic acids (HA) isolated from municipal solid waste compost (MWC) and from the corresponding MWC-amended soil, in comparison to those of the unamended soil HA using potentiometric titration and differential scanning potentiometry (DSP).

Potentiometric titration and the first derivative of −Q versus pH (negative charge development versus pH) curves could be used to determine proton-affinity distribution and the chemical heterogeneity of the HA as well as the average pK_app and buffer capacity in a wide range of pH.

Differential scanning potentiometry allows determination of the pK_app values in a narrower range of pH than potentiometric titrations and is another simple methodology to study acid–base behavior of HA.

DSP allows us to determine seven different pK_app values for HA-S and HA-E and four different pK_app for HA-C. Each one of these values corresponds to known acidic groups that can be present in the macromolecule of HA.     

Passivation of the calcite surface with phenylmalonate and benzylmalonate ions

We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations (5 x 10(-2), 5 x 10(-3), and 5 x 10(-4) M) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 A diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface.     

A colorimetric and ratiometric fluorescent chemosensor based on furan-pyrene for selective and sensitive sensing Al3+

A new pyrene derivative BF bearing a furan group was synthesized via a one-step reaction as a colorimetric and ratiometric chemosensor for Al³⁺in ethanol-H₂O (9:1,v/v,pH 7.2,HEPES buffer) solution.This chemosensor could selectively recognize Al³⁺ in the presence of other competing ions.Low limit of detection (LOD) and high association constant revealed its superior sensitivity and binding affinity toward Al³⁺.Besides,the probe BF performed perfectly in a reversibility test using EDTA.The mechanism of the interaction has been confirmed by ¹H NMR titration.Importantly,chemosensor BF has also been utilized to detect Al³⁺ on test paper strips,which showed its potential for practical applications.     

Direct ICP-MS determination of trace and ultratrace elements in geological materials after decomposition in a microwave oven. Part II. Quantitation of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl

A new method has been developed for the rapid determination of traces of Ba, Cs, Ga, Hf, In, Mo, Nb, Pb, Rb, Sn, Sr, Ta and Tl in silicate rocks and lake, stream and river sediments. The method involved dissolution of samples in a microwave oven by heating in a pressure decomposition Teflon vessel with a mixture of HF + HNO₃ + HCl + H₃BO₃ + EDTA followed by direct multielement determination using inductively coupled plasma-mass spectrometry (ICP/MS). The method is faster than conventional dissolution of samples by open vessel acid digestion and fusion and determination by instrumental methods. The accuracy and precision of the developed method were tested by replicate analyses of a number of international geochemical reference samples of established trace element contents. Satisfactory correlation with the “recommended” or “consensus” values was found and recoveries were in most cases 95–100%. New values for Ga, In, Nb and Tl in several international geochemical reference materials are first reported in this paper.     

Chemical conditions inside occluded regions on corroding aircraft aluminum alloys

Corrosion of aluminum alloy structures costs the US Air Force in the order of US$1×10⁹ annually. Corrosion develops in areas of overlap such as aircraft lap-splice joints and under protective organic coatings. Capillary electrophoresis (CE) has been used to determine the local chemistries at these corrosion sites of solutions that were extracted using a microsampling system. Analysis of the local solution within lap-splice joints from aircraft has been performed in two ways: rehydration of corrosion products and direct microsampling. The solutions collected were analyzed with CE to quantitatively determine the species present during corrosion. The most common ions detected were Cl⁻, NO₂⁻, NO₃⁻, HCO₃⁻, K⁺, Al³⁺, Ca²⁺, Na⁺ and Mg²⁺. Studies of the solution chemistry under local coating defects are required to understand coating failure and develop more durable coatings. A microsampling system and micro pH sensor were developed to extract solution from and measure pH in defects with diameters as small as 170 μm. Actively corroding defects contained high concentrations of Cl⁻, Al³⁺, Mg²⁺, Mn²⁺ and Cu²⁺ whereas only trace levels of Mg²⁺ were found in repassivated defects. The effects of these species on initiation and propagation of corrosion are discussed.     

结冰过程对溶解性有机质典型组分还原Cr(Ⅵ)的影响

研究了结冰过程对溶解性有机质(DOM)的4种典型组分草酸、 酒石酸、 苹果酸和柠檬酸还原Cr(Ⅵ)的影响. 结果表明, 在低浓度下Cr(Ⅵ)在水溶液中不能被4种有机酸所还原; 而在冰中, 不同的有机酸对Cr(Ⅵ)的去除均有促进作用, 且去除效果随着有机酸浓度的增大逐渐增强. 4种有机酸的作用效果强弱顺序为草酸>酒石酸>苹果酸>柠檬酸. 通过使用不同浓度的无机盐和无机酸可以改变冰表面上类似液体层的厚度来抑制Cr(Ⅵ)的还原, 作用效果与无机盐种类无关. 溶液的初始pH值和有机酸结构是影响Cr(Ⅵ)还原的重要因素. 实验条件下冷冻浓缩效应的富集倍数至少可达10³, 对冰中草酸去除Cr(Ⅵ)有明显的促进作用.     

Anion-exchange separation and determination of bisphosphonates and related analytes by post-column indirect fluorescence detection

Bisphosphonic acids and their salts can be detected after their liquid chromatographic separation by post-column indirect fluorescence detection (IFD). After separation the analyte is combined with the highly fluorescent Al³⁺–morin (2′,3,4′,5,7-pentahydroxyflavone) solution and fluorescence decreases because of the formation of the nonfluorescent Al³⁺–bisphosphonate complex. The decrease in fluorescence is proportional to the amount of bisphosphonate present. Separation of the multivalent anionic bisphosphonate analytes from other anions and sample matrix is achieved on a strong base anion-exchange column with a strong, basic eluent. The post-column reaction variables, which influence IFD, are identified and optimized for the detection of the bisphosphonates after separation on the anion exchanger. The method is selective, since only a few anions will undergo a reaction with the Al³⁺–morin solution, and sensitive, detection limit for difluoromethylene bisphosphonate, F₂MDP, is 4 ng for S/N=3. The separation–IFD method can be applied to the determination of bisphosphonates, such as F₂MDP, ethane-1-hydroxy-1,1-bisphosphonic acid, dichloromethylene bisphosphonic acid, 4-amino-1-hydroxybutane-1,1-bisphosphonic acid, in biological samples. The separation–IFD method is also applicable to the detection of inositol phosphate anions.     

Using capillary electrophoresis to study the chemical conditions within cracks in aluminum alloys

The environment-assisted cracking (EAC) susceptibility of some aluminum alloys used for airplane structural components currently limits their use in the peak strength condition. Understanding the mechanism of EAC will facilitate the development of crack-resistant alloys with optimum mechanical properties. One component towards understanding the fundamental processes responsible for EAC is a comprehensive knowledge of the chemical conditions within cracks. The present work uses capillary electrophoresis (CE) to quantify the crack chemistry in order to provide insight into the nature of the mechanism controlling cracking. The highly restricted geometry of cracks in metals means that a crack typically contains less than 10 μl of solution. The high mass sensitivity combined with the inherently robust nature of CE makes it an ideal analytical technique for this application. Complicating factors in the accurate determination of the crack environment include high levels of sodium present from the test solution. Low sample volume and analyte matrix complexity necessitated the development of specific sampling, extraction and analysis methods. Analysis of the crack solutions in EAC-susceptible material revealed high levels of Al³⁺, Mg²⁺, Zn²⁺, and Cl⁻ near the crack tip. Cations arise from the anodic dissolution of the alloy, whereas chloride ingress from the external environment occurs to maintain solution electroneutrality within the crack. In contrast, EAC-resistant material exhibited significantly lower concentrations of dissolution products.     

Hydrolysis and polycondensation of ethyl silicates. 2. Hydrolysis and polycondensation of ETS40 (ethyl silicate 40)

The effects of catalysts, pH and reaction conditions on the course of the hydrolysis and condensation of ETS40 (ethyl silicate 40), and on the composition of the reaction products were studied with the aid of gas and gel chromatography, potentiometry and gelation tests. Strong acids (HCl, HClO₄, HNO₃, H₂SO₄, p-toluenesulphonic acid), weak acids (Cl₃, CCOOH, ClCH₂COOH, (COOH)₂, CH₃COOH and HCOOH) and bases (LiOH, NH₄,OH) were used as catalysts.

The hydrolysis rate increased with increasing temperature, catalyst concentration, initial water concentration and initial ethyl silicate concentration, whereas it decreased with increasing number of Si atoms in the ethyl silicate molecules. At pH 0–7 the hydrolysis was acid catalysed, but at pH above 7.0 it was base catalysed. Simultaneously with the hydrolysis, condensation occurred at a rate which increased with increasing temperature, catalyst concentration, ETS40 concentration and, above all, with increasing initial water concentration. The condensation rate depended on the pH. The condensation was at its slowest for pH around 2.0. For pH below 2.0, the condensation increased with increasing hydrogen ion concentration; for pH above 2.0 the condensation increased with decreasing hydrogen ion concentration. Phosphoric acid and hydrofluoric acid increased the rate of condensation considerably. The reaction of ETS40 with water at pH around 2.0 gave rise during the hydrolysis to solutions of ethoxyhydroxysiloxanes with an average of 14–20 Si atoms in a molecule, which displayed long-term stability.     

2-羟基萘甲醛苯甲酰腙衍生物对Al~(3+)的裸眼识别和荧光传感

设计合成了化合物4-羟基苯甲酰-(2-羟基萘甲醛)腙(L)探针,经金属离子识别研究发现探针L对Al~(3+)具有良好的荧光增强识别效果且不受其它金属离子的干扰,且识别过程中溶液的颜色发生了明显变化,可以实现Al~(3+)的可视法检测,核磁滴定、job-plot、基质辅助激光解吸电离飞行时间质谱(MALDI-TOF)等实验结果显示,探针L与Al~(3+)以摩尔比2∶1的方式进行配位。通过对紫外滴定数据的非线性拟合分析,探针L与Al~(3+)的结合常数为1.3×10~4L/mol,最低检测限为3.71×10~(-6)L/mol。因此,该腙类衍生物作为Al~(3+)的荧光及比色探针,识别体系线性范围较宽,检测限低,在痕量Al~(3+)的检测方面具有潜在的应用价值。     

Ion-interaction chromatographic studies on metal ions completed with Plasmocorinth B dye

The ion-interaction chromatographic behaviour of Plasmocorinth B (a disulphonated azo dye) and of its complexes formed with metal ions in oxidation states + 2 and + 3 (Cu²⁺ Ni²⁺, Al³⁺, CO³⁺, Fe³⁺, Ga³⁺) was investigated. The effect of cationic ion-pairing agents (tetramethyl-, benzyltrimethyl- and tetrabutylammonium) was also evaluated in the presence of alkali metal ions competitors (Li⁺ and Na⁺). The effects of organic modifier and of pH were also considered. The remarkably different behaviour of the ligand and the complexes suggests the formation of M(II)L⁻ and M(III)L₂²⁻. The stoichiometry of complexes was confirmed by applying the electrostatic theory derived from Gouy-Chapman and a modified Langmuir adsorption isotherm to the experimental data.     

Preparation, Characterization, and Catalytical Application of MgCoAl-Hydrotalcite-Like Compounds

MgCoAl-hydrotalcite-like compounds(MgCoAl-HTLcs)were synthesized using the copre- cipitation method of variable pH values.The effect of each factor on the preparation of HTLcs was discussed systematically,which included pH values,mole ratios of Mg~(2 )to Co~(2 ),the concentrations of the solution,and the temperature and time of the hydrothermal treatment.Besides.the thermal de- composition of MgCoAl-HTLcs was discussed.X-ray diffraction,thermogravimetric analysis,and FT-IR spectroscopy were performed to characterize the MgCoAl-HTLcs samples.The results showed that when the pH=7.6-8.5 or 5.5-6.2,atomic ratios of(Mg~(2 ) Co~(2 ))/Al~(3 )=2 and Mg~(2 )/Co~(2 )ranging from 1.00 to 2.00,temperature and time of hydrothermal treatment being 110℃and 6 h,unique MgCoAl-HTLcs with high crystallinity could be obtained.When the calcination temperature was up to 250℃,the MgO phase was detected coexisting with Al_2O_3 and MgAl_2O_4 was highly spreaded on the derived mixed oxides. The synthesis reaction of benzoin methyl ether with methanol and benzaldehyde was chosen to study the catalytic activity of MgCoAl-HTLcs.The catalyst showed high activity and high stability in the synthesis of benzoin methyl ether in the feasible condition.     

Biotic and abiotic experimental identification of bacterial influence on calcium isotopic signatures

In this study, we tested experimentally the influence of plant and bacterial activities on the calcium (Ca) isotope distribution between soil solutions and plant organs. Abiotic apatite weathering experiments were performed under two different pH conditions using mineral and organic acids. Biotic experiments were performed using either apatite or Ca-enriched biotite substrates in the presence of Scots pines, inoculated or not with the rhizosphere bacterial strain Bulkholderia glathei PML1(12), or the B. glathei PML1(12) alone. For each experiment, the percolate was collected every week and analyzed for Ca concentrations and Ca isotopic ratios. No Ca isotopic fractionation was observed for the different abiotic experimental settings. This indicates that no Ca isotopic fractionation occurs during apatite dissolution, whatever the nature of the acid (mineral or organic). The main result of the biotic experiments is the 0.22 ‰ (44)Ca enrichment recorded for a solution in contact with Scots pines grown on the bacteria-free apatite substrate. In contrast, the presence of bacteria did not cause Ca isotopic fractionation of the solution collected after 14 weeks of the experiments. These preliminary results suggest that bacteria influence the Ca isotopic signatures by dissolving Ca from apatite more efficiently. Therefore, Ca isotopes might be suitable for detecting bacteria-mediated processes in soils.     

The influence of interparticle surface forces on the coagulation of weakly magnetic mineral ultrafines in a magnetic field

In this paper, it is shown that the coagulation of dispersions of weakly magnetic mineral ultrafines (such as hematite and chromite) in an external magnetic field can be described theoretically by invoking interparticle forces. Essentially, coagulation occurs when the short-range London—van der Waals interactions and the long-range magnetic forces outweigh the stabilizing electric double layer repulsion. From classical colloid chemistry theory, we have calculated the various components of the potential energy for different-sized particles at a series of ionic strengths and magnetic field intensifies. Principles governing the stability of the suspensions were derived and the computations lead to the establishment of criteria which can be used to predict the stability of the suspensions of weakly magnetic oxide mineral ultrafines in a “wet magnetic separation process”.

Experimentally, the magnetic-field induced coagulation of ultrafines of natural hematite and chromite in aqueous suspensions at moderate ionic strength was investigated using a laboratory-scale electromagnetic solenoid. The experimental results relate the coagulation process (as determined by magnetosedimentation analysis) to particle size, slurry pH and the external magnetic field. In the magnetic fields, maximum coagulation occurred near the pH of the point of zero charge (pH_PZC) of the minerals (where the electrostatic double layer repulsion was reduced to a minimum) enabling the particles to enter the “primary minimum” energy sink. In contrast, in cases where the electrostatic repulsion was not suppressed, the long-range magnetic forces enabled coagulation to occur in the “secondary minimum”. This caused the formation of chains which appeared to be relatively stable at enhanced rates of settling. The experimental results could be interpreted from a theoretical analysis of the interparticle forces controlling the process.     

Proton transfer reaction studies of multiply charged proteins in a high mass-to-charge ratio quadrupole mass spectrometer

Proton transfer reaction of multiply charged ions at high mass-to-charge ratios were explored with a low frequency quadrupole mass spectrometer. This instrument enabled a qualitative comparison of proton transfer reaction rates at low charge states for ions generated by electrospray ionization (ESI) from different solution conformations and for disulfide-linked versus disulfide-reduced protein ions. Proton transfer reactions that efficiently reduced the number of charges for ESI-generated ions to approximately the number of arginines in the polypeptide sequence were observed. No significant differences in gas-phase reaction rates were noted between different solution conformers. Differences in reaction rates between “native” and disulfide-reduced proteins were much smaller than those observed below m/z 2000 with lower proton affinity reagents or by using lower reagent concentrations. These smaller differences in reaction rates are thought to reflect the reduced electrostatic contributions from widely spaced charge sites and thus, the reduced sensitivity to an ion's three-dimensional structure or “compactness.”     

Dissolution of resistate minerals containing uranium and thorium: Environmental implications

Summary Minerals in the soil range from those that easily weather to those that are very resistant to the weathering processes. The minerals used in this study are referred to as “resistates” because of their resistance to natural weathering processes.¹ It is also known that there are some resistate minerals that have a tendency to contain uranium and thorium within their crystal structure. These resistates can contain as much as 15-20% of the total uranium and thorium present in the soil.⁹ Do resistates dissolve in acids, particularly in the HF/HNO₃ procedures, if not what can be done to the HF/HNO₃ process to dissolve more of the resistate minerals? How would these acid techniques compare to the fusion method used for mineral dissolution? Could the resistate minerals contain considerable amount of uranium and thorium? These were the questions addressed in this research. The comparative data indicate that the use of H₂SO₄ in the dissolution process resulted in ~25% overall increase in the minerals dissolving therefore resulting in a higher yield of extracted uranium and thorium.     

The behaviour of some selenoglycollic acid derivatives in aqueous solutions and spectrophotometric determination of constants of the system Pd(II)/ethylene-bis- selenoglycollic acid

Interactions between ethylselenoglycollic, selenoglycollic and ethylene-bis- selenoglycollic acids and some “soft”, “borderline” and “hard” metallic ions have been studied. The interactions of [PdCl₄]_aq²⁻ with the three ligands were verified conductometrically and spectrophotometrically. The stability constants β₁ and β₂ for the system [PdCl₄]^2-- ethylene-bis-selenoglycollic acid have been determined at 25°C at ionic strength 3.0 M (NaCl). The stoichiometric ionization constant of the mentioned acid was also studied.