Ultrasound-assisted sequential extraction method for the evaluation of mobility of toxic elements in contaminated soils

A method for the fast sequential extraction of toxic elements in contaminated soil samples using an ultrasonic water bath, followed by determination with inductively coupled plasma optical emission spectrometry (ICP-OES), was developed and compared with other methods introduced in the literature. The five-step sequential extraction (Tessier scheme) was shortened using ultrasound-assisted sequential extraction (UASE). The optimization of the five-step sequential extraction was based on the analysis of SRM 2710 using Tessiers’s method as a reference. Several extracting solutions with different sonication times and temperatures were tested in the optimization procedure. Concentrations of arsenic, cadmium, copper, lead, and zinc were determined in SRM 2710, SRM 2711, and contaminated soil samples with high accuracy and precision. The certified acid-leachable concentrations of the SRM 2710 were obtained for all elements investigated by using an optimized UASE method. Tessiers’s method yielded total element concentrations that were too high. The determination of zinc in SRM 2711 yielded concentrations that were too low, whereas arsenic determination yielded concentrations that were too high by the UASE method and analysis by ICP-OES. The analysis of the SRMs showed that the UASE method is highly comparable with the other methods used for such purposes. The major advantages of the UASE method are the high treatment rate (40 samples simultaneously with a sonication time of 54 min) and a low sample and reagent usage.     

"Click chemistry" in zeolites: copper(I) zeolites as new heterogeneous and ligand-free catalysts for the Huisgen [3+2] cycloaddition

For the first time, copper(I)-exchanged zeolites were developed as catalysts in organic synthesis. These solid materials proved to be versatile and efficient heterogeneous, ligand-free catalytic systems for the Huisgen [3+2] cycloaddition. These cheap and easy-to-prepare catalysts exhibited a wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by filtration), and are recyclable (up to three times without loss of activity). Investigations with deuterated alkynes and deuterated zeolites proved that this Cu(I)-zeolite-catalyzed "click" reaction exhibited a mechanism different from that reported for the Meldal-Sharpless version.     

Occurrence of methylated arsenic species in parts of plants growing in polluted soils

Arsenic compounds were determined in extracts of branches, leaves and roots from plants growing in a mining contaminated area. The selected species were Dryopteris filix-max, Quercus pubescens, Dipsacus fullonum, Alnus glutinosa, Buxus sempervirens and Brachythecium cf. reflexum. Total arsenic content in the subsamples was analysed by ICPMS after acidic digestion. In general, concentrations in the plant parts followed the gradient roots?>?branches?>?leaves indicating that they are arsenic-resistant plants. Arsenic species were determined in water/methanol (9?+?1, v/v) extracts by HPLC-ICPMS. Different levels of organoarsenicals were found depending on plant part and plant species. Higher percentages of organoarsenic compounds were recorded in branches and leaves (up to 35% in the boxtree sample), than in roots (0.7–5.2% in the same plant species). The absence of organic arsenic species in the soil where the plants were collected and the low levels of organoarsenicals found in the roots, indicate that the studied plants have the ability to accumulate or synthesise organoarsenic compounds in relatively high percentages, and this information contributes to enlarge the knowledge of arsenic uptake and speciation in plants.     

Investigation of heavy-metal uptake by vegetables growing in contaminated soils using the modified BCR sequential extraction method

The heavy metal (Cu, Fe, Co, Ni, Cd, Cr, Pb, Zn, and Mn) concentrations in soils and in vegetable samples, i.e. lettuce (Lactuca sativa L.), parsley (Petroselinum crispum), dill (Anethum graveolens), and onion (Allium cepa L.), taken from three urban vegetable gardens in Kayseri, Turkey, were determined by FAAS. The modified three-step sequential extraction procedure proposed by the European Bureau of References (BCR), now the Standards, Measurements and Testing Programme, was used in order to evaluate trace elements mobility in soil samples, and heavy-metal uptake by vegetables. Three operationally defined fractions were isolated using the BCR procedure: acid extractable (i.e. bound to carbonates), reducible (bound to Fe/Mn oxides), and oxidizable (bound to organic matter and sulphides). The vegetable samples were prepared to analysis using the wet-ashing procedure. To estimate the accuracy of the method used in analysis of the vegetable samples, the standard reference material (NIST SRM 1573a, Tomato leaves) was used. The results of recovery for all the elements were relatively satisfactory (87.7–108%). For the soil samples, the recovery values were calculated by proportioning the sum of the steps of the BCR procedure to those of the pseudototal digestion (i.e. aqua regia). In soils, the mobility of heavy metals followed the order Mn>Cd>Cu>Pb>Zn>Cr>Ni>Co>Fe. The relationship between the vegetable–metal and soil–extractable metal concentrations was examined in order to evaluate the bioavailability of metals, and the positive correlation, especially for the first (i.e. water, acid-soluble and exchangeable fraction) and for the third (i.e. oxidizable fraction) extraction steps, was obtained.     

Determination of organic acids and ketones in contaminated soils

Hydrocarbons and metabolites from biodegradation in soil have been isolated and separated using Soxhlet extraction, with n-heptane and dichloromethane, combined with solid-phase extraction on silica gel and basic aluminum oxide using n-pentane, dichloromethane, methanol, and sulfuric acid – methanol as eluents. This procedure can be used for determination of metabolites both in laboratory-prepared soil samples containing mineral oils and in actual contaminated soil. After microbiological degradation, organic acids and ketones which were not original components of the diesel fuel and lubricating oil contaminating the soil samples were identified using capillary gas chromatography – mass spectrometry in batch-soil experiments. Predominantly alicyclic and branched-chain aliphatic organic acids and diacids, and aromatic ketones, were found to be formed after a few weeks degradation.     

State of alkali azides in zeolites studied by thermal analysis

Thermal behaviour of pure LiN₃, NaN₃, CsN₃ and their mixture with the respective LiY-FAU, NaY-FAU, CsY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. Thermodesorption of CO₂ was applied to compare the basicity of the alkali ionexchanged Y zeolites. Two of the investigated systems, the NaN₃/NaY-FAU and the CsN₃/CsY-FAU gave single, well defined and reproducible azide decomposition features rendering these samples to apply as catalyst precursors for preparation of zeolite with basic character.     

Theoretical study on reactions catalyzed by gallium-substituted zeolites

The dehydrogenation and cracking reactions of light alkanes in gallium-containing zeolites were studied using density functional theory. Gallium isomorphically substituted, generating Brønsted acid sites, was used in the computations. The following reactions were examined: dehydrogenation of methane, ethane, propane, isobutane and cracking of ethane, propane and isobutene, all catalyzed by the framework gallium species. The cracking reaction seems to be favored relative to the dehydrogenation when framework gallium species are used. This behavior is also observed in aluminum-containing zeolites (H-ZSM5). The geometries and energetics of the transition states found for the gallium zeolites were compared with theoretical data for the same transition states in aluminum zeolites. There seems to be no significant difference between framework gallium and framework aluminum species. Therefore the framework gallium should not be the species responsible for the catalytic enhancement observed in gallium-containing zeolites.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

The removal of heavy metal cations by natural zeolites

In this study, the adsorption behavior of natural (clinoptilolite) zeolites with respect to Co²⁺, Cu²⁺, Zn²⁺, and Mn²⁺ has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using metal concentrations in solution ranging from 100 to 400 mg/l. The percentage adsorption and distribution coefficients (K_d) were determined for the adsorption system as a function of sorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of clinoptilolite metal cations match to Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity metals has been calculated. It was found that the adsorption phenomena depend on charge density and hydrated ion diameter. According to the equilibrium studies, the selectivity sequence can be given as Co²⁺ > Cu²⁺ > Zn²⁺ > Mn²⁺. These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.     

Alkylation of dichlorobenzene isomers by olefins on zeolites Y and pentasil

Catalytic alkylation of dichlorobenzene isomers by ethylene and propylene on zeolite catalysts has been studied. It has been determined that using catalysts based on zeolite Y makes it possible to change the ratio of 1-alkyldichlorobenzenes formed within a wide range by varying the acidic properties of the catalysts.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1486–1488, August, 1995.     

Cooling/heating-assisted headspace solid-phase microextraction of polycyclic aromatic hydrocarbons from contaminated soils

A simple, low-cost, and effective cooling/heating-assisted headspace solid-phase microextraction (CHA–HS–SPME) device, capable of direct cooling the fiber to low temperatures and simultaneous heating the sample matrix to high temperatures, was fabricated and evaluated. It was able to cool down the commercial and handmade fibers for the effective tapping of volatile and semi-volatile species in the headspace of complex solid matrices, with minimal manipulation compared with conventional SPME. The CHA–HS–SPME system can create large temperature gaps (up to 200 °C) between the fiber and the sample matrix, because the cooling process is directly applied onto the fiber.     

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1 M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1 M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.     

The polarographic determination of copper and zinc in plants and soils

A method is described whereby the extraction and polarisation of copper and zinc with maximum, sensitivity is possible. Interference from cobalt is prevented by extracting with dithizonc in the presence of dimethylglyoxime.The supporting electrolyte used is dccimolar potassium hydrogen phthalate which permits satisfactory waves for both copper and zinc (with greater sensitivity for copper, than is the case with the ammonia-ammonium chloride electrolyte).     

碘量法测定废杂铜屑中的铜含量

采用硝酸-盐酸溶解样品,在硫酸体系下加入氢溴酸,使得氢溴酸与试样中的砷、锑、锡等元素反应生成易挥发的溴化物,从而消除其干扰,滴定前用氟化氢氨掩蔽铁,在pH=3.0～4.0的范围采用碘量法测定废杂铜屑中的铜含量。用于测定金属样废杂铜屑中铜的含量,测定结果的相对标准偏差(RSD,n=7)为0.20%～0.25%,加标回收率在98.8%～101%,方法简单准确,能够满足日常检测需求。     

Thermal stability of products prepared by the combination of cyclodextrins and zeolites

Derivatographic and calorimetric measurements were used to study the thermal properties of combined inclusion compounds of zeolite-cyclodextrin type and of zeolite-cyclodextrin-pharmaceutical type. There were differences in the characteristic decomposition temperature intervals and in the modes of cyclodextrin and pharmaceutical liberation from the products. Calorimetric measurements revealed that the process in the newly-formed complex host is connected with a glass transition. The products are intended for use in veterinary medicine.     

Determination of total As in onion plants growing in contaminated substrates by total reflection X-ray fluorescence

The onion (Allium cepa L.) is one of the most important cultivars in the world and its production level occupies the second place in Venezuela. It becomes important to develop analytical procedures for arsenic determination and to study the effect of this element on the cultures, as well the absorption, transport and translocation processes. A TXRF method for As determination in onions was developed. Two treatments were applied to the onion plants, As contaminated and control. The contaminant was added to the plants to an amount of 100 μg, in a single time 3 weeks after the transplant of plantlets. The green leaves bulbs, and roots together with the stems were separated 45 days after transplant and analyzed by TXRF and HG-AAS for total Arsenic determination. A good agreement was found between these two techniques, demonstrating the accuracy of the TXRF procedure. It was found that the highest concentration corresponded to the root and stems (37 ± 31 μg g⁻¹), followed by the bulbs (11 ± 7 μg g⁻¹), being the smallest level found in the green leaves (4 ± 3 μg g⁻¹). At low As contamination levels of 0.25 μg g⁻¹, a risk for translocation of the toxic element to the edible parts of the onion plants exists. At this level the normal development of the plant is not affected, being the only exception the root length, which is significantly higher in the contaminated treatment.     

乙炔、丙烯在多种分子筛上的吸附和脱附性质

在80℃下研究了ZSM5、13X、Y、MOR、5A、SAPO34等多种分子筛和常见载体上乙炔和丙烯的吸附和脱附性能。结果表明,乙炔和丙烯在SiO2、γ-Al2O3上不吸附,而与分子筛存在较强的相互作用。对于同类型的分子筛,两者的饱和吸附量均随分子筛硅铝比的增大而减小。在同一种分子筛上,以摩尔计的丙烯吸附量均明显高于乙炔。在80℃改性β分子筛上乙炔和丙烯饱和吸附量可分别达到0.11mmol/g和4.89mmol/g,该结果明显高于文献报道的结果。