Solid-phase extraction using multiwalled carbon nanotubes and quinalizarin for preconcentration and determination of trace amounts of some heavy metals in food,water and environmental samples

A solid phase extraction procedure has been developed using multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and quinalizarin [1,2,5,8-tetrahydroxyanthracene-9,10-dione] as a chelating agent for separation and preconcentration of trace amounts of some heavy metal ions, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) before their determination by flame atomic absorption spectroscopy (FAAS). The influences of the analytical parameters, including pH, amounts of quinalizarin and adsorbent, sample volume, elution conditions such as volume and concentration of eluent, flow rates of solution and matrix ions, were investigated for the optimum recoveries of the analyte ions. No interference effects were observed from the foreign metal ions. The preconcentration factor was 100. The detection limit (LOD) for the investigated metals at the optimal conditions were observed in the range of 0.30–0.65 μg L^?1. The relative standard deviation (RSDs), and the recoveries of standard addition for this method were lower than 5.0% and 96–102%, respectively. The new procedure was successfully applied to the determination of analytes in food, water and environmental samples with satisfactory results.     

Capillary electrophoretic separation of serum proteins of workers occupationally exposed to heavy metals

Metallurgy processes are associated with many hazardous and toxic factors, including heavy metals. Exposure to heavy metals can cause damage to different organs, which can be observed through variation in the concentration of proteins in serum. The aim of this study was to evaluate the changes in a serum protein profile of copper smelters exposed to As, Cd and Pb ions, and xenobiotics present in tobacco smoke. A 2.3-fold higher Pb concentration in the blood and a 2.8-fold greater As concentration have been observed in the urine of non-smoking smelters compared to a control group. In the blood of smoking smelters, Cd concentration was 2-fold higher than in non-smoking ones. Serum proteins were separated by capillary electrophoresis, and in the group of non-smoking smelters, a higher amount of α₁-globulins was observed. In the group of smoking smelters, fewer α₁-globulins were noted. Furthermore, a greater amount of α₂-globulins in the serum of smoking and non-smoking workers in relation to the control group was revealed. A positive correlation between the concentration of Cd in the blood and the content of a fraction containing α₁- and α₂-globulins was revealed. Urine Cd concentration was found to be negatively associated with the α₁- and α₂-globulins fraction. Observed abnormalities in the proteins profiles of smelters can be important markers when assessing exposure to heavy metals and in the early diagnosis of diseases caused by them.     

Ligandless-ultrasound-assisted emulsification microextraction followed by inductively coupled plasma-optical emission spectrometry for simultaneous determination of heavy metals in water samples

In this study, a simple and efficient method of ligandless-ultrasound-assisted emulsification microextraction (LL-USAEME) followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) has been developed for simultaneous extraction, preconcentration and determination of manganese, cadmium, cobalt and nickel in water samples. In the proposed approach, tetrachloroethylene was selected as extraction solvent. The effect of important experimental factors such as volume of extraction solvent, pH, sonication time, salt concentration, and temperature was investigated by using a fractional factorial design (2^5?1) to identify important factors and their interactions. In the next step, a Box-Behnken design (BBD) was applied for optimisation of significant factors. The obtained optimal conditions were: 30?µL for extraction solvent, 12 for pH, 5?min for sonication time, and 5% w/v for salt concentration. The limits of detections (LODs) for Cd(II), Co(II), Mn(II) and Ni(II) were 0.20, 0.13, 0.21 and 0.28?µg?L^?1, respectively. Relative standard deviations (RSD, C?=?200.0?µg?L^?1, n?=?9) were between 3.4–7.5% and the calibration graphs were linear in the range of 0.25 to 1000.0?µg?L^?1 for Mn, 0.5–1000.0?µg?L^?1 for Co and Ni and 1.0–250.0?µg?L^?1 for Cd. The determination coefficients (R ²) of the calibration curves for the analytes were in the range of 0.993 to 0.999. The proposed method was validated by using two certified reference materials, and also the method was applied successfully for the determination of heavy metals in different real water samples.     

Chemically bonded multiwalled carbon nanotubes as efficient material for solid phase extraction of some metal ions in food samples

Multiwalled carbon nanotubes chemically functionalized with 2-((3-silylpropylimino) methyl) phenol (SPIMP-MWCNT) and successfully applied for the solid phase extraction (SPE) of some metal ions in food samples. The influences of the analytical parameters including pH, amounts of solid phase, eluent conditions (type, volume and concentrations), sample volume and interference of some metal ions on the recoveries of ions Cu²⁺, Pb²⁺, Fe²⁺, Ni²⁺ and Zn²⁺ ion were investigated. The metal ions retained on SPIMP-MWCNT was eluted using 6?mL of 4?mol?L^?1 HNO₃ solution and their content was determined by flame atomic absorption spectrometry (FAAS) with recoveries more than 95% and relative standard deviations (n?=?5) between 2.4–3.4% for both reproducibility and repeatability. The detection limit of this metal ions was between 1.0–2.6?ng?mL^?1 (3S _b , n?=?10) and their preconcentration factor was 100, while their loading capacity was above 32.9?mg?g^?1 of SPIMP-MWCNT. The proposed method was successfully applied for the preconcentration and determination of analytes in different samples.     

Are accurate computations of the 13C′ shielding feasible at the DFT level of theory?

The goal of this study is twofold. First, to investigate the relative influence of the main structural factors affecting the computation of the ¹³C′ shielding, namely, the conformation of the residue itself and the next nearest‐neighbor effects. Second, to determine whether calculation of the ¹³C′ shielding at the density functional level of theory (DFT), with an accuracy similar to that of the ¹³C^α shielding, is feasible with the existing computational resources. The DFT calculations, carried out for a large number of possible conformations of the tripeptide Ac‐G XY ‐NMe, with different combinations of X and Y residues, enable us to conclude that the accurate computation of the ¹³C′ shielding for a given residue X depends on the: (i) (?,ψ) backbone torsional angles of X ; (ii) side‐chain conformation of X ; (iii) (?,ψ) torsional angles of Y ; and (iv) identity of residue Y . Consequently, DFT‐based quantum mechanical calculations of the ¹³C′ shielding, with all these factors taken into account, are two orders of magnitude more CPU demanding than the computation, with similar accuracy, of the ¹³C^α shielding. Despite not considering the effect of the possible hydrogen bond interaction of the carbonyl oxygen, this work contributes to our general understanding of the main structural factors affecting the accurate computation of the ¹³C′ shielding in proteins and may spur significant progress in effort to develop new validation methods for protein structures. © 2013 Wiley Periodicals, Inc.     

Critical Evaluation of Adsorption–Desorption Hysteresis of Heavy Metal Ions from Carbon Nanotubes: Influence of Wall Number and Surface Functionalization

Single‐, double‐, and multi‐walled carbon nanotubes (SWCNTs, DWCNTs, and MWCNTs), and two oxidized MWCNTs with different oxygen contents (2.51 wt % and 3.5 wt %) were used to study the effect of the wall number and surface functionalization of CNTs on their adsorption capacity and adsorption–desorption hysteresis for heavy metal ions (Ni^II, Cd^II, and Pb^II). Metal ions adsorbed on CNTs could be desorbed by lowering the solution pH. Adsoprtion of heavy metal ions was not completely reversible when the supernatant was replaced with metal ion‐free electrolyte solution. With increasing wall number and amount of surface functional groups, CNTs had more surface defects and exhibited higher adsorption capacity and higher adsorption–desorption hysteresis index (HI) values. The coverage of heavy metal ions on the surface of CNTs, solution pH, and temperature affect the metal ion adsorption–desorption hysteresis. A possible shift in the adsorption mechanism from mainly irreversible to largely reversible processes may take place, as the amount of metal ions adsorbed on CNTs increases. Heavy metal ions may be irreversibly adsorbed on defect sites.     

Tuning Deazaflavins Towards Highly Potent Reducing Photocatalysts Guided by Mechanistic Understanding – Enhancement of the Key Step by the Internal Heavy Atom Effect

Deazaflavins are well suited for reductive chemistry acting via a consecutive photo-induced electron transfer, in which their triplet state and semiquinone – the latter is formed from the former after electron transfer from a sacrificial electron donor – are key intermediates. Guided by mechanistic investigations aiming to increase intersystem crossing by the internal heavy atom effect and optimising the concentration conditions to avoid unproductive excited singlet reactions, we synthesised 5-aryldeazaflavins with Br or Cl substituents on different structural positions via a three-component reaction. Bromination of the deazaisoalloxazine core leads to almost 100 % triplet yield but causes photo-instability and enhances unproductive side reactions. Bromine on the 5-phenyl group in ortho position does not affect the photostability, increases the triplet yield, and allows its efficient usage in the photocatalytic dehalogenation of bromo- and chloroarenes with electron-donating methoxy and alkyl groups even under aerobic conditions. Reductive powers comparable to lithium are achieved.     

电感耦合等离子体质谱(ICP-MS)法同时测定荞麦秸秆中的8种重金属元素

基于硝酸-盐酸-氢氟酸消解体系,建立了马弗炉-微波消解-电感耦合离子体质谱(ICP-MS)法同时测定荞麦秸秆中的Cr、Cu、Ag、Mn、Fe、As、Ni、Pb等重金属含量测定方法。在微波消解的过程中,分别考察5种不同组合的混合酸体系及两种消解方法对荞麦秸秆中8种重金属测试结果的影响。实验结果表明,浓硝酸-浓盐酸-氢氟酸(6∶2∶2)混酸体系和马弗炉-微波消解样品前处理优于其他方法。在优化条件下,8种重金属加标回收率为91.2%~102%,相对标准偏差(RSD,n=5)为0.22%~4.7%,检出限为0.18~9.41μg/L。方法操作简便、快速、准确,结果可靠,能同时测定荞麦秸秆中8种重金属元素。     

Ornamental Plant Efficiency for Heavy Metals Phytoextraction from Contaminated Soils Amended with Organic Materials

Accumulation of heavy metals (HMs) by ornamental plants (OPs) from contaminated agriculture soils is a unique technique that can efficiently reduce the metal load in the food chain. Amaranthus tricolor L. has attractive characteristics acquiring a higher growth rate and large biomass when grown at heavy metal contaminated soils. Site-specific detailed information is not available on the use of A. tricolor plant in metal phytoremediation from the polluted sites. The study aimed to enhance the uptake of HMs (Pb, Zn, and Cu) via amending poultry litter extract (PLE), vinasse sugarcane (VSC), and humic acid (HA) as natural mobilized organic materials compared to ethylene diamine tetraacetic acid (EDTA), as a common mobilized chemical agent by A. tricolor plant. The studied soils collected from Helwan, El-Gabal El-Asfar (Cairo Governorate), Arab El-Madabeg (Assiut Governorate), Egypt, and study have been conducted under pot condition. Our results revealed all organic materials in all studied soils, except EDTA in EL-Gabal El-Asfar soil, significantly increased the dry weight of the A. tricolor plant compared to the control treatment. The uptake of Pb and Zn significantly (p > 0.05) increased due to applying all organic materials to the studied soils. HA application caused the highest uptake as shown in Pb concentration by more than 5 times in Helwan soil and EDTA by 65% in El-Gabal El-Asfar soil while VSC increased it by 110% in El-Madabeg soil. Also, an increase in Zn concentration due to EDTA application was 58, 42, and 56% for Helwan, El-Gabal El-Asfar, and El-Madabeg soil, respectively. In all studied soils, the application of organic materials increased the remediation factor (RF) than the control. El-Madabeg soil treated with vinasse sugarcane gave the highest RF values; 6.40, 3.26, and 4.02% for Pb, Zn, and Cu, respectively, than the control. Thus, we identified A. tricolor as a successful ornamental candidate that, along with organic mobilization amendments, most efficiently develop soil health, reduce metal toxicity, and recommend remediation of heavy metal-contaminated soils. Additionally, long-term application of organic mobilization amendments and continued growth of A. tricolor under field conditions could be recommended for future directions to confirm the results.     

Linear Group 13 E≡E Triple Bonds in E2Li62+

The triply bonded heavier main-group compounds have a textbook trans-bent geometry, in contrast to a familiar linear form found for the lightest analogues. Strikingly, the unexpected linear group 13 E≡E triple bonds were herein found in the D_4h-symmetry E₂Li₆²⁺ clusters, and they possess a large barrier (>18.0 kcal/mol) towards the dissociation of Li⁺. The perfectly surrounded Li₄ motifs and two linear coordinated Li atoms strongly suppress the increasing nonbonded electron density of heavier E atoms, making two degenerate π bonds and one multi-center σ bond in linear heavier main-group triple bonds. The surrounding Li₆ motifs not only creates an effective electronic structure to form a linear E≡E triple bond, but the resulting electrostatic interactions account for the highly stable global E₂Li₆²⁺ clusters.