Rapid Low-Cost Determination of Lead(II) in Cassava by an iPod-Based Digital Imaging Colorimeter

An iPod-based digital image colorimeter was developed for the determination of lead(II) in cassava. The method is based on the color values of a lead(II) solution following its reaction with dithizone. Lead(II) from cassava was extracted using an ultraviolet-digestion unit followed by the color-forming reaction and image capture using the ColorConc application operated on an iPod touch. The concentration was predicted by comparing the color values with those collected in a database. The time needed for complete digestion was 30?min. The determined concentrations of lead(II) were from 0.10 to 1.00?µg mL^?1. The limits of detection and quantitation were 0.0120 and 0.0399?µg mL^?1, respectively. The recovery values were 105?±?7.07% and 109?±?6.61% at 0.2?µg mL^?1 and 0.4?µg mL^?1 lead(II) (n?=?5). The reported method was demonstrated to be simple, accurate, rapid, precise, and low cost.     

Electrochemical Determination of Lead(II) in Environmental Waters Using a Sulfydryl Modified Covalent Organic Framework by Square Wave Anodic Stripping Voltammetry (SWASV)

A novel sulfhydryl-modified covalent organic framework was designed for the selective determination of lead(II) using square wave anodic stripping voltammetry. The introduction of sulfhydryl groups enhanced the selectivity and sensitivity of the covalent organic framework for analytes. The sulfhydryl-modified covalent organic framework was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Under the optimized conditions, a sulfhydryl-modified covalent organic framework/gold electrode was successfully used for the determination of lead(II) in water samples. The newly developed square wave anodic stripping voltammetry method exhibited wide linearity (0.05 to 20?ng mL^?1, r?=?0.991), a low limit of detection (0.015?ng mL^?1) and good precision, with a relative standard deviation values <5.1%. The limit of detection was lower than 10?ng mL^?1, the level of lead(II) in drinking water permitted by the World Health Organization. The recoveries of three spiked samples ranged from 90.0% to 104.0%, with relative standard deviations <4.9%. Satisfactory reproducibility and good repeatability demonstrated that the newly developed method is very suitable for the detection of lead(II) in real water samples, with significant advantages over existing methods.     

Double-imprinted polymer based on cross-linked poly(vinylimidazole–trimethylolpropane trimethacrylate) in solid phase extraction for determination of lead from wastewater samples by UV–vis spectrophotometry

The monitoring of the heavy metal pollution in wastewater is increasingly becoming a crucial global issue since they tend to accumulate in food chains and can cause many biological abnormalities. In this work, it was developed a novel lead ion-imprinted polymer (IIP) using sodium dodecyl sulphate (SDS) as a second template to be used as adsorbent in solid phase extraction (SPE) for determination of lead from wastewater samples by UV–vis spectrophotometry. The polymer called IIP–SDS was synthesised by a double-imprinting process with lead (template) and SDS (template). IIP–SDS was characterised by infrared spectroscopy Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. IIP–SDS showed good recovery for lead (around 82.0%), while the IIP (only lead as template) was 72.2% and non-IIP was 44.9%. Thus, the double-imprinting process for the preconcentration of Pb²⁺ proved to be a more adequate methodology than IIP with a single template. The optimised parameters of sample preparation were washing solvent (2.0 mL of tetrahydrofuran), type and volume of eluent (5 mL of 1 mol L^?1 hydrochloric acid), sample amount (30 mL of water spiked with 10.0 µg mL^?1), amount of IIP–SDS (400 mg) and sample pH (pH = 4.5). Linearity ranged from 10 to 125 µg L^?1 with r > 0.992. The limit of detection and quantification were 6.3 and 10 µg L^?1, respectively. The precision (relative standard deviation, %) and accuracy (relative error, %) were lower than 15%. Finally, IIP–SDS may be an alternative and effective adsorbent for SPE procedures in monitoring of wastewater samples.     

Investigation of the Crystallisation Behaviour of Lead Titanate (PT), Lead Zirconate (PZ) and Lead Zirconate Titanate (PZT) by EXAFS-Spectroscopy and X-Ray Diffraction

Two solid solutions of lead zirconium titanates PbZr _x Ti_{1 – x} O₃ (x = 0.1 and 0.35) as well as the reference compounds lead titanate and lead zirconate were prepared from zirconium and titanium n-propoxide, dissolved in 2-methoxyethanol, by sol-gel process. The amorphous products after pyrolysis of the dried gels and the crystalline phases were studied by EXAFS spectroscopy to monitor the structural changes from the amorphous oxide mixture to the crystalline ceramics after calcination. Additionally, the crystalline phases were identified by X-ray diffraction (XRD).It follows from the analysis of the EXAFS data that the local order of the amorphous phases seems to be completely different from that of the crystalline phase. There is no indication of a preformation of the local order of the perovskite structure. The analysis of our EXAFS spectra can be interpreted very consistently with the assumption that in the amorphous samples a segregation exists on molecular level and the low crystallisation temperatures are a consequence of very short diffusion paths.     

Phase transitions in ternary caesium lead bromide

Phase transitions in ternary caesium lead bromide (CsPbBr₃) were studied by means of DSC, TMA and high temperature X-ray diffraction. The samples were prepared from the solution by water evaporation and from the melt. on the DSC curves as well as on the temperature dependence of the lattice constants of CsPbBr₃ only two effects were found belonging to the earlier published phase transitions at 88 and 130°C and no further effects. Linear thermal expansion coefficient α of individual CsPbBr₃ modifications were calculated from both TMA and high temperature X-ray diffraction. The structural parameters of the room temperature orthorhombic phase were refined and the results are presented. CsPbBr₃ prepared from the solution contained about 10% of CsPb₂Br₅ and so the DSC curve of pure CsPb₂Br₅ was also measured and an effect at a temperature of 68.5°C was found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Syntheses,Characterization, and Fluorescence Properties of Four Divalent Lead Coordination Polymers based on Zwitterionic Ligands

Four novel divalent lead coordination polymers based on a series of zwitterionic ligands, Pb₂Cl₄L₁ ( 1 ), [Pb₂Cl₄L₂]·2H₂O ( 2 ), Pb₂Cl₂(CH₃COO)₂L₂ ( 3 ), and Pb₃Cl₄(NO₃)₂L₃ ( 4 ) were solvothermally synthesized and successfully characterized. Single crystal structure studies reveal that compound 1 is a chain structure based on the inorganic “PbCl₂” chain motif, whereas compounds 2 – 4 are sheet structures each constructed by inorganic “PbCl₂”, “PbCl(CH₃COO)”, and “Pb₃Cl₄” chain motifs. Hydrogen bonding interactions in term of C–H ··· Cl and C–H ··· O play a key role to form supramolecular 3D structures of 1 – 4 . Additionally, studies of solid state fluorescence indicate 1 – 4 emit in the ultraviolet and visible region that can be assigned to the inter‐ligand π*–π and/or π*–n transitions.     

Coordination polymers of CdII and PbII derived from bipyridine–glycoluril: influence of metal‐ion size and counter‐ions

Two new one‐dimensional (1D) coordination polymers (CPs), namely catena‐poly[[[aquacadmium(II)]‐bis(μ‐4b,5,7,7a‐tetrahydro‐4b,7a‐epiminomethanoimino‐6H‐imidazo[4,5‐f][1,10]phenanthroline‐6,13‐dione)] bis(perchlorate) dihydrate], {[Cd(C₁₄H₁₀N₆O₂)₂(H₂O)](ClO₄)₂·2H₂O}_n or {[Cd(BPG)₂(H₂O)](ClO₄)₂·2H₂O}_n, 1 , and catena‐poly[[lead(II)‐bis(μ‐4b,5,7,7a‐tetrahydro‐4b,7a‐epiminomethanoimino‐6H‐imidazo[4,5‐f][1,10]phenanthroline‐6,13‐dione)] bis(perchlorate) dihydrate], {[Pb(C₁₄H₁₀N₆O₂)₂](ClO₄)₂·2H₂O}_n or {[Pb(BPG)₂](ClO₄)₂·2H₂O}_n, 2 , have been synthesized using bipyridine–glycoluril (BPG; systematic name: 4b,5,7,7a‐tetrahydro‐4b,7a‐epiminomethanoimino‐6H‐imidazo[4,5‐f][1,10]phenanthroline‐6,13‐dione), a urea‐fused tecton, in a mixed‐solvent system. The Cd^II ion in 1 is heptacoordinated and the Pb^II ion in 2 is hexacoordinated, with the Cd^II ion adopting a pentagonal bipyramidal geometry and the Pb^II ion adopting a distorted octahedral geometry. Both CPs form infinite linear chain structures which are hydrogen bonded to each other leading to the formation of three‐dimensional supramolecular network structures. Topological analysis of CPs 1 and 2 reveals that the structures exhibit 1D chain‐like arrangements in an AB–AB sequence and shows platonic uniform 2‐connected uninodal topologies. Furthermore, a comparative analysis of a series of structures based on the BPG ligand indicates that the size of the metal ion and the types of counter‐ions used have a great influence on the resulting frameworks and properties.     

A simple two‐stage column chromatographic separation scheme for strontium,lead, neodymium and hafnium isotope analyses in geological samples by thermal ionization mass spectrometry or multi‐collector inductively coupled plasma mass spectrometry

Here, a two‐stage column separation scheme is developed for the concomitant isolation of Sr, Pb, Nd, and Hf from geological samples. The first column, which consists of three resin layers (AG50W‐X8 ion exchange resin + Ln specific resin + Sr specific resin), separates the high field strength element + rare earth element, Sr and Pb from the matrices. Subsequently, Nd and Hf are further separated from the high field strength element + rare earth element fraction on the second column using 1 mL of Ln specific resin. The two‐stage column process can be completed within about seven and a half hours for a batch of samples (20–30). The separated Sr fraction was ready for isotope ratio measurements by thermal ionization mass spectrometry. The Pb, Nd, and Hf fractions were converted to nitrate prior to isotopic analyses by multi‐collector inductively coupled plasma mass spectrometry. The feasibility of this new procedure is confirmed by the analyses of four international rock standards (BCR‐2, AGV‐2, BHVO‐2, and JB‐3), which yielded isotope ratios that were in good agreement with other published data.     

Extremely Photostable Electron-Deficient Phthalocyanines that Generate High Levels of Singlet Oxygen

A robust lead-mediated synthetic procedure for the generation of phthalocyanines substituted with electron-withdrawing groups has been developed. The free-base phthalocyanine and various metal complexes were prepared without discernible degradation of the peripheral electron-withdrawing substituents. Upon irradiation with red light, some of the thus-obtained metal complexes generated high levels of singlet oxygen. In particular, a palladium complex exhibited attractive photostability upon exposure to singlet oxygen as a bleaching agent. The photostability of such complexes that may manifest concomitantly to the generation of high levels of singlet oxygen was attributed to the presence of the electron-withdrawing groups, which results in energetically low-lying highest occupied molecular orbitals.     

Two-Step Structure Phase Transition,Dielectric Anomalies,and Thermochromic Luminescence Behavior in a Direct Band Gap 2D Corrugated Layer Lead Chloride Hybrid of [(CH3)4N]4Pb3Cl10

A direct band gap 2D corrugated layer lead chloride hybrid, [(CH₃)₄N]₄Pb₃Cl₁₀ ( 1 ), shows analogous topology to the {Mg₃F₁₀⁴⁻}_∞ layer in Cs₄Mg₃F₁₀, and with the (CH₃)₄N⁺ cations locating in the inorganic layer voids and between the interlayers. Two reversible structural phase transitions occur in 1 at 225/210 K and 328/325 K upon heating/cooling, respectively. On going from the low- to intermediate-temperature phase, the space group changes from P2₁/c to Cmca, and the crystallographic axis perpendicular to the layers is doubled with the order–disorder transformation of (CH₃)₄N ⁺ cations between the interlayers. The intermediate- and high-temperature phases are isomorphic with similar cell parameters and packing structure; their main difference concerns the disorder degree of the (CH₃)₄N ⁺ cations between the interlayers. The two-step structural phase transitions lead to dielectric anomalies around the corresponding T_c. Interestingly, 1 shows multiband emission, originating from the recombination of exciton and emission of defects. Moreover, 1 exhibits divergent thermochromic luminescent features around the T_c on the intermediate to low temperature transition.