Speciation of inorganic and organic arsenic in marine sediments from La Coruña estuary

The speciation of As(III), As(V), MMA and DMA in marine sediments from La Coruña estuary is described. The arsenic species have been separated by ion-exchange chromatography and detected by hydride generation atomic absorption spectrometry (HGAAS). The redox potential has been determined in order to relate the concentration of arsenic species to this parameter.     

Automated system for on-line determination of dimethylarsinic and inorganic arsenic by hydride generation–atomic fluorescence spectrometry

A multisyringe flow-injection approach has been coupled to hydride generation-atomic fluorescence spectrometry (HG-AFS) with UV photo-oxidation for dimethylarsinic (DMA), inorganic As and total As determination, depending on the pre-treatment given to the sample (extraction or digestion). The implementation of a UV lamp allows on-line photo-oxidation of DMA and the following arsenic detection, whereas a bypass leads the flow directly to the HG-AFS system, performing inorganic arsenic determination. DMA concentration is calculated by the difference of total inorganic arsenic and measurement of the photo-oxidation step. The detection limits for DMA and inorganic arsenic were 0.09 and 0.47 μg L(-1), respectively. The repeatability values accomplished were of 2.4 and 1.8%, whereas the injection frequencies were 24 and 28 injections per hour for DMA and inorganic arsenic, respectively. This method was validated by means of a solid reference material BCR-627 (muscle of tuna) with good agreement with the certified values. Satisfactory results for DMA and inorganic arsenic determination were obtained in several water matrices. The proposed method offers several advantages, such as increasing the sampling frequency, low detection limits and decreasing reagents and sample consumption, which leads to lower waste generation.     

Functionalization of mesostructured inorganic–organic and porous inorganic materials

The capability to functionalize the interior channels and/or high internal surface areas of mesostructured inorganic–organic or porous inorganic solids with specific organic or inorganic moieties has dramatically expanded the potential applications for these versatile materials in catalysis, separations, optical and opto-electronic devices, drug delivery, sensors, and energy conversion. Key to the widespread application of these materials are the various synthetic schemes that have been developed to provide control over the types of species incorporated and, more importantly, their distributions within the mesostructured hosts. Furthermore, multiple active species can often be independently incorporated and collectively optimized to yield multifunctional properties that widen application prospects. Several recent developments and examples in this rapidly growing field of materials chemistry and engineering are highlighted and discussed.     

SPE HG-AAS method for the determination of inorganic arsenic in rice—results from method validation studies and a survey on rice products

The present paper describes the development, validation and application of a method for inorganic arsenic (iAs) determination in rice samples. The separation of iAs from organoarsenic compounds was done by off-line solid-phase extraction (SPE) followed by hydride generation atomic absorption spectrometry (HG-AAS) detection. This approach was earlier developed for seafood samples (Rasmussen et al., Anal Bioanal Chem 403:2825–2834, 2012) and has in the present work been tailored for rice products and further optimised for a higher sample throughput and a lower detection limit. Water bath heating (90 °C, 60 min) of samples with dilute HNO₃ and H₂O₂ solubilised and oxidised all iAs to arsenate (As^V). Loading of buffered sample extracts (pH 6?±?1) followed by selective elution of arsenate from a strong anion exchange SPE cartridge enabled the selective iAs quantification by HG-AAS, measuring total arsenic (As) in the SPE eluate. The in-house validation gave mean recoveries of 101–106 % for spiked rice samples and in two reference samples. The limit of detection was 0.02 mg kg^?1, and repeatability and intra-laboratory reproducibility were less than 6 and 9 %, respectively. The SPE HG-AAS method produced similar results compared to parallel high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The SPE separation step was tested collaboratively, where the laboratories (N?=?10) used either HG-AAS or ICP-MS for iAs determination in a wholemeal rice powder. The trial gave satisfactory results (HorRat value of 1.6) and did not reveal significant difference (t test, p?>?0.05) between HG-AAS and ICP-MS quantification. The iAs concentration in 36 rice samples purchased on the Danish retail market varied (0.03–0.60 mg kg^?1), with the highest concentration found in a red rice sample.      

Elastic organic–inorganic hybrid aerogels and xerogels

Novel aerogels and xerogels with methylsilsesquioxane (MSQ, CH₃SiO_1.5) networks have been prepared by a modified sol–gel process using surfactant and urea as a phase-separation inhibitor and as an accelerator for the condensation reaction, respectively. Optimized aerogels dried under a supercritical condition not only showed the similar properties as conventional pure silica aerogels such as high transparency and porosity etc, but also demonstrated outstanding mechanical strength against compression; the aerogel drastically shrank upon loading and then recovered when unloaded, which is called a “spring-back” behavior. On ambient pressure drying, the wet gel also exhibited the similar response against compression stress originated from the capillary pressure, and thus xerogels with the comparative structure and properties to those of corresponding aerogels have also been obtained. This unusual mechanical behavior is attributed to the trifunctional flexible networks of MSQ, low silanol concentration which prevents the irreversible shrinkage, and high concentration of a hydrophobic methyl group directly attached to every silicon atom which helps re-expansion after the temporal shrinkage.     

Elastic and thermoelastic properties of “inorganic rubber”

Polymerization of cyclic phosphonitrilic chloride trimer was carried out at sufficiently high temperatures and for sufficiently long periods to cause gelation of the poly(dichlorophosphazene) formed. The resulting crosslinked material, called “inorganic rubber”, was found to be stable enough in the absence of moisture to permit reliable stress-strain and stress-temperature (thermoelastic) measurements in elongation. The stress-strain isotherms at low and moderate values of the elongation, α, showed that the networks had relatively low degrees of crosslinking; at high α and low temperature, they underwent strain-induced crystallization. The thermoelastic data confirmed the occurrence of crystallization at high α and low T. Thermoelastic values of the fraction f_e/f of the force that is of energetic origin were negative and generally large, with a magnitude that increased with increase in α, presumably because of the crystallization. In any case, the experimental values of f_e/f are in at least qualitative agreement with rotational isomeric state theory, which predicts this ratio to be large and negative.     

Is it possible to agree on a value for inorganic arsenic in food? The outcome of IMEP-112

Two of the core tasks of the European Union Reference Laboratory for Heavy Metals in Feed and Food (EU-RL-HM) are to provide advice to the Directorate General for Health and Consumers (DG SANCO) on scientific matters and to organise proficiency tests among appointed National Reference Laboratories. This article presents the results of the 12th proficiency test organised by the EU-RL-HM (IMEP-112) that focused on the determination of total and inorganic arsenic in wheat, vegetable food and algae. The test items used in this exercise were: wheat sampled in a field with a high concentration of arsenic in the soil, spinach (SRM 1570a from NIST) and an algae candidate reference material. Participation in this exercise was open to laboratories from all around the world to be able to judge the state of the art of the determination of total and, more in particular, inorganic arsenic in several food commodities. Seventy-four laboratories from 31 countries registered to the exercise; 30 of them were European National Reference Laboratories. The assigned values for IMEP-112 were provided by a group of seven laboratories expert in the field of arsenic speciation analysis in food. Laboratory results were rated with z and ζ scores (zeta scores) in accordance with ISO 13528. Around 85?% of the participants performed satisfactorily for inorganic arsenic in vegetable food and 60?% did for inorganic arsenic in wheat, but only 20?% of the laboratories taking part in the exercise were able to report satisfactory results in the algae test material.     

Biodegradable and bioactive hybrid organic–inorganic PEG-siloxane fibers. Preparation and characterization

A mixture of triethoxysilanefunctionalized poly(ethylene glycol), f-PEG, and tetraethoxysilane, TEOS, was used as precursors in the preparation of continuous hybrid f-PEG-siloxane sol–gel derived fibers. The fibers were spun by extrusion through a spinneret. The thus prepared fibers had a diameter of 20–50 m. ²⁹Si-CPMAS NMR measurements confirmed that the functionalized PEG is incorporated into the siloxane network through covalent bonds. The hybrid fiber elasticity was much higher than that of fibers spun from sols with TEOS as the only source for silica. However, the f-PEG chain length plays a crucial role for the spinnability of the sol, since, as a result of bridging flocculation, macroscopic phase separation occurred readily with increasing chain length of the f-PEG. The fibers were shown to be effective substrates for the nucleation and growth of bone-like hydroxyapatite.     

Flexible inorganic–organic hybrids with dual inorganic components

Combining multiple inorganic components is an effective approach to improve the mechanical properties of inorganic–organic hybrid materials. The inorganic components can form interactions with the organic polymer matrix, and there is thus a need to understand the reinforcement mechanism under the optimal combination of organic polymer and inorganic particles. In this work, we prepared a series of dual inorganic particle–based titania/silica–poly(tetrahydrofuran)–poly(ε-caprolactone) (TiO₂/SiO₂–PTHF–PCL) hybrids by means of simultaneous cationic ring-opening polymerization and sol–gel reaction. In addition to constructing hybrid networks, the SiO₂ and TiO₂ components play important roles in multiple toughening mechanisms. The prepared dual inorganic hybrids feature enhanced thermal stability and mechanical properties when compared with the ones with a single inorganic component. The optimized mixing of such two inorganic components is identified through mechanical tests, revealing that the hybrid polymer₇₀/(Si_0.6Ti_0.4)₃₀ (70/18/12 mass ratio) has the highest compressive failure strain (80%) and compressive ultimate strength (1.3 MPa) as well as storage modulus (120 kPa), enabling elongation of up to 37% when compared with its original length. We thus find that the dual inorganic component approach is an effective strategy to enhance the mechanical properties of hybrid materials, suggesting potential applications as scaffolds for tissue engineering and soft robotics.     

Biodegradable and biocompatible inorganic–organic hybrid materials. I. Synthesis and characterization

The hydroxyl or vinyl end-groups of linear or three-arm star-shaped poly(ε-caprolactone) (PCL) chains have been derivatized into triethoxysilane groups reactive in the sol-gel process. New transparent hybrid materials that combine tetraethylorthosilicate (TEOS) and PCL known for biodegradability and biocompatibility have accordingly been prepared. The sol-gel process is, however, limited by the early vitrification of the reactive system. However, thermal posttreatment can overcome these diffusional and/or kinetic limitations as assessed by a set of analytical methods. The thermal stability of PCL is improved by incorporation into the silica network. Conversely, the thermal stability of the ceramer depends on the effective PCL content. The extent of PCL incorporation into the silica network depends on PCL molecular weight, number, and reactivity of the PCL functional groups. IR spectroscopy has shown that hydrogen bonding occurs between the ester groups of PCL and residual OH groups of the silicate component. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2295–2309, 1997     

Structure and surface properties of fluorinated organic–inorganic hybrid films

Fluorinated organic–inorganic hybrid films were prepared by sol–gel process from tridecafluoroctyltriethoxysilane (PFAS), 3-glycidoxypropyltrimethoxysilane, and tetraethoxysilane (TEOS). It has been found that the fluorinated hybrid films possessed fluorinated side chains originating from PFAS as top layer, and silica network as bottom layer, which had very low surface energy and could be used as water repellent functional coatings. The outermost layer of the water-repellent film may be fully covered by the perfluoroalkyl side chains as the molar ratio of PFAS/TEOS increases up to about 0.005:1. The addition of BPA can enhance the cross-link density of fluorinated hybrid films, and make more perfluoroalkyl groups enriching at the coating film-air interface to lower the surface free energy. However, the improvement of the cross-link density of fluorinated hybrid films tends to exhibit brittleness and micro-cracks. Consequently, it can be concluded that a small BPA additive content is preferred for the formation of fluorinated hybrid films with a smooth surface and less detectable cracks.     

Synthesis and properties of organic–inorganic hybrid liquid crystal gels

Organic–inorganic hybrid liquid crystal (LC) gels have been synthesised by the thiol-ene reaction of a multifunctional cyclic siloxane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (TVMCTS) and alkane dithiols, 1,6-hexanedithiol (HDT) or 1,9-decanedithiol (DDT), in LC matrices, 4-cyano-4?-pentylbiphenyl (5CB) or 4′-n-octyl-4-cyano-biphenyl (8CB). The LC gels were prepared in an isotropic phase at 70°C or mesophases at 25°C using radical initiators. The phase transition temperatures from a mesophase to an isotropic phase of the resulting gels were lower than those of the original LCs. The gels containing 8CB (8CB gels) prepared at 25°C showed two phase transitions: smectic-to-nematic and nematic-to-isotropic transitions. By contrast, the 8CB gels synthesised in the isotropic phase showed only one phase transition from smectic phase directly to isotropic phase. Reaction conversions in the LC gels prepared at 70°C were higher than that in the gels prepared at 25°C. Scanning microscopic light scattering analysis of the LC gels cleared homogeneous small size mesh with a small amount of large defect. Polarisation micrographs of the LC gels showed framed optical textures derived from the LC molecules at room temperature. The LC gels containing more than 90 wt% of LC showed electro-optic response.     

Organic–inorganic hybrids based on polyoxometalates and copper coordination complexes

Two new hybrids based on Keggin polyoxometalates have been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, and single-crystal X-ray diffraction. The crystal structure analyses reveal that complex 1 has an infinite 1D chain structure, constructed from [Cu(2,2′-bpy)(4,4′-bpy)(H₂O)] fragments and [H₂PMo₁₁VO₄₀]^2? building blocks. Complex 2 has a 2D molecular ladder structure, with a basic structural unit composed of one bis(µ-OH) dicopper(II) [Cu₂(OH)₂(H₂O)₂(4,4′-bpy)₃] fragment, one [HPMo₁₂O₄₀], and four water molecules. The [Cu₂(OH)₂(H₂O)₂(4,4′-bpy)₃] units connect alternately to form edge rails. The [HPMo₁₂O₄₀] clusters act as rungs of the ladder, linking pairs of Cu atoms from the two adjacent edge rails. The electrochemical behavior of the complexes in modified carbon paste electrodes and their electrocatalytic reduction of nitrite were investigated.     

3D-printed,TiO<Subscript>2</Subscript> NP–incorporated minicolumn coupled with ICP-MS for speciation of inorganic arsenic and selenium in high-salt-content samples

To extend the applicability of solid phase extraction devices manufactured using 3D printing technologies, a stereolithographic 3D printer and resins incorporating titanium dioxide nanoparticles (TiO₂ NPs) were employed to fabricate a demountable minicolumn with TiO₂ NP–incorporated packing as a sample pretreatment device for the selective extraction of inorganic As and Se species from high-salt-content samples, and to facilitate their analyses when coupled to an inductively coupled plasma mass spectrometer. After optimization, the automatic system enabled highly sensitive determinations of As and Se species with detection limits as low as 0.004–0.033 μg L^?1 for As and 0.061–0.128 μg L^?1 for Se. Reliability was confirmed through analyses of the reference materials 1643f, SLEW-3, CASS-4, and 2670a, as well as spike analyses of samples of water and human urine. These 3D-printed minicolumns appear to be very useful for multi-elemental speciation of these elements from high-salt-content samples. Thus, the incorporation of active nanomaterials into raw printing resins can enable 3D printing technologies—not only to fabricate functionalized devices for diverse sample pretreatment applications but also to encourage the future development of multifunctional devices for analytical science.

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Graphical abstract Schematic presentation of a demountable minicolumn fabricated using a stereolithographic 3D printer and the resins incorporating with TiO₂ NPs. They were used to selectively extract As and Se species through controlling the sample acidities.

     

Electrodeposition and stripping voltammetry of arsenic(III) and arsenic(V) on a carbon black–polyethylene composite electrode in the presence of iron ions

In this work, a new sensor is proposed for the stripping voltammetric determination (anodic stripping voltammetry—ASV) of total arsenic(V) or arsenic(III). The sensor is based on an Fe-modified carbon composite electrode containing 30 % carbon black–high-pressure polyethylene (CB/PE). The modification with iron is achieved by the addition of Fe(III) or Fe(II) ions to the sample solution and co-electrodeposition of iron and arsenic on the CB/PE electrode. In anodic stripping voltammetry, two peaks are observed: an Fe peak at ?0.45 or ?0.29 V and a peak at 0.12?±?0.07 V which depends on the arsenic concentration and corresponds to the As(0) → As(III) oxidation, as is the case with other solid electrodes. The optimum conditions proposed for ASV determination of As(V) and As(III) in solutions in the presence of dissolved oxygen are the following: the background electrolyte is 0.005 M HCl containing 0.5–1 mg/?L Fe(III) for As(V) and containing 1.0–1.5 mg/?L Fe(III) for As(III), respectively; E _dep?=??2.3 V; rest period at ?0.10 V for 3–5 s before the potential sweep from ?0.2 to +0.4 V; scan rate is 120 mV/?s. The detection limit (LOD, t?=?120 s) for As(III) and As(V) is 0.16 and 0.8 μg/?L, respectively. Various hypotheses on the effect of Fe ions and atoms on the electrodeposition and dissolution of arsenic are considered. The new method of determination of As(III) and As(V) differs from known analogues by its simplicity, low cost, and easy accessibility of the electrode material. It allows the voltammetric determination of total arsenic after chemical reduction of all its forms to As(III) or after their oxidation to As(V).     

ICP-MS-based characterization of inorganic nanoparticles—sample preparation and off-line fractionation strategies

Validated and easily applicable analytical tools are required to develop and implement regulatory frameworks and an appropriate risk assessment for engineered nanoparticles (ENPs). Concerning metal-based ENPs, two main aspects are the quantification of the absolute mass concentration and of the “dissolved” fraction in, e.g., (eco)toxicity and environmental studies. To provide information on preparative aspects and on potential uncertainties, preferably simple off-line methods were compared to determine (1) the total concentration of suspensions of five metal-based ENP materials (Ag, TiO₂, CeO₂, ZnO, and Au; two sizes), and (2) six methods to quantify the “dissolved” fraction of an Ag ENP suspension. Focusing on inductively coupled plasma–mass spectrometry, the total concentration of the ENP suspensions was determined by direct measurement, after acidification and after microwave-assisted digestion. Except for Au 10 nm, the total concentrations determined by direct measurements were clearly lower than those measured after digestion (between 61.1 % for Au 200 nm and 93.7 % for ZnO). In general, acidified suspensions delivered better recoveries from 89.3 % (ZnO) to 99.3 % (Ag). For the quantification of dissolved fractions two filtration methods (ultrafiltration and tangential flow filtration), centrifugation and ion selective electrode were mainly appropriate with certain limitations, while dialysis and cloud point extraction cannot be recommended. With respect to precision, time consumption, applicability, as well as to economic demands, ultrafiltration in combination with microwave digestion was identified as best practice.

Four inorganic–organic hybrid complexes built from tetravanadate and macrocyclic oxamide

Four inorganic–organic hybrid compounds, [M₂(CuL)₄(V₄O₁₂)]·2H₂O (M?=?Co (1), Mn (2)), [Mn₂(NiL)₄(V₄O₁₂)]·2H₂O (3), and [Zn₂(CuL)₄(V₄O₁₂)]·2CH₃OH·2H₂O (4) (M′L, H₂L?=?2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien), have been synthesized and characterized by elemental analysis, IR, UV, fluorescence spectra, and X-ray diffraction analysis. Single-crystal X-ray analysis reveal that both [V₄O₁₂]^4? and M₂V₄ adapt a chair-like configuration in four structures. The cyclovanadate group [V₄O₁₂]^4? is a tetradentate bridging ligand linking two [M(M′L)₂]²⁺ fragments, producing centroantisymmetric heterometallic hexanuclear [M₂M′₄] complexes. The variable-temperature magnetic susceptibility measurements (2–300?K) of 1 and 2 show weak antiferromagnetic interactions.     

Mechanism study on inorganic oxidants induced inhibition of Ru(bpy)₃²+ electrochemiluminescence and its application for sensitive determination of some inorganic oxidants

Inhibited Ru(bpy)₃²⁺ electrochemiluminescence by inorganic oxidants is investigated. Results showed that a number of inorganic oxidants can quench the ECL of Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) system, and the logarithm of the decrease in ECL intensity (ΔI) was proportional to the logarithm of analyte concentrations. Based on which, a sensitive approach for detection of these inorganic oxidants was established, e.g. the log-log plots of ΔI versus the concentration of MnO₄⁻, Cr₂O₇²⁻ and Fe(CN)₆³⁻ are linear in the range of 1 × 10⁻⁷ to 3 × 10⁻⁴ M for MnO₄⁻ and Cr₂O₇²⁻, and 1 × 10⁻⁷ to 1 × 10⁻⁴ M for Fe(CN)₆³⁻, with the limit of detection (LOD) of 8.0 × 10⁻⁸ M, 2 × 10⁻⁸ M, and 1 × 10⁻⁸ M, respectively. A series of experiments such as a comparison of the inhibitory effect of different compounds on Ru(bpy)₃²⁺/TPrA ECL, ECL emission spectra, UV-Vis absorption spectra etc. were investigated in order to discover how these inorganic analytes quench the ECL of Ru(bpy)₃²⁺/TPrA system. A mechanism based on consumption of TPrA intermediate (TPrA^·) by inorganic oxidants was proposed.     

Fabrication of organic–inorganic nano-complexes using ABC type triblock copolymer and polyoxotungstates

New organic–inorganic nano-complexes were produced from a micelle of tri-block polymers; poly(styrene)-b-poly(2-vinylpyridine)- b-poly (ethylene oxide) (PS-PVP-PEO) and tungsten compounds such as tungstate (W₁²⁻), undecatungstophospate (PW₁₁⁷⁻) and undecatungstosilicate (SiW₁₁⁸⁻) in acidic aqueous solutions. The size and morphology of the complexes were characterized by measurements of dynamic light scattering, atomic force microscopy, and scanning electron microscopy. This complex is assembled mainly by the charge interaction between the inorganic polyanions and the positively charged PVP block in the PS-PVP-PEO molecule, which was confirmed by zeta-potential and fluorescence spectroscopic studies. In the absence of the inorganic anions, the zeta-potential of the micelle was +11 mV at pH 3 due to the positive charge of the PVP block. When the inorganic anion was mixed with the PS-PVP-PEO micelle, decrease in the zeta-potential due to charge neutralization occurred with incorporation of inorganic anions into the PS-PVP-PEO micelle. The minimum zeta-potential was 0, −33, and −35 mV for W₁²⁻ /PS-PVP-PEO, PW₁₁⁷⁻ /PS-PVP-PEO, and SiW₁₁⁸⁻ /PS-PVP-PEO complexes, respectively. Excess negative charge which occurred in the latter two complexes indicates that PS-PVP-PEO molecules bound PW₁₁⁷⁻ and SiW₁₁⁸⁻ by forces other than charge interaction. In addition, the incorporation of an inorganic polyanion into the micelle gave a new morphology to the micelle. In the absence of the polyanion, the PS-PVP-PEO micelles showed an extended conformation due to repulsive forces working among the positively charged PVP blocks. Addition of the polyanion caused the formation of shrunken forms of the micelles, since the charge repulsion was cancelled by the polyanion. This feature may be useful in developing a new type of functioning micelle.     

A new organic–inorganic hybrid based on Mn–salen and decavanadate

An organic–inorganic hybrid based on Mn-salen and decavanadate, [NH₄]₂[Mn(salen)(H₂O)₂]₄[V₁₀O₂₈]?·?6H₂O (1) (salen?=?N,N′-ethylene-bis(salicylideneiminate)), has been synthesized by the strategy of secondary building units in mixed methanol–water solution and was structurally characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV-Vis. The [Mn(salen)(H₂O)₂]⁺ cations and water molecules are located in the interspaces among the polyoxoanions [V₁₀O₂₈]^6? forming a POM-based supramolecule. Compound 1 is the first example of metal-Schiff-base polyoxovanadates. The photocatalytic analysis, cyclic voltammetry, and electrocatalytic analysis of 1 have been investigated.