Determination of boron in biological tissues by inductively coupled plasma optical emission spectrometry (ICP-OES)

Summary The application of inductively coupled plasma optical emission spectrometry (ICP-OES) to the determination of boron was studied with regard to the optimization of boron neutron capture therapy (BNCT), a method used in cancer radiotherapy. In order to enable trace determinations of B in tissue down to the sub g/g-level (as this application requires), the different parameters of ICP-OES (gas flow, power, observation height) were optimized towards highest power of detection. Two different nebulizers (Babington and Meinhard nebulizer) as well as ICPs with argon or nitrogen as outer gases were used. The optimization was carried out with the aid of a modified simplex. The lowest detection limit for B (25 ng/ml) is obtained in the case of a Babington nebulizer and with an ICP using Ar as outer gas as well as a forward power of 1.3 kW (plate voltage at the r.f. generator: 2.75 kV). Therefore, the nebulizer gas flow had to be set at 1.1 l/min (at 4.5 bar) and an intermediate gas flow of 5 l/min in the case of a Greenfield-type torch was required. After optimization the natural concentration of B in biological tissues (0.1–0.3 g/g) could be determined after decomposition of 1–1.5 g of the sample with 5 ml HNO₃ (63%) at high temperature and pressure during 2 h in closed PTFE vessels. Results obtained with spiked liver standards were precise (RSD 5%–8%) and accurate in a concentration range of 5 g/g to 100 g/g. The method developed could be satisfactorily used for the analysis of tissue samples of mice tumors. Furthermore, the uptake and metabolization of boron and its derivatives could be well monitored at the 1–5 g/g level.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthday     

Thermal reduction of NO by H2: Kinetic measurement and computer modeling of the HNO + NO reaction

The kinetics and mechanism of the thermal reduction of NO by H₂ have been investigated by FTIR spectrometry in the temperature range of 900 to 1225 K at a constant pressure of 700 torr using mixtures of varying NO/H₂ ratios. In about half of our experimental runs, CO was introduced to capture the OH radical formed in the system with the well-known, fast reaction, OH + CO → H + CO₂. The rates of NO decay and CO₂ formation were kinetically modeled to extract the rate constant for the rate-controlling step, (2) HNO + NO → N₂O + OH. Combining the modeled values with those from the computer simulation of earlier kinetic data reported by Hinshelwood and co-workers (refs. [3] and [4]), Graven (ref.[5]), and Kaufman and Decker (ref. [6]) gives rise to the following expression: . This encompasses 45 data points and covers the temperature range of 900 to 1425 K. RRKM calculations based on the latest ab initio MO results indicate that the reaction is controlled by the addition/stabilization processes forming the HN(O)NO intermediate at low temperatures and by the addition/isomerization/decomposition processes producing N₂O + OH above 900 K. The calculated value of k₂ agrees satisfactorily with the experimental result. © 1995 John Wiley & Sons, Inc.     

Switched voltammetric determination of ractopamine by using a temperature-responsive sensing film

This study describes an electrochemical sensor for the animal growth promoter ractopamine. The method is based on the use of a glassy carbon electrode (GCE) modified with a temperature-responsive sensing film composed of reduced graphene oxide, C₆₀ fullerene, and the temperature-sensitive polymer poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO₂MA). The modified GCE was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. A large oxidation peak current can be observed (maximum typically at 0.57 V vs. Ag/AgCl) when the temperature is raised to above the lower critical solution temperature of PMEO₂MA. This peak disappears at lower temperature. Under optimum conditions, the sensor has a detection range for ractopamine from 0.1 to 3.1 μM, with an 82 nM detection limit. The method was successfully applied to the determination of ractopamine in spiked pork samples.

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Graphical abstract Schematic presentation of the reversible, temperature-controlled “on/off” electrochemical behavior of ractopamine at a glassy carbon electrode modified with a film composed of reduced graphene oxide (rGO), C₆₀ fullerene and the poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA).

     

Determination of arsenic in mussels by slurry sampling and electrothermal atomic absorption spectrometry (ETAAS)

A method for the determination of arsenic in slurries of mussel tissue using palladium-magnesium nitrate as modifier was optimized. The slurry was stabilized by a 0.015% (v/v) of Triton X-100. To achieve complete mineralization the slurries were ashed at 480 °C for 10s in an air flow (50 ml/min) and at 1200 °C for 15s in an argon flow (300 ml/min) in the presence of Pd—Mg(NO₃)₂ as modifier. The optimum atomization temperature was 2200 °C. The precision and accuracy of the method were studied using the Reference Material BCR n ° 278 Mussel Tissue (Mytilus edulis). The detection limit (LOD) of the final slurry solution was 1 g/l of arsenic corresponding to an arsenic level in the mussel of 1.3 g/g, for a 0.5% (m/v) slurry. Results of calibration using aqueous standards and the standard additions method were compared. The method was applied to the determination of arsenic in mussels from the Galician coast. The levels found lie between 2 and 9.3 g/g of arsenic.     

Characterization of solute-membrane interactions by TMA-measurements

On the basis of relationships derived by Oplatka et al. [1] correlating the derivative of tensile stress with respect to temperature for a polymer strip at constant length, (/T) _t , with the derivative of entropy with respect to strip length, (S/l)_T, relationships are derived relating the derivation of strip length with respect to temperature under constant tensile stress, (l/T), with the derivative of entropy with respect to tensile load, (S/) _T . The developed relationships are applied to evaluate TMA (thermomechanical analysis) measurements performed with asymmetric and homogeneous cellulose acetate membranes where the membrane strips were kept in deionized water. Moreover, TMA measurements were performed with homogeneous CA membranes while maintaining the membrane strips in bathing solutions of different, but in each instance, constant electrolyte concentrationc _s (e.g., LiCl, LiNO₃, Li₂SO₄, CaCl₂; 0 c _s saturation). Under constant tensile stress, , as-cast asymmetric CA membranes, which are kept in deionized water, first elongate with increasing temperature at temperatures up to about 50°C. However, they shrink with a further increase of temperature in the temperature range 50°C up to about 90°C, whereas creeping starts at temperatures beyond 90°C, leading again to an elongation of the strip with a further increase of temperature. The negative apparent coefficient of thermal expansion, existing between 50° to 90°C, is consistent with shrinking phenomena observed with asymmetric CA membranes [2]. In addition, it correlates well with both an entropy decrease with increasing tensile stress at constant strip length and an entropy increase with decreasing strip length at constant tensile stress. Contraction of the strip with increasing temperature at constant tensile load might be due to increasing coil formation of polymer molecules rendered possible by disintegration of joints such as H-bonds between polymer chains. Depending on the electrolyte of the bathing solution and its concentration, homogeneous CA membranes exhibit positive and negative apparent linear coefficients of thermal expansion under constant tensile stress.     

Gas Chromatographic Determination of Sulfur Mustard and Lewisite in Community Air

A gas chromatographic procedure is developed for the determination of ,-dichlorodiethylsulfide (yperite, sulfur mustard) and -chlorovinyldichloroarsine (lewisite) in the working area and community air at a level defined by the hygienic regulations for community air (2 × 10^–6 and 4 × 10^–6 mg/m³ for sulfur mustard and lewisite, respectively) and at the maximum permissible level for a working area (2 × 10^–4 mg/m³). The procedure for the determination of sulfur mustard is based on the trapping of the analyte from air with Silochrom S-120 impregnated with Apiezon L with further extraction by a 1 : 1 acetone–hexane mixture, the evaporation of the extract to a small residual volume, and chromatography with an electron capture detector. The procedure for the determination of -chlorovinyldichloroarsine (lewisite) involves the absorption of the analyte with a 2.2% solution of triethanolamine in 0.1 M hydrochloric acid, the conversion of lewisite to acetylene by treating the trap contents with 30% alkali solution, and the chromatography of the vapor phase using a flame ionization detector. The error of the determination is no more than ±23 rel %. The analysis takes 1.5 h.     

A rechargeable molecular solar thermal system below 0 °C

An optimal temperature is crucial for a broad range of applications, from chemical transformations, electronics, and human comfort, to energy production and our whole planet. Photochemical molecular thermal energy storage systems coupled with phase change behavior (MOST-PCMs) offer unique opportunities to capture energy and regulate temperature. Here, we demonstrate how a series of visible-light-responsive azopyrazoles couple MOST and PCMs to provide energy capture and release below 0 °C. The system is charged by blue light at −1 °C, and discharges energy in the form of heat under green light irradiation. High energy density (0.25 MJ kg⁻¹) is realized through co-harvesting visible-light energy and thermal energy from the environment through phase transitions. Coatings on glass with photo-controlled transparency are prepared as a demonstration of thermal regulation. The temperature difference between the coatings and the ice cold surroundings is up to 22.7 °C during the discharging process. This study illustrates molecular design principles that pave the way for MOST-PCMs that can store natural sunlight energy and ambient heat over a wide temperature range.

We demonstrate rationally designed arylazopyrazoles as MOST-PCM that can be circularly charged and discharged below 0 °C with visible light.     

Temperature sensitive molecularly imprinted microspheres for solid-phase dispersion extraction of malachite green,crystal violet and their leuko metabolites

This article demonstrates the feasibility of an alternative strategy for producing temperature sensitive molecularly imprinted microspheres (MIMs) for solid-phase dispersion extraction of malachite green, crystal violet and their leuko metabolites. Thermo-sensitive MIMs can change their structure following temperature stimulation. This allows capture and release of target molecules to be controlled by temperature. The fabrication technique provides surface molecular imprinting in acetonitrile using vinyl modified silica microspheres as solid supports, methacrylic acid and N-isopropyl acrylamide as the functional monomers, ethyleneglycol dimethacrylate as the cross-linker, and malachite green as the template. After elution of the template, the MIMs can be used for fairly group-selective solid phase dispersion extraction of malachite green, crystal violet, leucomalachite green, and leucocrystal violet from homogenized fish samples at a certain temperature. Following centrifugal separation of the microspheres, the analytes were eluted with a 95:5 mixture of acetonitrile and formic acid, and then quantified by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) with isotope internal calibration. The detection limits for malachite green, crystal violet and their metabolites typically are 30 ng·kg^?1. Positive samples were identified by UHPLC-MS/MS in the positive ionization mode with multiple reaction monitoring. The method was applied to the determination of the dyes and the respective leuko dyes in fish samples, and accuracy and precision were validated by comparative analysis of the samples by using aluminum neutral columns.

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Graphical abstract We describe an alternative strategy for producing temperature sensitive molecularly imprinted microspheres for solid-phase dispersion extraction of malachite green, crystal violet and their metabolites in fish samples.

     

NiO-CaO materials as promising catalysts for hydrogen production through carbon dioxide capture and subsequent dry methane reforming

In this work, CaO-NiO mixed oxide powders were evaluated as consecutive CO_2 chemisorbents and catalytic materials for hydrogen production thought the CH_4 reforming process. Between the NiO impregnated CaO and CaO-NiO mechanical composite, the first one presented better chemical behaviors during the CO_2 capture and CH_4 reforming processes, obtaining syngas(H_2+ CO) as final product. Results showed that syngas was produced at two different temperature ranges, between 400 and 600 °C and at T 800 °C, where the first temperature range corresponds to the CH_4 reforming process but the second temperature range was attributed to a different catalytic reaction process: CH_4 partial oxidation. These results were confirmed through different isothermal and cyclic experiments as well as by XRD analysis of the final catalytic products, where the nickel reduction was evidenced. Moreover, when a CO-O_2 flow was used during the carbonation process a triple process was achieved:(i) CO oxidation,(ii) CO_2 chemisorption and(iii) CH_4 reforming. Using this gas flow the hydrogen production was always higher than that obtained with CO_2.     

Upconversion luminescence assay for the detection of the vascular endothelial growth factor,a biomarker for breast cancer

Upconversion nanoparticles (UCNPs) of the type α-NaYF₄:Yb³⁺, Er³⁺ and a typical diameter of 6–7 nm were synthesized by thermal decomposition of the respective rare-earth stearate. The oleic acid on the surface of the UCNPs was then replaced by aptamer DNA. The assay was performed in a microplate format with a capture probe immobilized in the wells. Following binding of the vascular endothelial growth factor (VEGF), an auxiliary probe DNA is added that is labeled with UCNPs and binds to the VEGF-loaded capture probe. The method enables highly sensitive and highly specific detection of the VEGF which is a marker for breast cancer. Under the optimum conditions, the intensity of the upconversion luminescence (at excitation/emission wavelengths of 980/541 nm) is linearly proportional to the VEGF concentration in the 50 pM to 2000 pM concentration range, with a 6 pM detection limit. The method was applied to the determination of VEGF in spiked serum, typically at a 500 pM level, and gave recoveries that ranged from 98 to 113 %, with RSDs between 2.9 and 3.6 %. This makes it a viable tool for early diagnosis of breast cancer.

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Graphical abstract An upconversion luminescence based assay is presented for trace analysis of vascular endothelial growth factor. It is based on a sequence fragment-linked technique of target-induced aptamer (AP) and upconversion nanoparticles (UCNPs) and has potential application in the early diagnosis of breast cancer.

     

Synthesis and Characterization of Functional Thienyl‐Phosphine Microporous Polymers for Carbon Dioxide Capture

A novel kind of functional organic microporous polymer is designed by introducing polar organic groups (P=O and P=S) and electron‐rich heterocyclic into the framework to obtain high carbon dioxide capture capacity. The estimated Brunauer–Emmett–Teller (BET) surface areas of these polymers are about 600 m² g⁻¹ and the highest CO₂ uptake is 2.26 mmol g⁻¹ (1.0 bar/273 K). Interestingly, the polymer containing P=O groups shows greater CO₂ capture capacity than that containing P=S groups at the same temperature. In addition, these polymers show high isosteric heats of CO₂ adsorption (28.6 kJ mol⁻¹), which can be competitive with some nitrogen‐rich networks. Therefore, these microporous polymers are promising candidates for carbon dioxide capture.

     

Fluorescent aptasensor for adenosine based on the use of quaternary CuInZnS quantum dots and gold nanoparticles

The authors describe a fluorescence based aptasensor for adenosine (AD), a conceivable biomarker for cancer. The assay is based on the immobilization of capture DNA on newly synthesized quaternary CuInZnS quantum dots (QDs) and the conjugation of probe DNA on gold nanoparticles (AuNPs). The capture DNA is an adenosine-specific aptamer that is partly complementary to the probe DNA. Once the capture aptamer hybridizes probe DNA, the fluorescence of the QDs (measured at excitation/emission wavelengths of 522/650 nm) is quenched by the AuNPs. However, when AD is added, it will bind to the aptamer and restrain the hybridization between capture DNA and probe DNA. Therefore, the fluorescence of the QDs will increase with increasing AD concentration. Under optimal conditions, fluorescence is linearly related to the AD concentration in the range from 50 to 400 μM, the detection limit being 1.1 μM. This assay is sensitive, selective, reproducible and acceptably stable. It was applied to the determination of AD in spiked human serum samples where it gave satisfactory results.

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Graphical abstract Aptamer based fluorescent assay of adenosine using quaternary CuInZnS quantum dots and gold nanoparticles

     

SERS based monitoring of toluene vapors at ambient and elevated temperatures by using a ruffled silver nanolayer as a substrate

The authors describe a Surface enhanced Raman spectroscopy (SERS)-based method for the detection of gaseous toluene at different temperature regimes using 3D ruffled silver SERS substrates and a commercially available handheld Raman system equipped with a 785 nm laser. The 3D silver SERS substrates were synthesized via electroless deposition of silver on the ruffled sandpaper and HF-etched silicon wafers. The morphological characterization of the silver SERS substrates was carried out by atomic force microscopy and scanning electron microscopy. UV-Vis spectroscopy absorption spectra of the silver nanostructures showed plasmonic peaks at 522 nm and 731 nm. Toluene vapors were collected with a syringe at ambient temperature and at 100 °C, while SERS detection was always performed at room temperature. Toluene detection was based on the measurement of the Raman bands at 787 cm^?1 and 1003 cm^?1 (in the fingerprint region). The method allow gaseous toluene to be detected at its vapor concentrations of 522 ppm (mg/L), 261 ppm (mg/L) and 26 ppm (mg/L).

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Graphical abstract Schematic presentation of an original method for the detection of toluene vapors by SERS technique. The collection of toluene vapors was carried out at room and at high temperatures. The vapors were transferred to methanol by bubbling. The SERS measurements were carried out at room temperature.

     

Separation of nitrophenols by capillary zone electrophoresis

Separation conditions suitable to a rapid resolution of a group of eight nitrophenols by capillary zone electrophoresis (CZE) were found. Required differences in their effective mobilities were achieved via host-guest complexation of -cyclodextrin combined with intermolecular interactions involved by polyvinylpyrrolidone. When both additives were present in the carrier electrolyte at pH=9.1 nitrophenols could be separated in the column of a, 300 m I.D. and 180 mm in the length within 8–9 minutes. It is shown that the column of such an I.D. providing enhanced sample load capacity, can operate with high separation efficiencies as maintaining zone dispersions due to Joule heating on a tolerable level. CZE on-line coupled with isotachophoretic sample pretreatment is shown to provide the concentration limits of detection at low ppb concentrations by using an on-column photometric detector operating at 254 and 405 nm detection wavelengths.     

SERS based aptasensor for ochratoxin A by combining Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Au magnetic nanoparticles and Au-DTNB@Ag nanoprobes with multiple signal enhancement

A SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe₃O₄@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm^?1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe₃O₄@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL^?1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee.

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Graphical abstract Schematic of an aptamer based SERS assay for OTA by integrating Fe₃O₄@AuNPs (MGNPs) with Au-DTNB@Ag NPs with multiple signal enhancement. Aptamer modified Au-DTNB@Ag NPs are used as Raman probes, and MGNPs modified with cDNA are used as capture probes and reinforced substrates.

     

Synthesis and Characterization of Nano-Crystalline Fluorine-Doped Tin Oxide Thin Films by Sol-Gel Method

Thin films of fluorine-doped tin-oxide (FTO) were prepared by sol-gel dip-coating technique. Stannous chloride (SnCl₂2H₂O) and hydrogen fluoride (HF) were mixed with isopropyl alcohol to serve as source solution. X-ray diffraction (XRD) spectrum showed all the peaks of the crystalline SnO₂. Analysis of XRD spectrum showed the particle size to be nearly 6 nm, which indicated the nanocrystalline structure of the films. Strain calculation by integral breadth (IB) method from XRD data showed a value of 0.010. UV-Visible spectrophotometric measurement showed high transparency of the films in the visible region and the band gap was calculated to be 3.34 eV. The room temperature resistivity of the films were of the order of 1 cm. Fluorine concentration in the films was determined from energy dispersive X-ray (EDX) study. Current-voltage (I-V) characteristics at high temperatures showed the Poole-Frenkel effect of thermionic emission. SEM study indicated the existence of fine grains in the film. FT-IR spectroscopy showed strong Sn—O and Sn—O—Sn bonding.     

Modification of Non-Hydrolytic Sol-Gel Derived Alumina by Solvent Treatments

The effect of wetting non-hydrolytic derived alumina xerogels with water and organic solvents in the 20–70°C range on the alumina's properties was investigated. Wetting with organic solvents does not affect the alumina. However, contact with water was found to change the sharp crystallization at 800°C to a continuous crystallization starting at 450°C. Water treatment for a day at room temperature (RT) followed by second calcination decreased the surface area by 10%. This decrease in surface area is less pronounced with increasing wetting periods. On the other hand water treatment at 50–70°C followed by a second calcination resulted in a surface area increase of up to 15%. Upon water treatment the total pore volume has decreased from 0.65 (cm³/gr) to 0.48 (cm³/gr) and the average pore size decreased from 6.8 nm to 4.1 nm. The Cl content was found to be uneffected by the water treatment, remaining at 2.5% wt. Wetting with water at elevated temperature (70°C) accelerated the morphological changes, eliminating the crystallization peak at 800°C in one hour. A dissolution-reprecipitation mechanism is suggested to explain the results. In addition, Mass-Spectroscopy of the effluent gas during heat treatment revealed the emission of CO₂ and water upon phase transition into -Al₂O₃, at 1150–1300°C.     

Sound absorption studies of ternary systems

The peak sound absorption region of ternary systems of water-2-propanolurea, water-2-propanol-tetraethylammonium bromide, water-2-propanol-1,10-bis(triethylammonium)decane dibromide, and the binary system water-2-propanol has been studied at 10, 30, and 50 MHz, and in the temperature range 1.4 to 35°C. The results from the binary system show that the peak sound absorption composition (PSAC) is shifted to higher alcohol composition and (/f ²)_max decreases with increasing temperature. At constant frequency, increased urea concentration has the same effect on PSAC and (/f ²)_max values as does an increase in temperature for the binary system. All salts decrease /f ² values at low concentrations but differ remarkably at higher concentrations. The results are interpreted qualitatively as showing the excess sound absorption in the PSAC region to be intimately related to the structural characteristics of water.