DTA and TG analysis of heteropolyacids of the series H(3+x)PMo(12−x)VxO40·nH2O

DTA, TG and DTG of molybdovanadophosphoric acids of the series H_(3+x)Mo_(12–x)V_xO₄₀· nH₂O (x=0, 1, 2, 3) were carried out. The samples with the highest content of water of crystallization (n=19–34) fuse above 40 °C, giving solutions of heteropolyacids which boil at 110 to 130 °C. The total loss of crystallization water occurs below 170–200 °C. The anhydrous acids decompose (dehydroxylation) at temperatures decreasing from the average value of 433 °C forx=0 to about 293 °C forx=3. For these vanadium-containing samples, an exothermic peak not accompanied by weight change appears at about 450, 430 and 390 °C forx=1,2 and 3, respectively, indicating a transformation in the solid state. Ifx=0, a weaker endothermic effect of dehydroxylation overlaps with a stronger exothermic effect, and only one exothermic effect exists, at 435 °C.

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Zusammenfassung An Molybdovanadophosphorsäuren der Formel H_(3+x)Mo_(12–x)V_xO₄₀· H₂O (x=0, 1, 2, 3) wurden DTA-, TG- und DTG-Untersuchungen durchgeführt. Die Proben mit dem größten Kristallwassergehalt (n=19–34) schmelzen oberhalb 40 °C und liefern damit Lösungen von Heteropolysäuren mit einem Siedepunkt zwischen 110 und 130 °C. Der vollständige Verlust des Kristallwassers erfolgt unterhalb 170–200 °C. Die wasserfreien Säuren zersetzen sich (Dehydroxylierung) bei Temperaturen mit einem Durchschnittswert von 433 °C fürx=0 bis herab zu 293 °C fürx=3. Bei diesen vanadiumhaltigen Proben tritt fürx=1, 2 und 3 bei den Temperaturen 450, 430 und 390 °C ein exothermer Peak auf, der von keinem Gewichtsverlust begleitet wird und somit auf eine Strukturänderung des festen Zustandes hinweist. Beix=0 wird ein stärkerer exothermer Effekt von einem schwächeren endothermen überlagert und es existiert bei 435 °C nur ein exothermer Effekt.

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, H_3+xMo_12–xV_xO₄₀·nH₂O, x=, 1, 2, 3. (n=19–34) 40°, 110–130°. ( ) 433° =0 293° =3. , , , 340,430 390° x=1,2,3, , . x=0 , 435°.

     

Synthesis of thiazolines by the reaction of aryl ketonitriles with cysteamine via microwave irradiation

Thiazolines were synthesized in a one‐pot reaction in excellent yield using a newly developed methodology. Ketonitriles were directly condensed with cysteamine (2‐amino‐thioalcohol) via microwave irradiation at 210°C for 10 minutes under solvent free conditions and without any solid support. All the compounds were characterized by ¹H nmr, ¹³C nmr spectroscopy and elemental analyses.     

Low-frequency modes of the benzoic acid dimer in chloroform observed by the optical Kerr effect

The low frequency Raman spectral density associated with the intermolecular hydrogen-bonding interaction of benzoic acid in chloroform was investigated through the ultrafast optically-heterodyne-detected optical Kerr effect. The low-frequency solute Raman spectrum was obtained by Fourier transform analysis and subtraction of the solvent spectrum from the solution spectrum. The resulting difference spectrum has a broad band below 150 cm(-1) with a peak at around 80 cm(-1). Previous studies of aromatic liquids suggest that the origin of such a low-frequency band is librational motion, although intermolecular hydrogen-bonding modes in benzoic acid may also contribute. To clarify these contributions to the low-frequency band, methyl benzoate was used to estimate the librational component; its structure is similar to benzoic acid, but it forms no intermolecular hydrogen bonds. Both librational and intermolecular modes were found to contribute to the low-frequency Raman spectrum of the dimer and thus can be separated. These experimental results were compared with the results of density functional theory calculations. In addition, the effect of deuteration on the Raman spectrum was also investigated.     

Simplified and rapid determination of polychlorinated biphenyls, polybrominated diphenyl ethers, and polycyclic aromatic hydrocarbons in fish and shrimps integrated into a single method

In this study, a new rapid and flexible method for the simultaneous determination of 18 key representatives of polychlorinated biphenyls (PCBs), 7 polybrominated diphenyl ethers (PBDEs), and 32 polycyclic aromatic hydrocarbons (PAHs) in fish and shrimps by gas chromatography coupled to mass spectrometry (GC-MS) was developed and validated. A substantial simplification of sample processing prior to quantification step was achieved: after addition of water to homogenized sample, transfer of hydrophobic analytes into ethyl acetate was supported by added inorganic salts. Bulk fat, contained in crude organic extract obtained by partition, was subsequently removed on a silica minicolumn. This approach enabled to process six samples in less than 1h; moreover, the volume of an extraction solvent and consumption of other chemicals can be significantly reduced compared to, e.g., traditional Soxhlet extraction followed by gel permeation chromatography. The recoveries of target analytes were in the range of 73-120% even at the lowest spiking level (1 μg kg(-1)), repeatabilities (relative standard deviations, RSDs) ranged from 1 to 20%. Under optimized GC-MS conditions (time-of-flight mass analyzer, TOF), the limits of quantification (LOQs) were as follows: PCBs 0.1-0.5 μg kg(-1), PBDEs 0.5 μg kg(-1), and PAHs 0.05-0.25 μg kg(-1). Ambient mass spectrometry employing a direct analysis in real time (DART) ion source was shown as an effective tool for fat control in extract, which is needed during the method development and examination of unknown samples prior to the analysis. Further extension of a method scope by other similar analytes is easily possible.     

Monitoring of dopamine and its metabolites in brain microdialysates: method combining freeze-drying with liquid chromatography-tandem mass spectrometry

A sensitive assay method was developed for a parallel, rapid and precise determination of dopamine and its metabolites, homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid, from brain microdialysates. The method consisted of a pre-treatment step, freeze-drying (lyophilization), to concentrate dopamine and its metabolites from the microdialysates, and a detection step using liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). In particular, the reaction monitoring mode was selected for its extremely high degree of selectivity and the stable-isotope-dilution assay for its high precision of quantification. The developed method was characterized by the following parameters: the precision of the developed method was determined as ≥88.6% for dopamine, ≥89.9% for homovanillic acid, ≥86.1% for 3-methoxytyramine and ≥88.1% for 3,4-dihydroxyphenylacetic acid; the mean accuracy was determined as ≥88.2% for dopamine, ≥88.3% for homovanillic acid, ≥85.9% for 3-methoxytyramine and ≥88.6% for 3,4-dihydroxyphenylacetic acid. The developed method was compared to (1) other combinations of pre-treatment methods (solid phase extraction and nitrogen stripping) with LC-MS and (2) another detection method, liquid chromatography, with electrochemical detection. The novel developed method using combination of lyophilization with LC-ESI-MS/MS was tested on real samples obtained from the nucleus accumbens of rat pups after an acute methamphetamine administration. It was proven that the developed assay could be applied to both a simultaneous analysis of all four substrates (dopamine, homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) in microdialysis samples acquired from the rat brain and the monitoring of their slight concentration changes on a picogram level over time following methamphetamine stimulus.     

CdS nanoparticles deposited on montmorillonite: preparation, characterization and application for photoreduction of carbon dioxide

CdS nanoparticles were precipitated by the reaction of cadmium acetate with sodium sulphide in the presence of cetyltrimethylammonium (CTA) and deposited on montmorillonite (MMT). The resulting CdS-MMT nanocomposite contained 6 wt.% of CdS and 30 wt.% of CTA. Band-gap energy of CdS was estimated at 2.63±0.09 eV using the Tauc plot. The size of CdS nanoparticles was calculated from the band-gap energy at 5 nm and from the micrographs of transmission electron microscopy (TEM) at 5 nm. Selected area electron diffraction (SAED) recognized the cubic structure of CdS (Hawleite). The dynamic light scattering (DLS) method confirmed that CdS nanoparticles were anchored on the surface of MMT particles. CTA was found to be intercalated into MMT and adsorbed on its external surface. CdS-MMT was used for the photoreduction of carbon dioxide dissolved in NaOH solutions. The yields of originating gas products can be arranged in the order: H(2) ? CH(4) > CO. Amounts of these products were 4-8 folds higher then those obtained with TiO(2) Evonic P25. Hydrogen reduced CO(2) to CO and CH(4).     

The study of properties of HPLC determination of polycyclic aromatic nitrogen heterocycles

The study of the separation of polycyclic aromatic nitrogen heterocycles (PANHs) by reverse-phase liquid chromatography with an octadecyl stationary phase is presented. The retention behaviour of a mixture of PANHs was studied under different chromatographic conditions. A mixture of phosphate buffer/acetonitrile was used as mobile phase in isocratic and gradient modes. The effect of different pH mobile phase in the range from 2.5 to 6.5 has been investigated to describe retention changes of PANHs as a function of their acid/base properties. Different concentrations of phosphate buffer as a component of the mobile phase were used to study the effect of ionic strength. Very good RP-HPLC separation of 24 PANHs and 16 EPA polycyclic aromatic hydrocarbons (PAHs) was obtained without a pre-separation step in a test mixture and the extract of a real soil sample. Limits of detection of PANHs obtained by two detection techniques, ultraviolet-diode array detection (UV-DAD) and fluorescence detector (FD), are compared. The proposed method is tested with a real soil sample.     

Rapid and simple method for determination of hexabromocyclododecanes and other LC–MS–MS-amenable brominated flame retardants in fish

In this study, a novel analytical approach for simultaneous determination of hexabromocyclododecane isomers (HBCDs), tetrabromobisphenol A (TBBPA), three brominated phenols, and four hydroxylated derivatives of polybrominated diphenyl ethers (OH-PBDEs) was developed and validated for muscle tissue of both lean and fatty fish. The rapid, simple, and high-throughput sample-preparation procedure was based on acetonitrile extraction then purification by dispersive solid-phase extraction (d-SPE) with a combination of C₁₈ and primary–secondary amine (PSA) sorbents. Ultra-high performance liquid chromatography (UHPLC) coupled to tandem mass spectrometry (MS–MS) was used for identification and quantification of the analytes. Method recovery for both matrices ranged from 80 to 115 % with relative standard deviations (RSDs) <13 % for all analytes. Limits of quantification (LOQs) were in the range 0.1–1 μg kg^?1 wet weight. The validated method was used for analysis of brominated compounds in 32 fish and five bivalve samples collected from different European markets within the monitoring survey organized in the framework of the CONffIDENCE project. Of the 12 targeted analytes, only α-HBCD, 2,4-dibromophenol (2,4-DBP), and 2,4,6-tribromophenol (2,4,6-TBP) were quantified in the samples. α-HBCD was found in six fish samples (herring and mackerel) in the range of 0.8–2.5 μg kg^?1 wet weight. 2,4-DBP and 2,4,6-TBP were found in three blue mussel samples in the range of 19.6–43.5 and 2.3–7.5 μg kg^?1 wet weight, respectively.     

Phase transitions of octamethylcyclotetrasiloxane confined inside aluminosilicate and silicate nanoporous matrices

We report the melting behaviour of a dipolar cyclic siloxane liquid: octamethylcyclotetrasiloxane (OMCTS) confined in three mesoporous silica matrices: Al-SBA-15, SBA-15 and CPG glasses, using differential scanning calorimetry and dielectric spectroscopy. We investigate the influence of acid sites on the adsorptive properties of mesoporous silica materials, which were synthesized by applying Pluronic-type polymers as pore-creating agents. Aluminosilicate matrices have been synthesized by direct synthesis procedure using aluminium chloride. These materials characterized by N₂ sorption measurements, and the small-angle X-ray scattering data exhibit the same hexagonal P6 mm structure with a mean mesopores size of 4.6 nm (Al-SBA-15) and 4.9 nm (SBA-15). The controlled pore glasses used in this experiment have pores of mean diameter of 7.5 nm. For all systems studied, the OMCTS melting point in pores has been found to decrease with decreasing pore diameter. This result is in qualitative agreement with that obtained in molecular simulation where the adsorbate-wall interactions are weak compared to the adsorbate–adsorbate interactions.     

Evaluation of the lipophilicity of selected sunscreens—A chemometric analysis of thin‐layer chromatographic retention data

The lipophilicities of 22 selected sunscreens, preservatives, and vitamins used in topical skin products were measured by thin‐layer chromatography. Lipophilicity was calculated in silico from the sunscreen molecular structures and compared to the experimental octanol/water partition coefficients found in the literature. The retention of the compounds was investigated on an RP‐18 stationary phase with mobile phases consisting of water and one of six organic modifiers (dioxane, tetrahydrofuran, acetone, acetonitrile, methanol, and dimethylformamide) at different concentrations. The theoretical lipophilicities were calculated by several computational algorithms and the results of these calculations were compared using cluster analysis. The results showed that two out of the six investigated organic modifiers (dioxane and acetone) may be used to estimate the octanol/water partition coefficients of highly lipophilic compounds having lipophilicities that cannot be measured directly by the shake‐flask method.