Solid‐phase preconcentration and determination of mercury(II) using activated carbon in drinking water by X‐ray fluorescence spectrometry

A novel and simple method was developed for the preconcentration and determination of mercury(II) from hydrochloric acid solutions through their adsorption on Aliquat 336 (tri‐octylmethylammonium chloride)‐activated carbon. The determinations were made directly on the solid by X‐ray fluorescence spectrometry, which had the advantage of eliminating the step of elution of the mercury retained. This preconcentration system enabled the determination of Hg(II) in drinking water samples at µg l^?1 levels. A 1700‐fold enrichment factor was obtained. The described methodology showed excellent reproducibility, accuracy, and detection limits improvement by eliminating the step of elution of the analyte, replacing those methods based on cold vapor generation, reducing reagent consumption, and handling of samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of oxytetracycline in milk samples by polymer inclusion membrane separation coupled to high performance liquid chromatography

The determination of oxytetracycline in milk samples using a polymer inclusion membrane concept with high performance liquid chromatography (HPLC) was studied. The membranes developed are composed by cellulose acetate as polymer base, Cyanex 923 as carrier and o-nitrophenyl octyl ether as plasticizer. In the optimal conditions, the method exhibits good linearity in the range 0.03–0.20 mg L⁻¹ with a limit of detection and quantification of 8.2 and 27.3 μg L⁻¹ respectively. The method was successfully applied to the analysis of milk samples with high selectivity.     

Overall calibration procedure via a statistically based matrix-comprehensive approach in the stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry analysis of pesticide residues in fruit-based soft drinks

Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatography mass spectrometry (GC-MS) and the statistical variance component model (VCM) is applied to the determination of semi-volatile compounds including organochlorine and organophosphorus pesticides in various synthetic and real fruit-based soft drink matrices. When the matrix effects are corrected using isotopically labelled or non labelled internal standard, but matrix/calibration run-induced deviations are still present in the measurements, the adoption of a variance component model (VCM) in the quantitative analysis of various matrices via an overall calibration curve is successful. The method produces an overall calibration straight line for any analyte accounting for the uncertainty due to all the sources of uncertainty, namely matrix-induced deviations, calibration runs performed at different times, measurement errors. Small increases in the detection limits and in uncertainty in the concentration values obtained in the inverse regression face favourably the decrease in times and costs for routine analyses.     

Block copolymers in the synthesis of gold nanoparticles. Two new approaches: Copolymer aggregates as reductants and stabilizers and simultaneous formation of copolymer aggregates and gold nanoparticles

In this article, innovative applications of amphiphilic triblock and pentablock copolymers in the synthesis of gold nanoparticles are reported. The synthesis of gold nanoparticles is performed using two methods. In the first method, micellar aggregates of block copolymers and AuCl₄^? ions directly react in water; the nanoparticles obtained by this method are variable in size and are associated with copolymer aggregates. In the second method, two processes take place simultaneously: the aggregation of block copolymers and the reduction of Au (III) by the copolymers to form nanoparticles. In contrast with the first method, in this case, the nanoparticles obtained are located inside the copolymer aggregates. In both methods of synthesis, the block copolymers act simultaneously as reducing and stabilizing agents. To understand the role of copolymer aggregates in the synthesis of nanoparticles, molecular simulation methods are used. The gold nanoparticles, copolymer aggregates, and nanocomposite systems are characterized using transmission electron microscopy and dynamic light scattering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3069–3079     

Determining Contact Angles of Powders by Liquid Penetration

The wettability of a powder is important, especially in chemical and pharmaceutical technologies when considering the manufacturing process and the properties of the final product. However, contact angle methods for powders are problematic. The common measurement techniques are the sessile drop method and the liquid penetration method. In this work the determination of contact angles of powders by liquid penetration is considered. In particular, we investigated the influence of the sample preparation and sampling device on the wetting process. A bulk with constant properties during the measurement must be guaranteed. We postulate a packing procedure to obtain reproducible measurements by ensuring constant powder properties.     

Synthesis of (−)‐Isofagomine

Abstract

1,3‐Dipolar cycloaddition of N‐benzyl nitrone 2 to D‐threo δ‐lactone 15 proceeded with excellent stereoselectivity to provide only one adduct 16. Cycloadduct 16 was subsequently subjected to a sequence of reactions involving rearrangement to γ‐lactone, glycolic cleavage/reduction, protection of the terminal hydroxymethyl group, reduction of the lactone, desilylation/mesylation, and hydrogenolysis of the N‐O bond providing (?)‐isofagomine and its N‐substituted derivatives. The biologic activity of N‐substituted (?)‐isofagomines toward commercially available α‐ and β‐glucosidases, α‐D‐mannosidase, α‐L‐fucosidase, β‐D‐glucuronidase, and β‐D‐galactosidase was tested.     

The influence of structural changes of the N‐substituent on liquid crystalline behaviour of ester imides

Several new ester imide derivatives with different N‐substituents in the imide ring were synthesized and their mesogenic properties investigated by thermal analysis, optical microscopy and X‐ray diffraction. All the esters of N‐4‐[(4′‐decyloxybiphenyl‐4‐yl)oxycarbonyl]phthalimideacetic acid and aliphatic alcohols exhibited monolayer SmA and SmC phases. In addition, for the ethyl and propyl esters a monotropic hexatic (F or I) phase was observed. The introduction of additional substituents at the carbon atom in the methylenemethoxycarbonyl group (in the vicinity of the nitrogen atom) substantially influenced liquid crystalline properties: the compounds with a flexible chain exhibited monotropic SmA–SmB dimorphism, but liquid crystalline properties vanished for the substituent containing the more rigid phenyl ring.     

Computer modeling of synthesis of calcium hydroxyapatite (CHAp)

In our previous papers (Mackevi?ius et al. in Cent Eur J Chem 10(2):380–385, 2012, J Math Chem 50(8):2291–2302, 2012), we presented a method for estimation of the diffusion and reaction rates of synthesis at high temperatures using limited information, such as synthesis time and dimensions of reactants, from real laboratory experiments. The method was limited to the two-reactant case. In order to extend the method to the three-reactant case, the form and distribution of particles of three reactants must satisfy requirements of periodicity and symmetry. In our model, we achieve this by taking rhombic particles and a triangular synthesis space. Solving in the latter an inverse modeling problem, we obtain explicit formulas for the diffusion coefficient and reaction rate as functions of temperature by calculating the activation energies and other parameters of CHAp synthesis.     

Catalytic and stoichiometric reduction of ketones and aldehydes by the hydridotetracarbonyl ferrate anion

Acetone is catalytically reduced to isopropyl alcohol by carbon monoxide and water in the presence of iron carbonyls and triethylamine at 100°C and 100 bar. Use of NaOH in place of triethylamine gives a much less efficient catalyst system. The Et₃NH·HFe(CO)₄ system also catalyses the reduction of n-butyraldehyde to n-butyl alcohol at room temperature in a fast stoichiometric reaction, whereas NaHFe(CO)₄ is inactive under the same conditions. The Et₃NH⁺ cation is necessary for the transfer of a proton to the carbonyl group, while the HFe(CO)₄^? anion carries out nucleophilic attack on carbonyl group and supplies the hydride ion.