Rapid determination of pyridine derivatives by dispersive liquid–liquid microextraction coupled with gas chromatography/gas sensor based on nanostructured conducting polypyrrole

Polypyrrole (PPy) gas sensor has been prepared by polymerization of pyrrole on surfaces of commercial polymer fibers in the presence of an oxidizing agent. The sensing behavior of PPy gas sensor was investigated in the presence of pyridine derivatives. The resistive responses of the PPy gas sensor to pyridine derivatives were in the order of quinoline > pyridine > 4-methyl pyridine and 2-methyl pyridine. The PPy gas sensor was used as gas chromatography (GC) detector and exhibited linear responses to pyridine derivatives in the ranges 40–4000 ng. Dispersive liquid–liquid microextraction (DLLME) combined with GC/PPy gas sensor has been developed for simultaneous determination of pyridine derivatives and quinoline. The purposed method was used for determination of pyridine derivatives from cigarette smoke. The GC runs were completed in 4 min. The reproducibility of this method is suitable and good standard deviations were obtained. RSD value is less than 10% for all analytes.     

Headspace-solid phase microextraction of selenium(IV) from human blood and water samples using polypyrrole film and analysis with ion mobility spectrometry

The analysis of incurred material from animals treated with pharmacologically active substances is an efficient way to check the accuracy of a method. Tylosin A was chosen for the preparation of that material because it is highly effective in controlling active infections of American Foulbrood (AFB), a global threat to apiculture, but residues in honey are not allowed according to European legislation. For this reason an in-house reference material of honey containing the macrolide tylosin A and its degradation product desmycosin (tylosin B) was prepared. After the treatment of a beehive with the appropriate macrolide tylosin A, the honey samples were collected. The incurred honey material was diluted by mixing with blank honey. Concentrations of 25.81 μg kg(-1) for tylosin A and of 19.28 μg kg(-1) for its degradation product desmycosin (tylosin B) were reached. The homogeneity was checked by analysing 12 bottles in duplicate. The stability was tested at different defined temperatures and storage conditions. The reference material described above was homogeneous and stable. Samples of this in-house reference material were used for the realisation of a proficiency test with international participation. All participants accomplished satisfying results with the exception of one laboratory.     

A theoretical investigation of hydrogen bonding effects on oxygen and hydrogen chemical shielding tensors of aspirin

A computational investigation was carried out to characterize the ¹⁷O and ¹H chemical shielding (CS) tensors in crystalline aspirin. It was found that O–H⋯O and C–H⋯O hydrogen bonds around the aspirin molecule in the crystal lattice have a different influence on the calculated ¹⁷O and ¹H CS eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the BLYP, B3LYP, and M06 functionals employing 6-311++G(d,p) standard basis set. Calculated CS tensors were used to evaluate the ¹⁷O and ¹H chemical shift isotropy (δ_iso) and anisotropy (Δσ) in crystalline aspirin, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the CS tensors of each nucleus.     

Nontrivial tensile behavior of rutile TiO<Subscript>2</Subscript> nanowires: a molecular dynamics study

In this paper, we study the tensile behavior of cylindrical rutile TiO₂ nanowires, employing molecular dynamics (MD) simulation technique. The third-generation charge optimized many-body (COMB3) has been used for interatomic potential modeling. The influence of temperature and nanowire diameter on Young’s modulus is investigated. Our simulations exhibit the anisotropic behavior of Young’s modulus as a function of diameter for different crystallographic orientations. Although our results are in good accord with the existing results in [1 0 0] direction, Young’s modulus adds up monotonically with increasing the cross-sectional diameter of nanowire in [0 0 1] direction. It is found that Young’s modulus of the nanowires are lower (higher) than the bulk value for [0 0 1] ([1 0 0]) direction. Furthermore, simulation results also indicate that Young’s modulus of rutile TiO₂ nanowire increases as a function of temperature for a given diameter, unexpectedly. The obtained results may be useful in the field of nanotechnology for optimizing mechanical performance to gain specific applications.     

Effects of deformability of RBCs on their dynamics and blood flow passing through a stenosed microvessel: an immersed boundary-lattice Boltzmann approach

In this paper, the motion of high deformable (healthy) and low deformable (sick) red blood cells in a microvessel with and without stenosis is simulated using a combined lattice Boltzmann-immersed boundary method. The RBC is considered as neo-Hookean elastic membrane with bending resistance. The motion and deformation of the RBC under different values of the Reynolds number are evaluated. In addition, the variations of blood flow resistance and time-averaged pressure due to the motion and deformation of the RBC are assessed. It was found that a healthy RBC moves faster than a sick one. The apparent viscosity and blood flow resistance are greater for the case involving the sick RBC. Blood pressure at the presence of stenosis and low deformable RBC increases, which is thought of as the reason of many serious diseases including cardiovascular diseases. As the Re number increases, the RBC deforms further and moves easier and faster through the stenosis. The results of this study were compared to the available experimental and numerical results, and good agreements were observed.     

Copper(II)-selective membrane electrode based on a recently synthesized naphthol-derivative Schiff’s base

A PVC membrane electrode for copper(II) ions based on a recently synthesized naphthol-derivative Schiff’s base as membrane carrier was prepared. The sensor exhibits a Nernstian response for Cu²⁺ ions over a wide concentration range (5.0 × 10^–6–5.0 × 10^–2 mol/L) with a detection limit of 3.1 × 10^–6 mol/L (0.2 μg/mL). It has a very short response time of about 5 s and can be used for ¶3 months without any divergence in potential. The proposed electrode revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 4.0–7.0. It was successfully applied to the direct determination and potentiometric titration of copper ion.     

A Simple Method for Melatonin Determination in the Presence of High Levels of Tryptophan using an Unmodified Carbon Paste Electrode and Square Wave Anodic Stripping Voltammetry

Electrochemical determination of melatonin in the presence of tryptophan is a challenge because of the coincidence of voltammetric signals of these compounds when executing a voltammetric technique. The new method for selective determination of melatonin based on the square wave anodic stripping voltammetry determination of an electroactive product of melatonin was suggested here. This product is produced by previously applied positive pre-potential to a carbon paste electrode, immersed in the test solution. By this means, the electrochemical signal of melatonin was separated effectively from that of tryptophan, making it possible to determine melatonin in the presence of a high concentration of tryptophan. The effect of important parameters on electrode performance was studied and optimized. The optimum response was obtained at pH=2 and utilizing the pre-potential magnitude of +0.8 V, applied for 10 s. A linear relationship was found between peak current intensity and melatonin concentrations over the range of 5.00×10⁻⁷ to 8.00×10⁻⁵ mol L⁻¹. A detection limit of 8.30×10⁻⁸ mol L⁻¹ was calculated for the method (S/N=3). The selectivity of the method was considerably high, because of the independence of melatonin signal to the presence of higher amounts of some potentially interfering agents such as ascorbic acid, tryptophane glucose, etc. As an analytical application, the proposed sensor was used for the determination of melatonin in pharmaceutical and food samples.