Solubilities of cinnamic acid esters in binary mixtures of ionic liquids and organic solvents

The solubilities of three cinnamic acid esters, namely, methyl ferulate, methyl p-coumarate, and methyl sinapate, have been measured in mixed solvent systems of tert-butanol with 1-butyl-3-methyl-imidazolium hexafluorophosphate ([BMIM][PF₆]), 1-butyl-3-methyl-imidazolium tetrafluoroborate ([BMIM][BF₄]) and 1-methyl-3-octyl-imidazolium tetrafluoroborate ([OMIM][BF₄]) at 303.15 and 321.15 K, and in mixed solvent systems of ethyl acetate with [BMIM][BF₄] and [OMIM][BF₄] at 303.15 K. In eight cases, out of the 22 data sets, an additive behaviour of the solubility was observed, positive deviations from additivity were observed in six cases, a positive synergistic effect in five cases, and, finally, negative deviations from additivity in the remaining three cases. Prediction of the solubilities of the solutes in the various ternary systems was performed with the NRTL and UNIQUAC activity coefficient models. The binary interaction parameters of the models between solute and solvent molecules were taken from the literature. When the parameters between the solvent molecules are fitted to literature data, satisfactory predictions are not always obtained. On the other hand, very good predictions are obtained when only one of the two interaction parameters between the two solvent molecules is fitted to one single point of the solubility isotherm and the other interaction parameter is set equal to zero.     

Dynamic in situ spectroscopic ellipsometry of the reaction of aqueous iron(II) with 2,2'-bipyridine in a thin Nafion film

Dynamic in situ spectroscopic ellipsometry studies of the chemical reaction between ferrous ion and 2,2'-bipyridine (bpy) in a thin Nafion film are presented. A simple prototype system composed of a thin Nafion film on a glass substrate was used throughout the work. The reaction was detected by optically monitoring the formation of the strongly absorbing complex ion, Fe(bpy)3(2+) (epsilon 520 = 7.70 x 10(3) M(-1) cm(-1) in 0.1 M NaCl). The changes in film optical constants, n and k, and the thickness upon exposure of it to various solutions were monitored in a flow cell with the film on the backside of the substrate relative to the interrogation by light. A "step-by-step" approach was used to isolate the component parts of the system in which the film was consecutively exposed to solutions in the following order: supporting electrolyte, bpy, and, last, ferrous iron solution. The optical properties of the materials were quantitatively described before and during mass transport within the film by modeling using the appropriate multilayer optical models, i.e., the Cauchy equation for nonabsorbing media and the Urbach and Tauc-Lorentz (oscillator) functions for a film that absorbed. The experiments done allowed study of the diffusion in the film and the chemical reactions that are important in the sensing scheme for ferrous iron. Ligand (bpy) diffusion followed a two-stage diffusion mechanism described by a Berens-Hopfenberg model for incremental sorption (D25 = 7.04 x 10(-13) cm2 s(-1)). The stabilities of the appropriate systems, i.e., Nafion film with bpy, iron, and iron complex, were studied by exposing equilibrated films to circulating supporting electrolyte solutions. The measurements gave important insights into a set of film chemical reactions and, in turn, selective film dynamics. This work exemplifies the usefulness of spectroscopic ellipsometry in monitoring the kinetics of a chemical reaction in situ, as well as the changes in the film physical properties under dynamic conditions.     

The nuclear spinspin coupling in the hydrogen molecule: its equilibrium value and bond-length dependence

Beckett and Carr's recent accurate measurements of nuclear spinspin coupling in HD gas over a wide range of temperature have been used to obtain the magnitude of the coupling at equilibrium and the bond length dependence of the coupling at equilibrium. The value of 40.62 ± 0.06 Hz for the coupling at equilibrium is significantly less than 42.94 ± 0.1 Hz which is the value measured in pure liquid HD. The coupling is very sensitive to bond length.     

Ultrasensitive Determination of Vitamin B12 Using Disposable Graphite Screen‐Printed Electrodes and Anodic Adsorptive Voltammetry

A facile, rapid and ultra‐sensitive method for the determination of vitamin B₁₂ (cyanocobalamin) at the sub‐nanomolar concentration range by using low‐cost, disposable graphite screen‐printed electrodes is described. The method is based on the cathodic preconcentration of square planar vitamin B_12s, as occurred due to the electro reduction of Co(III) center in vitamin B_12a to Co(I), at ?1.3 V versus Ag/AgCl/3 M KCl for 40 s. Then, an anodic square wave scan was applied and the height of the peak appeared at ca. ?0.73 V versus Ag/AgCl/3 M KCl, due to the oxidation of Co(I) to Co(II) in the adsorbed molecule, was related to the concentration of the vitamin B₁₂ in the sample. EDTA was found to serve as a key‐component of the electrolyte by eliminating the background signal caused by metal cations impurities contained in the electrolyte (0.1 M phosphate buffer in 0.1 M KCl, pH 3). It also blocks trace metals contained in real samples, thus eliminating their interference effect. The method was optimized to various working parameters and under the selected conditions the calibration curve was linear over the range 1×10^?10–8×10^?9 mol L^?1 vitamin B₁₂ (R²=0.994), while the limit of detection for a signal‐to‐noise ratio of 3 (7×10^?11 mol L^?1 vitamin B₁₂) is the lowest value of any reported in the literature for the electrochemical determination of vitamin B₁₂. The sensors were successfully applied to the determination of vitamin B₁₂ in pharmaceutical products.     

Phenolic profiles of Serbian autochthonous variety ‘Prokupac’ and monovarietal international wines from the Central Serbia wine region

Phenolic profiles of young monovarietal white and red wines from the Central Serbia were investigated. Quantification of phenolics was done using ultra-high-performance liquid chromatography (UHPLC) coupled with a diode array detector and a triple-quadrupole mass spectrometer. Generally, red wines were characterised with higher phenolics content when compared to the white wines. This applies also for the total phenolics content (TPC) and radical scavenging activity (RSA) values. Among all the samples, the red wine from autochthonous Serbian variety ‘Prokupac’ stood out with unique composition, showing the highest TPC, RSA and the highest concentration of the individual phenolics. Finally, based on a specific phenolic pattern, principal component analysis (PCA) indicated clustering of red and white wines, with the ‘Prokupac’ as a prominent outlier.     

Analysis of Tea for Metals by Flame and Graphite Furnace Atomic Absorption Spectrometry with Multivariate Analysis

The concentrations of iron, zinc, manganese, copper, chromium, nickel, lead, arsenic, and cadmium were determined using flame and graphite furnace atomic absorption spectrometry in nine herbal tea samples. Hawthorn, yarrow, elderflower, and bearberry are herbal teas for which the metal content has been rarely determined. The concentration of cadmium in St John’s wort exceeded the maximum permissible limit of 0.3?mg/kg. The metals were also determined in aqueous extracts following 5, 10, and 20?min of boiling and using different preparations, including acidification with lemon juice. The influence of these factors on metal release was demonstrated using multivariate analyses by redundancy analysis and principal component analysis. The metal release was not considerably affected by the boiling time, while the acidity of the medium was generally positively correlated. For the infusions, arsenic was detected only in acidified mint tea. The extraction efficiencies of metals were determined and classified as highly, moderately, and poorly extractable, with chromium showing largest variations.