Size effects under a strong magnetic field: Hall effect induced by electron-surface scattering on thin gold films deposited onto mica substrates under high vacuum

We report measurements of the Hall effect performed on 4 gold films evaporated onto mica substrates where the signal arises primarily from electron-surface scattering. The measurements were performed at low temperatures T (4 K < or = T < or = 50 K) under high magnetic field strengths B (1.5 T < or = B < or = 9 T), with B oriented perpendicular to the films.     

Electrochemical Portable Method for on site Screening of Scopolamine in Beverage and Urine Samples

Scopolamine (SCP) is a psychoactive drug often added to beverages for recreational or abuse purposes (loss of memory and non‐consensual practices). In this work, a simple and portable method for fast in field screening of SCP in beverage (beer, coke, energy drink, sugarcane spirit, vodka, and whisky) and urine samples is presented. The proposed method is based on batch injection analysis with square wave voltammetric (BIA‐SWV) detection using boron‐doped diamond (BDD) as the working electrode. A voltammetric profile with accurate information on the presence or absence of SCP is obtained using a small sample volume (～50 μL) and a simple sample pretreatment step (dilution in supporting electrolyte). Around two hundred analyses are possible using the proposed system (injection of single sample plug – 120 μL) without the need of electrodes handling or supporting electrolyte exchange (friendly to point‐of‐care or on site screenings). The quantification of SCP in beverages is also possible using the proposed portable protocol, with a limit of detection of 0.18 μmol L^?1 and recovery values between 87 to 113 %.     

Rapid method for simultaneous determination of ascorbic acid and zinc in effervescent tablets by capillary zone electrophoresis with contactless conductivity detection

Ascorbic acid and zinc are essential nutrients that play important roles in nutrition, immune support, and maintenance of health. For this reason, both compounds are widely used as ingredients in dietary supplements. We report, for the first time, an analytical method for fast simultaneous determination of ascorbic acid and zinc. A single analysis run is possible every 80 s (45 injections/h). The method is based on capillary electrophoresis with capacitively coupled contactless conductivity detection using a fused silica capillary with 50 cm length (effective length of 10 cm). The separation was achieved by using a background electrolyte composed by 30 mmol/L of 2‐(morpholin‐4‐yl)ethane‐1‐sulfonic acid and 30 mmol/L of histidine, pH 6.1. The detection limits were 10 and 20 μmol/L and recovery values for spiked samples were 101 and 100% for zinc and ascorbic acid, respectively. The results obtained with the developed procedure were compared to those obtained by titration (ascorbic acid) and flame atomic absorption spectroscopy (zinc), and no statistically significant differences were observed (95% confidence level).     

Etude des systemes ternaires: polymere-polymere-solvant. Application au systeme polystyrene-polydimethylsiloxane-benzene

The ternary system benzene-polydimethylsiloxane-polystyrene has been investigated by light scattering. Apparent molecular weight and solvation coefficient have been determined by applying the relations established for the ternary system of polymer in mixed solvents. The range of validity of these relations for our system has been discussed. We have also determined the χ₂₃ parameter (interaction between the both polymers), following the variations of apparent molecular weight or the compositions at the spinodal.     

Spirophosphoranes a liaison P-OH. Synthese,tautomerie

Spirophosphoranes with a P-OH bond have been prepared as free acid (compound 5c), triethylammonium salts (compounds 2c–6c), or adducts $\text{1}\text{1}$ with DMF (compounds 5c and 6c). The ionic feature of triethylammonium salts of compounds 1c–6c, shows that these Spirophosphoranes are relatively strong Brønsted's acids. Tautomeric equilibrium phosphoric ester—phosphorane with a P-OH bond [Scheme 9), shown in many cases, has been studied by means of ³¹PN, MRspectroscopy. Influence of factors ruling this equilibrium is analysed. Some elements of dynamic stereochemistry are examined.     

Tautomeric equilibrium of pyridoxine in water. Thermodynamic characterization by 13C and 15N nuclear magnetic resonance

A remarkable temperature dependence on the 13C NMR and 15N NMR chemical shifts of pyridoxine in water (pH = 7.0) has been observed. C-3, C-6, and N-1 were the most sensitive nuclei to the temperature effect. This dependence has been explained on the basis of an equilibrium shift thermally induced between the neutral and the dipolar form of this molecule. The thermodynamic characterization of tautomeric equilibria that interconvert quickly on the NMR time scale can be carried out from the observed average 13C NMR and 15N NMR chemical shifts at different temperatures (5-90 degrees C). We have developed a new method for the estimation of the thermodynamic parameters of a given equilibrium by fitting the experimental data to a theoretical curve. This new method allows us to improve the fitting results on our previously proposed methodology. We show that there are linear correlations between the average chemical shifts obtained from different nuclei at the same temperature. This indicates that the parameters of the pure forms are related among them. We have carried out a simultaneous multiple function curve fitting of all data obtained from the most sensitive signals together using these linear correlations as restricted conditions in order to diminish the number of independent parameters to fit. To test the new methodology, we have studied the thermodynamics of the tautomeric equilibrium of pyridoxine in water. We have obtained delta H degree values ranging from -23.6 +/- 1.3 to -25.8 +/- 1.7 kJ/mol for this equilibrium depending on the used data set. This kind of methodology has, among others, the following advantages: It allows the use of a great number of experimental points from different signals in the fitting process, it yields very precise and accurate values of the tautomeric process, and it allows the resolution of the problem with only 13C NMR data in some cases saving NMR time.     

Determination of Amlodipine and Atenolol by Batch Injection Analysis with Amperometric Detection on Boron‐doped Diamond Electrode

This work describes the sequential determination of amlodipine (AML) and atenolol (ATN) by batch injection analysis (BIA) with pulsed amperometric detection (BIA‐PAD). Boron doped diamond (BDD) was used as working electrode. AML was detected at +1.00 V and ATN at +1.65 V. The proposed BIA method is simple, robust, precise (RSD <3.2 %; n=10), presents high analytical frequency (>70 injections h^?1), generates reduced volume of waste (without use of organic solvent) and requires minimal sample manipulation (dissolution and dilution in electrolyte). The limits of detection were 0.074 and 0.073 µmol L^?1 for AML and ATN, respectively. The results obtained with the proposed BIA method were compared to those obtained by HPLC and similar results were obtained (at 95% of confidence level).     

Voltammetric Lead Determination in Aviation Fuel Samples Using a Screen‐Printed Gold Electrode and Batch‐Injection Analysis

This work presents the lead determination in aviation (bio)fuels using disposable screen‐printed gold electrodes (SPGEs) adapted on a batch‐injection cell associated with a micropipette for portable analysis. The method involves injections of 200 µL of sample or standard solutions at controlled dispensing rate (4.8 µL s^?1) during deposition step (?550 mV for 90 s), followed by anodic‐stripping voltammetry. Either samples treated by sonication or dry‐ashing can be analyzed with detection limits of 0.0071 and 0.0008 µg g^?1 Pb, respectively. A single SPGE can be applied for 60 consecutive measurements (or 120 for samples dry‐ashed). The ultrasound‐assisted treatment is faster, safer, and easily adapted for on‐site analyses, especially considering the portable characteristics of commercially‐available potentiostats and batch‐injection analysis cell using SPGEs.