Determination at low ppm levels of dithiocarbamate residues in foodstuff by vapour phase-liquid phase microextraction-infrared spectroscopy

A methodology based on the vapour phase (VP) generation of carbon disulphide from non-volatile dithiocarbamate compounds has been developed for determination of pesticide residues in foodstuff at low ppm levels. The method involves a selective reaction combined with liquid phase microextraction (LPME) and transmission infrared measurements. The use of a home made transmission cell improved the detection limits (LOD) compared to the use of attenuated total reflectance measurements by a factor of approximately 80. Using the most appropriate experimental conditions for the CS₂ generation and LPME preconcentration, the precision of the methodology, expressed as the relative standard deviation (RSD), was of the order of 3.1% and the absolute LOD was 0.3 μg dithiocarbamate, which corresponds to 60–120 μg kg⁻¹, for a sample mass ranging from 2.5 to 5 g. The usefulness of the methodology has been evidenced by the determination of mancozeb residues in strawberries, lettuce and corn samples at concentrations between 1 and 5 mg kg⁻¹, where the VP-LPME IR provided results comparable with those obtained by a head space gas chromatography mass spectrometry reference procedure.     

Mesoscopic Structure in Mixtures of Water and 1-Butyl-3-methyl imidazolium tetrafluoborate: A Multinuclear NMR Study

This work is devoted to highlighting some peculiar aspects of ionic liquid self-aggregation in water, which is still a matter of wide debate. Here, the whole water /1-butyl-3-methyl imidazolium (bmim⁺) tetrafluoborate ( $ {\text{BF}}_{4}^{ - } $ ) phase diagram was thoroughly re-investigated, at a molecular level, by means of ¹H and ¹⁹F PGSTE and ¹¹B relaxation NMR experiments performed at room temperature. The analysis of H₂O, bmim⁺ and $ {\text{BF}}_{4}^{ - } $ ions self-diffusion coefficients and the ¹¹B relaxation times revealed that ion-pair dissociation is a progressive process starting at a H₂O molar fraction equal to 0.2 and ending at high water content. More importantly, the collected results indicate that H₂O and ions diffuse within different domains, strongly suggesting that the system under investigation is actually nanostructured. This fact agrees with some other recent works focusing on the possible mesoscopic order that ionic liquids possess when dissolved in water because of their hydrophobic tail segregation.     

Opening of Epoxide Rings Catalyzed by Niobium Pentachloride

Abstract

The behavior of several epoxides when treated with NbCl₅ was studied. In general, the studied epoxides reacted rapidly with NbCl₅, giving, in most cases, more than one product (chlorohydrins, products containing solvent residues, as well as rearrangement products). A detailed study was performed to verify the effects of the temperature (rt, 0°C, or ?78°C) and of the NbCl₅ molar concentration on the composition of the products, yield, and time required for the reactions.     

Synthesis of Spiro-β-Methylene-γ-Butyrolactones

The Bakkenolide group 1 ³ of sesquiterpenes present two interesting synthetic problems. The cisdimethyl cis-hydrindane portion 2, because of its structural and stereochemical relationship with the eremophilane sesqui terpenes,⁴ has synthetic solutions available.⁵ The spiro-β-methylene-γ-butyrolactone unit 3,⁶ which is presently unique to this class of natural products, has been synthesised by four different routes.^7–10     

Expedient Synthesis of Hydroxytyrosol and its Esters

An efficient and friendly method for obtaining hydroxytyrosol from tyrosol, a component of olive waste, is reported. Hydroxytyrosol also may be obtained in the form of enzymatically convertible precursors (e.g., hydroxytyrosyl acetate), thus increasing the stability of the active principle.     

Biomimetic synthesis of diversifolin

The conversion of a germacranolide structure (tagitinin C) into a furanoheliangolide one (diversifolin) was achieved by hydride conjugate addition using Stryker’s reagent.     

Multi-determination of organic pollutants in water by gas chromatography coupled to triple quadrupole mass spectrometry

A multi-determination method has been developed for the determination and confirmation of 68 organic pollutants in water samples by gas chromatography coupled to triple quadrupole mass spectrometry (GC-MS/MS). The following chemical families were determined in a chromatographic run of less than 26?min: polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenylethers (PBDEs), and pesticides (organochlorine, organophosphorus, triazine and others). The sample preparation involved a liquid-liquid extraction (LLE) procedure, obtaining recoveries ranging from 70 to 130% when dichloromethane was used as the extracting solvent. The detection limits of the proposed method were between 0.75 and 19.8?ng?L^?1. Samples from the Maipo River in central Chile were taken from 29 different points. Seven pesticides and two PAHs were detected in field collected samples with concentrations ranging from 10 to 95?ngL^?1. Concentrations of benzo[a]pyrene in environmental samples ranged from 25 to 33?ngL^?1 and were near the maximum levels established by the European Union Directives (50?ng?L^?1).     

Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2‐ethylhexyl)sulfosuccinate

The behavior of aqueous solutions of sodium bis(2‐ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N⁰_AOT AOT^? anions (N⁰_AOT = 0, 5, 10) and N⁰_Na sodium ions (N⁰_Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N⁰_AOT and N⁰_Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Antibiotic Detection in Urine Using Electrochemical Sensors Based on Vertically Aligned Carbon Nanotubes

A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan‐rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate‐buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0–10.0 µmol L^?1, with a detection limit of 75.2 nmol L^?1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure.