Photocatalytic degradation of phenyl-urea herbicides chlortoluron and chloroxuron: characterization of the by-products by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

The first stages of the photocatalytic degradation of the compounds chlortoluron [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] and chloroxuron [3-[4-(4-chlorophenoxy)phenyl]-1,1-dimethylurea], belonging to the class of phenyl-urea herbicides, were investigated using high-performance liquid chromatography (HPLC) coupled to electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS). Degradation was accomplished under solar radiation, using TiO2 embedded into a polyvinylidene fluoride (PVDF) transparent matrix as a heterogeneous photocatalyst. Aliquots of the chlorinated herbicide solutions were withdrawn at different times and subjected to gradient elution, reversed-phase HPLC separations, specifically optimized to obtain the highest resolution between peaks related to the herbicide degradation by-products. The latter were then investigated using MS detection; in particular, MS/MS measurements were made and structural information was obtained from the interpretation of fragmentation data. Several by-products were identified; the most important ones are hydroxylated compounds arising from the interaction between the two chlorinated herbicides and OH radicals generated at the TiO2 surface under irradiation. Other by-products were generated by slightly different processes, namely demethylation, dearylation and dechlorination, eventually followed by interaction with OH radicals.     

Determination of α-Tocopherol in Olive Oil by Solid-Phase Microextraction and Gas Chromatography–Mass Spectrometry

Olive oil has great human health benefits and is an important component of the Mediterranean diet. Its quality, sensory attributes, and oxidative stability are linked to the presence of minor compounds. Vitamin E (α-tocopherol) is a key component in these properties. In this work, solid-phase microextraction coupled to gas chromatography–mass spectrometry was used for the determination of α-tocopherol in olive oil. The analytical performance of the method has been assessed in fortified olive oil with negligible vitamin E concentrations. The calibration curve was linear from 0.020 to 0.500?mg/g. The limits of detection and quantification were 0.006 and 0.021?mg/g, respectively. Intraday and interday relative standard deviations were 3.2 and 10.0, respectively, and were concentration independent. The method was used for the determination of α-tocopherol in virgin and extra virgin olive oil, reporting average concentrations of 0.044?±?0.03 and 0.200?±?0.05?mg/g, respectively. Overall, the method is simple, sensitive, rapid, and solvent free, and provided high recoveries of 97.7?±?3.1%. In addition, vitamin E stability in extra-virgin olive oil was characterized by a shelf-life study.     

Silver nanofractals: electrochemical synthesis, XPS characterization and application in LDI-MS

Silver nanofractals (Ag-NFs) have been electrosynthesized and characterized by means of morphological and spectroscopic analytical techniques. In particular, X-ray photoelectron spectroscopy has been used to assess the nanomaterial surface chemical state. Ag-NFs show interesting perspectives in bioanalytical applications, particularly as non-conventional desorption and ionization promoters in laser desorption ionization mass spectrometry.     

Comparison of phosphatidylcholine vesicle properties related to geometrical isomerism

Glycerophosphatidylcholine containing trans-unsaturated fatty acid residues was prepared by reaction of the corresponding naturally occurring cis lipid with photochemically generated thiyl radicals. This modified lipid was chosen as the simplest model for gaining some insights of the complex scenario of membrane formation, in connection with the role of lipid geometry and the predominance of cis lipids in eukaryotic cells. The critical aggregation concentration for the spontaneous formation of vesicles was determined for cis and trans isomers with cis-parinaric acid used as a fluorescent probe and it was found to be similar for both lipids. Vesicle dimensions were investigated by light scattering and electron microscopy, and the type of fatty acid residues influenced the vesicle diameter, with a decrease along the series cis > trans > saturated. Fluorescence measurement of dye release from trans and cis vesicles showed also a different permeability. A picture emerged of the geometrical isomer preference in cells as a process driven by natural selection during the life evolution of different organisms, both in terms of compartment dimensions and membrane functionality.     

Needle-type glucose microbiosensor based on glucose oxidase immobilised in an overoxidised polypyrrole film (an in-vitro study)

A fast response, needle-type glucose microbiosensor has been fabricated by a one-step electrochemical immobilisation of glucose oxidase in a polypyrrole film. The sensor shows a remarkable rejection of electroactive interferences, especially paracetamol. The maximum bias observed in the worst situation never exceeded the value of 6%. The fabrication procedure delivered very reproducible devices and the sensitivity of a newly prepared biosensor was typically 650 nA mM(-1) cm(-2). The kinetic parameters, obtained from an existing model, permitted to understand the sensor behaviour.     

Catalytic currents in fused salts: Discharge mechanism of nitrite in molten alkali nitrates(II)

The electrooxidation of NO₂^? ion in the (Na,K)NO₃ eutectic mixture containing water in the concentration range 10^?6–10^?2 mol kg^?1 has been studied on a platinum RDE. More work was done to confirm the preliminary mechanism reported by the authors:

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In the course of the present study step (a) was found to be potential determining under all experimental conditions while step (b) behaves as a “true” equilibrium reaction. By an approximate method based on the reaction layer concept the equilibrium constant for reaction (b) K=K′/[NO₃^?]=[H⁺]²[NO₂^?]/[NO₂]²[H₂O] was calculated. In the given nitrate solvent it was found to be K=(2.90±0.56)×10^?1 at 520 K. A value of ΔH equal to ?125.2 kJ mol^?1 was obtained on the basis of the temperature dependence of the equilibrium constant in the range 505–566 K.     

Analytical characterization of poly(pyrrole-3-carboxylic acid) films electrosynthesised on Pt, Ti and Ti/Al/V substrates

With the aim of developing a polymeric multilayer film for application in advanced biomaterials, as a first step poly(pyrrole-3-carboxylic acid) films (abbreviated as PPy-3-carbox) were electropolymerised from pyrrole-3-carboxylic acid solutions by cyclic voltammetry and chronoamperometry on platinum, titanium and Ti90Al6V4 substrates and characterised both electrochemically (cyclic voltammetry) and spectroscopically (X-Ray Photoelectron Spectroscopy, XPS). Electrochemical experiments showed that the potential range adopted for electropolymerization affects the polymer electroactivity, by analogy with unsubstituted polypyrrole. The combination of conventional and chemical derivation-XPS provided information on PPy-3-carbox surface structure, showing no significant difference between films grown on different substrates and an increase of the COOH groups amount (one group over three pyrrole rings, as an average) with respect to unsubstituted polypyrrole (PPy), as expected. Finally, a preliminary Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) investigation was performed in order to get further information on the polymer structure and electroactivity.     

Oxygen electrodes in fused salts: Investigation and mechanistic remarks on the system (Ni)CO2, O2/CO32− in molten (Na,K)NO3

A potentiometric investigation on the system (Ni)CO₂, O₂/CO₃^2? was carried out at 507–637 K in the (Na, K)NO₃ equimolar mixture containing carbonate ions in the range 10^?5≤[CO₃^2?]≤10^?2 mol kg^?1 and under a mixture of O₂ and CO₂ at variable partial pressure. The potential behaviour of the nickel electrodes was found largely dependent on the working temperature. At the highest tested temperature the system behaves irreversibly under potentiometric conditions and the potential was found to be independent of the oxygen concentration. At lower temperatures a large irreversibility of the system was still found, while a certain dependence (different from the theoretical one) of the potential on both oxygen and carbon dioxide partial pressure was experimentally demonstrated. The entire set of results was interpreted on the basis of the two following mechanistic models involving, in the potential determining step, solid species formed on the electrode surface by contact with the melt. Mechanism 1 (high temperature)

Mechanism 2 (low temperature)