Voltammetric behavior and determination of tocopherols with partial least squares calibration: analysis in vegetable oil samples

The voltammetric behavior of Vitamin E in the presence of olive oil is studied at the glassy carbon electrode, in a hexane-ethanol medium, with diverse techniques: sampled DC, differential pulse, and square-wave voltammetry. The influence of such variables as the hexane-ethanol proportion, sulfuric acid concentration, and instrumental parameters is studied. Separate voltammetric peaks are obtained for α-tocopherol and δ-tocopherol, but the peaks for β-tocopherol and γ-tocopherol overlap. For the simultaneous determination of α-, β+γ-, and δ-tocopherols in vegetable oils by the PLS-1 multivariate calibration method, the results using sampled DC and DPV voltammograms are compared. The DPV voltammograms are found to be the best data set. The proposed method is applied to the determination of the tocopherols in different vegetable oil samples. The olive oil samples needed a prior cleaning stage by solid-phase extraction on silica cartridges. The results are very acceptable.     

Proton-electron double resonance: Spectroscopy and imaging in very low magnetic fields

Proton-electron double resonance, also named dynamic nuclear polarization (DNP) is characterized by an enhancement of the proton NMR signal when the electron resonance of a free radical coupled to water protons is saturated. In very low magnetic fields, new EPR transitions are allowed. The complete theory of DNP in nitroxide solutions is recalled, in order to interpret the experimental spectra. Proton-electron double resonance images (PEDRI) were obtained with 7 out of the 10 EPR transitions allowed in low fields. Field cycled PEDRI were obtained in magnetic fields as low as 0.6 G. The optimum field strength for PEDRI is discussed according to the theoretical and experimental results of DNP obtained with nitroxide solutions.     

Sensitive SPE GC-MS-SIM screening of endocrine-disrupting herbicides and related degradation products in natural surface waters and robustness study

This paper describes a very sensitive capillary gas chromatographic mass spectrometric selective ion monitored method for the simultaneous determination of three chloro-s-triazine herbicides, Atrazine (AT), Simazine (SI) and Propazine (PP), three thiomethyl-s-triazine ones: Ametryn (AM), Prometryn (PM) and Terbutryne (TB) and three chloro-s-triazine degradation products, Deethyl-atrazine (DEA), Deisopropyl-atrazine (DIA) and Deethyldeisopropyl-atrazine (DD) with herbicide activity too. The instrumental parameters affecting GC separation and MS/SIM detection were investigated and from this study the best conditions were selected. A previous extraction and preconcentration step was applied by means of an off-line solid phase extraction process getting so an enrichment factor of 10⁴. The analytical performance characteristics of our method (stability, precision, linearity, LODs, LOQs, accuracy and robustness) were evaluated by means of a validation study on tap and deionised water samples using di-phenyl amide (DPA) as internal standard to achieve quantification. Natural water samples from different locations suspected to contamination were analysed by this off line SPE-GC-MS-SIM procedure and the results were also confirmed by an HPLC method.     

Simultaneous determination of carminic acid, riboflavine, curcumin and erythrosine by derivative spectrophotometry and ratio spectra derivative

A quaternary mixture of carminic acid, riboflavine, curcumin and erythrosine can be resolved with a previous extraction step into metyl-isobutyl ketone and, resolving the binary mixtures obtained in the aqueous phase and organic phase, using derivative spectrophotometry on the basis of the zero-crossing measurements in the first derivative spectra as well as the first derivative of ratio spectra. The conditions of extraction established and the proposed methods have been tested to determine these colorants in several synthetic mixtures of four dyes, obtaining good recoveries. The methods have been applied in yoghurt samples spiked with the dyes.     

Photo‐Fenton and Riboflavin‐photosensitized Processes of the Isoxaflutole Herbicide

The proherbicide Isoxaflutole (IXF) hydrolyzes spontaneously to diketonitrile (DKN) a phytotoxic compound with herbicidal activity. In this work, the sensitized degradation of IXF using Riboflavin (Rf), a typical environmentally friendly sensitizer, Fenton and photo‐Fenton processes has been studied. The results indicate that only the photo‐Fenton process produces a significant degradation of the IXF. Photolysis experiments of IXF sensitized by Riboflavin is not a meaningful process, IXF quenches the Rf excited triplet (³Rf*) state with a quenching rate constant of 1.5 · 10⁷ m ^?1 s^?1 and no reaction is observed with the species O₂(¹Δ_g) or ${\mathrm{O}}_2^{·?}$ generated from ³Rf*. The Fenton reaction produces no changes in the IXF concentration. While the photo‐Fenton process of the IXF, under typical conditions, it produces a degradation of 99% and a mineralization to CO₂ and H₂O of 88%. A rate constant value of 1.0 × 10⁹ m ^?1 s^?1 was determined for the reaction between IXF and HO˙. The photo‐Fenton process degradation products were identified by UHPLC‐MS/MS analysis.     

Decay rates of solutions of an anisotropic inhomogeneousn-dimensional viscoelastic equation with polynomially decaying kernels

We consider the anisotropic and inhomogeneous viscoelastic equation and we prove that the first and second order energy decay polynomially as time goes to infinity when the relaxation function also decays polynomially to zero. That is, if the kernelG _ijkl satisfies

Phase transformations induced by implantation of12C− ions into α-Fe and AISI 304 and 316 stainless steels studied by CEMS and SEM

Samples of AISI 304 and 316 stainless steels, initially in austenitic (first set) and martensitic states (second set) and -Fe (third set), were implanted with 180 keV¹²C^– to a dose of 10¹⁷ atoms/cm² at room temperature. Surfaces were examined by SEM (scanning electron microscopy) and the crystalline-phase fractions were estimated through CEMS (conversion electron Mössbauer spectroscopy). Different grades of etching were produced by sputtering during the implantations on the stainless steel samples depending on the previous crystallographic states. CEMS data reveal the transformation in the initially martensitic samples and no noticeable modifications as a result of the implantation on -Fe and austenitic samples.     

Modeling nonbilinear total synchronous fluorescence data matrices with a novel adapted partial least squares method

A new residual modeling algorithm for nonbilinear data is presented, namely unfolded partial least squares with interference modeling of non bilinear data by multivariate curve resolution by alternating least squares (U-PLS/IMNB/MCR-ALS). Nonbilinearity represents a challenging data structure problem to achieve analyte quantitation from second-order data in the presence of uncalibrated components. Total synchronous fluorescence spectroscopy (TSFS) generates matrices which constitute a typical example of this kind of data. Although the nonbilinear profile of the interferent can be achieved by modeling TSFS data with unfolded partial least squares with residual bilinearization (U-PLS/RBL), an extremely large number of RBL factors has to be considered. Simulated data show that the new model can conveniently handle the studied analytical problem with better performance than PARAFAC, U-PLS/RBL and MCR-ALS, the latter modeling the unfolded data. Besides, one example involving TSFS real matrices illustrates the ability of the new method to handle experimental data, which consists in the determination of ciprofloxacin in the presence of norfloxacin as interferent in water samples.     

Morphology and Phase Composition of Particles Produced by Electro-Discharge-Machining of Iron

Towards producing metallic particles of controlled size and spherical shape, which are of technological importance, we have collected in the filters of an electro-discharge-machine (EDM) the material ejected from the surface of EDM iron pieces. The conditions of machining were varied for kerosene and water as dielectrics, using a discharge current of 25 A and duration times of 16 and 3072 μs for kerosene and of 32, 384 and 768 μs for water, respectively. Scanning electron microscopy was used to assess the effect of the time of discharge on the size of the particles. Mössbauer spectroscopy and X-ray diffraction revealed that for kerosene EDM particles only cementite-like carbides of diverse stoichiometry were formed. While no oxide was found for kerosene spheres, the analyses showed that besides the main fraction of α-Fe, a small percentage of wüstite (and traces of hematite for the 384 μs sample) formed on the water EDM ones.     

Surface Phase Transformations Induced on Fe0.86Mn0.14 by Carbon Ion-Irradiation

Conversion electron Mössbauer spectroscopy and X-ray diffraction have been used to investigate the modifications induced by room-temperature irradiation with 360 keV C^? ions on a Fe_0.86Mn_0.14 alloy. The data show that the irradiation produces γ-FeMn along with an increase in the amount of α-FeMn at the expense of ∈-FeMn, both originally present. The initial distribution of Mn atoms in the α-FeMn martensitic phase is observed to change after irradiation.