D-optimal designs and N-way techniques to determine sulfathiazole in milk by molecular fluorescence spectroscopy

The present work proposes an analytical procedure to determine sulfathiazole in milk by using molecular fluorescence spectroscopy. For this sulfonamide the European Union in Regulation 37/2010 has established a maximum residue limit in milk of 100 μg kg(-1). The study includes the effect of six factors on the recovery of sulfathiazole. The factors are: (i) The one related to the matrix depending on the heat treatment of the milk (UHT, pasteurized); (ii) Those related to the protein precipitation step, namely the ratio between the volume of trichloroacetic acid (TCA) and milk, centrifugation speed and temperature; (iii) Those affecting the derivatization reaction: derivatization time and volume of fluorescamine. To do this, two chemometric tools are used together: a D-optimal design for studying the effect of the factors on the recovery of sulfathiazole, considerably reducing the number of needed experiments; and the second-order property of the PARAFAC (Parallel Factor Analysis) decomposition that avoids the need of fitting a new calibration model each time that the experimental conditions change. It has been found that the type of milk, the TCA:milk ratio and the volume of fluorescamine have significant effect on the response. The rest of factors and interactions are not significant. The best recovery is obtained with UHT milk, 4:6 rate for TCA:milk volumes and 40 μL of fluorescamine. In UHT milk, the mean recovery (n=5) in the optimal conditions is 88.7% (RSD=12.4%). As some non-linear behaviour may occur when using fluorescence spectroscopy, the calibration model that relates the fluorescence spectra with the concentration is computed by a partial least squares regression and a multi-layer feed-forward neural network. In both cases, the proposed procedures have been validated according to Decision 2002/657/EC, concluding that the two are accurate although the calibration model built with the neural network has better figures of merit, the decision limit (CCα) for x(0)=100 μg L(-1) is 103.3 μg L(-1) and the detection capability (CCβ) is 106.5 μg L(-1), with the probabilities of false noncompliance (α) and false compliance (β) equal to 5%.     

Direct classification of olive oils by using two types of ion mobility spectrometers

In this work, we explored the use of an Ion Mobility Spectrometry (IMS) device with an ultraviolet (UV) source, and of a Gas Chromatographic (GC) column coupled to an IM Spectrometer with a tritium source, for the discrimination of three grades of olive oil, namely: extra virgin olive oil (EVOO), olive oil (OO) and pomace olive oil (POO). The three types of oil were analyzed with both equipment combinations as coupled to a headspace system and the obtained ion mobility data were consecutively processed with various chemometric tools. The classification rate for an independent validation set was 86.1% (confidence interval at 95% [83.4%, 88.5%]) with an UV-IMS and 100% (confidence interval at 95% [87%, 100%]) using a GC-IMS system. The classification rate was improved by using a more suitable ionization source and a pre-separation step prior to the IM analysis.     

Single solid phase extraction method for the simultaneous analysis of polar and non-polar pesticides in urine samples by gas chromatography and ultra high pressure liquid chromatography coupled to tandem mass spectrometry

A new multiresidue method has been developed and validated for the simultaneous extraction of more than two hundred pesticides, including non-polar and polar pesticides (carbamates, organochlorine, organophosphorous, pyrethroids, herbicides and insecticides) in urine at trace levels by gas and ultra high pressure liquid chromatography coupled to ion trap and triple quadrupole mass spectrometry, respectively (GC-IT-MS/MS, UHPLC-QqQ-MS/MS). Non-polar and polar pesticides were simultaneously extracted from urine samples by a simple and fast solid phase extraction (SPE) procedure using C₁₈ cartridges as sorbent, and dichloromethane as elution solvent. Recovery was in the range of 60-120%. Precision values expressed as relative standard deviation (RSD) were lower than 25%. Identification and confirmation of the compounds were performed by the use of retention time windows, comparison of spectra (GC-amenable compounds) or the estimation of the ion ratio (LC-amenable compounds). For GC-amenable pesticides, limits of detection (LODs) ranged from 0.001 to 0.436 μg L⁻¹ and limits of quantification (LOQs) from 0.003 to 1.452 μg L⁻¹. For LC-amenable pesticides, LODs ranged from 0.003 to 1.048 μg L⁻¹ and LOQs ranged from 0.011 to 3.494 μg L⁻¹. Finally, the optimized method was applied to the analysis of fourteen real samples of infants from agricultural population. Some pesticides such as methoxyfenozide, tebufenozide, piperonyl butoxide and propoxur were found at concentrations ranged from 1.61 to 24.4 μg L⁻¹, whereas methiocarb sulfoxide was detected at trace levels in two samples.     

Thiophene–Diazine Molecular Semiconductors: Synthesis,Structural, Electrochemical,Optical, and Electronic Structural Properties; Implementation in Organic Field‐Effect Transistors

New transportation : New thiophene‐based semiconductors have been produced and studied by electrochemistry, various spectroscopic methods, and structural and morphological techniques in conjunction with model chemistry. Their electrical properties have been analyzed by implementation in field‐effect transistor devices (see figure).

     

Mosaic CuI−CuII−InIII 2D Perovskites: Pressure-Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method

The perovskite (BA)₄[Cu^II(Cu^IIn^III)_0.5]Cl₈ ( 1_BA ; BA⁺=butylammonium) allows us to study the high-pressure structural, optical, and transport properties of a mixed-valence 2D perovskite. Compressing 1_BA reduces the onset energy of Cu^I/II intervalence charge transfer from 1.2 eV at ambient pressure to 0.2 eV at 21 GPa. The electronic conductivity of 1_BA increases by 4 orders of magnitude upon compression to 20 GPa, when the activation energy for conduction decreases to 0.16 eV. In contrast, Cu^II perovskites achieve similar conductivity at ≈50 GPa. The solution-state synthesis of these perovskites is complicated, with more undesirable side products likely from the precursor mixtures containing three different metal ions. To circumvent this problem, we demonstrate an efficient mechanochemical synthesis to expand this family of halide perovskites with complex composition by simply pulverizing together powders of 2D Cu^II single perovskites and Cu^IIn^III double perovskites.     

Hybrid organic semiconductors including chalcogen atoms in pi-conjugated skeletons. Tuning of optical, redox, and vibrational properties by heavy atom conjugation

In this work, the interactions between heteroatoms (S, Se, and Te) and conjugated skeletons are analyzed. The study is carried out by using electronic absorption and fluorescence spectroscopies, electrochemistry, vibrational Raman spectroscopy, and theoretical calculations in the framework of DFT and TD-DFT theories. Optical spectra are described in terms of one-electron promotions between orbitals around the energy gap. Electrochemistry, in the framework of the Koopman's approach, is also interpreted. The vibrational Raman spectra are assigned to molecular modes and the evolution changing the heteroatom is addressed and an effective tuning of these properties is found. Part of this modulation is associated with local electronic interactions depending on the relative S, Se, and Te electronegativities. Unconventional long-range heteroatom-heteroatom interactions have been proposed which arise from the existence of effective pi-conjugated channels. The molecular level understanding of structure-property relationships in these organic/inorganic semiconductors are of great interest in the interdisciplinary area of material science.     

A comparison of Bayesian,Hazard, and Mixed Logit model of bankruptcy prediction

Computational Management Science - The purpose of this study is to examine the impact of the choice of cut-off points, sampling procedures, and business cycles on the forecasting accuracy of...     

Quinoidal Oligothiophenes: Towards Biradical Ground‐State Species

A family of quinoidal oligothiophenes, from the dimer to the hexamer, with fused bis(butoxymethyl)cyclopentane groups has been extensively investigated by means of electronic and vibrational spectroscopy, electrochemical measurements, and density functional calculations. The latter predict that the electronic ground state always corresponds to a singlet state and that, for the longest oligomers, this state has biradical character that increases with increasing oligomer length. The shortest oligomers display closed‐shell quinoidal structures. Calculations also predict the existence of very low energy excited triplet states that can be populated at room temperature. Aromatization of the conjugated carbon backbone is the driving force that determines the increasing biradical character of the ground state and the appearance of low‐lying triplet states. UV/Vis, Raman, IR, and electrochemical experiments support the aromatic biradical structures predicted for the ground state of the longest oligomers and reveal that population of the low‐lying triplet state accounts for the magnetic activity displayed by these compounds.     

Diels-Alder reactions of masked o-benzoquinones: new experimental findings and a theoretical study of the inverse electron demand case

Diels-Alder reactions of the masked o-benzoquinone (MOB) 2 with vinylene carbonate (3), the bicyclic derivatives 4, 5, and 6, and the intramolecular version of the 2-hydroxymethylfuran-MOB Diels-Alder reaction are described. In addition, a theoretical study of the Diels-Alder reactions of MOBs with enol and thioenol ethers is presented.     

Influence of glycopolymers structure on the copolymerization reaction and on their binding behavior with lectins

The copolymerization of two glycomonomers bearing lactonolactone and maltonolactone pendant groups with methyl acrylate is here described. The synthesis and characterization of these glycomonomers are fully presented. The analysis of monomer reactivity ratios of both copolymerization systems is performed and compared to those previously obtained for glycomonomers bearing glucosamine and gluconolactone pendant groups. The glass transition temperature is also analyzed as a function of their structure and finally, the molecular recognition behavior is tested against two lectins, Concanavalin A and Ricinus communis Agglutinin.