Simultaneous extraction of tocotrienols and tocopherols from cereals using pressurized liquid extraction prior to LC determination

Tocopherols and tocotrienols have been simultaneously determined in food samples using a rapid and simple analytical method including pressurized liquid extraction (PLE) and LC with electrochemical detection. Separation was carried out on a Phenomenex Synergi 4 μm Hydro‐RP 80A column, using a solution of 2.5 mM acetic acid/sodium acetate in methanol/water (99:1, v/v) as mobile phase at a flow rate of 1.0 mL/min. Column temperature was maintained at 30°C. Detection was performed by coulometric detection at 500 mV except for (β+γ)‐tocotrienol, in wheat and rye samples, which was at +350 mV. A palm oil containing a relatively large amount of γ‐tocotrienol and lower concentrations of α‐ and δ‐tocotrienols and α‐ and γ‐tocopherols was used to provide reference retention times for the tocotrienols. Analyte quantification was performed using the external standard method. The calibration equations of tocopherols were used to quantify both tocopherols and their corresponding tocotrienols. The extraction recoveries obtained using the optimized PLE conditions were in the 80–114% range, with RSDs lower than 15%. The method was successfully applied to the determination of tocotrienols and tocopherols in cereal (wheat, rye, barley, maize and oat) and palm oil samples.     

Ultrasound-assisted pressurized solvent extraction for aliphatic and polycyclic aromatic hydrocarbons from soils

In the present work the efficiency of extraction of aliphatic diesel range organics (DROs) and polycyclic aromatic hydrocarbons (PAHs) from soil was assessed by using dynamic modes of pressurized solvent extraction (PSE), and ultrasound-assisted pressurized solvent extraction (US-PSE). Optimization studies were carried out using a blank soil (Non-Polluted Soil#1, CLN-1, RTC) and a real soil which was previously spiked with the analyte mixture and aged for 90 days. A laboratory-made manifold with controlled temperature and pressure was used to carry out the leaching processes. The extraction cell was inserted into an oven for PSE and into an ultrasound bath for US-PSE. The following variables were studied in each case, keeping the pressure at about 1800 psi: extraction temperature, time of static and dynamic extraction and solvent flow rate. In addition, the time of ultrasound application was also studied in US-PSE. For PSE with dichloromethane (DCM) the recoveries were about 90-95% for both the families of analytes, using extraction times of 20 min. Analyte extraction was quantitative by using US-PSE with DCM for 10 min. In all cases, after the extraction process, the analytes were determined by GC-MS. Application of the method to a natural contaminated sample suggests that either the extraction time used in US-PSE should be increased to 20 min or the solvent (DCM) should be replaced by a mixture of DCM:acetone (1:1), to reach comparability with Soxhlet extraction.     

Sol-gel processing of a bimetallic alkoxide precursor confined in a porous glass matrix: a route to novel glass/metal oxide nanocomposites

In this work we present the utilization of the heterometallic alkoxide [FeCl{Ti(2)(OPr(i))(9)}] as the first sol-gel single-source precursor to achieve nanocomposites made of iron and titanium oxides incorporated into Porous Vycor Glass (PVG). The nanocomposites were prepared by the impregnation of the precursor in a PVG plate followed by hydrolysis reactions. Different samples were obtained by further thermal treatment of the hydrolyzed sample. The nanocomposites were characterized by UV-vis-NIR, Raman and EPR spectroscopies, XRD and TEM. The results indicate that the room-temperature hydrolyzed samples are formed by nanoparticles of FeOOH and brookite-TiO(2) embedded on a glassy matrix. After the heat treatment at temperatures above 900 degrees C, a pseudobrookite Fe(2)TiO(5) was formed. All samples present high transparency and homogeneity. The results showed here indicate that the sol-gel process using the single-source precursor [FeCl{Ti(2)(OPr(i))(9)}] should be a novel and efficient approach to the preparation of nanometric Fe/Ti oxides incorporated into a glassy matrix.     

Potentiometric behavior of ion-selective electrodes to large cationic species modulated by decyl alcohol

The effect of 1-decanol on the potentiometric response of three ion-selective electrodes to large cationic species is analyzed. The electrodes were constructed with plasticized PVC membranes. The results suggest that 1-decanol alters the ionic transport through the membrane/water interface to an extent that depends on the strength of the active ion pair. The water solubility of the cation, its molecular weight, and the size of the ion pair seem to be relevant factors in this type of behavior. The potentiometric selectivity coefficients are also dependent on the presence of 1-decanol in the membrane. These results are similar to those already described in ion-selective electrodes with membranes capable of sensing anionic benzene sulfonate-type systems. Thus, the effect of the alcohol appears to be general by affecting mainly the membrane surface polarity.     

Construction of the vector space concept from the viewpoint of APOS theory

We apply APOS theory to propose a possible way that students might follow in order to construct the vector space concept. We describe the mental mechanisms and constructions that might take place when students are learning this concept. We then report on a study that we performed with 10 undergraduate mathematics students through the application of a questionnaire and an interview. In this paper we focus on the coordination between the two operations that form part of the vector space structure and the relation of the vector space schema to other concepts such as linear independence and binary operations.     

Irreducibility of the unitary principal series of p-adic {\widetilde{Sp(n)}}

Let F be a p-adic field. Let Sp(n) denote the sympletic group of rank n over F, and let ${\widetilde{Sp(n)}}$ be the unique (up to isomorphism) metaplectic double cover of Sp(n). We prove irreducibility of the unitary principal series of the group ${\widetilde{Sp(n)}}$ over F using theta correspondence.     

Rapid direct analysis in real time (DART) mass spectrometric detection of juvenile hormone III and its terpene precursors

Direct analysis in real time (DART) is a plasma-based ambient ionization technique that enables rapid ionization of small molecules with high sample throughput. In this work, DART was coupled to an orthogonal (oa) time-of-flight (TOF) mass spectrometer and the system was optimized for analyzing a vital hormonal regulator in insects, juvenile hormone (JH) III and its terpene precursors, namely, farnesol, farnesoic acid, and methyl farnesoate. Optimization experiments were planned using design of experiments (DOE) full factorial models to identify the most significant DART variables contributing to JH III analysis sensitivity by DART-TOF mass spectrometry (MS). The optimized DART-TOF MS method had femtomole to sub-picomole detection limits for terpene standards, along with mass accuracies below 5 ppm. Finally, the possibility of distinguishing between two farnesol isomers by in-source-collision-induced dissociation (CID) in the first differentially pumped region of the oaTOF mass spectrometer was investigated. DART-MS enabled high-throughput, sensitive analysis with acquisition times ranging from 30 s to a minute. To the best of our knowledge, this is the first report on the application of DART-MS to the detection and identification of volatile or semi-volatile insect terpenoids, and on the use of DOE approaches to optimize DART-MS analytical procedures.     

Parabolic induction and Jacquet functors for metaplectic groups

In this paper, we give a new formulation of a geometric lemma for the metaplectic groups over p-adic field F, analogous to the existing one for classical groups. This enables us to give a Zelevinsky type classification of irreducible admissible genuine representations of metaplectic groups. As an application of our Jacquet module technique, we explicitly calculate Jacquet modules of even and odd Weil representations.     

Electrochemical nitration of naphthalene in the presence of nitrite ion in aqueous non-ionic surfactant solutions

The nitration of naphthalene (NapH) at a Pt electrode in aqueous NaNO₂ solutions both in the absence and presence of a non-ionic surfactant, Brij®35 (polyoxyethylene (23) dodecanol), has been studied. The electrochemical behaviour of the reactants NapH and NaNO₂ and a mixture of the two was investigated by cyclic voltammetry (CV) to determine the optimal electrolysis conditions. The peak current of NapH decreases with increasing NaNO₂ concentration, indicating that the oxidation product of the NO₂⁻ ion interacts with the NapH radical cation (NapH⁺). Controlled potential electrolysis (CPE) was carried out and the products were analysed by HPLC. The main products detected in the micellar medium were 1-nitronaphthalene, 2-nitronaphthalene, 1,2-naphthoquinone, and 1,4-naphthoquinone. In the absence of Brij 35, the naphthoquinones were produced but no nitration products were obtained. In both cases, unknown products are inferred by mass balance, which are believed to be derived from the oxidation of 1,1′-binaphthyl (BinapH) formed by NapH⁺ coupling in both micellar and aqueous media. A mechanism of nitration by the attack of NO₂ to NapH⁺ is proposed. The higher selectivity for formation of 2-nitronaphthalene in comparison to non-aqueous homogeneous media is attributed to the effect of the micellar microenvironment.     

Continuous flow system for lead determination by faas in spirituous beverages with solid phase extraction and on-line copper removal

A continuous flow system for the determination of lead in home made spirituous beverages was developed. The determination was based on the formation of a neutral chelate of the element with ammonium pyrrolidine dithiocarbamate, its adsorption onto a minicolumn packed with sodium faujasite type Y synthetic zeolite, followed by elution with methyl isobutyl ketone and determination by flame atomic absorption spectrometry. Ethanol and copper interfere strongly in the determination and therefore, must be separated prior to the analysis. Copper is removed by precipitation with rubeanic acid, while ethanol is eliminated by rotaevaporation. Sample solutions containing Pb²⁺ in the concentration range from 5 to 120 μg l⁻¹ at pH 2.5 could be analyzed, by using a preconcentration time of 3 min. Preconcentration factors from 80 to 140 were achieved for a sample volume of 6 ml and the detection limit varied from 1.4 to 3.5 μg l⁻¹, depending on the matrix composition. The relative standard deviations for 60 μg l⁻¹ Pb was 3.2% (n = 10) and the recovery of spikes (20, 40, 60 and 80 μg l⁻¹) added to the samples was estimated within 92–105% range, suggesting that lead can be quantitatively determined in such samples. Determining lead in several samples by an alternative technique further checked the accuracy. Finally, the concentrations of Pb²⁺ determined in 28 samples of Venezuelan spirituous beverages were in 12.6–370.0 μg l⁻¹ range, depending on the fermenting material based on different mixtures of agave, raw sugar cane and white sugar.