Measurement of squalene in olive oil by fractional crystallization or headspace solid phase microextraction coupled with gas chromatography

Squalene is the most abundant component in the unsaponifiable fraction of olive oil with strong antioxidant properties. Its concentration in olive oils varies between 0.2 and 16.2 g/kg depending on the cultivar(s) used. The propose of this work was to determine the effectiveness of two different extraction methods for squalene determination by gas chromatography (GC) coupled to a flame ionization detector (FID) or to mass spectrometry (MS). In a first approach, oil samples were dissolved in methanol/acetone mixture 7:3 (v/v) and triglycerides separated by fractional crystallization at −20°C. The organic layer was removed, reduced to dryness and the residue reconstituted in n-heptane (containing squalane as external standard) and analyzed by GC-FID. A headspace (HS) solid phase microextraction (SPME) GC-MS method has been also developed in order to have an environmentally friendly (i.e. solventless) extraction procedure. The linear range investigated with both methods was 1.0-10 g/kg. Within-day and between days precision values, expressed as RSD%, were 4 and 7% (GC-FID), and 3 and 6% (GC-MS), respectively. The limit of detection (LOD) at a signal-to-noise (S/N) ratio of 3 were 0.019 (GC-FID) and 0.003 (GC-MS) g/kg; the limit of quantification (LOQ) calculated at S/N = 10 were 0.063 (GC-FID) and 0.008 (GC-MS) g/kg, well below the typical squalene concentration levels found in olive oils. The obtained percentage recoveries were 70 ± 2 (GC-FID) and 98 ± 3 (GC-MS), and were not concentration dependent. The potential of the method has been demonstrated by the analysis of several different olive oil samples produced from different cultivars and different locations

In-line preconcentration capillary zone electrophoresis for the analysis of haloacetic acids in water

Two in-line enrichment procedures (large volume sample stacking (LVSS) and field amplified sample injection (FASI)) have been evaluated for the capillary zone electrophoresis (CZE) analysis of haloacetic acids (HAAs) in drinking water. For LVSS, separation on normal polarity by using 20 mM acetic acid-ammonium acetate (pH 5.5) containing 20% acetonitrile as BGE was required. For FASI, the optimum conditions were 25 s hydrodynamic injection (3.5 kPa) of a water plug followed by 25 s electrokinetic injection (-10 kV) of the sample, and 200 mM formic acid-ammonium formate buffer at pH 3.0 as BGE. For both FASI and LVSS methods, linear calibration curves (r2>0.992), limit of detection (LOD) on standards prepared in Milli-Q water (49.1-200 µg/L for LVSS and 4.2-48 µg/L for FASI), and both run-to-run and day-to-day precisions (RSD values up to 15.8% for concentration) were established. Due to the higher sensitive enhancement (up to 310-fold) achieved with FASI-CZE this method was selected for the analysis of HAAs in drinking water. However, for an optimal FASI application sample salinity was removed by solid phase extraction (SPE) using Oasis WAX cartridges. With SPE-FASI-CZE, method detection limits in the range 0.05-0.8 µg/L were obtained, with recoveries, in general, higher than 90% (around 65% for monochloroacetic and monobromoacetic acids). The applicability of the SPE-FASI-CZE method was evaluated by analyzing a drinking tap water from Barcelona where seven HAAs were found at concentration levels between 3-13 µg/L

A nonradial bifurcation result with applications to supercritical problems

In this paper we consider the problem $-\Delta u=|x|^{\alpha} F(u)$ in $R^N$, with $\alpha>0$ and $N\ge3$. Under some assumptions on $F$ we deduce the existence of nonradial solutions which bifurcate from the radial one when $\alpha$ is an even integer.Comment: 20 page

Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates

Physical effects of bilayer coupling on the tunneling spectroscopy of high T$_{c}$ cuprates are investigated. The bilayer coupling separates the bonding and antibonding bands and leads to a splitting of the coherence peaks in the tunneling differential conductance. However, the coherence peak of the bonding band is strongly suppressed and broadened by the particle-hole asymmetry in the density of states and finite quasiparticle life-time, and is difficult to resolve by experiments. This gives a qualitative account why the bilayer splitting of the coherence peaks was not clearly observed in tunneling measurements of double-layer high-T$_c$ oxides.Comment: 4 pages, 3 figures, to be published in PR

In-line preconcentration capillary zone electrophoresis for the analysis of haloacetic acids in water

Two in-line enrichment procedures (large volume sample stacking (LVSS) and field amplified sample injection (FASI)) have been evaluated for the capillary zone electrophoresis (CZE) analysis of haloacetic acids (HAAs) in drinking water. For LVSS, separation on normal polarity by using 20 mM acetic acid-ammonium acetate (pH 5.5) containing 20% acetonitrile as BGE was required. For FASI, the optimum conditions were 25 s hydrodynamic injection (3.5 kPa) of a water plug followed by 25 s electrokinetic injection (-10 kV) of the sample, and 200 mM formic acid-ammonium formate buffer at pH 3.0 as BGE. For both FASI and LVSS methods, linear calibration curves (r2>0.992), limit of detection (LOD) on standards prepared in Milli-Q water (49.1-200 µg/L for LVSS and 4.2-48 µg/L for FASI), and both run-to-run and day-to-day precisions (RSD values up to 15.8% for concentration) were established. Due to the higher sensitive enhancement (up to 310-fold) achieved with FASI-CZE this method was selected for the analysis of HAAs in drinking water. However, for an optimal FASI application sample salinity was removed by solid phase extraction (SPE) using Oasis WAX cartridges. With SPE-FASI-CZE, method detection limits in the range 0.05-0.8 µg/L were obtained, with recoveries, in general, higher than 90% (around 65% for monochloroacetic and monobromoacetic acids). The applicability of the SPE-FASI-CZE method was evaluated by analyzing a drinking tap water from Barcelona where seven HAAs were found at concentration levels between 3-13 µg/L

Discrimination of geographical origin of oranges (Citrus sinensis L. Osbeck) by mass spectrometry-based electronic nose and characterization of volatile compounds

An untargeted method using headspace solid-phase microextraction coupled to electronic nose based on mass spectrometry (HS-SPME/MS-eNose) in combination with chemometrics was developed for the discrimination of oranges of three geographical origins (Italy, South Africa and Spain). Three multivariate statistical models, i.e. PCA/LDA, SELECT/LDA and PLS-DA, were built and relevant performances were compared. Among the tested models, SELECT/LDA provided the highest prediction abilities in cross-validation and external validation with mean values of 97.8% and 95.7%, respectively. Moreover, HS-SPME/GC-MS analysis was used to identify potential markers to distinguish the geographical origin of oranges. Although 28 out of 65 identified VOCs showed a different content in samples belonging to different classes, a pattern of analytes able to discriminate simultaneously samples of three origins was not found. These results indicate that the proposed MS-eNose method in combination with multivariate statistical analysis provided an effective and rapid tool for authentication of the orange's geographical origin

CO2 modified atmosphere packaging: stress condition or treatment to preserve fruit and vegetable quality?

In addition to the adoption of proper temperature and relative humidity, the selection of an atmosphere surrounding packaged fresh produce with reduced O2 and/or increased CO2 is one of the most widely used and useful tools to prolong the shelf-life of horticultural crops. However, as  O2 and/or CO2 values that might cause injury are strictly related to the commodity, they should be optimized for each product. Here three study cases are reported about the application of modified atmospheres (MA), with different CO2 concentrations (0-40 kPa), to table grapes (cv. Italia) and sweet cherries (cv. Ferrovia) and, as short-term treatment (48 h at 0 °C), to fresh-cut artichokes (cv. Violet de Provence). In each trial, the effect of high CO2 treatment on quality parameters was observed during cold storage. Concerning table grape “Italia”, our results show that low CO2 (up to 10kPa) MA preserved the quality and sensory parameters of the fruit, whereas high CO2 (> 20 kPa) caused a fermentative metabolism. As for sweet cherries 'Ferrovia', 20 kPa CO2 MA helped to maintain the quality traits during storage. On the other hand, this fruit proved to be sensitive to CO2 accumulation (over 20kPa) in hypoxic conditions, since it caused an increase in respiration rate and the biosynthesis of volatile fermentative metabolites. Finally, for fresh-cut artichokes, a short-term CO2 treatment, up to 10kPa, reduced respiration rate and browning index, preserving the volatile profile, while high CO2 (40 kPa) may have caused fermentative metabolism. In conclusion, the application of a MA enriched in CO2 has been shown to have different effects on the quality parameters of the three products, in agreement with the fact that CO2 sensibility depends on each specific fruit or vegetable under study

Structural Origin of Apparent Fermi Surface Pockets in Angle-Resolved Photoemission of Bi₂Sr_2-xLa_xCuO_6+δ

We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission. From detailed low-energy electron diffraction measurements and an analysis of the angle-resolved photoemission polarization dependence, we show that these pockets are not intrinsic but arise from multiple overlapping superstructure replicas of the main and shadow bands. We further demonstrate that the hole pockets reported recently from angle-resolved photoemission [Meng et al., Nature (London) 462, 335 (2009)] have a similar structural origin and are inconsistent with an intrinsic hole pocket associated with the electronic structure of a doped CuO2 plane.</p