Analysis of 27 polycyclic aromatic hydrocarbons by matrix solid-phase dispersion and isotope dilution gas chromatography-mass spectrometry in sewage sludge from the Spanish area of Madrid

A method for the determination of 27 polycyclic aromatic hydrocarbons (PAHs) in sludge from wastewater treatment plants (WWTPs) located in urban, industrial or rural zones is presented. PAHs were extracted by matrix solid-phase dispersion (MSPD) assisted by sonication. Purification of extracts was carried out by solid-phase extraction with C(18) and PAHs were eluted with acetonitrile. PAHs were determined by isotope dilution gas chromatography with electron impact mass spectrometric detection in the selected ion-monitoring mode (GC-MS-SIM), using deuterated PAHs as internal standards. The limits of detection ranged from 0.03 ng/g for acenaphthylene to 0.45 ng/g for benzo[b]naphtho[2,1-d]thyophene. After optimization, the method was validated with a certified reference sludge. The proposed analytical method was applied to determine PAH levels in sewage sludge samples collected from 19 water treatment plants located in the province of Madrid (Spain). In most of the examined samples, phenanthrene was the main compound with a mean concentration of 1062 ng/g. PAHs were detected in all of the samples, with total concentrations between 390 and 6390 ng/g dry weight for the 27 PAHs analyzed and from 310 to 5120 ng/g dry weight for the sum of the 10 PAHs considered in the draft European Union directive.     

Light‐triggered antifouling coatings for porous silicon optical transducers

Nanostructured porous silicon (PSi) is an attractive platform for the design of biosensors because of its high sensitivity and selectivity towards various biological targets. Its use for biosensing applications, however, is compromised as a result of interfacial interactions with biological molecules that may accumulate on their surfaces and degrade their performance. We describe a new hybrid system comprising an oxidized PSi (PSiO₂) nanostructure and antifouling (anti‐adsorption), light‐triggered pre‐polymers that promote crosslinking and surface anchoring to Si walls. The incorporation of the pre‐polymers allowed the production of a thick hydrogel layer on the inorganic nanostructure. Coating completely prevents fouling of proteins on the surface without compromising biosensor performance in terms of sensitivity. The strategy developed here provides a convenient means to combine two distinct features of crosslinking and organic–inorganic hybrid fabrication in a “one‐pot” process. Copyright © 2017 John Wiley & Sons, Ltd.     

Reusable sensor based on functionalized carbon dots for the detection of silver nanoparticles in cosmetics via inner filter effect

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots (a-CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440 nm. The presence of cit-AgNPs produces a remarkably quenching of a-CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in “turn-on” of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23 × 10⁻⁵ to 6.19 × 10⁻⁵ mol L⁻¹, with limits of detection (LOD) and quantification (LOQ) of 5.17 × 10⁻⁶ and 1.72 × 10⁻⁵ mol L^−1, respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods.     

Isocratic and gradient elution in micellar liquid chromatography with Brij‐35

Polyoxyethylene(23)lauryl ether (known as Brij‐35) is a nonionic surfactant, which has been considered as an alternative to the extensively used in micellar liquid chromatography anionic surfactant sodium lauryl (dodecyl) sulfate, for the analysis of drugs and other types of compounds. Brij‐35 is the most suitable nonionic surfactant for micellar liquid chromatography, owing to its commercial availability, low cost, low toxicity, high cloud temperature, and low background absorbance. However, it has had minor use. In this work, we gather and discuss some results obtained in our laboratory with several β‐blockers, sulfonamides, and flavonoids, concerning the use of Brij‐35 as mobile phase modifier in the isocratic and gradient modes. The chromatographic performance for purely micellar eluents (with only surfactant) and hybrid eluents (with surfactant and acetonitrile) is compared. Brij‐35 increases the polarity of the alkyl‐bonded stationary phase and its polyoxyethylene chain with the hydroxyl end group allows hydrogen‐bond interactions, especially for phenolic compounds. This offers the possibility of using aqueous solutions of Brij‐35 as mobile phases with sufficiently short retention times. The use of gradients of acetonitrile to keep the concentration of Brij‐35 constant is another interesting strategy that yields a significant reduction in the peak widths, which guarantee high resolution.     

Structural effects behind the low temperature nonconventional relaxor behavior of the Sr2NaNb5O15 bronze

An exhaustive temperature dependent structural and dielectric study of the tetragonal tungsten bronze-type Sr(2)NaNb(5)O(15) (SNN) compound has been performed in the 300-100 K temperature range, by combining X-ray, neutron diffraction, and transmission electron microscopy with dielectric measurements, in order to clarify the structural effects responsible for the observed low temperature dielectric properties. Interestingly, a relevant second anomaly in the dielectric constant, in addition to the ferroelectric (FE) to paraelectric (PE) transition at T(C) = 518 K is found at T ≈ 240 K, revealing a relaxor-like behavior of the material at low temperature. This phenomenon has been previously observed in FE perovskite-type phases and referred to as the re-entrant phenomenon. However, FE polarization tends to vanish below this low temperature dielectric anomaly and this fact is not expected for a classical relaxor-ferroelectric phase. Although there is no structural transition from RT to 100 K, there is a change in the elastic properties of the material in the considered temperature range and the intense anomaly at ~240 K could be associated to a smeared-out phase transition to a frustrated FE/ferroelastic (FEL) low temperature state in correlation with subtle structural effects.     

A matter-dominated cosmological model with variable G and Λ and its confrontation with observational data

In the framework of renormalization-group improved cosmologies, we analyze both theoretically and observationally the exact and general solution of the matter-dominated cosmological equations, by using the expression of the cosmological term as a function of the Newton parameter already determined by the integration method employed in a previous paper. A rough comparison between such a model and the concordance ΛCDM model from the point of view of the magnitude-redshift relationship has been already considered, without showing any appreciable differences. Here we test our model by using astrophysical data (the Union2 type Ia supernovae (SNIa) dataset, the Hubble diagram constructed from some gamma ray bursts luminosity distance indicator), to constrain its parameters. We also apply a cosmographic approach to our cosmological model. In order to estimate the cosmographic parameters we fit a large dataset, including not only the Hubble diagram, as traced by SNIa and gamma ray bursts, but also the H(z) measurements from passively evolving galaxies, baryon acoustic oscillations and the distance priors from the cosmic microwave background radiation anisotropy spectrum. We show that this matter-dominated cosmological model with variable Newton parameter and variable cosmological term is indeed compatible with the observations above. The cosmographic approach adopted confirms such conclusions. Last, it seems possible to include radiation into the model, since numerical integration of the equations derived by the presence of both radiation and matter shows that, after inflation, the total density parameter is initially dominated by the radiation contribution and later by the matter one.     

Determination of tetrabromobisphenol-A,tetrachlorobisphenol-A and bisphenol-A in soil by ultrasonic assisted extraction and gas chromatography–mass spectrometry

In this work, an isotope dilution method for the determination, in agricultural and industrial soil samples, of tetrabromobisphenol-A, tetrachlorobisphenol-A and bisphenol-A by gas chromatography–mass spectrometry was developed. The compounds were extracted from soil by sonication assisted extraction in small columns (SAESC) with a low volume of ethyl acetate as extraction solvent. For dirty soil samples, such as industrial soils, a simultaneous clean-up on an acidified Florisil–anhydrous sodium sulfate mixture was carried out to remove interferences. After extraction, solvent was evaporated and analytes were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and determined by isotope dilution gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC–MS–SIM), using ¹³C₁₂ labeled compounds as internal standards. Recoveries from spiked samples were between 88% and 108% and the estimated limits of detection (S/N = 3) varied from 30 pg g⁻¹ to 90 pg g⁻¹. The response obtained with this method was linear over the range assayed, 5–300 ng ml⁻¹, with correlation coefficients equal or higher than 0.999. The validated method was used to investigate the levels of these phenolic compounds in soil samples collected from different locations in Spain. Bisphenol-A was detected in all samples at concentrations from 0.7 ng g⁻¹ to 4.6 ng g⁻¹ in agricultural soils and from 1.1 ng g⁻¹ to 44.5 ng g⁻¹ in industrial soils. Tetrabromobisphenol-A was found in various soil samples at levels in the range of 3.4–32.2 ng g⁻¹ in industrial soils and at 0.3 ng g⁻¹ in one agricultural soil, whereas tetrachlorobisphenol-A was not detected.     

Self-aggregation of fibrillar collagens I and II involves lysine side chains

Several properties of fibrillar collagens depend on abundance and position of ionic amino acids. We recently demonstrated that N-methylation and N-acetylation of Lys/Hyl amino group did not significantly alter the thermal stability of the triple helical conformation and that the binding of modified collagens I and II to decorin is lost only on N-acetylation. The positive charge at physiological pH of Lys/Hyl side chains is preserved only by N-methylation. We report here the new aspect of the influence of the same modifications on collagen self-aggregation in neutral conditions. Three collagen preparations are very differently affected by N-methylation: acid-soluble type I collagen maintains the ability to form banded fibrils with 67-nm periodicity, whereas almost no structured aggregates were detected for pepsin-soluble type I collagen; pepsin-soluble type II collagen forms a very different supramolecular species, known as segment long spacing (SLS). N-acetylation blocks the formation of banded fibrils in neutral conditions (as did all other chemical modifications reported in the literature), demonstrating that the positive charge of Lys/Hyl amino groups is essential for self-aggregation. Kinetic measurements by turbidimetry showed a sizeable increase of absorbance only for the two N-methylated samples forming specific supramolecular aggregates; however, the derivatization affects aggregation kinetics by increasing lag time and decreasing maximum slope of absorbance variation, and lowers aggregation competency. We discuss that the effects of N-methylation on self-aggregation are caused by fewer or weaker salt bridges and by decrease of hydrogen bonding potential and conclude that protonated Lys side chains are involved in the fibril formation process.