Luís Moreira Gonçalves

Dye-sensitized solar cells: A safe bet for the future.

This review describes the main features of dye-sensitized solar cells (DSCs) and highlights recent breakthroughs in this promising thin-film photovoltaic (PV) technology. After a brief presentation of the commercially available technologies, the general operation principles and the most relevant characteristics of DSCs are summarized. Recent major advances in high efficiency sensitizers, nanostructured semiconductors and robust electrolytes offer an opportunity for DSCs integration into the marketplace. With attractive features, like low-cost potential, simple processing, wide range of applicability – from low-power electronics to semi-transparent windowpanes for electricity generation – and good performance under typical operating conditions, these cells are one step from large-scale commercialization. We describe major strategies that are under way to make DSCs a key technology in the future PV paradigm.

Isolation of phenolic compounds from hop extracts using polyvinylpolypyrrolidone: characterization by high-performance liquid chromatography-diode array detection-electrospray tandem mass spectrometry.

The aim of the present work was the development of a suitable methodology for the separation and determination of phenolic compounds in the hop plant. The developed methodology was based on the sample purification by adsorption of phenolic compounds from the matrix to polyvinylpolypyrrolidone (PVPP) and subsequent desorption of the adsorbed polyphenols with acetone/water (70:30, v/v). At last, the extract was analyzed by HPLC-DAD and HPLC-ESI-MS/MS. The first phase of this work consisted of the study of the adsorption behavior of several classes of phenolic compounds (e.g. phenolic acids, flavonols, and flavanols) by PVPP in model solutions. It has been observed that the process of adsorption of the different phenolic compounds to PVPP (at low concentrations) is differentiated, depending on the structure of the compound (number of OH groups, aromatic rings, and stereochemistry hindrance). For example, within the phenolic acids class (benzoic, p-hydroxybenzoic, protocatechuic and gallic acids) the PVPP adsorption increases with the number of OH groups of the phenolic compound. On the other hand, the derivatization of OH groups (methylation and glycosylation) resulted in a greatly diminished binding. The use of PVPP revealed to be very efficient for adsorption of several phenolic compounds such as catechin, epicatechin, xanthohumol and quercetin, since high adsorption and recovery values were obtained. The methodology was further applied for the extraction and isolation of phenolic compounds from hops. With this methodology, it was possible to obtain high adsorption values (>or=80%) and recovery yield values (>or=70%) for the most important phenolic compounds from hops such as xanthohumol, catechin, epicatechin, quercetin and kaempferol glycosides, and in addition it allows the identification of about 30 phenolic compounds by HPLC-DAD and HPLC-ESI-MS/MS.

Another glimpse over the salting-out assisted liquid–liquid extraction in acetonitrile/water mixtures

The use of the salting-out effect in analytical chemistry is very diverse and can be applied to increase the volatility of the analytes in headspace extractions, to cause the precipitation of proteins in biological samples or to improve the recoveries in liquid-liquid extractions. In the latter, the salting-out process can be used to create a phase separation between water-miscible organic solvents and water. Salting-out assisted liquid-liquid extraction (SALLE) is an advantageous sample preparation technique aiming HPLC-UV analysis when developing analytical methodologies. In fact, some new extraction methodologies like QuEChERS include the SALLE concept. This manuscript discusses another point of view over SALLE with particular emphasis over acetonitrile-water mixtures for HPLC-UV analysis; the influence of the salting-out agents, their concentration and the water-acetonitrile volume ratios were the studied parameters. α-dicarbonyl compounds and beer were used as test analytes and test samples, respectively. The influence of the studied parameters was characterized by the obtained phase separation volume ratio and the fraction of α-dicarbonyls extracted to the acetonitrile phase. Results allowed the distribution of salts within three groups according to the phase separation and their extractability: (1) chlorides and acetates, (2) carbonates and sulfates and (3) magnesium sulfate; of all tested salts, sodium chloride had the highest influence on the α-dicarbonyls fraction extracted.

Analysis of aldehydes in beer by gas-diffusion microextraction: Characterization by high-performance liquid chromatography–diode-array detection–atmospheric pressure chemical ionization–mass spectrometry

In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis.

Increased sensitivity of anodic stripping voltammetry at the hanging mercury drop electrode by ultracathodic deposition.

An improved approach to the anodic stripping voltammetric (ASV) determination of heavy metals, using the hanging mercury drop electrode (HMDE), is reported. It was discovered that using very cathodic accumulation potentials, at which the solvent reduction occurs (overpotential deposition), the voltammetric signals of zinc(II), cadmium(II), lead(II) and copper(II) increase. When compared with the classical methodology a 5 to 10-fold signal increase is obtained. This effect is likely due to both mercury drop oscillation at such cathodic potentials and added local convection at the mercury drop surface caused by the evolution of hydrogen bubbles.

Supramolecular interactions in dye-sensitised solar cells

A new Li+-coordinating perylene monoimide dye has been synthesised. The dye was used as a sensitiser in dye-sensitised solar cells (DSCs), and the effect of Li+ coordination on the device performance was analyzed using various spectroscopic techniques.

Determination of Free and Total Sulfites in Wine using an Automatic Flow Injection Analysis System with Voltammetric Detection

An automated flow injection analysis (FIA) system, based on an initial analyte separation by gas-diffusion and subsequent determination by square-wave voltammetry (SWV) in a flow cell, was developed for the determination of total and free sulfur dioxide (SO2) in wine. The proposed method was compared with two iodometric methodologies (the Ripper method and a simplified method commonly used by the wine industry). The developed method displayed good repeatability (RSD lower than 6%) and linearity (between 10 and 250 mg l−1) as well as a suitable LOD (3 mg l−1) and LOQ (9 mg l−1). A major advantage of this system is that SO2 is directly detected by flow SWV.

An Overview on Cardamonin

Cardamonin, as shown by the increasing number of publications, has received growing attention from the scientific community due to the expectations toward its benefits to human health. In this study, research on cardamonin is reviewed, including its natural sources, health promoting aspects, and analytical methods for its determination. Therefore, this article hopes to aid current and future researchers on the search for reliable answers concerning cardamonins value in medicine.

Gas-diffusion microextraction.

Gas-diffusion microextraction (GDME) is an innovative technique that combines the advantages of membrane-aided gas-diffusion with microextraction concepts. GDME makes uses of a novel portable and low-cost device that comprises a small, commercially available, semi-permeable membrane. Furthermore, if derivatization is integrated into the GDME concept, considerable enrichment factors can be obtained. It may become a powerful tool for any analyst who intends to quantify volatile and semi-volatile analytes in various kinds of matrices. The analysis of vicinal diketones in beer was used as a case study to show GDME applicability and capabilities. Vicinal diketones were derivatized with o-phenylenediamine and then determined by HPLC-UV. Obtained results showed good repeatability and precision with extraction periods at the minute time span.

The indirect electrochemical detection and quantification of DNA through its co-adsorption with anthraquinone monosulphonate on graphitic and multi-walled carbon nanotube screen printed electrodes

The voltammetric responses arising from the co-adsorption of anthraquinone monosulfonate and DNA on to a graphitic electrode are reported. The electrochemical responses of these two species show that the adsorbed species are non-interacting and further they occupy similar sites upon the electrode surface. Consequently it is demonstrated that there is an inverse linear relationship between the surface concentrations of the two species, such that it is possible to indirectly measure the quantity of adsorbed DNA to the electrode through the voltammetric signal of the co-adsorbed anthraquinone monosulfonate. This system is developed through the use of multiwalled carbon nanotube screen-printed electrodes to provide a proof-of-concept analytical methodology via which it is possible to accurately analyse the concentration of a DNA solution, where the limit of detection is shown to be 8.8 μM (equivalent to 5.9 μg/mL).