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A matrix assisted laser desorption/ionization time-of-flight mass spectrometer has been built with an ion source that can be operated in either constant-energy or constant-momentum acceleration modes. A decreasing electric field distribution in the ion-accelerating region makes it possible to direct ions onto a space-focal plane in either modes of operation. Ions produced in the constant-momentum mode have velocities and, thus, flight times that are linearly dependent on mass and kinetic energies that are inversely dependent on mass. The linear mass dispersion doubles mass resolving power of ions accelerated with space-focusing conditions in constant-momentum mode. The mass-dependent kinetic energy is exploited to disperse ions according to mass in a simple kinetic energy filter constructed from two closely spaced, oblique ion reflectors. Focusing velocity of ions of the same mass can substantially improve ion selection for subsequent post source decay or tandem time-of-flight analyses. (J Am Soc Mass Spectrom 2007, 18, 92-101)

Eight vegetable dyes extracted from flowers, fruits and leaves abundant in the wide biodiversity of the Andes region of South America were extracted with ethanol without purification to explore as vegetable photosensitizers in dye-sensitized solar cells (DSSCs). The absorbance spectra were measured by UV-visible spectroscopy and the photoelectrical performance of the DSSCs based on these dyes with a homemade solar simulator, constructed only for educational purposes under 1 sun of illumination. The open-circuit voltages (V oc) and the short-circuit photocurrent densities (J sc) varied from 0.39 to 0.48 V and from 0.04 to 0.56 mA cm −2 , and the power conversion efficiency (PCE) ranged from 0.01 to 0.18%. Particularly, the highest V oc and PCE values of the DSSCs sensitized by the ethanol extracts of Mortiño fruit (Vaccinium floribundum) and Jamaica flowers (Hibiscus sabdariffa) without purification were presumably associated with anthocyanin, the most effective component present in both vegetable photosensitizers. Hence, various components of the ethanol extracts obtained from these two vegetable dyes were purified by liquid-liquid extraction using different organic solvents of different polarity, namely petroleum ether, chloroform, ethyl acetate, n-butanol, and distilled water. Ethyl acetate resulted as the most favorable solvent for purification of ethanol extracts from Mortiño fruit and Jamaica flowers to use as vegetable photosensitizers in DSSCs. The PCE of the DSSC fabricated with the dye extracted in ethyl acetate from Mortiño fruit achieved 0.33%, with V oc of 0.520 V and J sc of 1.014 mA cm −2 , whereas the corresponding values obtained from the dye extracted from Jamaica flowers reached 0.22% with V oc of 0.541 V and J sc of 0.678 mA cm −2. Thus, the purification of vegetable dyes used as photosensitizer impacts the photoelectrochemical performance of DSSCs.

Photovoltaic energy presents environmental advantages; however, these advantages are limited by the cost of manufacturing solar cells and in many cases, scarce or dangerous materials are incorporated. Therefore, the use of natural dyes from mortiño (Vaccinium floribundum) as sensitizers in solar cells is proposed. The dyes were extracted by maceration in acidified methanol (HCl, citric acid and trifluoroacetic acid TFA) and were characterized by High-Performance Liquid Chromatography (HPLC), Thin-Layer Chromatography (TLC) and spectrometric methods (UV-Vis, IR and MS-MALDI). The construction and characterization of cells were in standard conditions. The study confirms that pigments in mortiño are flavonoids of the anthocyanidin group as: cyanidin-3-galactoside, and cyanidin-3-arabinoside. The efficiency of solar cells was between 0.18–0.26%; the extraction with TFA in methanol leads to the best performance. Although they have low power conversion efficiency, mortiño dyes could be an alternative to artificial sensitizers for solar cell technologies because they are harmless and abundant substances.

A matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometer has been built with the capabilities to perform structural analyzes. The first time-of-flight mass spectrometer includes a timing ion gate to select the ions to be analyzed. After the selection process, the ions are activated using an electrically floating collision cell. The fragments produced in the collision cell are analyzed in the second time-of-flight stage. A two-step mass calibration procedure is introduced that allows one to obtain accurate mass values. The characteristics of this calibration procedure make possible to automate it. The experimental results of the tandem mass spectrometer and calibration procedure using different standard peptides are presented.

Most dyes used in the textile industry are chemically stable and poorly biodegradable, therefore, they are persistent in the environment and difficult to degrade by conventional methods. An alternative treatment for this kind of substance is heterogeneous photocatalysis using TiO2, so, in this work, it is proposed to degrade Direct Blue 1 (DB1) using microparticulate TiO2 irradiated with e-beam at three different doses: 5, 10 and 20 kGy (J/kg). The DB1 degradation was implemented in a batch reactor (DB1 initial concentration = 50 mg L−1, pH 2.5, TiO2 concentration = 200 mg L−1). We have demonstrated that the photocatalytic power of TiO2, when irradiated with e-beam (5, 10, 20 kGy), varies slightly, with minor effects on photodegradation performance. However, the dose of 10 kGy showed a slightly better result, according to the DB1 photodegradation rate constant. Adsorption process was not affected by irradiation; its isotherm was fitted to Freundlich’s mathematical model. The DB1 photodegradation rate constants, after one hour of treatment, were: 0.0661 and 0.0742 min−1 for irradiated (10 kGy) and nonirradiated TiO2, respectively. The degradation rate constant has an increase of 12.3% for irradiated TiO2. Finally, there was no evidence of mineralization in the degradation process after 60 min of treatment. According to the results, the irradiation of microparticulate TiO2 with e-beam (10 kGy) slightly improves the photodegradation rate constant of DB1.

The characterization of a mixture of cucurbit [n]uril (n=6,7,8) was carried out by MALDI MS (Matrix-assisted Laser Desorption/Ionization Mass Spectrometry Mass Spectrometry). The solid mixture of the titled compounds was synthesized as part of a research study involving supramolecular chemistry at the Departamento de Química e Ingeniería Química at USFQ. For the MALDI analysis, an appropriate procedure was implemented for sample preparation, which includes the effective dissolution of the solid mixture of cucurbit[n]uril in a solution of water and formic acid, and the addition of alpha-cyano-4-hydroxy cinamic acid as MALDI matrix (10g/l in 70:30 (v:v) of methanol:acetonitrile). In the sample preparation process for MALDI, other solvents were employed to try dissolving the cucurbit[n]uril mixture with poor results. The addition of formic acid to deionized water was important to achieve satisfactory dissolution of the cucurbit[n]uril compounds and to assure its compatibility with the matrix. To acquire the corresponding mass spectra, a MALDI-Time-of-Flight Mass Spectrometer (MALDI-TOF MS) was used, which was built in the Departamento de Física at EPN. The mass spectra of the detected cucurbit[n]uril ions were characterized by the presence of the single protonated peaks of three molecular species corresponding to n=6,7,8 as inferred from their m/z values. Additionally, the mass spectra contained abundant peaks of the MALDI matrix in the mass region up to 500 Da. The mass spectra were satisfactorily internally calibrated with the help of multiple peaks of a PEG600 polymer that was introduced as an internal standard in the sample. The instrumental molecular mass resolution allowed for isotopical resolution over the whole mass range and the overall mass accuracy was about 0.1 %. The most intense signal among the cucurbit[n]uril peaks was assigned to the cucurbit [7]uril compound. A discussion is advanced to rationalize the observed molecular cucurbit[n]uril species under the used methodology. Keywords. cucurbit[n]uril, glicoluril, MALDI, alpha-cyano-4-hydroxy cinnamic acid, TOF MS ResumenLa caracterización de una mezcla de cucurbit[n]uriles (n=6,7,8) se ha realizado por medio de espectrometría de masas con la técnica de ionización MALDI (Matrix-assisted Laser Desorption/Ionization). Los cucurbit[n]uriles fueron sintetizados como parte de una investigación de química supramolecular dentro del Departamento de Química e Ingeniería Química de la USFQ. Para el análisis con MALDI se ha introducido un procedimiento adecuado para la preparación de muestras, que incluye la disolución efectiva de la mezcla sólida de cucurbit[n]uriles en una solución de agua y ácido fórmico, y el uso del ácido alfa-ciano-4-hidroxi-cinámico como matriz MALDI, en una solución 10g/l en 70:30 (v:v) de metanol y acetronitrilo. En el proceso de preparación de muestras para MALDI se intentó utilizar otros solventes para el cucurbit[n]uril con pobres resultados. La adición del ácido fórmico al agua desionizada fue importante para lograr la corr...

Abstract. In the future dye-sensitized solar cells might become an attractive alternative to primary energy sources, due to their low cost and low environmental impact. However, the most efficient sensitizer molecule is based on Ruthenium, a low abundance material. Therefore, many research groups all over the world try to find alternative novel and efficient dye molecules. Among various approaches, one research area focuses on natural pigments. This work describes the extraction and purification of genipin, a monoterpene iridoid extracted from Genipa Americana L., and the synthesis of an allnatural sensitizer based on it. The genipin-based dyes were characterized by FT-IR spectroscopy, UV/VIS spectroscopy and thermogravimetric analysis. Synthesized pigments showed absorption spectra around 590 nm and thermal stability up to 100 °C. Finally, the energy conversion efficiency of genipin-based dye sensitized solar cells was evaluated.