Evaluation of Electrospray as a Sample Preparation Tool for Electron Microscopic Investigations: Toward Quantitative Evaluation of Nanoparticles.

The potential of electrospray deposition, for the controlled preparation of particles for imaging in electron microscopes, is evaluated on various materials: from mono-modal suspensions of spherical particles to multimodal suspensions and to real-world industrial materials. It is shown that agglomeration is reduced substantially on the sample carrier, compared with conventional sample preparation techniques. For the first time, it is possible to assess the number concentration of a tri-modal polystyrene suspension by electron microscopy, due to the high deposition efficiency of the electrospray. We discovered that some suspension stabilizing surfactants form artifact particles during electrospraying. These can be avoided by optimizing the sprayed suspension.

A flowing atmospheric pressure afterglow as an ion source coupled to a differential mobility analyzer for volatile organic compound detection.

Atmospheric pressure glow discharges have been widely used in the last decade as ion sources in ambient mass spectrometry analyses. Here, an in-house flowing atmospheric pressure afterglow (FAPA) has been developed as an alternative ion source for differential mobility analysis (DMA). The discharge source parameters (inter-electrode distance, current and helium flow rate) determining the atmospheric plasma characteristics have been optimized in terms of DMA spectral simplicity with the highest achievable sensitivity while keeping an adequate plasma stability and so the FAPA working conditions finally selected were: 35 mA, 1 L min(-1) of He and an inter-electrode distance of 8 mm. Room temperature in the DMA proved to be adequate for the coupling and chemical analysis with the FAPA source. Positive and negative ions for different volatile organic compounds were tested and analysed by FAPA-DMA using a Faraday cup as a detector and proper operation in both modes was possible (without changes in FAPA operational parameters). The FAPA ionization source showed simpler ion mobility spectra with narrower peaks and a better, or similar, sensitivity than conventional UV-photoionization for DMA analysis in positive mode. Particularly, the negative mode proved to be a promising field of further research for the FAPA ion source coupled to ion mobility, clearly competitive with other more conventional plasmas such as corona discharge.

Differentiation and identification of white wine varieties by using electropherogram fingerprints obtained with CE.

This article reports a method for determining organic acids by CE in order to obtain a characteristic fingerprint with a view to classifying white wine samples with the aid of multivariate statistics. The proposed method was optimized for the determination of the most abundant organic acids in wine (viz. succinic, malic, tartaric, citric, acetic and lactic). The acids were separated in a running buffer consisting of 180 mM disodium hydrogen phosphate, 0.5 mM CTAB and 10% methanol, adjusted to pH 7.5. The applied voltage was 10 kV and the working temperature 25 degrees C. The precision of the method was assessed by replicate analysis of a wine sample; the resulting RSD was less than 5.2% in peak area and less than 1% in migration time for all organic acids. Calibration curves exhibited good linearity throughout the studied concentration range for all acids. Principal component analysis and linear discriminant analysis allowed accurate classification of wine samples with variable alcohol contents from their electrophoretic fingerprints. The discriminant potential of various electropherogram regions was examined. Based on the results, the proposed method is an effective choice for classifying wine samples.

Novel techniques for detection and characterization of nanomaterials based on aerosol science supporting environmental applications.

The number of people exposed to nanoparticles is growing accordingly to the production and development of new nanomaterials. Moreover, this increase is expected to continue in the future. However, there is a lack of standardized sampling and metric methods to measure the level of exposure to nanoparticles, and the information related to possible adverse health effects is scarce. Aerosol technology has been detecting and characterizing nanoparticles for decades and some of their developments can be of use in nanotechnology characterization. We present here two current developments based on used principles in aerosol science, which can widen its application to the characterization of nanomaterials. On the one hand, a sample preparation technique for nanoparticle analysis by electron microscopy based on electrospray atomization technology. Several samples prepared in this way have been analysed and compared to more traditional sample preparation strategies like the "drop on grid" method. It was found that the particles deposited by electrospray generally show a much more homogeneous spatial distribution on the substrate and the number of single particles increases substantially. On the other hand, it is presented an electrical mobility classification system, DMA, with enormous possibilities for the quick and economic size characterization of suspensions of nanoparticles, thanks to its injection system by electrospray and to its high resolution in the lower range of the nanoscale. The first assessment of the abovementioned devices highlights its potential applications in exposure assessment and nanotechnological contexts.

Structure of liquids composed of shifted dipole linear molecules.

Simulation results for liquids composed of linear molecules interacting through dispersion forces and off-center dipoles are presented. Remarkable differences are found on the vapor-liquid equilibrium respect to that of centered dipole molecules. Even more remarkable is the appearance of additional short-range liquid structure at relatively large dipoles and aspect ratios. The existence of dipole dimers is clearly established, and some suggestions allowing for the correspondence between a particular macroscopic phenomenology and a particular dispersion potential function are presented.

Characterization of a new mobility separation tool: HRIMS as differential mobility analyzer.

High resolution ion mobility spectrometer (HRIMS) is a new instrument that uses parallel plate Differential Mobility Analysis as principle of separation. Gas phase analysis of volatile organic compounds (VOCs) has been performed for the characterization of this new mobility system using an UV-lamp for ionization. Studies of the effect of temperature and the presence of a desiccant are detailed. Identification of the different peaks obtained with an electrometer was successfully carried out for a group of alcohols, aromatic compounds and ketones (ethanol, 1-propanol, isopropanol, 1-butanol, 1-pentanol, 1-heptanol, acetone, 2-butanone, 2-pentanone, 2-octanone, benzene, toluene, xylene and bromobenzene) following a modified Millikan equation. Moreover, the investigation of the discrimination capabilities within the different VOCs families as well as the mobility dependence with molecular mass was successfully achieved.

Feasibility study on the use of infrared spectroscopy for the direct authentication of Iberian pig fattening diet.

The feasibility of using both middle- and near-infrared spectroscopy for discrimination between subcutaneous fat of Iberian pigs reared on different fattening diets has been evaluated. The sample set was formed by subcutaneous fat of pigs fattened outdoors (extensively) with natural resources (montanera) and pigs fattened on commercial feeds, either with standard feed or with especial formulations with higher content in oleic acid (HO-formulated feed). Linear discriminant analysis was used to classify the samples according to the fattening diet using the scores obtained from principal component analysis of near- and middle-infrared spectra as variables to construct the discriminant functions. The most influential variables were identified using a stepwise procedure. The discriminant potential of each spectral region was investigated. Best results were obtained with the combination of both regions with 91.7% of the standard feed and 100% of montanera and HO-formulated feed samples correctly classified. Chemical explanations are provided based on the correlation of these variables with fatty acid content in the samples.