Use of Uncertainty Calculation Software as a Didactic Tool to Improve the Knowledge of Chemistry Students in Analytical Method Validation.

Calculating analytical uncertainties as a part of method validation is a relevant aspect of field and laboratory practices in instrumental analytical chemistry subjects, which usually require complex algorithms. This work describes the development and didactic use of an automatic and straightforward informatics tool, implemented in an Excel macro, for calculating and interpreting the uncertainty of an analytical method against a reference method on field measurements. The software was initially developed for field testing of low-cost air quality monitoring analytical methods against reference methods, and the present work shows its adaptation to a didactic environment. The uncertainty calculation software was implemented through an Excel macro based on Visual Basic as a graphical user interface. It finds a best-fit line that describes the relation between concentrations determined by the candidate and reference methods. The software generates the analytical validation results (slope and intercept with their respective confidence limits, and expanded uncertainty of a concentration determined by the candidate method), hiding the intermediate functions and calculations. The Excel interface eases uncertainty calculations for undergraduate students, although the background mathematics can be quickly unveiled to students for didactic purposes. This tool has been applied to a laboratory exercise focused on validating experimental results obtained in the measurement of ozone levels in ambient air by passive sampling and spectrophotometric detection. The uncertainty calculation software has proved valuable by providing the student a resource to check the analytical quality of the data generated in the laboratory, while assimilating the fundamentals behind the calculations.

Wearable system for outdoor air quality monitoring in a WSN with cloud computing: Design, validation and deployment.

Breathing poor-quality air is a global threat at the same level as unhealthy diets or tobacco smoking, so the availability of affordable instrument for the measurement of air pollutant levels is highly relevant for human and environmental protection. We developed an air quality monitoring platform that comprises a wearable device embedding low-cost metal oxide semiconductor (MOS) gas sensors, a PM sensor, and a smartphone for collecting the data using Bluetooth Low Energy (BLE) communication. Our own developed app displays information about the air surrounding the user and sends the gathered geolocalized data to a cloud, where the users can map the air quality levels measured in the network. The resulting device is small-sized, light-weighted, compact, and belt-worn, with a user-friendly interface and a low cost. The data collected by the sensor array are validated in two experimental setups, first in laboratory-controlled conditions and then against referential pollutant concentrations measured by standard instruments in an outdoor environment. The performance of our air quality platform was tested in a field testing campaign in Barcelona with six moving devices acting as wireless sensor nodes. Devices were trained by means of machine learning algorithms to differentiate between air quality index (AQI) referential concentration values (97% success in the laboratory, 82.3% success in the field). Humidity correction was applied to all data.

Accelerating Aging of White and Red Wines by the Application of Hydrostatic High Pressure and Maceration with Holm Oak (Quercus ilex) Chips. Influence on Physicochemical and Sensory Characteristics.

BACKGROUND: The use of holm oak (Quercus ilex) chips as a potential alternative wood and the application of hydrostatic high pressure (HHP) as an alternative technique to accelerate the release to the wine of wood-related compounds within a short processing time were evaluated. METHODS: Five treatments were investigated: (i) bottling without any treatment (B); (ii) and (iii) bottling after maceration (5 g/L) of holm oak chips with HHP treatments (400 MPa, 5 and 30 min) (HHP5, HHP30); (iv) bottling after maceration during 45 days with chips (M), and; (v) maceration in tanks without chips (T). The effects of treatments on general parameters, polyphenols, color, and sensorial characteristics of red and white wines were investigated over 180 days. RESULTS: HHP5, HHP30, and M increased the polyphenols content, thus modified the chromatic characteristics regarding B and M treatments of white wines, also the tasters differentiated HHP5, HHP30, and M from B and T. However, these effects were not observed in red wines. Thus, the effect of the wood depends on the type of wine in which it is used. CONCLUSIONS: This research contributes to better knowledge about these chips as a new alternative wood species and the use of HHP as a useful technology to accelerate the aging of wines.

Screen-Printed Gold Electrodes as Passive Samplers and Voltammetric Platforms for the Determination of Gaseous Elemental Mercury.

We present a methodology for the determination of gaseous elemental mercury (GEM). It is based on passive sampling of Hg on screen-printed gold electrodes (SPGEs), followed by the measurement of amalgamated mercury by square wave anodic stripping voltammetry. We have explored in detail the behavior of the SPGE electrode surface during the sampling process (by time-of-flight secondary ion mass spectrometry), the stability of the voltammetric signals, and the inter-electrode reproducibility, and obtained acceptable results. Adsorption of mercury onto the SPGE follows a nearly linear behavior until the sorbent becomes saturated (equilibrium phase) for different mercury concentrations, allowing to select a sampling time of 30 min for calibration. The theoretical behavior of the sampling system was modeled, considering the changes in the diffusive path length between the porous diffusive barrier and the adsorbed surface, L. Finally, we have tested two GEM calibration protocols. The first one is based on the measurement of the mercury stripping peak area, AHg, and the second one is based on the measurement of the mass of mercury, mHg, by standard additions. We found good correlation coefficients between the GEM concentration for both AHg (R2 = 0.9591) and mHg (R2 = 9615) in the range of 5.82 to 59.29 ng dm-3 GEM. Detection limits were 5.32 and 5.22 ng dm-3 for AHg and mHg, respectively. Our results open a new line of electroanalytical strategies for the determination of GEM in atmospheric samples.

Radon and thoron exhalation rate, emanation factor and radioactivity risks of building materials of the Iberian Peninsula.

Radon (222Rn) and thoron (220Rn) are radioactive gases emanating from geological materials. Inhalation of these gases is closely related to an increase in the probability of lung cancer if the levels are high. The majority of studies focus on radon, and the thoron is normally ignored because of its short half-life (55.6 s). However, thoron decay products can also cause a significant increase in dose. In buildings with high radon levels, the main mechanism for entry of radon is pressure-driven flow of soil gas through cracks in the floor. Both radon and thoron can also be released from building materials to the indoor atmosphere. In this work, we study the radon and thoron exhalation and emanation properties of an extended variety of common building materials manufactured in the Iberian Peninsula (Portugal and Spain) but exported and used in all countries of the world. Radon and thoron emission from samples collected in the closed chamber was measured by an active method that uses a continuous radon/thoron monitor. The correlations between exhalation rates of these gases and their parent nuclide exhalation (radium/thorium) concentrations were examined. Finally, indoor radon and thoron and the annual effective dose were calculated from radon/thoron concentrations in the closed chamber. Zircon is the material with the highest concentration values of 226Ra and 232Th and the exhalation and emanation rates. Also in the case of zircon and some granites, the annual effective dose was higher than the annual exposure limit for the general public of 1 mSv y-1, recommended by the European regulations.

Nafion-Protected Sputtered-Bismuth Screen-Printed Electrode for On-site Voltammetric Measurements of Cd(II) and Pb(II) in Natural Water Samples.

In this work, we explore the protection with Nafion of commercial sputtered-bismuth screen-printed electrodes (BiSPSPEs), to improve its ability for on-site determination of Cd(II) and Pb(II) ions in ambient water samples. The modified screen-printed platform was coupled with a miniaturized cell, in combination with a battery-operated stirring system and a portable potentiostat operated by a laptop for decentralized electrochemical measurements using Square-Wave Anodic Stripping Voltammetry (SWASV). We also describe a detailed electrode surface characterization by microscopy and surface analysis techniques, before and after the modification with Nafion, to get insight about modification effect on signal size and stability. Optimization of the chemical composition of the medium including the optimization of pH, and instrumental parameters, resulted in a method with detection limits in the low ng/mL range (3.62 and 3.83 ng·mL-1 for Cd and Pb respectively). Our results show an improvement of the sensitivity and stability for Nafion-protected BiSPSPEs in pH = 4.4 medium, and similar or lower detection limits than comparable methods on commercial BiSPSPEs. The values obtained for Pb(II) and Cd(II) in natural water samples agreed well with those obtained by the much more costly Inductively Coupled Plasma Mass Spectrometry, ICP-MS, technique as a reference method (recoveries from 75% to 111%).

Assessment fertigation effects on chemical composition of Vitis vinifera L. cv. Albariño.

Vineyard management can influence the growth and yield components in the vineyards and therefore on the grape and wine quality. In this work, a chemical study was conducted (2014-2015) to examine the effect of fertigation on chemical composition of Albariño. A control (Rain-fed) and fertigation (60% and 100%) treatments were apply at same irrigation depth, where fertigation 100% is complete nutrient requirements to Albariño trellis system in this location (Rias Baixas AOC, NW Spain). Results showed that non-volatile compounds of Albariño musts were not affected by fertigation treatments. However, the effect of fertigation treatments on the volatile composition was observed. Terpenes and C13-norisoprenids were the most affected families of volatile compounds by fertigation treatments, where 60% fertigation exhibited the highest concentration, improving the wine aroma quality. Application of principal component analysis (PCA) showed a good separation of Albariño grape according to fertigation treatments and vintages.

Theoretical study of the preferential solvation effect on the solvatochromic shifts of para-nitroaniline.

The origin of the nonlinear solvatochromic shift of para-nitroaniline was investigated using a mean-field sequential QM/MM method, with electron transitions computed at the CASPT2/cc-pVDZ level. Experimental data shows that the solvatochromic shift has a strong nonlinear behavior in certain solvent mixtures. We studied the case of cyclohexane-triethylamine mixtures. The results are in good agreement with the experiments and correctly reproduce the nonlinear variation of the solvent shift. Preferential solvation is clearly observed, where the local solvent composition in the neighborhood of the solute is significantly different from the bulk. It is found that even at low triethylamine concentrations a strong hydrogen bond is formed between para-nitroaniline and triethylamine, and cyclohexane is practically absent from the first solvation layer already at a molar fraction of 0.6 in triethylamine. The hydrogen bond formed is sufficiently long-lived to determine an asymmetric environment around the solute molecule. The resulting nonlinear solvent effect is mainly due to this hydrogen bond influence, although there is also a small contribution from dielectric enrichment.