Diseño y optimización de nuevos sistemas de análisis de metales pesados en aguas mediante voltamperometría de redisolución adsortiva y sensores ópticos

En la actualidad y, cada vez más, las sustancias contaminantes conocidas por su toxicidad y alta persistencia, no dejan de acumularse en el medioambiente debido fundamentalmente a la actividad del hombre. Las áreas costeras al ser ecosistemas bastante sensibles, son los entornos que se ven más afectados por las actividades industriales y el desarrollo urbanístico. Diversos organismos internacionales, así como numerosos investigadores, advierten ya sobre las consecuencias negativas que la creciente presión demográfica ejercerá en un futuro no muy lejano sobre estos ecosistemas. En particular, la rápida difusión de metales pesados como contaminantes medioambientales ha despertado una gran preocupación, comprobándose en el alto interés que existe actualmente por su determinación, a pesar de que se suelen encontrar a niveles de concentración de trazas y ultratrazas. De hecho, tales elementos tienen tendencia a concentrarse en la mayoría de las matrices acuáticas del medioambiente (materia suspendida, sedimentos y biota), provocando por consiguiente la presencia de los mismos en la cadena alimentaria, como consecuencia de la consumición de productos marinos, llegando finalmente al hombre. La presente Tesis Doctoral tiene como objetivo fundamental el desarrollo de nuevas metodologías analíticas de elevada sensibilidad, bajo coste, capaces de realizar análisis in-situ, así como rápidas y sencillas, entre otras muchas ventajas, para la cuantificación de metales pesados en aguas naturales mediante la formación de quelatos metálicos. Para la consecución de dicho objetivo se han llevado a cabo dos líneas diferentes de investigación para el diseño y optimización de nuevos sistemas de análisis de metales pesados aplicables en aguas naturales, de mar, de río, etc. Por un lado, técnicas de elevada sensibilidad con bajos límites de detección, como es la voltamperometría de redisolución catódica adsortiva (AdCSV) y por otro, técnicas rápidas y sencillas que requieran de pequeña instrumentación, permitiendo así el análisis in-situ, como es el desarrollo de sensores ópticos. Para la formación de los quelatos, se han empleado ligandos orgánicos de la familia de las aroilhidrazonas, ampliamente estudiados y caracterizados como agentes complejantes de metales pesados. La presente Tesis Doctoral comienza con una Introducción General y a continuación, se incluyen dos partes bien diferenciadas: Parte A y Parte B. La parte A consta de los capítulos 1, 2 y 3, y la parte B está formada por los capítulos 4, 5, y 6. En la parte A se lleva a cabo el desarrollo de nuevas metodologías de análisis empleando la voltamperometría de redisolución adsortiva: En el capítulo 1 se hace una revisión general de los aspectos fundamentales tratados en esta primera parte. En el capítulo 2 se detalla una nueva y sensible metodología de análisis para plomo empleando 2-APSH como reactivo orgánico quelatante. Y en el capítulo 3 se describe la aplicabilidad de otra aroilhidrazona, la 2-HBBH en este caso, para la determinación simultánea de metales pesados. Por otro lado, la parte B está dedicada al desarrollo de nuevas metodologías de análisis empleando los sensores ópticos: En el capítulo 4 se exponen los aspectos fundamentales de los sensores ópticos. En el capítulo 5 se estudia el ligando orgánico 2-HBBH como quimiosensor molecular fluorescente selectivo para cobre y se propone como un potencial indicador en el campo de los sensores ópticos. Y, por último, en el capítulo 6 se lleva a cabo el diseño de un sensor de fibra óptica para la determinación de cobre basado en la extracción en fase sólida colorimétrica

Determination of ultra-trace amounts of silver in water by differential pulse anodic stripping voltammetry using a new modified carbon paste electrode

A highly sensitive and selective new procedure for the determination of silver in aqueous media was developed using a modified carbon paste electrode (MCPE) by differential pulse anodic stripping voltammetry (DPASV). The modified electrode was based on the incorporation of 2-hydroxybenzaldehyde benzoylhydrazone (2-HBBH) in the carbon paste electrode. Silver ions were preconcentrated on the modified electrode at open-circuit by complexation with the ligand and reduced to zero valent at a potential of 0V, and followed by the reoxidation of adsorbed ions on to the electrode by scanning the potential in a positive direction. The oxidation peak of Ag (I) was observed at 0.2V (versusAg/AgCl). The analysis of Ag (I) was carried out in a cell containing the sample solution (20mL) buffered by 0.1molL 1K2HPO4/NaOH at pH 5.5 in aqueous solution and nitric acid (pH1) in real water samples. The optimum conditions for the analysis of silver include are duction potential of 0V and a pulse amplitude of 100mV, among others. The optimum carbon paste composition was found to be 14.1% (w/w) 2-HBBH, 56.2% (w/w) graphite powder and 29.7%(w/w) paraffin oil. Differential pulse anodic stripping voltammetric response was used as the analytical signal. Under the selected conditions, the voltammetric signal was proportional to the Ag(I) concentration in the range of 0.001–100 μg L 1 with favorable limits of detection and quantification of 1.1ngL 1 and 3.7ngL 1 after 3 min of accumulation time, respectively. By increasing the accumulation time to 10 min, detection and quantification limits can be further improved up to 0.1ngL 1 and 0.34ngL 1, respectively. In addition, the results showed a highly reproducible procedure showing a relative standard deviation of 1.5% for 12 replicate measurements. Many coexisting metal ions were investigated and very few interferences were found on the determination of Ag(I). The proposed method was validated using certified reference estuarine waters (SLEW-3) with a relative error of 1.3% and applied to the determination of silver ions in three river water samples collected from Guadalquivir river (relative errors of þ3.4%, þ1.5% and 0.7%). Moreover,the method was successfully applied to the speciation analysis of total silver, free silver ions and silver nanoparticles in aqueous solutions. The results were in good agreement with those obtained by inductively coupled plasma mass spectrometry (ICP-MS)

Novel method based on ion mobility spectroscopy for the quantification of adulterants in honeys

According to European Union Regulation, honey is a food product whose composition cannot be modified. However, high-quality honey is often adulterated by adding sweeteners of other sugar compounds. This paper studies the suitability of Ion Mobility Spectra from generated headspace as a method for the detection and discrimination of honey adulterated by different substances. A Box-Behnken design in conjunction with a re sponse surface methodology was employed to optimize five different variables related to headspace generation (incubation temperature, incubation time, injection volume, weight of the samples and pre-heating time). The resulting model showed a regression coefficient of R2 = 88.07%, it is therefore suitable for a reliable selection of the experimental variables. Repeatability and intermediate precision were also evaluated, and coefficients of variation below 5% were obtained (CV of 4.6% and 4.2% respectively). The developed method has been applied to different samples resulting for the mixture of honey and other sweeteners at different percentages (5%–50%) in an attempt to mimic the adulterated products that are more commonly found in the market. A thorough and exact classification (100%) with regards to the presence/absence of adulterant as well as the type of adulterant used has been achieved. A Partial Least Squares regression model was completed in order to determine the percentage of the different adulterants. The prediction error was below 4% in all the cases. These results de monstrate the applicability of the developed method for the detection and quantification of adulterated honey with different adulterant contents

Determination of iodide and total iodine in estuarine waters by cathodic stripping voltammetry using a vibrating silver amalgam microwire electrode

Iodide in natural waters is an important nutrient to aquatic organisms and its determination is of relevance to marine aquaculture. For this reason it is of interest to have a simple analytical method for determination of iodide in water samples. Iodide in seawater can be determined electrochemically by cathodic stripping voltammetry (CSV) with a mercury drop electrode which has environmental drawbacks. In an attempt to minimise the use of mercury in voltammetry, a-vibrating silver amalgam microwire electrode is used here for the determination by CSV of iodide speciation in natural waters including seawater. Microwire electrodes were made from silver wires (diameter: 12.5 mu m) and electrochemically coated with mercury. The electrode surface was stable for extended periods of analyses (at least one week) and was then replaced. The optimised conditions include a pH 8, a frequency of 500 Hz and a deposition time of 60 s, among others. The microwire was reactivated between scans using a conditioning potential at 3 V for 1 s. The detection limit for iodide in seawater was found to be 0.7 nM I- at a deposition time of 60 s. The response increased linearly with the concentration of iodide in seawater up to 100 nM I-. The method was successfully applied to various samples from the estuary of the river Mersey (Liverpool Bay). An existing procedure for iodine speciation was modified to enable determination of iodate and total iodine as well as iodide in estuarine waters

Extraction of Anthocyanins and Total Phenolic Compounds from Açai (Euterpe oleracea Mart.) Using an Experimental Design Methodology. Part 3: Microwave-Assisted Extraction

In this work, two methods based on microwave-assisted extraction techniques for the extraction of both anthocyanins and total phenolic compounds from acai have been developed. For that, a full factorial design (Box-Behnken design) has been used to optimize the following four variables: solvent composition (25-75% methanol in water), temperature (50-100 degrees C), pH (2-7), and sample/solvent ratio (0.5 g: 10 mL-0.5 g: 20 mL). The anthocyanins and total phenolic compounds content have been determined by ultra high-pressure liquid chromatography and Folin-Ciocalteu method, respectively. The optimum conditions for the extraction of anthocyanins were 38% MeOH in water, 99.63 degrees C, pH 3.00, at 0.5 g: 10 mL of ratio, while for the extraction of total phenolic compounds they were 74.16% MeOH in water, 99.14 degrees C, pH 5.46, at 0.5 g: 20 mL of ratio. Both methods have shown a high repeatability and intermediate precision with a relative standard deviation lower than 5%. Furthermore, an extraction kinetics study was carried out using extraction periods ranging from 2 min until 25 min. The optimized methods have been applied to acai-containing real samples. The results with such real samples have confirmed that both methods are suitable for a rapid and reliable extraction of anthocyanins and total phenolic compounds

Extraction of anthocyanins and total phenolic compounds from açai (euterpe oleracea mart.) using an experimental design methodology. part 1: Pressurized liquid extraction

Currently, açai is one of the most important fruits present in the world. Several studies have demonstrated its high content in phenolic compounds and anthocyanins. Both of them are responsible of interesting properties of the fruit such as anti-inflammatory, antioxidant or anticancer. In the present study, two optimized pressurized liquid extraction (PLE) methods have been developed for the extraction of anthocyanins and total phenolic compounds from açai. A full factorial design (Box-Behnken design) with six variables (solvent composition (25%-75% methanol-in-water), temperature (50-100°C), pressure (100-200 atm), purge time (30-90 s), pH (2-7) and flushing (50%-150%)) were employed. The percentage of methanol in the extraction solvent was proven to be the most significant variable for the extraction of anthocyanins. In the case of total phenolic compounds, the extraction temperature was the most influential variable. The developed methods showed high precision, with relative standard deviations (RSD) of less than 5%. The applicability of the methods was successfully evaluated in real samples. In conclusion, two rapid and reliable PLE extraction methods to be used for laboratories and industries to determine anthocyanins and total phenolic compounds in açai and its derived products were developed in this work

Extraction of Anthocyanins and Total Phenolic Compounds from Acai (Euterpe oleracea Mart.) Using an Experimental Design Methodology. Part 2: Ultrasound-Assisted Extraction

Two optimized methods for ultrasound-assisted extraction were evaluated for the extraction of two types of acai bioactive compounds: Total anthocyanins (TAs) and total phenolic compounds (TPCs). For the extraction optimization, a Box Behnken factorial design of different variables in the following intervals was used: Methanol-water (25%-75%) for solvent composition, temperatures between 10 and 70 degrees C, amplitude in the range between 30% and 70% of the maximum amplitude -200 W), extraction solvent pH (2-7), the ratio for sample-solvent (0.5 g:10 mL-0.5 g:20 mL), and cycle between 0.2 and 0.7 s. The extraction kinetics were studied using different periods between 5 and 30 min. TA and TPC were analyzed by UHPLC and the Folin-Ciocalteu method, respectively. Optimized conditions for TA were: 51% MeOH in water, 31 degrees C temperature, pH 6.38, cycle 0.7 s, 65% amplitude, and 0.5 g:10 mL of sample-solvent ratio. Optimized conditions for the TPC were: 49% MeOH in water, 41 degrees C temperature, pH 6.98, cycle 0.2 s, 30% amplitude, and 0.5 g:10 mL of sample-solvent ratio. Both methods presented a relative standard deviation below 5% in the precision study. The suitability of the methods was tested in real samples. It was confirmed that these methods are feasible for the extraction of the studied bioactive compounds from different acai matrices

Exposure to Essential and Toxic Elements via Consumption of Agaricaceae, Amanitaceae, Boletaceae, and Russulaceae Mushrooms from Southern Spain and Northern Morocco

The demand and interest in mushrooms, both cultivated and wild, has increased among consumers in recent years due to a better understanding of the benefits of this food. However, the ability of wild edible mushrooms to accumulate essential and toxic elements is well documented. In this study, a total of eight metallic elements and metalloids (chromium (Cr), arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), copper (Cu), zinc (Zn), and selenium (Se)) were determined by ICP-MS in five wild edible mushroom species (Agaricus silvicola, Amanita caesarea, Boletus aereus, Boletus edulis, and Russula cyanoxantha) collected in southern Spain and northern Morocco. Overall, Zn was found to be the predominant element among the studied species, followed by Cu and Se. The multivariate analysis suggested that considerable differences exist in the uptake of the essential and toxic elements determined, linked to species-intrinsic factors. Furthermore, the highest Estimated Daily Intake of Metals (EDIM) values obtained were observed for Zn. The Health Risk Index (HRI) assessment for all the mushroom species studied showed a Hg-related cause of concern due to the frequent consumption of around 300 g of fresh mushrooms per day during the mushrooming season

Toxic elements and trace elements in Macrolepiota procera mushrooms from southern Spain and northern Morocco

Anthropogenic activities, such as mining and fossil fuel combustion, produce large amounts of pollutants that affect environmental homeostasis. Wild edible mushrooms fructify exposed to environmental conditions, proving to be efficient accumulators of trace elements and toxic and potentially toxic elements. Due to the increasing consumption of mushrooms worldwide, this is of public health concern. In this work, the total content of chromium (Cr), arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), copper (Cu), zinc (Zn), and selenium (Se) was determined by ICP-MS in the caps and stipes of the high valued wild edible mushroom Macrolepiota procera collected in several locations of the South of Spain and the North of Morocco. The results obtained have indicated that the cap of M. procera contains a broad spectrum of both toxic elements and trace elements, occurring in higher contents in this part of the fruiting body with respect to the stipe. Moreover, Cu was the predominant element found in the samples studied, followed by Zn in most of the cases. The one-way ANOVA/Kruskal-Wallis test indicated that there were no significant differences in metal and metalloid content between the geographical areas studied. In addition, the results obtained through Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) support the conclusions drawn through univariate statistical studies, indicating that there is no obvious clustering trend for the M. procera cap samples based on the sampling area. The health risk assessment for M. procera caps showed a cause for concern related to Cr, Cd, As, and Hg due to frequent consumption of around 300 g of fresh caps per day during the mushrooming season. © 2022 The Author(s

Optimization of ultrasound-assisted extraction of bioactive compounds from jabuticaba (Myrciaria cauliflora) fruit through a Box-Behnken experimental design

Jabuticaba is a very popular fruit in Brazil being a great source of compounds with considerable biological activities. Novel optimized ultrasound-assisted extraction (UAE) methods have been proposed for anthocyanins and total phenolic compounds from jabuticaba. A Box–Behnken experimental design (BBD) with a response surface methodology (RSM) was used to investigate the effect of six independent variables (solvent composition, solvent-to-sample ratio, ultrasound amplitude and cycle, pH, and temperature) on the UAE. Solvent composition was found to be the most significant variable for the extraction of both anthocyanins (51%) and total phenolic compounds (72%). The other optimum conditions for anthocyanins were as follows: pH 7.00, 39.8 ºC, 20:1.5 mL:g solvent-to-sample ratio, 34% ultrasound amplitude and cycle of 0.47 seconds. The optimum conditions for the extraction of phenolic compounds were: pH 7.00, 26.0 ºC, 20:1.5 (mL:g) solvent-to-sample ratio, 68.5% ultrasound amplitude and cycle of 0.5 seconds. The extraction kinetic was also evaluated. The developed methods showed a high precision, with coefficients of variation of less than 5% for both repeatability and intermediate precision (within-lab reproducibility). The applicability of the new methods was successfully evaluated on several fruits and jams from jabuticaba