Screen-printed gold electrodes as passive samplers and voltammetric platforms for the determination of gaseous elemental mercury

 We present a novel 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 measurement of the amalgamated mercury by square wave anodic stripping voltammetry (SWASV). We have explored in detail the behaviour of the SPGE electrode surface during the sampling process (by applying Time Of Flight Secondary Ions Mass Spectrometer, TOF-SIMS), the stability of the voltammetric signals and the inter-electrode reproducibility, with acceptable results. The adsorption of mercury on the SPGE follows a nearly linear behaviour until the sorbent becomes saturated (equilibrium phase) for different mercury concentrations, allowing to select a sampling time of 30 minutes for calibration. The theoretical behaviour of the sampling system was modelled, considering the changes in the diffusive path length between the porous diffusive barrier and the absorption surface, . Finally, we have tested two GEM calibration protocols. The first one is based on the measurement of 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  (R² = 0.9591) and   (R² = 9615) in the range from 5.82 to 59.29 ng dm^-3 of 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 gaseous elemental mercury in atmospheric samples.

Read the full text at: https://dx.doi.org/10.1021/acs.analchem.0c04347 

Presence of fallout 236U and plutonium isotopes, 239Pu and 240Pu, in soils from Southern Hemisphere

236U, 239Pu and 240Pu are present in soils mainly as a result of the local- and global-fallout from the atmospheric nuclear weapons tests carried out mainly in the 1950's and 1960's. In this work we provide new data on the presence of 236U and 239,240Pu in surface soils (i.e. up to 5 cm depth) from Chile and Africa. The results were obtained by low-energy Accelerator Mass Spectrometry (AMS). In the case of the Chilean samples, 236U/239Pu atom ratios show a high variability and are in general higher than the reported value for the global fallout in the Northern Hemisphere, ranging from 0.2 to 1.5. The 236U atomic concentrations range from 3.5 × 106 to 9.1 × 106 atoms/g, and are at least two orders of magnitude lower than the reported values in the Northern Hemisphere. The measured 240Pu/239Pu atom ratio in soils from South-Africa and Mozambique are of about 0.17, in agreement with the expected one for global-fallout at those coordinates. To best knowledge of the authors the present work is the first publication on 236U concentrations and 236U/239Pu atom ratios in soils from South-America and Africa. Read more.

A passive sampling – voltammetric detection approach based on screen-printed electrodes modified with indigotrisulfonate for the determination of ozone in ambient air

We explore in this work a novel analytical concept consisting on the combined use of chemically modified commercial screen-printed electrodes as passive samplers and voltammetric detectors for monitoring of ozone levels in ambient air, a highly relevant pollutant for air quality assessment. The proposed approach is based on the modification of commercial carbon screen-printed electrodes by surface deposition of a known amount of indigotrisulfonate (ITS). The screen-printed platforms are then inserted in passive sampler diffusive bodies and exposed to ambient air for a relatively short period (5 hours), allowing the reaction of ITS with tropospheric ozone to proceed. After the sampling stage, the remaining ITS onto the electrode surface is solubilized in 0.1 M perchloric acid and quantified by square wave voltammetry using a portable potentiostat. The optimization of the experimental conditions allows to measure 5-hour average ambient air ozone levels in the range 20
– 120 mg/m³ (detection limit 1.6 mg/m³), covering the usual ozone range in most urban and rural environments. The relative standard deviation of the combined passive sampling – voltammetric detection system varied from 9.5 to 17.6 %. The proposed methodology was tested in field conditions against a reference UV absorption equipment with acceptable results showing a significant correlation at the 95% confidence level, with slope and intercepts not statistically different from expected values. The uncertainty of the proposed method was estimated to be in the range 25.6 – 26.2 according to ISO 13752. The combination of cheap and simple sampling and detection based on chemically modified screen-printed electrodes opens new analytical options in ambient air monitoring, with promising applicability for decentralized testing by simple and affordable air pollution sensors. Read more.

Disposable sputtered-bismuth screen-printed sensors for voltammetric monitoring of cadmium and lead in atmospheric particulate matter samples

We report here the use of commercial screen-printed disposable sensors comprising a sputtered bismuth working electrode, a silver pseudo reference electrode and a carbon auxiliary electrode (whole set referred as BispSPE), as a new and advantageous alternative for reliable and convenient monitoring of Cd and Pb in atmospheric particulate matter (PM10 fraction) by anodic stripping voltammetry after acid digestion. After a detailed exploration of surface composition and depth profiles of the BispSPE by SEM, EDX, XPS and EIS, chemical and instrumental variables have been optimized to develop a reliable method capable of measuring Cd and Pb with detection limits of 11.8 ng mL−1 and 6.1 ng mL−1 respectively. These detection limits are useful for pollution monitoring of these elements in ambient air under the requirements of international health and environmental protection standards. The accuracy of the method was assessed by voltammetric measurements
of Cd and Pb in ERM®-CZ120 Fine dust (PM10-like) and ERM® 1648a Urban Particulate Matter certified reference materials. The applicability of the method to Cd and Pb determination in real samples was demonstrated by analysis of PM10 samples from the air quality network in Extremadura, with a good correlation respect to the standard ICP-MS methodology. Our work constitutes the first reference about the use of disposable sensors based on BispSPE for the determination of heavy metals in atmospheric particulate matter samples. Read more.

Spatial gradient of human health risk from exposure to trace elements and radioactive pollutants in soils at the Puchuncaví-Ventanas industrial complex, Chile

The Punchuncaví Valley in central Chile, heavily affected by a range of anthropogenic emissions from a localized industrial complex, has been studied as a model environment for evaluating the spatial gradient of human health risk, which is mainly caused by trace elemental pollutants in soil. Soil elemental profiles in 121 samples from five selected locations representing different degrees of impact from the industrial source were used for human risk estimation. Distance to source dependent cumulative non-carcinogenic hazard indexes above 1 for children (max 4.4 – min 1.5) was found in the study area, ingestion being the most relevant risk pathway. The significance of health risk differences within the study area was confirmed by statistical analysis (ANOVA and HCA) of individual hazard index values at the five sampling locations. As was the dominant factor causing unacceptable carcinogenic risk levels for children (<10−4) at the two sampling locations which are closer to the industrial complex, whereas the risk was just in the tolerable range (10−6 – 10−4) for children and adults in the rest of the sampling locations at the study area. Furthermore, we assessed gamma-ray radiation external hazard indexes and annual effective dose rate from the natural radioactivity elements (226Ra, 232Th and 40K) levels in the surface soils of the study area. The highest average values for the specific activity of 232Th (31 Bq kg−1), 40K (615 Bq kg− 1), and 226Ra (25 Bq kg−1) are lower than limit recommended by OECD, so no significant radioactive risk was detected within the study area. In addition, no significant variability of radioactive risk was observed among sampling locations. Read more

Antimony speciation in soils, sediments and volcanic ashes by microwave extraction and HPLC-HG-AFS detection

On the 5th of May 2008, the first recorded eruption of the Chaitén Volcano in southern Chile occurred. Because one of the main natural sources of Sb is volcanic activity, it was necessary to study the distribution of Sb and its species in the nearby ecosystem. The present study aims to develop a methodology for total Sb determination by ICP-MS and a method for Sb(V) and Sb(III) determination by HPLC-HG-AFS in soils, sediments and volcanic ash.

Chaiten eruption, Xinhua Photo

Microwave digestion in a 6 mL HNO₃ and 0.5 mL HBF₄ acid digestion mixture can achieve total solubilization of Sb in solid samples. Thirty minutes at 200 °C with 100 mmol L^− 1 of oxalic acid were suitable conditions for fast and efficient microwave extraction to obtain a good extraction yield. However, Sb(III) stabilization was strongly inhibited; thus, the mixture of 100 mmol L^− 1 + 20 mmol L^− 1 of ascorbic acid was the best for Sb solubilization and Sb(III) stabilization. A total of 1.8 ± 0.1 μg g^− 1 of Sb was quantified in the volcanic ash from the first eruption. The Sb concentrations in the sediments were 3 times higher than the Sb concentrations in the sediments from the reference zone. In the extracts of the volcanic ash and sediment, Sb(III) was the most abundant species, accounting for 70 to 97% of the total Sb found in the extracts. The results suggest that most of the Sb thrown from the Chaitén Volcano accumulated in the sediments at the mouths of the Yelcho and Chaitén Rivers, mainly in the form of Sb(III). Read more

A semiautomatic system for soluble lead and copper monitoring in atmospheric deposition by coupling of passive elemental fractionation sampling and voltammetric measurement on screen printed gold electrodes

We propose here the concept of semiautomatic measurement of soluble copper and lead in atmospheric deposition by the coupling of filtrating-bulk passive sampling by an atmospheric elemental fractionation sampler (AEFS) designed for fractionation of soluble and insoluble elemental species, and square wave anodic stripping voltammetric detection on screen printed electrodes. The voltammetric parameters were optimized to provide a reliable method for Pb(II) and Cu(II)monitoring with detection limits in the low ng mL−1 range. The method was validated
by analyzing ambient water certified referencematerials with good agreement between measured and certified values. The monitoring system was tested during a 1 month experimental campaign in a suburban area and proved useful to monitor copper changes in the atmospheric deposition. Leadwas alsomeasurable after fortification since its levels were under the detection limit of the voltammetric method. The results obtained were contrasted by a lab based standard ICP-MS method with good correlation.Our results are promising about the possibility of routine field use of unattended
voltammetric measurements of trace element monitoring in atmospheric deposition. Published in Microchemical Journal, 2016. Read more

Temporal and spatial variation of trace elements in atmospheric deposition around the industrial area of Puchuncaví-Ventanas (Chile) and its influence on exceedances of lead and cadmium critical loads in soils

Fractionation of elemental contents in atmospheric samples is useful to evaluate pollution levels for risk assessment and pollution sources assignment. We present here the main results of long-term characterization of atmospheric deposition by using a recently developed atmospheric elemental fractionation sampler (AEFS) for major and trace elements monitoring around an important industrial complex located in Puchuncaví region (Chile). Atmospheric deposition samples were collected during two sampling campaigns (2010 and 2011) at four sampling locations: La Greda (LG), Los Maitenes (LM), Puchuncaví (PU) and Valle Alegre (VA). Sample digestion and ICP-MS gave elements deposition values (Al, As, Ba, Cd, Co, Cu, Fe, K, Mn, Pb, Sb, Ti, V and Zn) in the insoluble fraction of the total atmospheric deposition. Results showed that LG location, the closest location to the industrial complex, was the more polluted sampling site having the highest values for the analyzed elements. PU and LM were the next more polluted and, finally, the lowest elements concentrations were registered at VA. The application of Principal Component Analysis and Cluster Analysis identified industrial, traffic and mineral-crustal factors. We found critical loads exceedances for Pb at all sampling locations in the area affected by the industrial emissions, more significant in LG close to the industrial complex, with a trend to decrease in 2011, whereas no exceedances due to atmospheric deposition were detected for Cd. Paper published in Chemosphere. Read more

Long-term assessment of ecological risk from deposition of elemental pollutants in the vicinity of the industrial area of Puchuncaví-Ventanas, central Chile

The present work investigates soil pollution by elemental contaminants and compares ecological risk indexes related to industrial activities for the case study of Puchuncaví-Ventanas: a relevant industrial zone located in central Chile. Selected elements (As, Pb, Cd, Ni, Hg, V, Mn, Zn, Sr, Sb, Cr, Co, Cu, K, and Ba) were analyzed during a long-term period (yearly sampling campaigns during 2007–2011), at 5 sampling stations representing different degrees of impact. PCA and cluster analysis allowed identifying a copper smelter and a coal-fired power plant complex asmajor pollution sources. Geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (Cf), contamination degree (Cdeg), and integrated pollution index (IPI) are critically discussed for quantitative ecological risk assessment. Igeo, EFandCf indexes are producing comparable environmental information, showing moderate to high pollution risks in the area that demands furthermonitoring and adoption of prevention and remediation measures. Published in Science of the Total Environment. Read more

Ambient air levels and health risk assessment of benzo(a)pyrene in atmospheric particulate matter samples from low polluted areas: application of an optimized microwave extraction and HPLC-FL methodology

A new methodology involving a simple and fast pretreatment of the samples by microwave-assisted extraction and concentration by N2 stream, followed by HPLC with fluorescence detection, was used for determining the concentration of benzo(a)pyrene (BaP) in atmospheric particulate matter (PM10 fraction). Obtained LOD, 1.0 × 10−3 ng/m3, was adequate for the analysis of benzo(a)pyrene in the samples, and BaP recovery from PAH in Fine Dust (PM10-like) certified reference material was nearly quantitative (86 %). The validated procedure was applied for analyzing 115 PM10 samples collected at different sampling locations in the low-polluted area of Extremadura (Southwest Spain) during a monitoring campaign carried out in 2011–2012. BaP spatial variations and seasonal variability were investigated as well as the influence of meteorological conditions and different air pollutants concentrations. A normalized protocol for health risk assessment was applied to estimate lifetime cancer risk due to BaP inhalation in the sampling areas, finding that around eight inhabitants per million people may develop lung cancer due to the exposition to BaP in atmospheric particulates emitted by the investigated sources. Published in Environmental Science and Pollution Research. Read more

Mercury pollution assessment in soils affected by industrial emissions using miniaturized ultrasonic probe extraction and ICP-MS

A combination of probe ultrasonic extraction, optimized by surface response methodology, and Inductively coupled plasma mass spectrometry (ICP-MS) detection is described in this work as an effective methodology  for mercury monitoring in soils affected by industrial emissions. Minute amounts of samples (typically
20 mg) can be extracted in 3 min by 1 mL of HCl-based extracting solution, without risk of mercury losses, and sub sequentially assayed by ICP-MS. The method was successfully tested on soil standard reference materials and then applied to mercury monitoring in a large set of real soil samples collected during a long-term monitoring survey (2007–2011) around the industrial area of Puchuncaví, Chile. The method proved to be useful for investigation of spatial and temporal mercury variability in the area, showing an intermediate to high mercury contamination with potential impact on the surrounding ecosystem. Published in the International Journal of Environmental Science and Technology.  Read more

Wearable electrochemical sensors: innovative tools for the emerging mobile health ecosystem

Wearable electrochemical sensors: innovative tools for the emerging mobile health ecosystem, Journal of Applied Bioanalysis 1(3) (2015) 68-71. With an estimated present global market of US$ 86.3 billion and expected annual increase around 7.9 % from now to 2020, sensors are nowadays one of the most active areas of research and technological developments [1] and a basic pillar of the emerging mobile health strategy that is expected to be revolutionizing healthcare in the near future. The biosensor and chemical sensor category is one of the most growing segment of this market, mainly due to increased use for medical purposes. Wearable electrochemical sensors conform a particularly flourishing category that benefits from the improvements in micro and nano fabrication of electrodes and instrumental components based on a range of new electrode materials (e.g. graphene). They are also expanding thanks to the widespread availability of advanced signal processing and management technologies on smartphones, tablets and similar portable devices. The aim of this contribution is to highlight the most outstanding recent progresses in the field of wearable electrochemical sensors for decentralized bioanalysis and show some examples of research trends that will shape the sector and expand applicability fields in the near future.

Long-term assessment of ecological risk from deposition of elemental pollutants in the vicinity of the industrial area of Puchuncavi-Ventanas, central Chile

Long-term assessment of ecological risk from deposition of elemental pollutants in the vicinity of the industrial area of Puchuncavi-Ventanas, central Chile: Science of The Total Environment, Volume(s) 527-528, 14-May-2015, Pages 335-343. The present work investigates soil pollution by elemental contaminants and compares ecological risk indexes related to industrial activities for the case study of Puchuncaví-Ventanas: a relevant industrial zone located in central Chile. Selected elements (As, Pb, Cd, Ni, Hg, V, Mn, Zn, Sr, Sb, Cr, Co, Cu, K, and Ba) were analyzed during a long-term period (yearly sampling campaigns during 2007–2011), at 5 sampling stations representing different degrees of impact. PCA and cluster analysis allowed identifying a copper smelter and a coal-fired power plant complex asmajor pollution sources. Geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (Cf), contamination degree (Cdeg), and integrated pollution index (IPI) are critically discussed for quantitative ecological risk assessment. Igeo, EF and Cf indexes are producing comparable environmental information, showing moderate to high pollution risks in the area that demands further monitoring and adoption of prevention and remediation measures.

Quality assurance in aerosol analysis

The journal Accreditation and Quality Assurancew has recently published our paper "Method validation and quality assurance of an ICP-MS protocol for the evaluation of trace and major elements in ambient aerosol samples and application to an air quality surveillance network". This study presents the results of a quality assurance evaluation program applied to the method routinely used for the evaluation of a large elemental profile in aerosol samples from the air quality surveillance network of Extremadura, Spain, where low pollution levels are usually encountered. A critical evaluation of the most relevant analytical steps is presented, including long-term blank values evaluation, limits of detection, certified reference material recoveries, method uncertainty and results of comparison studies for gravimetric and trace element analysis. Results obtained at the air quality network of Extremadura for the gravimetric and multielemental analysis are presented for the 2008 campaign. Read more.

Determination of Zn(II) in undisturbed samples using the bismuth electrode

The journal Analytical Methods has just published our paper about the use of the bismuth bulk rotating disk electrode (BiB-RDE) as a new and advantageous alternative to determine heavy metal ions in undisturbed environmental and biological samples (pH 7.5) by anodic stripping voltammetry, with demonstrated applicability to the determination of Zn(II) in rainwater, tap water and urine. The proposed method benefits from the insensitiveness of the bismuth bulk electrode to the Bi(III) hydrolysis that affects the common “in situ” Bi film approach preventing its use at intermediate to alkaline pH. See the whole paper at http://dx.doi.org/10.1039/C4AY01626B

Filtrating-bulk passive sampling for elemental fractionation in atmospheric deposition

We have recently published the paper entitled "Fractionation of trace elements in total atmospheric deposition by filtrating-bulk passive sampling" in the journal Talanta. We have developed and validated a new simple and effective methodology for fractionation of soluble and insoluble forms of trace elements in total atmospheric deposition. The proposed methodology is based on the modification of a standard total deposition passive sampler by integrating a quartz fiber filter that retains the insoluble material, allowing the soluble fraction to pass through and flow to a receiving bottle. The quartz filter containing the insoluble fraction and the liquid containing the soluble fraction are then separately assayed by standardized ICP–MS protocols. The proposed atmospheric elemental fractionation sampler (AEFS) was validated by analyzing a Coal Fly Ash reference material with proper recoveries, and tested for field fractionation of a set of 10 key trace elements in total atmospheric deposition at the industrial area of Puchuncaví–Ventanas, Chile. The AEFS was proven useful for pollution assessment and also to identify variability of thes oluble and insoluble fractions of the selected elements within the study area, improving the analytical information attainable by standard passive samplers for total deposition without the need of using sophisticated and high cost wet-only/dry-only collectors.

New publication about screen printed electrode characterization

Our research group has just published a paper entitled "Characterisation of screen-printed gold and gold nanoparticle-modified carbon sensors by electrochemical impedance spectroscopy", in the Journal of Electroanalytical Chemistry. Gold-based screen-printed electrodes have been characterised by electrochemical impedance spectroscopy (EIS) to better understand their behaviour in electroanalytical applications, particularly in the anodic stripping voltammetry of Hg(II). After a first exploration by cyclic voltammetry, impedance spectra of gold-based screen-printed sensors were recorded in 0.1 M HCl electrolyte solution, in the presence of dissolved oxygen and with no electrochemical pre-treatment of the surface. The spectra demonstrated the differences in the interfacial characteristics of each kind of sensor. Structural changes in the surface of SPGEs caused by amalgam formation in the presence of Hg(II) were investigated by EIS. The results obtained were used to elucidate the implications for using the sensor in the stripping voltammetric determination of Hg(II) in environmental samples.

Research work in Valparaíso, Chile

Seven members of the group are currently in Chile for a two weeks stay. We`re sharing research results and carrying out environmental sampling and monitoring campaigns around Valparaíso, with colleagues from Universidad Técnica Federico Santa María and UEx.

Analyzing environmental pollution in snow at the Andes, Chile

The journal "Atmospheric Environment" has recently published our results about the evaluation of the impact of Santiago de Chile urban pollution on trace elements levels content in snow precipitation at the nearby heights of Cerro Colorado in Central Andes.

Voltammetric determination of mercury on screen printed electrodes modified with gold nanoparticles

The journal "Sensors and Actuators B: Chemical" has just accepted for publication our work about the voltammetric stripping determination of mercury on gold nanoparticles modified screen printed electrodes, with application to environmental water samples. Go to "Selected Publications" for details.