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