A disposable electrochemical sensor was developed for detection of gaseous formaldehyde. The sensor is composed of a three-electrode screen-printed system modified with hydrazinium polyacrylate which was synthesized to serve simultaneously as an accumulation / derivatization medium for gaseous formaldehyde, and as a polyelectrolyte enabling voltammetric measurements. It exhibited linear response in the examined concentration range of 4 – 16 ppm gaseous formaldehyde in combination with 120 min accumulation; sub-ppm concentration levels could also be detected when the exposure time was extended. Further development of such sensors might result in their potential applications in the fields of clinical diagnostics (aldehydes in exhaled human breath as markers of lung cancer), cultural heritage preservation (detection of gaseous aldehydes as early indicators for deterioration of artistic objects made of plastic materials) and environmental monitoring.
COBISS.SI-ID: 5949210
A study of bismuth film electrode (BiFE) under less acidic conditions for anodic stripping voltammetric measurements of Zn(II) in complex organic sample, i.e. in the cell culture medium containing ZnO nanoparticles, was presented. The BiFE was prepared in-situ on a substrate glassy carbon electrode in solution containing 0.1 mol/L piperazine-N,N’-bis(2-ethanesulfonic acid) (PIPES) and 0.1 mol/L KNO3 as supporting electrolyte, adjusted to pH 6.5, and in the presence of dissolved oxygen. In the model solution, i.e. in the absence of cell culture medium and ZnO nanoparticles, the BiFE revealed good linear response in the examined concentration range of 10 – 100 µg/L Zn(II) with r2 of 0.994, the LOD of 0.14 µg/L Zn(II) associated with only 120 s accumulation step, and favorable repeatability of 1.7 %. Upon the addition of cell culture medium, the signal of Zn(II) attenuated for ca. 64 %; however, the BiFE still exhibited excellent linear response in the same examined concentration range of 10 – 100 µg/L Zn(II) with r2 of 0.999, favorably low LOD of 0.15 µg/L Zn(II) after 120 s accumulation, and satisfactory repeatability of 3.0 %. Finally, the applicability of BiFE was successfully demonstrated through measuring Zn(II) in a cell culture medium containing 5 mg/L ZnO nanoparticles for the purpose of a nanotoxicological study.
COBISS.SI-ID: 5997082
The preparation of nanostructured bismuth film electrode (nsBiFE) via ex-situ multi-pulse galvanostatic deposition protocol was presented. The nsBiFE was prepared on a glassy carbon substrate electrode and studied for anodic stripping voltammetric detection of trace (heavy) metal ions. Several important parameters were examined and optimized, such as the composition of plating solution, pulse deposition current, pulse duration (pulse deposition time and relaxation time) etc. The nsBiFE exhibited excellent sensitivity associated with well-defined and reproducible signals of both test analytes, i.e. Cd(II) and Pb(II), accompanied with low background contribution. It revealed good linear behaviour in the examined concentration range of 20 - 100 µg/L along with remarkable low limits of detection, i.e. 0.4 µg/L for Cd(II) and 0.1 µg/L for Pb(II) after 300 s accumulation, and good repeatability with RSDs of 5.1 % and 3.8 % for Cd(II) and Pb(II), respectively.
COBISS.SI-ID: 6198298
Iridium based particles, as the most promising proton exchange membrane electrolyser electrocatalysts, were investigated by transmission electron microscopy (TEM), and by coupling of electrochemical flow cell with on-line inductively coupled plasma mass spectrometer (ICP-MS). Additionally, a thin-film rotating disc electrode (RDE), an identical location transmission and scanning electron microscopy (IL-TEM and IL-SEM) as well as an X-ray absorption spectroscopy (XAS) studies have been performed. Extremely sensitive on-line time- and potential-resolved electrochemical dissolution profiles revealed that iridium particles dissolved already well below oxygen evolution reaction (OER) potentials, presumably induced by iridium surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile type IrO2 particles (T-IrO2) are substantially more stable and less active in comparison to as prepared metallic (A-Ir) and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER relevant conditions E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism where the formation of unstable Ir()IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyser.
COBISS.SI-ID: 6203674
Pulsed laser ablation (LA) devices in laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) elemental imaging have become very advanced, delivering laser pulses with high temporal accuracy and stable energy density. However, unintentional imaging artifacts may be generated in 2D elemental maps when the LA repetition rate and the data acquisition parameters of sequential ICP-MS instrument are desynchronized. This may potentially lead to interference patterns, visible as ripples in elemental images, and thus, compromised image quality. This paper describes the background of aliasing in continuous scanning mode through simulation experiments and approaches to modulate the effect. The existence of this image degradation source is demonstrated experimentally via real-life imaging of a homogeneous glass standard.
COBISS.SI-ID: 6321178
This work focuses on the structural similarity (SSIM) index as a tool for optimization of the perceived visual image quality obtainable by continuous scanning 2D LA-ICP-MS elemental bioimaging; also other mass spec imaging techniques may benefit from this approach. This index quantifies the differences between a distorted image and a reference image based on parameters associated with luminance, contrast, and noise. Since reference images are not normally available, a protocol was developed to virtually apply distortion-related information introduced by the LA-ICP-MS imaging system to a reference image of one’s choice. Distortion-related information in the form of blur and noise was experimentally retrieved from line scans across a laser milled knife edge on custom-prepared gelatin standards mimicking proteinaceous biomatrixes. Distorted images were generated via computational procedures developed earlier, warranting objective image quality assessment via the SSIM indices. We illustrated the potential of this approach for elemental image quality optimization for a suite of LA-ICP-MS elemental imaging conditions.
COBISS.SI-ID: 6351642
It is well known that yellow-colored nitrocatechols are secondarily formed in the atmosphere, especially during the nighttime at conditions of high relative humidity. This keeps them apart from the conventional radical chemistry of the atmosphere. Therefore, the intriguing role of HNO2 (catalytic and oxidative) in the transformations of important pollutant 3-methylcatechol (3MC) under atmospherically relevant aqueous-phase conditions was investigated. Three possible pathways of dark 3-methyl-5-nitrocatechol and 3-methyl-4-nitrocatechol formation, markedly dependent on reaction conditions, were considered. In the dominant pathway, HNO2 is directly involved in the transformation of 3MC via consecutive oxidation and conjugated addition reactions (nonradical reaction mechanism), which is consistent with field observations. The two-step nitration dominates at a pH around the pKa of HNO2, which is typical for atmospheric aerosols, and is moderately dependent on temperature. Under very acidic conditions, the other two nitration pathways, oxidative aromatic nitration (electrophilic) and recombination of radical species, gain in importance. The predicted atmospheric lifetime of 3MC according to the dominant mechanism at these conditions (2.4 days at pH 4.5 and 25°C) is more than 3-times shorter than that via the other two competitive pathways. Our results highlight the significance of a catechol oxidation-conjugated addition reaction in a nighttime secondary nitroaromatic chromophore formation in the atmosphere, especially in polluted environments with high NOx concentrations and relatively acidic particles (pH around 3). The results of this study will considerably contribute to the development of atmospheric models.
COBISS.SI-ID: 6426650
Our current understanding of the importance of surface-active substances (SAS) on atmospheric aerosol cloud-forming efficiency is limited, as explicit data on the content of size-resolved ambient aerosol SAS, which are responsible for lowering the surface tension of activating droplets, are not available. We report on the first data comprising seasonal variability of size-segregated SAS concentrations in ambient aerosol particulate matter (PM). To assess the impact of SAS distribution within PM on cloud droplet activation and growth, a concept of surfactant activity was adopted and a parametrization developed; i.e., surfactant activity factor was defined, which allowed translation of experimental data for use in cloud parcel modeling. This part of the study was performed in collaboration with colleagues from Leibniz-Institute for Tropospheric Research (TROPOS), Germany, with whom we have reestablished close collaboration in the past few years. The results show that SAS-induced surface tension depression during cloud activation may significantly affect droplet number, especially if considering also size distribution of particulate SAS. This study underscores the importance of size-resolved SAS perspective on cloud activation, as data typically obtained from aqueous extracts of PM2.5 and PM10 may result in misleading conclusions about droplet growth due to large mass fractions of supermicron particles with SAS deficit and little or no influence on cloud activation and droplet number.
COBISS.SI-ID: 6426394
Many ambiguities surround the possible mechanisms of colored nitrophenols formation in natural systems. Nitration of a biologically and environmentally relevant aromatic compound, guaiacol (2-methoxyphenol), under mild aqueous-phase conditions (ambient temperatures, pH 4.5) was investigated. Some results of our respective studies have already been published in esteemed journals (Sci. Rep. 2015, Environ. Sci. Technol. 2015), however in this paper we sum up/confirm the conclusions made therein and upgrade them with new important insights. In this work, temperature-dependent experimental modeling was coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways. The importance of dark non-radical reactions is emphasized, involving nitrous (HNO2) and peroxynitrous (HOONO) acids. Oxidation by HOONO is shown to proceed via a non-radical pathway, possibly involving the nitronium ion (NO2+) formation. Using quantum chemical calculations at the MP2/6 31++g(d,p) level, NO2• is shown capable of abstracting a hydrogen atom from the phenolic group on the aromatic ring. In a protic solvent, the corresponding aryl radical can combine with HNO2 to yield OH• and, after a subsequent oxidation step, nitrated aromatic products. The demonstrated chemistry is especially important for understanding the aging of nighttime atmospheric deliquesced aerosol. The relevance should be further investigated in the atmospheric gaseous phase. The results of this study have direct implications for accurate modeling of the burden of toxic nitroaromatic pollutants, and the formation of atmospheric brown carbon and its associated influence on Earth’s albedo and climate forcing.
COBISS.SI-ID: 6519834
A novel, simple method was developed to synthesize biocompatible composites containing 50% cellulose (CEL), 50% keratin (KER) and silver in the form of either ionic Ag(I) or metalic Ag(0) nanoparticles (NPs). Solution of [CEL+KER] was prepared in [BMIm+Cl-] ionic liquid, and silver chloride was added during the dissolution process. The silver in the composites can be maintained as ionic silver Ag(I) or completely converted to Ag(0) by reducing it with NaBH4. Results of spectroscopy (FTIR, XRD and SEM) measurements confirm that CEL and KER remain chemically intact and homogeneously distributed in the composites. Powder XRD and SEM results show that silver is homogeneously distributed throughout the composites in the form of Ag(I) NPs with size of 27 ± 2 nm or Ag(0) NPs with size of 9 ± 1 nm. Both composites were found to exhibit excellent antibacterial activity against many bacteria including Escherichia coli, Staphylococus aureus, Pseudomonas aeruginosa, methicillin resistant Staphylococus aureus (MRSA), and ancomycin resistant Enterococus faecalis (VRE), which increases with the silver content in the composites. For the same content of silver, [CEL+KER+Ag(I) NPs] composite exhibits relatively greater antimicrobial activity against bacteria compared to the corresponding [CEL+KER+Ag(0) NPs] composite. By using highly sensitive thermal lens spectrometry, which we developed recently, we confirmed that the release of Ag(0) NPs from the [CEL+KER+Ag(0) NPs] composite was negligible, and hence its antimicrobial activity is due entirely to the Ag(0) NPs embedded in the composite. Both Ag(I) NPs and Ag(0) NPs were found to be toxic to human fibroblasts at higher concentration ()0.72 mmol). At Ag(0) NPs concentrations up to 0.48 mmol, the [CEL+KER+Ag(0) NPs] composite is biocompatible while still retaining its antimicrobial activity against E. coli, S. aureus, P. aeruginosa, MRSA and VRE. These results indicate that [CEL+KER+Ag(0) NPs] composite possesses all required properties to be successfully used as high performance dressing to treat chronic ulcerous infected wounds.
COBISS.SI-ID: 4588539