Pseudopolarografija metala u tragovima. III dio. Određivanje konstanta stabilnosti labilnih metalnih kompleksa

Suitability of the pseudopolarographic approach for determination of the stability constants of labile metal complexes at low metal concentrations is explored. It is shown that the methodology based on the DeFord-Hume principle can be successfully applied to treat data obtained from pseudopolarograms. For reversible electrochemical systems, such as thallium(I)–chloride or cadmium(II)–chloride, the half-wave potential of a pseudopolarogram, or the corresponding "critical" potential, can be used to calculate the stability constants. A "formal" potential, evaluated by manual fitting of experimental and simulated (pseudo)polarograms, or a potential in a range where all curves yield a reversible slope, can be used as the "critical" potential. For systems in which reversibility of the electrochemical reaction changes (zinc(II)–oxalate and bismuth( III)–chloride), the shift of the half-wave potential depends both on the complexation parameters and on reversibility of the electrochemical reaction. Therefore, in such cases only the "critical" potential can be used for determination of stability constants. All calculated stability constants presented in the paper are in good agreement with the literature values. The benefit of using pseudopolarographic approach lies in the minimization of various effects (such as precipitation, adsorption, ligand excess, etc.), which can influence determination of stability constants at higher metal concentrations.Istražene su mogućnosti pseudopolarografske metode u određivanju konstanta stabilnosti labilnih metalnih kompleksa u niskim koncentracijama. Prikazano je kako se metodologija temeljena na DeFord-Humeovu načelu može uspješno primijeniti na podatke dobivene iz pseudopolarograma. Za reverzibilne elektrokemijske sustave, kao što su talij(I)–klorid i kadmij(II)–klorid, za izračun konstanta stabilnosti može se koristiti poluvalni potencijal pseudopolarograma ili odgovarajući "kritični" potencijal. Kao "kritični" potencijal može poslužiti "formalni" potencijal koji se dobiva usporedbom simuliranih i eksperimentalnih (pseudo)polarograma ili potencijal koji se odabire iz područja gdje sve krivulje imaju reverzibilni nagib. Kod sustava s promjenljivom reverzibilnosti elektrokemijske reakcije (cink(II)–oksalat i bizmut(III)–klorid) na pomak poluvalnog potencijala utječe kompleksiranje, ali i promjena reverzibilnosti elektrokemijske reakcije. Poradi toga se za računanje konstanta stabilnosti koristi isključivo "kritični" potencijal. Sve konstante stabilnosti izračunate u ovom radu vrlo se dobro slažu s već publiciranim vrijednostima. Prednost pseudopolarografskoga pristupa je u izbjegavanju različitih smetnja (poput precipitacije, adsorpcije, suviška liganda, itd.) koje mogu utjecati na određivanje konstanta stabilnosti kod visokih koncentracija metala

Pseudopolarografija metala u tragovima. III dio. Određivanje konstanta stabilnosti labilnih metalnih kompleksa

Suitability of the pseudopolarographic approach for determination of the stability constants of labile metal complexes at low metal concentrations is explored. It is shown that the methodology based on the DeFord-Hume principle can be successfully applied to treat data obtained from pseudopolarograms. For reversible electrochemical systems, such as thallium(I)–chloride or cadmium(II)–chloride, the half-wave potential of a pseudopolarogram, or the corresponding "critical" potential, can be used to calculate the stability constants. A "formal" potential, evaluated by manual fitting of experimental and simulated (pseudo)polarograms, or a potential in a range where all curves yield a reversible slope, can be used as the "critical" potential. For systems in which reversibility of the electrochemical reaction changes (zinc(II)–oxalate and bismuth( III)–chloride), the shift of the half-wave potential depends both on the complexation parameters and on reversibility of the electrochemical reaction. Therefore, in such cases only the "critical" potential can be used for determination of stability constants. All calculated stability constants presented in the paper are in good agreement with the literature values. The benefit of using pseudopolarographic approach lies in the minimization of various effects (such as precipitation, adsorption, ligand excess, etc.), which can influence determination of stability constants at higher metal concentrations.Istražene su mogućnosti pseudopolarografske metode u određivanju konstanta stabilnosti labilnih metalnih kompleksa u niskim koncentracijama. Prikazano je kako se metodologija temeljena na DeFord-Humeovu načelu može uspješno primijeniti na podatke dobivene iz pseudopolarograma. Za reverzibilne elektrokemijske sustave, kao što su talij(I)–klorid i kadmij(II)–klorid, za izračun konstanta stabilnosti može se koristiti poluvalni potencijal pseudopolarograma ili odgovarajući "kritični" potencijal. Kao "kritični" potencijal može poslužiti "formalni" potencijal koji se dobiva usporedbom simuliranih i eksperimentalnih (pseudo)polarograma ili potencijal koji se odabire iz područja gdje sve krivulje imaju reverzibilni nagib. Kod sustava s promjenljivom reverzibilnosti elektrokemijske reakcije (cink(II)–oksalat i bizmut(III)–klorid) na pomak poluvalnog potencijala utječe kompleksiranje, ali i promjena reverzibilnosti elektrokemijske reakcije. Poradi toga se za računanje konstanta stabilnosti koristi isključivo "kritični" potencijal. Sve konstante stabilnosti izračunate u ovom radu vrlo se dobro slažu s već publiciranim vrijednostima. Prednost pseudopolarografskoga pristupa je u izbjegavanju različitih smetnja (poput precipitacije, adsorpcije, suviška liganda, itd.) koje mogu utjecati na određivanje konstanta stabilnosti kod visokih koncentracija metala

Automation of voltammetric measurements by polarographic analyser PAR 384B

A specific software package >>ElectroAnalytical Research Software 95%) in the analyzed natural seawater sample

Voltametrijsko određivanje konstanta stabilnosti kompleksa olova sa C-vitaminom

Interactions between lead and ascorbic acid were investigated by polarography and voltammetry. The following techniques were applied: sampled polarography, differential pulse anodic stripping voltammetry, and square-wave voltammetry. Measurements were performed in perchlorate aqueous solutions under physiological ionic strength (0.15 mol dm–3). Electrochemical reaction of the lead(II) ascorbate complex was studied in various electrolyte compositions to find the optimal measurement conditions for determination of the corresponding stability constants ([Pb2+]= 4 ×10–7 mol dm–3, pH = 5.5; total concentration of ascorbic acid between 10–5 and 10–1 mol dm–3). Determination of stability constants of labile lead(II) ascorbate complexes was based on the DeFord-Hume methodology, and they were calculated from the dependence of the shift of PbII peak potential on the free ascorbate ion concentration. The computed stability constants were: log β1 = 9.3 ±0.2 and log β2 = 18.0±0.1.Međudjelovanje olova i askorbinske kiseline (C-vitamina) istraživano je polarografskim i voltametrijskim metodama. Rabljene su sljedeće tehnike mjerenja: polarografija s linearnom promjenom potencijala, diferencijalna pulsna voltametrija s anodnim otapanjem i pravokutnovalna voltametrija. Mjerenja su izvođena u vodenim otopinama perklorata, fiziološke ionske jakosti 0,15 mol dm-3. Elektrokemijska reakcija askorbinato kompleksa olova(II) proučavana je u različitim eksperimentalnim uvjetima. Utvrđeni su optimalni uvjeti za određivanje pripadajućih konstanta stabilnosti proučavanih kompleksa ([Pb2+]= 4×10–7 mol dm–3, pH = 5,5; ukupna koncentracija askorbinske kiseline između 10-5 i 10-1 mol dm-3). Određivanje konstanta stabilnosti labilnih kompleksa olova sa C-vitaminom temeljeno je na metodi DeFord-Hume-a, a konstante su izračunate iz ovisnosti pomaka potencijala redukcije olova o koncentraciji slobodnih iona askorbinata. Izračunate su sljedeće konstante stabilnosti: log β1 = 9,3 ± 0,2 and log β2 = 18,0 ± 0,1

Alternativni pristup mjerenju koncentracije nanočestica ZnO u kulturama humanih limfocita - spoj elektrokemije i testova genotoksičnosti

Nanoparticle use has increased radically raising concern about possible adverse effects in humans. Zinc oxide nanoparticles (ZnO NPs) are among the most common nanomaterials in consumer and medical products. Several studies indicate problems with their safe use. The aim of our study was to see at which levels ZnO NPs start to produce adverse cytogenetic effects in human lymphocytes as an early attempt toward establishing safety limits for ZnO NP exposure in humans. We assessed the genotoxic effects of low ZnO NP concentrations (1.0, 2.5, 5, and 7.5 μg mL-1) in lymphocyte cultures over 14 days of exposure. We also tested whether low and high-density lymphocytes differed in their ability to accumulate ZnO NPs in these experimental conditions. Primary DNA damage (measured with the alkaline comet assay) increased with nanoparticle concentration in unseparated and high density lymphocytes. The same happened with the fragmentation of TP53 (measured with the comet-FISH). Nanoparticle accumulation was significant only with the two highest concentrations, regardless of lymphocyte density. High-density lymphocytes had significantly more intracellular Zn2+ than light-density ones. Our results suggest that exposure to ZnO NPs in concentrations above 5 μg mL-1 increases cytogenetic damage and intracellular Zn2+ levels in lymphocytes.S naglim porastom primjene nanočestica raste i mogućnost njihova štetna djelovanja u ljudi. Nanočestice cinkova oksida najčešći su oblik nanomaterijala u potrošačkim proizvodima i lijekovima. Nekoliko je istraživanja već upozorilo na probleme vezane uz njihovu sigurnu primjenu. Cilj je ovoga istraživanja bio utvrditi pri kojim razinama nanočestice ZnO počinju štetno citogenetski djelovati na humane limfocite i time otvoriti pitanje utvrđivanja graničnih razina za sigurnu primjenu nanočestica ZnO u ljudi. Stoga smo istražili genotoksične učinke niskih koncentracija nanočestica ZnO (1,0; 2,5; 5 i 7,5 μg mL-1) izloživši kulture humanih limfocita njihovu djelovanju tijekom 14 dana. Uz to smo izmjerili razlikuju li se limfociti niske gustoće od onih visoke gustoće u sposobnosti akumuliranja nanočestica ZnO pri istim eksperimentalnim uvjetima. Primarno oštećenje DNA (izmjereno alkalnim komet-testom) povećalo se s rastom koncentracije nanočestica u limfocitima koje nismo razdvojili po gustoći te u limfocitima visoke gustoće. Slično smo povećanje zamijetili s fragmentacijom tumorskoga supresorskoga gena TP53 (izmjereno komet-FISH testom). Nakupljanje Zn2+ iona u stanicama bilo je značajno samo kod primjene dviju najviših koncentracija nanočestica ZnO, bez obzira na gustoću limfocita. Osim toga, limfociti visoke gustoće iskazali su i značajno više razine unutarstaničnoga Zn2+ od limfocita niske gustoće. Naši rezultati upozoravaju na to da se izlaganjem razinama nanočestica ZnO višima od 5 μg mL-1 značajno povisuju razine Zn2+ u limfocitima te se povećava oštećenje tih stanica i njihova genoma

Nautical Tourism in Marine Protected Areas (MPAs): Evaluating an Impact of Copper Emission from Antifouling Coating

Copper (Cu) has a narrow range between optimal concentrations as a micronutrient critical for phytoplankton growth and concentrations potentially toxic to living organisms. This sensitivity indicates an ecosystem vulnerability that threatens not only nature but also human health due to bioaccumulation. An important source of elevated Cu concentrations in coastal environments are biocides used as antifouling protection on ships. A pilot study conducted in the Marine Protected Area (MPA) of the Krka Estuary (Croatia) over a period of 16 months investigated the relationship between ship traffic and Cu concentrations. The aim was to contribute to more informed environmental management by assessing the associated risks. In the study presented here, Cu concentrations were monitored, analyzed, and correlated with vessel traffic. Observations revealed that the seasonal increase in maritime traffic caused by nautical tourism was associated with an increase in Cu concentrations of more than five times, posing a toxicity risk to the environment. In order to understand the distribution of copper emissions, a mapping of maritime traffic was carried out by counting transits, radar imagery, and drone photography. This approach has proven sufficient to identify the potential risks to the marine environment and human health, thus providing an effective assessment tool for marine stakeholders

Distribution and speciation of dissolved iron in Jiaozhou Bay (Yellow Sea, China)

The distribution of total dissolved iron (DFe) and its chemical speciation were studied in vertical profiles of the shallow and semi-closed Jiaozhou Bay (JZB, China) during two contrasting periods: summer (July 19th, 2011) and spring (May 10th, 2012). Samples collected from the surface, middle and bottom layers were analyzed by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-aCSV). The mean DFe concentration during the summer period (median 18.8 nM ; average 20.7 nM) was higher than in the spring period (median 12.4 nM ; average 16.9 nM), whereas the spatio-temporal variation in spring was larger than in summer. The DFe-values showed distinct regional and seasonal differences, ranging from 5.6 to 107 nM in spring period and 13.4 to 43.4 nM in summer period. In spring, the highest DFe-values were observed in the eastern coastal region, especially near an industrial area (up to 107 nM), whereas the DFe distribution in summer was relatively even. Due to a tide influence, the vertical variations in the DFe and Lt in both seasons were not significant. On average, the Lt concentration (one class of ligand was estimated in all samples), was higher in spring (35.2 ± 23.4 nM) than in summer (31.1 ± 10.3 nM). A statistically significant correlation was found between Lt and DFe concentrations, it was higher for the summer period than for the spring period. The conditional stability constants (logK′) of organic complexes with iron were weaker in spring (11.7 ± 0.3) than in summer (12.3 ± 0.3). The concentrations of Lt were higher in comparison to DFe in all samples: the average [Lt]/[DFe] ratio in the spring and summer samples was 2.4 and 1.5, respectively. Speciation calculations showed that the DFe in the JZB existed predominantly (over 99.99%) in the form of strong organic complexes in both seasons

The Garden Candytuft (Iberis umbellata L.): At the Crossroad of Copper Accumulation and Glucosinolates

The copper accumulation ability and its impact on the glucosinolate content of the garden candytuft were studied. Different copper sources (adsorbents or solution) were used. Generally, the seedlings copper uptake from the adsorbents was in the amount needed for its growth and development with the beneficial or no impact on the glucosinolate content. The lowest copper concentration was detected in the total seedlings biomass which grew in the humus with the addition of Cu-exchanged zeolite NaX (27.88 μg g−1 DW) having glucosinolate content of 9757.81 µg g−1 DW (23.86 µmol g−1 DW). The highest copper concentration among all the garden candytuft samples was detected in the seedlings watered with CuSO4∙5H2O solution (514.63 μg g−1 DW) with a sharp decrease of the glucosinolate content 3103.33 µg g−1 DW (7.59 µmol g−1 DW). Based on the results obtained, the garden candytuft can be considered as a copper accumulator plant