Ivanka Pižeta - Academia.edu (original) (raw)

Papers by Ivanka Pižeta

Speciation of copper in the estuarine waters of the coastal area of the Northern Adriatic (Sloven... more Speciation of copper in the estuarine waters of the coastal area of the Northern Adriatic (Slovenia) was estimated by applying differential pulse anodic stripping voltammetry (DPASV). Total copper concentration ranged between 10 and 60 nM, while labile copper concentration at the natural pH of the site seawater was below the detection limit of the method applied. Two classes of organic ligands that complex with copper were identified, one of lower concentration, i.e. 120 nM with higher conditional stability constant, logK = 8.30, and the other of higher concentration, i.e. 220 nM, with lower conditional stability constants, logK = 7.10. Differences in speciation parameters were estimated using samples collected during both summer and winter and at both high and low tide. The results provided evidence that copper complexing capacity in this estuary significantly changed, amounting between 98 nM and 386 nM and indicating that copper speciation was fully controlled by complexing reactions.

Electrochemical characterization of iron(III)–glycine–nitrilotriacetate (iron(III)-Gly-NTA) mixed... more Electrochemical characterization of iron(III)–glycine–nitrilotriacetate (iron(III)-Gly-NTA) mixed ligand complexes and determination of their stability constants and retention time in aqueous solutions (I = 0.1 mol dm–3 in NaClO4, pH = 8.0±0.1 at 25±1 °C), using differential pulse cathodic voltammetry (DPCV), cyclic voltammetry (CV) and direct current (d.c.) polarography with a static mercury drop electrode (SMDE), were performed. Iron(III) concentrations were varied from 5×10–6 to 6×10–4 mol dm–3, NTA total concentrations varied from 2×10–5 to 1×10–3 mol dm–3 and glycine total concentrations were 0.2, 0.02 and 0.002 mol dm–3. Iron(III) redox reaction in the mixed ligand system (by the techniques employed) was found to be a one-electron reversible process. At total concentration ratios of 1 : 800 : 2 for iron(III), glycine and NTA, respectively, the iron(III)-Gly-NTA mixed ligand complexes were dissolved and stable (>18 hours) in the aqueous solution. The complexes were formed ei...

Marine Chemistry, 2015

Modeling the synthetic, CLE-ACSV-type titration dataset, which comprises 5 titration curves gener... more Modeling the synthetic, CLE-ACSV-type titration dataset, which comprises 5 titration curves generated at different analytical windows or levels of competing ligand added to the virtual sample, proved to be more challenging due to the random measurement error that was incorporated. Comparison of the submitted results was complicated by the participants' differing interpretations of their task. Most adopted the provided 'true' instrumental sensitivity in modeling the CLE-ACSV curves, but several estimated sensitivities using internal calibration, exactly as is required for actual samples. Since most fitted sensitivities were biased low, systematic error in inferred ambient [M f ] and in estimated weak ligand (L 2) concentrations resulted. The main distinction between the mathematical approaches taken by participants lies in the functional form of the speciation model equations, with their implicit definition of independent and dependent or manipulated variables. In 'direct modeling', the dependent variable is the measured [M f ] (or I p) and the total metal concentration ([M] T) is considered independent. In other, much more widely used methods of analyzing titration dataclassical linearization, best known as van den Berg/Ružić, and isotherm fitting by nonlinear regression, best known as the Langmuir or Gerringa methods-[M f ] is defined as independent and the dependent variable calculated from both [M] T and [M f ]. Close inspection of the biases and variability in the estimates of ligand parameters and in predictions of ambient [M f ] revealed that the best results were obtained by the direct approach. Linear regression of transformed data yielded the largest bias and greatest variability, while non-linear isotherm fitting generated results with mean bias comparable to direct modeling, but also with greater variability. Participants that performed a unified analysis of ACSV titration curves at multiple detection windows for a sample improved their results regardless of the basic mathematical approach taken. Overall, the three most accurate sets of results were obtained using direct modeling of the unified multiwindow dataset, while the single most accurate set of results also included simultaneous calibration. We therefore recommend that where sample volume and time permit, titration experiments for all natural water samples be designed to include two or more detection windows, especially for coastal and estuarine waters. It is vital that more practical experimental designs for multi-window titrations be developed. Finally, while all mathematical approaches proved to be adequate for some datasets, matrix-based equilibrium models proved to be most naturally suited for the most challenging cases encountered in this work, i.e., experiments where the added ligand in ACSV became titrated. The ProMCC program (Omanović et al., this issue) as well as the Excel Add-in based KINETEQL Multiwindow Solver spreadsheet (Hudson, 2014) have this capability and have been made available for public use as a result of this intercomparison exercise.

Collegium antropologicum, 2002

Bite force is the condition, expression and measure of the masticatory function. The purpose of t... more Bite force is the condition, expression and measure of the masticatory function. The purpose of this study was to examine, by means of a newly constructed electronic gnathodynamometer, the values of maximal bite forces in subjects with complete dentition, the time in which they express 50% and 75% respectively of the total forces value, and the shape of the bite curve during testing. The obtained data was statistically analyzed with respect to gender and age. Analysis of the variance confirmed the finding that there was no statistically significant correlation between the values of forces and subjects' age, but there was a statistically significant difference between males and females in the values of the bite forces in the front segment, as well as between the values of the force on anterior and posterior teeth. The correlation between the time T1 posterior right and T1 posterior left, and between T1 and T2 for anterior teeth are statistically significant. Analysis of the bite ...

Water Research, 2001

}The applicability of the previously developed method for electrochemical determination of dissol... more }The applicability of the previously developed method for electrochemical determination of dissolved uranium concentration has been tested on natural water samples taken from the Krka river estuary during various seasons and along different depth profiles. The method is based on the following treatment of the sample: destroying the uranyl-carbonato complexes by adjusting the pH to 3, enabling the formation of adsorbable uranyl-hydroxo complexes by adjusting the pH to 6.5-7.0 and measurement by cathodic stripping voltammetry technique. As the signal of the dissolved uranium reduction is sometimes masked by the signal of the matrix of the sample, a resolution enhancement including digestion and/or deconvolution has to be applied. The measured concentration of dissolved uranium varies in the range from 0.4 to 3.3 Â 10 À8 mol l À1 , corresponding to the data found in the literature. The depth profile of dissolved uranium concentration distributions shows conservative behaviour. The X-ray fluorescence spectroscopy (XRF) confirmed the applicability of the method, yet pointing out to its limitations caused by the matrix of the solution.

Science of The Total Environment, 2015

, and Cu is controlled by Fe precipitation. • More than 90% of DGT-labile fraction was found for ... more , and Cu is controlled by Fe precipitation. • More than 90% of DGT-labile fraction was found for Zn, Cd, Ni, Co and Mn. • Low labile Fe/Pb were due to their presence in colloidal DGT-inaccessible fraction. • High correlation between predicted and measured potentially bioavailable fractions.

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1991

A Fourier transform method is used for the resolution enhancement of the closely overlapping diff... more A Fourier transform method is used for the resolution enhancement of the closely overlapping diffusion-controlled main peak and the post-peak caused by adsorption in differential pulse polarography (DPP). The method is tested on a theoretical model. Complex DPP responses influenced by the reactant adsorption which follows Frumkin's isotherm are simulated. By varying the reactant bulk concentration and parameters responsible for the strength of adsorption and the interaction between molecules of adsorbed reactant, sets of theoretical current-potential curves are obtained on which the proposed method consisting of deconvolution of the signal in the Fourier domain by the appropriate deconvolution function is applied. The post-peak of the transformed signal is narrower than in the original DPP response, and consequently better separated from the transformed main peak. However, the transformation does not alter the peak potentials of both the main and the post-peak. The result of this investigation is the region of contribution of the method, i.e. the conditions under,which the adsorption process only after the deconvolution can be detected and defined. The method is proved useful for the detection of chloride-induced adsorption of Pb(II) ions to the surface of the mercury electrode at the potentials of the lead ion reduction.

Analytica Chimica Acta, 1994

Catalytic hydrogen evolution according to the Brdi6ka reaction was applied for the rapid detectio... more Catalytic hydrogen evolution according to the Brdi6ka reaction was applied for the rapid detection and determination of metallothionein isolated from rabbit liver. The heights of two catalytic hydrogen waves, of different widths, Cat, (overlapped with the reduction wave of Co t+) and Cat 2 (overlapped with Cat,) were evaluated as non-resolved peaks by polarography or by manual tangent fitting and after signal deconvolution applying windowing or straight-line subtraction, as the difference between the current at the peak potential and the baseline at the same potential. Calibration straight lines were statistically verified and compared. Additive interference of the overlapping peaks is the cause of the systematic error of the calibration straight lines. After deconvolution the interference was diminished but not completely eliminated. A significant improvement was achieved for the Cat, signal, applying deconvolution with straight-line subtraction. In this manner concentrations of metallothionein as low as 19,ug 1-1 could be determined. The sensitivity of the calibration straight line of the Cat, peak is nine times higher than that of the Cat2 peak. The error of the calibration straight line intercept for the Cat 2 peak is similar irrespective of whether it is evaluated as the unprocessed signal by manual tangent fitting or after deconvolution with straight-line subtraction .

European Chemical Bulletin, 2012

In this study, chemical water quality changes downstream a pool-riffle type stream located at a f... more In this study, chemical water quality changes downstream a pool-riffle type stream located at a former Pb-Zn mining site are discussed. The watershed of the Toka stream (Matra mountain, Hungary) being under rehabilitation is still continuously affected by a neutralised acidic mine drainage, and temporarily, by an abandoned mine tailing. Upstream the AMD confluence which gives the major part of the water flux in dry season, indeed, the stream is of high water quality, while, directly after that, the electric conductivity is app. quintupled, and the pH as well as the trace element concentrations increase, as expected. However, within 10 kilometres, Fe, Zn and Pb concentrations are all remarkably decreased in relation to the distance from the contamination source, and they almost reach the actual background levels. The electric conductivity does not show significant change along the investigated section of the stream, which would indicate dilution. At the same time, presence of amorpho...

a b s t r a c t BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Modeling th... more a b s t r a c t BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Modeling the synthetic, CLE-ACSV-type titration dataset, which comprises 5 titration curves generated at different analytical windows or levels of competing ligand added to the virtual sample, proved to be more challenging due to the random measurement error that was incorporated. Comparison of the submitted results was complicated by the participants' differing interpretations of their task. Most adopted the provided 'true' instrumental sensitivity in modeling the CLE-ACSV curves, but several estimated sensitivities using internal calibration, exactly as is required for actual samples. Since most fitted sensitivities were biased low, systematic error in inferred ambient [M f ] and in estimated weak ligand (L 2 ) concentrations resulted. The main distinction between the mathematical approaches taken by participants lies in the functional form of the speciation model equations, with their implicit definition of independent and dependent or manipulated variables. In 'direct modeling', the dependent variable is the measured [M f ] (or I p ) and the total metal concentration ([M] T ) is considered independent. In other, much more widely used methods of analyzing titration dataclassical linearization, best known as van den Berg/Ružić, and isotherm fitting by nonlinear regression, best known as the Langmuir or Gerringa methods -[M f ] is defined as independent and the dependent variable calculated from both [M] T and [M f ]. Close inspection of the biases and variability in the estimates of ligand parameters and in predictions of ambient [M f ] revealed that the best results were obtained by the direct approach. Linear regression of transformed data yielded the largest bias and greatest variability, while non-linear isotherm fitting generated results with mean bias comparable to direct modeling, but also with greater variability. Participants that performed a unified analysis of ACSV titration curves at multiple detection windows for a sample improved their results regardless of the basic mathematical approach taken. Overall, the three most accurate sets of results were obtained using direct modeling of the unified multiwindow dataset, while the single most accurate set of results also included simultaneous calibration. We therefore recommend that where sample volume and time permit, titration experiments for all natural water samples be designed to include two or more detection windows, especially for coastal and estuarine waters. It is vital that more practical experimental designs for multi-window titrations be developed. Finally, while all mathematical approaches proved to be adequate for some datasets, matrix-based equilibrium models proved to be most naturally suited for the most challenging cases encountered in this work, i.e., experiments where the added ligand in ACSV became titrated. The ProMCC program (Omanović et al., this issue) as well as the Excel Add-in based KINETEQL Multiwindow Solver spreadsheet have this capability and have been made available for public use as a result of this intercomparison exercise.

Journal of Electroanalytical Chemistry, 1994

ABSTRACT

Environmental Science and Pollution Research, 2014

An evaluation of the quality status of the pristine karst, tufa depositing aquatic environment of... more An evaluation of the quality status of the pristine karst, tufa depositing aquatic environment of the Plitvice Lakes National Park based on the analysis of heavy (ecotoxic) metals was examined for the first time. Analyses of trace metals in water, sediment and fish (Salmo trutta , Oncorhynchus mykiss, Squalius cephalus) samples were conducted either by stripping voltammetry (Zn, Cd, Pb and Cu) or cold vapour atomic absorption spectrometry (Hg). The concentration of dissolved trace metals in water was very low revealing a pristine aquatic environment (averages were, in ng/L: 258 (Zn), 10.9 (Cd), 11.7 (Pb), 115 (Cu) and 1.22 (Hg)). Slightly enhanced concentrations of Cd (up to 50 ng/L) and Zn (up to 900 ng/L) were found in two main water springs and are considered as of natural origin. Observed downstream decrease in concentration of Cd, Zn and Cu in both water and sediments is a consequence of the self-purification process governed by the formation and settling of authigenic calcite. Anthropogenic pressure was spotted only in the Kozjak Lake: Hg concentrations in sediments were found to be up to four times higher than the baseline value, while at two locations, Pb concentrations exceeded even a probable effect concentration. The increase of Hg and Pb was not reflected on their levels in the fish tissues; however, significant correlations were found between Cd level in fish tissues (liver and muscle) and in the water/sediment compartments, while only partial correlations were estimated for Zn and Cu. A high discrepancy between values of potentially bioavailable metal fraction estimated by different modelling programs/models raised the question about the usefulness of these data as a parameter in understanding/relating the metal uptake and their levels in aquatic organism. The aquatic environment of the Plitvice Lakes National Park is characterized, in general, as a clean ecosystem.

Analytica Chimica Acta, 2000

Uranyl-selenium interactions were studied at two different ionic strengths (I = 0.1 and 3.0 mol/l... more Uranyl-selenium interactions were studied at two different ionic strengths (I = 0.1 and 3.0 mol/l) using square wave voltammetry. The uranyl(+6) reduction signal is only slightly affected by selenium(+4) reduction to HgSe, which appears in virtually the same potential range. On the other hand, the height and shape of the selenium stripping peak (which corresponds to dissolution of accumulated HgSe) can be significantly changed by the uranyl(+6) concentration in the solution. The type and magnitude of such effects are highly dependent on the ionic strength. As a result of uranyl(+6) interaction with selenium(+6), a coordination species UO 2 SeO 4 is formed, whose stability constant at I = 3 mol/l (log β 1 = 1.57 ± 0.01) is in very good agreement with the literature value based on spectrophotometric data. The presence of higher complexes could not be confirmed unambiguously.

Croatica Chemica Acta, 2012

ABSTRACT Current minimum, which sometimes appears as a part of the net response in differential p... more ABSTRACT Current minimum, which sometimes appears as a part of the net response in differential pulse polarography (DPP), was studied in systems characterized by a pronounced IR drop or reactant adsorption. Experimental results obtained on a static mercury drop electrode (SMDE) clearly indicate that this effect is highly influenced not only by solution resistance (or intentionally added resistors) and reactant concentration, but also by both timing parameters (drop time, pulse duration) and electrode surface area. Presentation of the net response along with its components, demonstrates that the current minimum originates from the maximum on dc component, minimum on pulse component or both. In practice, DPP minimum, obtained in measurements with a SMDE, can be treated as an additional diagnostic parameter for the recognition of reactant adsorption or poor experimental conditions (i.e. high resistance within electrode system or low conductivity of the electrolyte medium). (doi: 10.5562/cca2054)