Lidija Ćurković

Simultaneous Determination of Six Inorganic Anions in Drinking Water by Non - Suppressed Ion Chromatography

A non-suppressed ion chromatographic method with conductometric detection is described for the simultaneous determination of six inorganic anions: fluoride, chloride, nitrite, bromide, nitrate and sulphate. The separation was achieved on a low-capacity anion-exchange column Metrohm IC Anion Column Super Sep, with a mobile phase consisting of phtalic acid dissolved in high-purity water, 2-amino-2-hydroxymethyl-1,3-propendiol and acetonitrile. In this work computer optimization procedures, using computer programs to select chromatographic conditions have been used, leading to the achievement of a desired separation. By using the different optimization methods in an integrated manner it is, however, possible to both speed method development, by reducing unnecessary experimentation, and to overcome the many shortcomings of each method, because of the different approaches. The purpose of this work is to improve and characterise the method for simultaneous determination of six inorganic anions in drinking water by non-suppressed ion chromatography, using optimization procedures, in order to be applied to the routine analysis. The proposed method has numerous advantages over the other widely used non-suppressed ion chromatography methods: higher selectivity, shorter analysis time, lower quantitation and detection limits. The performance characteristics of the method were established by determining the following validation parameters: precision and accuracy, linearity, detection limits and quantitation limits.

The sorption of sulfamethazine on soil samples: Isotherms and error analysis

In this paper, batch sorption of sulfamethazine on eight soil samples (six from Croatia and two from Bosnia and Hercegovina) with different organic matter contents ranging from 1.52 to 12.8% was investigated. The effects of various parameters such as agitation time, initial concentration, and ionic strength on the sulfamethazine sorption were studied. The experimental data were analysed using a one-parameter model, Linear isotherm, and two two-parameter models, the Freundlich and Dubinin-Radushkevich isotherms. The goodness of fit was measured using the linear regression and the determination coefficient (R(2)) value. Also, the equilibrium data of the two-parameter models were analysed using the residual root mean square error (RMSE), the sum of squares of errors (ERRSQ), and a composite fractional error function (HYBRID). Non-linear regression has better characteristics for analysing experimental data. The obtained sorption coefficients Kd (from 0.25 to 8.10 mL/g) and the Freundlich sorption coefficients KF (from 1.16 to 7.99 (μg/g)(mL/μg)(1/n)) exhibited quite low values, which indicated that sulfamethazine is weakly adsorbed on the evaluated soils, is highly mobile, and has a great potential to penetrate and pollute the ground water. The Dubinin-Radushkevich isotherm was used to estimate the apparent free energy of sorption.

Simple methods for characterization of metals in historical textile threads

Characterization of metal threads on historical textile materials is important for preservation of valuable cultural heritage. Obtained results dictate decisions on cleaning, conservation and restoration steps. The most important part of characterization is chemical analysis of originally applied materials, since this enables understanding the nature of chemical and physical degradation and determines the cleaning methods. Methods applied should be non-destructive and sensitive enough to detect trace elements in small sample amounts. The goal of this research was to describe the most useful procedures for fast and simple determination of specific metals of interest. Therefore we propose application of scanning electron microscopy equipped with EDS detector (SEM-EDS) for sample surface analysis and inductively coupled plasma-optical emission spectroscopy (ICP-OES) for chemical analysis of metals threads. For quality insurance reasons, a comparative method applied for chemical analysis was atomic absorption spectrometry (AAS). This combination of methods has proven to be very useful in analysis of historical samples, since SEM-EDS was a simple and non-destructive method which provided information on chemical composition of sample surfaces, while ICP-OES and AAS enabled the full insight into the average chemical composition of samples. Nevertheless, both ICP-OES and AAS were destructive methods which demanded dissolving of samples prior to the analysis. In this work nine different metal fibers collected from historical textile materials were characterized. Proposed methods enabled obtaining information on sample constitution, morphology, topology and chemical composition.

Kinetics and degradation pathways of photolytic and photocatalytic oxidation of the anthelmintic drug praziquantel

In this study, an anthelmintic drug, praziquantel(PZQ), was degraded using the direct photolysis, photocatalysis, and oxidation processes including UV radiation, TiO2 film, and hydrogen peroxide. The photolytic degradation with predominant wavelengths of 185/254nm (UV-C) proved to be more efficient with a half-life of 3.13min compared to the radiation of 365nm (UV-A) where the degradation did not occur. In order to enhance the rate of PZQ photolytic degradation, H2O2 was added, which resulted in two to three times higher degradation rates. In the photocatalytic degradation, TiO2 film was used as catalyst. The degradation was ten times faster in the photocatalytic experiments where UV-C light (k=0.2390min-1) was used than in those with UV-A (k=0.0201min-1). Comparing the results from all performed experiments it can be concluded that the UV-C/TiO2/H2O2 process yielded the highest degradation rate and complete degradation of PZQ was obtained in less than 7min. The degradation of PZQ followed the first order kinetics in all the experiments. The photo degradation was inhibited in the presence of methanol. The degradation pathways and the structural formulae of five degradation products (m/z 273, 269, 189, 147, 132) were proposed based on the liquid chromatography tandem mass spectrometry analysis.

SELECTION OF CRITERIA FOR COMPARING AND EVALUATING THE OPTIMIZATION OF SEPARATION IN ION CHROMATOGRAPHY

Optimization procedures in Ion Chromatography require unambiguous goals. Optimization criteria express such goals in mathematical terms. If the retention factor tR, varies as a function of the parameters to be optimized, criteria should be selected that enable simultaneous optimization of retention and selectivity. The non — suppressed Ion Chromatographic method with conductometric detection is described for simultaneous determination of six inorganic anions: fluoride, chloride, nitrite, bromide, nitrate, and sulphate. It is demonstrated that the result of the optimization process depends on the optimization criterion selected. The computer-simulated chromatograms were used for the comparison of optima calculated using four different criteria. General recommendations for double criteria optimization of separation in ion chromatography are suggested.

Effect of pH, fluoride and hydrofluoric acid concentration on ion release from NiTi wires with various coatings

Aim was to determine effect of pH, fluoride (F-) and hydrofluoric acid concentration (HF) on dynamic of nickel (Ni2+) and titanium (Ti4+) ions release. Nickel-titanium wires with untreated surface (NiTi), rhodium (RhNiTi) and nitride (NNiTi) coating were immersed once a week for five min in remineralizing agents, followed by immersion to artificial saliva. Ion release was recorded after 3, 7, 14, 21 and 28 days. Pearson correlations and linear regression were used for statistical analysis. Release of Ni2+ from NiTi and NNiTi wires correlated highly linearly positively with HF (r=0.948 and 0.940, respectively); for RhNiTi the correlation was lower and negative (r=-0.605; p<0.05). The prediction of Ti4+ release was significant for NiTi (r=0.797) and NNiTi (r=0.788; p<0.05) wire. Association with F- was lower; for pH it was not significant. HF predicts the release of ions from the NiTi wires better than the pH and F- of the prophylactic agents.

Corrosion Protection of AISI 316L Stainless Steel with the Sol-Gel Yttria Stabilized ZrO2 Films: Effects of Sintering Temperature and Doping

Nanostructured sol–gel zirconia (ZrO2) films containing 3, 5 and 7 mol % Y2O3 of one and three layers were prepared on stainless steel X2CrNiMo17-12-2 (AISI 316L) surface by the dip coating method. Yttria stabilized zirconia (YSZ) deposited films were sintered at 400 and 600 °C. For the preparation of sol zirconium(IV) butoxide was used as precursor, i-propyl alcohol as a solvent with addition of nitric acid as a catalyst, acetylacetone as chelating agent and water for hydrolysis. Thickness of sol-gel YSZ films deposited on stainless steel was determined by glow- discharge optical emission spectrometry (GD- OES). It was found that thickness of deposited films is barely affected by yttria content while increases by increasing the number of layers and temperature of sintering. The crystal structure of films was determined by X- ray diffraction. The corrosion resistances of uncoated and coated specimens were studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated marine environment (3.5 wt. % NaCl aqueous solution) at room temperature. The influence of yttria stabilized zirconia (YSZ) layers number and temperature of sintering on the corrosion protection was examined as well. Sol-gel derived YSZ films are capable of appreciable improvement in corrosion resistance of stainless steel in the investigated corrosive medium.

Fractionation of Heavy Metals in Fly Ash from Wood Biomass Using the BCR Sequential Extraction Procedure

The aim of this study was to extract the wood biomass fly ash fractions by a three-stage sequential extraction method for acetic acid and ion exchangeable (BCR 1), hydroxylamine hydrochloride reduction (BCR 2), and hydrogen peroxide oxidation (BCR 3) fractions in order to access the leaching behavior of this residue. The fly ash was collected as a by-product from the processing of mixed wood biomass in Udbina combustion facility, Croatia. Concentrations of several elements (As, Cd, Cr, Cu, Ni, Pb and Zn) in all extracts were determined by inductively coupled plasma atomic emission spectrometry. The acidic exchangeable form of the metals was used to evaluate the potential ecological risk of biomass fly ash. According to calculated potential ecological risk index, it is confirmed that mobility of Ni and As has major environmental impact. However the results of potential ecological risk show that biomass fly ash had a low risk.

Fracture toughness of alumina ceramics determined by Vickers indentation technique

Abstract Fracture toughness (KIC) of high purity cold isostatically pressed alumina ceramic (CIP-Al2O3) was determined from the size of cracks induced by Vickers hardness testing at wide range of loads. The observed cracks appeared at following loads: 4.905 N, 9.81 N, 29.43 N and 49.05 N. The studied material exhibits half-penny crack system at lower load of 4.905 N, but it proceeds as the Palmqvist crack system at higher loads, which was determined computationally. For the fracture toughness calculation different models were compared. It was found that fracture toughness increases by rising applied load for all kind of models, which is explained by the indentation size effect. As the fracture toughness overestimation can lead to product malfunction, it is suggested to use the Niihara model, which gives the smallest fracture toughness values.

Environmental Hazard Assessment of Jarosite Waste Using Batch Leaching Tests

M. Kerolli – Mustafa,a,** L. Ćurković,b M. Ujević Bošnjak,c and T. Rezićd aInternational Business College Mitrovica, Pajazit Boletini 22, 40000 Mitrovica, Kosovo bFaculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia cCroatian Institute of Public Health, Rockefellerova 7, 10000 Zagreb, Croatia dFaculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, 10000 Zagreb, Croatia