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Analysis of trace heavy metals in a sample droplet with lab-on-a-chip system
Nika Žurga, 2020, undergraduate thesis

Abstract: The aim of this work was to develop and validate an electroanalytical method for simultaneous determination of Zn(II), Cd(II), and Pb(II) in a sample droplet with lab-on-a-chip system. Unmodified screen-printed electrodes (bare SPE using Ag/AgCl reference electrode) and Bi-film SPEs (BiFSPE) were used as electrochemical sensors. Cyclic voltammetry of [Fe(CN)6]3–/[Fe(CN)6]4– redox couple was employed for testing the reversibility of the diffusion-controlled system and square-wave anodic stripping voltammetry (SWASV) for determination of Zn(II), Cd(II), and Pb(II). SWASV was performed at deposition potential of –1.5 V vs. Ag/AgCl and deposition time of 60 s. The following validation parameters were examined: limit of detection (LOD), limit of quantification (LOQ), linearity, accuracy, and precision. LOD and LOQ for Zn(II) were both lower with BiFSPE than with bare SPE. For Cd(II), LOD and LOQ were similar for both bare SPE and BiFSPE. For Pb(II), LOD and LOQ with bare SPE could not be determined (due to intense background contribution) but were obtained with BiFSPE. Linear concentration ranges were obtained for all analytes with bare SPE and BiFSPE. Accuracy and precision were evaluated for different spiked concentrations; however, the method with bare SPE was neither accurate nor precise. With BiFSPE, the method was found to be both accurate and precise for Pb(II) at a spiked concentration of 140.0 μg/L, but not for Zn(II) or Cd(II). For the latter, problems with accuracy and precision were encountered with both bare SPE and BiFSPE. Both methods were selective for Zn(II), Cd(II), and Pb(II) determination. It can be concluded that the optimization of both methods is required for future studies.
Keywords: SPE, BiFSPE, heavy metals determination, SWASV, validation
Published: 31.08.2020; Views: 286; Downloads: 85
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Structural differences in the self-determination of upper secondary students with and without disabilities in vocational education
Marta Licardo, Majda Schmidt, 2016, original scientific article

Abstract: The aim of the study was to analyze the differences in degree of self-determination between students with and without disabilities and to relate these differences to grade point average and gender in both groups. Students in both groups were equalized in pairs by age, gender and school program (n = 122; 61 pairs). Results indicate that students with disabilities have a lower level of self-determination than their peers without disabilities. With regards to gender, girls with disabilities have the lowest level of self-determination. An analysis of differences in self-determination by grade point average (GPA) showed that students with and without disabilities who had high GPAs have higher levels of self-determination than students with low GPAs. Results of this study reveal important fields of intervention, especially for students with disabilities.
Keywords: self-determination, vocational education, students with disabilities, academic achievement, gender
Published: 03.10.2017; Views: 510; Downloads: 74
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Synthesis, crystal structure and magnetic properties of a new hydroxylammonium fluoroferrate
Brina Dojer, Matjaž Kristl, Zvonko Jagličić, Amalija Golobič, Marta Kasunič, Mihael Drofenik, 2012, original scientific article

Abstract: This paper reports on the synthesis of a new hydroxylammonium fluoroferrate, with the formula $(NH_3OH)_3FeF_6$, obtained after dissolving iron powder in hydrofluoric acid and adding solid $NH_3OHF$. This new compound has been characterized by chemical and thermal analysis, single-crystal X-ray diffraction, and magnetic measurements. The title compound crystallizes trigonal, R3c, with cell parameters a = 11.4154(2) Å, c = 11.5720(2) Å, Z = 6. The structure consists of $NH_3OH^+$ cations and isolated $FeF_6^{3–}$ octahedra in which the central ion lies on a threefold axis. The oxygen and nitrogen atoms of the hydroxylammonium cations are donors of hydrogen bonds to fluoride anions, resulting in a network of hydrogen bonds between counterions. The effective magnetic moment $µ_{eff}$ = 5.8 BM was calculated and perfectly matches the expected value of high-spin Fe(III) ions. The thermal decomposition of the compound was studied by TG, DSC, and X-ray powder diffraction.
Keywords: inorganic chemistry, crystallography, coordination compounds, synthesis, crystal structure, characterization of compounds, determination of the structure of compounds, X-ray diffraction, magnetic measurements, thermal analysis, TG, DSC, hydrogen bond, metal complexes, hydroxylammonium fluoromethalatehydroxylammonium, fluoroferrate
Published: 25.08.2017; Views: 1102; Downloads: 50
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Ammoniumbis(hydroxylammonium) pentafluoridooxidovanadate(IV)
Brina Dojer, Matjaž Kristl, Zvonko Jagličić, Mihael Drofenik, Anton Meden, 2008, original scientific article

Abstract: Turquoise crystals of a new hydroxylammonium compound with the formula $NH_4(NH_3OH)_2[VOF_5]$ have been synthesized by the reaction of solid $NH_3OHF$ and the aqueous solution of vanadium in HF. The compound crystallizes monoclinic, $P2_1/n$, with cell parameters: a = 10.5658(2) Å, b = 6.6143(1) Å, c = 11.6618(2) Å, β = 96.282(1). Magnetic susceptibility was measured using a SQUID device over a temperature range 2–300 K at magnetic field $10^3 Oe$ giving the result $µ_{eff}$ = 1.65 BM. The thermal decomposition was studied by TG and DSC analysis. $NH_4(NH_3OH)_2[OF_5V]$ decomposes above 354 K in three steps, obtaining $NH_4VOF_3$ after the first step and $V_2O_5$ as the final residue.
Keywords: hydroxylammonium fluorovanadates, x-ray powder diffraction, x-ray structure determination, thermal analysis
Published: 17.08.2017; Views: 825; Downloads: 67
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Multivariate data analysis of natural mineral waters
Katja Šnuderl, Marjana Simonič, Jan Mocak, Darinka Brodnjak-Vončina, 2007, original scientific article

Abstract: Fifty samples of natural mineral waters from springs in Slovenia, Hungary, Germany, Czech Republic and further countries of former Yugoslavia have been analysed. The mass concentration of cations ($Na^+$, $K^+$, $Ca^{2+}$, $Mg^{2+}$, $Fe^{2+}$, $Mn^{2+}$, $NH^+_4$) and anions ($F^-$, $Cl^-$, $I^-$, $NO^-_3$, $SO_4^{2-}$, $HCO_3^-$), the spring temperature, pH, conductivity and carbon dioxide mass concentration have been measured using standard analytical methods. Appropriate statistical methods and different chemometric tools were used to evaluate the obtained data, namely, (i) descriptive statistics, (ii) principal component analysis (PCA), (iii) cluster analysis, and (iv) linear discriminant analysis (LDA). It was confirmed that Slovenian natural mineral water samples differ most from the German ones but are relatively similar to the Czech and Hungarian ones. Water samples from Hungary are similar to waters from the eastern part of Slovenia.
Keywords: natural mineral water, ion determination, principal component analysis, cluster analysis, linear discriminant analysis
Published: 21.12.2015; Views: 958; Downloads: 59
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Non-invasive methods for children's cholesterol level determination
Petra Povalej Bržan, Peter Kokol, Jernej Završnik, 2003, professional article

Abstract: Today, there is a controversy about the role of cholesterol in infants and the measurement and management of blood cholesterol in children. Several scientific evidences are supporting relationship between elevated blood cholesterol in children and high cholesterol in adults and development of adult arteriosclerotic diseases such as cardiovascular and cerebrovascular disease. Therefore controlling the level of blood cholesterol in children is very important for the health of the whole population. Non-invasive methods are much more convenient for the children because of their anxieties about blood examinations. In this paper we will present a new try to find non-invasive methods for determining the level of blood cholesterol in children with the use of intelligent system.
Keywords: cholesterol level determination, noninvasive method
Published: 01.06.2012; Views: 1387; Downloads: 19
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Sol-gel-based optical sensor for the detection of aqueous amines
Špela Korent Urek, Aleksandra Lobnik, Gerhard J. Mohr, 2007, original scientific article

Abstract: We present an optical sensor for the detection of aqueous amines obtained by incorporating chromoionophore XV (ETHT 4001) into sol-gel thin films. Acid- and base-catalyzed sol-gel processes were studied to prepare stable ormosil layers using various amounts of organically modified sol-gel precursor such asmethyltriethoxysilane (MTriEOS). The sensor layers were coated with a protective layer of microporous white polytetrafluoroethylene (PTFE) in order to prevent interference from ions and ambient light. The measurements were carried out in a flow-through cell in the reflection mode. Acid-catalyzed ormosil layers (pH 1) based on the copolymerization of tetraethoxysilane (TEOS) and MTriEOS did not show any change in signal upon exposure to aqueous amine solutions, while base-catalyzed sensor layers (pH 3 and 13) showed significant changes in signal. The response time (t100) for the base-catalyzedsensor layer L3 (pH 13) upon exposure to different solutions containing 0-608 mmol L-1 aqueous propylamine was 20-30 s, the regeneration time was 70 s and the detection limit was 0.1 mmol L-1. The sensor response was reproducible and reversible. The porous ormosil layers permit dry sensor storage conditions.
Keywords: analytical chemistry, optical sensors, sol-gel technology, determination of amines, fluorimetry
Published: 01.06.2012; Views: 2133; Downloads: 72
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Detection and visualization of visible surfaces
Danijel Žlaus, 2011, published scientific conference contribution

Keywords: visible surface, hidden surface, determination
Published: 01.06.2012; Views: 805; Downloads: 22
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Evaluation of analytical methods for the determination of free formaldehyde on textile substrate
Bojana Vončina, Alenka Majcen Le Marechal, Darinka Brodnjak-Vončina, 2007, original scientific article

Abstract: Release of formaldehyde from durable press-treated fabrics is a problem for human health and safety because formaldehyde is suspected to be carcinogenic. The accuracy of the standard test method for the free formaldehyde determination, Japan Law 112, depends on the formaldehyde content of the sample. The detection of low formaldehyde contents is particularly important in fields, like children clothing, so the application of high-performance liquid chromatography was evaluated. The results obtained by the standard testmethod, Japan Law 112, where UV/Vis spectrometer was used, were compared with the results obtained by HPLC method in which separation was performed on an RP C18 column with water-methanol as a mobile phase. It was shown that the detection limit and limit of quantification were improved using the HPLC method.
Keywords: analizna kemija, formaldehid, določevanje formaldehida, celulozna vlakna, HPLC, UV/VIS, analytical chemistry, formaldehyde, determination of formaldehyde, cellulose fibres, HPLC, UV/VIS
Published: 31.05.2012; Views: 2015; Downloads: 97
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