Volume 61, Issue 5

An easy and inexpensive method of potassium determination in fatty acid methyl esters (FAME) applying an ion-selective potassium electrode (ISE-K) is presented. FAME are considered alternative fuel for diesel engines. Simple apparatus and procedure were developed to avoid contact of ester samples with the sensitive ISE-K membrane, which can damage the ISE membrane surface in long time operation. Using different FAME samples with a wide range of known potassium content a calibration curve was constructed. Among all samples, ISE-K satisfactory predicted potassium content in FAME as identified by the AAS reference method.

A new solid-phase extraction method has been developed for the selective extraction of Cu(II) in an aqueous system using freshly precipitated lead diethyldithiocarbamate (Pb(DDTC)2) as a reagent. The method is based on the quantitative replacement of Pb(II) ions in the solid Pb(DDTC)2 phase by Cu(II) ions present in aqueous phase. The obtained solid Cu(DDTC)2 phase was dissolved in chloroform and determined spectrophotometrically at 435 nm. Beer’s law was obeyed over the concentration range of 0.2–5 mg dm−3. The molar absorptivity and the Sandell’s sensitivity coefficients of the solutions were 1.0689 × 104 dm3 mol−1 cm−1 and 0.0060 µg cm−2, respectively. The optimum conditions for each parameter were experimentally determined and possible interferences of various salts were also studied. The method has been validated and applied to determine Cu(II) in various alloys and water samples.

Classification of normal and different cancer groups (TNM classification) with univariate and multivariate statistical methods according to the contents of Cu, Fe, Mn, Se, and Zn in blood serum is discussed. All serum samples were digested by acid mixture in a microwave mineralization unit prior to the analysis by atomic absorption spectrometry. Results show that univariate methods can distinguish normal and cancer groups. Level of selenium evaluated as arithmetic mean with its standard deviation in colorectal cancer patients was (42.61 ± 23.76) µg L−1. Retransformed mean was used to evaluate levels of managanese (11.99 ± 1.71) µg L−1, copper (1.05 ± 0.06) mg L−1, zinc (2.14 ± 0.21) mg L−1, and iron (1.82 ± 0.22) mg L−1. Conclusions of multivariate statistical procedures (principal component analysis, hierarchical, and k-means clustering) do not correlate very well with the division of serum samples according to the TNM classification.

A sensitive chemiluminescence method, based on the enhancive effect of norfloxacin on the reaction between luminol and dissolved oxygen in a flow injection system, was proposed for the determination of norfloxacin. The increment of the chemiluminiscence intensity was proportional to the concentration of norfloxacin, giving a calibration graph linear over the concentration from 0.4 ng mL−1 to 400.0 ng mL−1 (r 2 = 0.9988) with the detection limit of 0.1 ng mL−1 (3 × σ noise). At the flow rate of 2.0 mL min−1, a complete determination of norfloxacin, including sampling and washing, could be accomplished in 30 s with the relative standard deviation lower than 3.0 %. The proposed method was applied successfully to determine norfloxacin in pharmaceuticals, human urine, and serum. Possible mechanism of the reaction was also discussed.

Optimization of immobilization conditions was carried out for covalent binding of Aureobasidium pullulans fructosyltransferase to a copolymer of butyl acrylate and ethylene glycol dimethacrylate using a glutaraldehyde method. It was found that the highest activity of the preparation could be obtained for the immobilization pH 6.0 and initial protein amount 8.5 g per dm3 of the carrier. Effects of the reaction pH, temperature, and initial sucrose concentration on the activity and stability of the preparation were analyzed. Further investigations involved storage stability and operational stability in a mechanically stirred-tank reactor.

A comparison was made between the catalytic properties of β-galactosidase from Penicillium canescens and Aspergillus oryzae using lactose in two-phase systems of an organic solvent and water. It was shown that the ability of β-galactosidase preparations to synthesize galactooligosaccharides depends on the type of the solvent used (cyclohexane, hexane, toluene) and on its proportion in the two-phase system. The use of cyclohexane in the reaction medium stabilized the activity of β-galactosidase from P. canescens which was immobilized on tosylated cotton cloth, and enabled its multiple use in galactooligosaccharides synthesis.

The thermal decomposition behavior in air of SrC2O4 · 1.25H2O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO3 and the decomposition of SrCO3 to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO3. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D2), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R3). The values of activation parameters obtained using different methods were compared and discussed.

Complexes of yttrium(III) and lanthanides(III) with 4-hydroxy-3,5-dimethoxybenzoic (syringic) acid were obtained as solids with metal to ligand mole ratio of 1: 3. The compounds were characterized by elemental analysis, IR spectroscopy, X-ray diffraction patterns, solubility, and thermal studies. The complexes are sparingly soluble in water and stable at room temperature. Compounds of light lanthanides (from La to Nd) are hydrated and they crystallize in a triclinic system. When heated, they lose water molecules in one step and in the next step they decompose to oxides. Complexes of yttrium and other lanthanides are anhydrous and crystallize in a monoclinic system. They are stable up to 300°C and then decompose to oxides. As the coordination number of lanthanide ions is usually equal to 9 or 8, one can suppose that hydroxy or methoxy groups take part in the coordination of these metal ions.

Polymerization kinetics and gloss of different formulations of coatings at different UV curing conditions were studied. The results showed that the photoinitiator type, its concentration, sample coating thickness, as well as the UV light intensity were the most significant factors affecting the polymerization course and the gloss of UV-cured films. The increasing concentration of the photoinitiator and the UV light intensity significantly decreased the gloss of the cured surface. The influence of the sample coating thickness on the kinetics and final gloss was also considerable.

Simple iron gall inks composed of gallic acid, ferrous sulfate, and gum arabic and in some cases also of copper(II) sulfate were prepared. The process of iron ion complex formation with gallic acid was investigated using UV-VIS spectroscopy, pH measurements, and by monitoring the concentration changes of Fe(II) ions. The admixture of Fe(II) ions to gallic acid induced a bathochromic shift of absorption bands at 215 nm and 265 nm in the UV-VIS spectra. Formation of a new absorbance band in the visible area was also observed and used to calculate the initial rate of complex formation. Concurrently, the pH values and the concentration of Fe(II) ions in the solution decreased. Gum arabic significantly enhanced the complex formation and its stability. On the contrary, the addition of Cu(II) ions to the solution decelerated the complex formation considerably.

Reduction of 9-alkyl-3-nitrocarbazoles (Ia–Ie) with lithium aluminium hydride gave corresponding 9,9′-dialkyl-3,3′-azocarbazoles (IIa–IIe) in moderate yield. By the action of zinc dust in alcohol and aqueous alkali on I or II, 5,13-dialkyldiindolo[3,2-a,d]phenazines (IIIa–IIId) were obtained. Parent compounds, viz. 3,3′-azocarbazole (IIf) and diindolo[3,2-a,d]phenazine (IIIf) could not be obtained in these ways. Compound IIf was obtained in Vorländer reaction and IIIf by thermal decomposition of 3-azidocarbazole. Formation of IIIa–IIId is explained as a result of ortho-benzidine rearrangement of hypothetical 9,9′-dialkyl-3,3′-hydrazocarbazoles.

Chemical composition of the essential oil of Aquilegia pancicii Degen endemic to Serbia is reported. Essential oil obtained by hydrodistillation from the aerial parts was analyzed by GC and GC/MS. The major constituents were hexadecanoic acid (24.3 %) and hexahydrofarnesyl acetone (14.1 %), among 130 identified compounds, representing 90.3 % of the total essential oil. The oil was marked by the presence of 69 fatty acid derivatives and low content of terpenoids representing 60.4 % and 7.8 % of the oil, respectively.

8-Amino-1-methoxy-6H-dibenzo[b,d]pyran-6-one was synthesized in a one-pot reaction of 2′,6′-dimethoxy-4-nitro-1,1′-biphenyl-2-carboxylic acid methyl ester using hydroiodic acid as a reagent to effect O-demethylation, lactonization, and nitro reduction to amine. This new reaction represents an improved alternative to the previously reported three-step reactions for this transformation.

A composite of iron oxide nanoparticles and mineral matrix has been studied by XRD, Mössbauer spectroscopy, and TEM. Magnetite and superparamagnetic magnetite have been identified by Mössbauer spectroscopy in the nanocomposite. A relationship between the hyperfine parameters and iron oxide particle size has been confirmed by TEM. The optimal concentration of “magnetite—bentonite” composite, when the MRI signal is fully reduced, was found for using this composite as a negative contrast agent.