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Membranes from polysulfone/N,N-dimethylacetamide/water system
Vladimir Kaiser, Črtomir Stropnik, 2000, izvirni znanstveni članek

Opis: Polymeric membranes were prepared by the wet-phase separation method from solutions of different contents of polysulfone in N,N-dimethylacetamide; solutions were cast in different thickness before immersion into the pure water coagulation bath. Two main processes take place during the formation of membranes: nucleation and growth of the polymer lean phase with subsequent solidification of the polymer rich phase, and the formation of channels, macrovoids and mega-macrovoids. By the first process a cellular structure is formed whilst the second process connects the cells by opening the space between them. The degree of interconnectedness is an additional factor that affects the pure water flux. By changing the cast solution compositions and/or their cast thickness the interconnectedness of the cells can be controlled.
Ključne besede: chemical technology, organic technology, polymer membranes, membrane preparation, wet phase inversion, polymers, polysulphon
Objavljeno: 18.08.2017; Ogledov: 4; Prenosov: 0
.pdf Polno besedilo (112,47 KB)

Mednarodni standardi veličine in enote
Peter Glavič, 2003, strokovni članek

Opis: V prispevku so predstavljeni mednarodni standardi ISO 31 (Veličine in enote) z naslednjimi deli: ISO 31-0 (Splošna načela), ISO 31-1 (Prostor in čas), ISO 31-2 (Periodični in sorodni pojavi), ISO 31-3 (Mehanika), ISO 31-4 (Toplota), ISO 31-5 (Elektrika in magnetizem), ISO 31-8 (Fizikalna kemija in molekulska fizika), ISO 31- 12 (Karakteristična števila) in drugimi. Poudarek je na splošnih načelih, ki so pomembna za pisanje poročil, referatov, člankov, knjig in za pedagoški proces.
Ključne besede: metrologija, mednarodni standardi ISO 31, simboli, veličine, enote, mednarodni sistem enot (SI), prostor, čas, periodični pojavi, mehanika, toplota, elektrika, magnetizem, fizikalna kemija, molekulska fizika, karakteristična števila
Objavljeno: 18.08.2017; Ogledov: 3; Prenosov: 0
.pdf Polno besedilo (210,40 KB)

Forward osmosis in wastewater treatment processes
Jasmina Korenak, Subhankar Basu, Malini Balakrishnan, Claus Hélix-Nielsen, Irena Petrinić, 2017, izvirni znanstveni članek

Opis: In recent years, membrane technology has been widely used in wastewater treatment and water purification. Membrane technology is simple to operate and produces very high quality water for human consumption and industrial purposes. One of the promising technologies for water and wastewater treatment is the application of forward osmosis. Essentially, forward osmosis is a process in which water is driven through a semipermeable membrane from a feed solution to a draw solution due to the osmotic pressure gradient across the membrane. The immediate advantage over existing pressure driven membrane technologies is that the forward osmosis process per se eliminates the need for operation with high hydraulic pressure and forward osmosis has low fouling tendency. Hence, it provides an opportunity for saving energy and membrane replacement cost. However, there are many limitations that still need to be addressed. Here we briefly review some of the applications within water purification and new developments in forward osmosis membrane fabrication.
Ključne besede: wastewater treatment, biomimetic membranes, desalination, draw solutions, forward osmosis
Objavljeno: 18.08.2017; Ogledov: 3; Prenosov: 0
.pdf Polno besedilo (403,57 KB)

Effects of translational and rotational degrees of freedom on the hydration of ionic solutes as seen by the popular water models
Tomaž Mohorič, Urban Bren, Vojko Vlachy, 2015, izvirni znanstveni članek

Opis: We employed molecular dynamics simulations with separate thermostats for translational and rotational temperatures in order to study the effects of these degrees of freedom on the hydration of ions. In this work we examine how water models, differing in charge distribution, respond to the rise of rotational temperature. The study shows that, with respect to the distribution of negative charge, popular water models lead to different responses upon an increase of the rotational temperature. The differences arise in hydration of cations, as the negative charge distribution on the model solvent represents the determining factor in such cases. The cation-water correlation increases with the increasing rotational temperature if negative charge is placed in (or close to) the centre of the water molecule (a typical example is the SPC water model) and decreases, when the negative charge is shifted from the centre (as in the TIP5P model of water). Because all the water models examined here have similar distributions of positive charge, they all exhibit similar trends in solvation of anions. In contrast to above, the effect of translational temperature variation is similar for all water-solute pairs; any increase in translational temperature decreases the solute-water correlations.
Ključne besede: ionic hydration, water models, degrees of freedom, molecular dynamics
Objavljeno: 18.08.2017; Ogledov: 8; Prenosov: 0
.pdf Polno besedilo (494,01 KB)

Effect of solid state fermentation medium optimization on Pleurotus ostreatus laccase production
Nataša Belšak, Andrej Gregori, Maja Leitgeb, Dušan Klinar, Štefan Čelan, 2015, izvirni znanstveni članek

Opis: The objective of this work was to increase laccase production by Pleurotus ostreatus PLAB through culture medium optimization using solid-state culture conditions. Increased laccase activity was obtained through the design of experiments (DOE) using the Taguchi orthogonal array (OA). Seven factors, viz. lignocellulose, glucose, yeast extract, peptone, $KH_2PO_4$, $MgSO_4$ · $7H_2O$ and $MnSO_4$ · $H_2O$ at three levels and pH at two levels with OA layout of L18 ($2^1 × 3^7$) were selected for the proposed experimental design using Minitab 17 software. Data analysis showed that lignocellulose (20%) and glucose (10 g $L^{–1}$) had a positive effect, whereas $KH_2PO_4$, $MgSO_4$ · $7H_2O$ and $MnSO_4$ · $H_2O$ did not have a significant effect on laccase production. Taguchi OA analysis showed that pH 6, lignocellulose 20%, glucose 10 g $L^{–1}$, yeast extract 6 g $L^{–1}$, peptone 15 g $L^{–1}$, $KH_2PO_4$ 3 g $L^{–1}$, $MgSO_4$ · $7H_2O$ 0.5 g $L^{–1}$ and $MnSO_4$ · $H_2O$ 0.1 g $L^{–1}$ were the optimal conditions to maximize laccase production. The model predicted a 30.37 U $g^{–1}$ dry wt., which agreed with the experimentally obtained laccase activity 29.15 U $g^{–1}$ dry wt. at optimal conditions.
Ključne besede: Taguchi method (DOE), orthogonal array, optimization, Pleurotus ostreatus, laccase production, solid state fermentation
Objavljeno: 18.08.2017; Ogledov: 15; Prenosov: 0
.pdf Polno besedilo (126,99 KB)

Effect of drying parameters on physiochemical and sensory properties of fruit powders processed by PGSS-, vacuum- and spray-drying
Urban Feguš, Uroš Žigon, Marcus Petermann, Željko Knez, 2015, izvirni znanstveni članek

Opis: Aim of this experimental work was to investigate the possibility of producing fruit powders without employing drying aid and to investigate the effect of drying temperature on the final powder characteristics. Raw fruit materials (banana puree, strawberry puree and blueberry concentrate) were processed using three different drying techniques each opera- ting at different temperature conditions: vacuum-drying (–27–17 °C), spray-drying (130–160 °C) and PGSS-drying (112–152 °C). Moisture content, total colour difference, antioxidant activity and sensory characteristics of the proces- sed fruit powders were analysed. The results obtained from the experimental work indicate that investigated fruit pow- ders without or with minimal addition of maltodextrin can be produced. Additionally, it was observed that an increase in process temperature results in a higher loss of colour, reduced antioxidant activity and intensity of the flavour profile.
Ključne besede: particles from gas saturated solutions drying, vacuum-drying, spray-drying, sensory evaluation, fruit powders
Objavljeno: 18.08.2017; Ogledov: 8; Prenosov: 0
.pdf Polno besedilo (249,24 KB)

Determination of topiramate in human plasma using liquid chromatography tandem mass spectrometry
Tanja Vnučec, Lea Cvitkovič-Maričič, Helena Prosen, Darinka Brodnjak-Vončina, 2013, izvirni znanstveni članek

Opis: The LC-MS/MS method for determination of the anti-epileptic drug topiramate (TPM) in human plasma was developed and validated for pharmacokinetic and bioequivalence study purposes. For quantitative determination of TPM values the method with deuterated internal standard (topiramate-d12) and liquid chromatography with tandem mass spectrometry was used. TPM was extracted from the human plasma using the solid-phase extraction procedure on a Strata X extraction column. Negative ions were monitored in the selected reaction monitoring mode (SRM) and transitions m/z 338.2 > 78.2 and m/z 350.3 > 78.2 were used for the quantitative evaluation of TPM and the internal standard, respectively. The results obtained from validation were statistically evaluated according to the requirements of European Medicines Agency (EMA) and Food and Drug Administration (FDA) regulatory guidelines. The linearity of the method was checked within a concentration range from 10 to 2000 ng/mL. Successful validation confirmed that this method is precise, accurate, sensitive and therefore suitable for determination of topiramate plasma levels in pharmacokinetic and bioequivalence studies.
Ključne besede: topiramate, liquid chromatography tandem mass spectroscopy, human plasma, bioequivalence study
Objavljeno: 18.08.2017; Ogledov: 8; Prenosov: 0
.pdf Polno besedilo (189,19 KB)

Determination of candesartan in human plasma with liquid chromatography - tandem mass spectrometry
Vanja Forjan, Lea Cvitkovič-Maričič, Helena Prosen, Darinka Brodnjak-Vončina, 2016, izvirni znanstveni članek

Opis: A sensitive, specific and rapid liquid chromatography - tandem mass spectrometry method was developed and validated for the determination of candesartan in human plasma. Analyte was separated from endogenous components present in plasma by solid phase extraction. Chromatographic separation was performed on Gemini C18 analytical column using mobile phase acetonitrile – 5 mM ammonium formate pH 2 (90:10, v/v) at flow rate of 0.3 mL/min. For detection, tandem mass spectrometry in SRM mode with positive electrospray ionization was used. The mass transitions m/z 441.1 > 263.1 and 445.1 > 267.1 were used to determine candesartan by using candesartan-d4 as an internal standard. After development, the method was validated according to the requirements of EMA regulatory guidelines in the concentration range 1 - 400 ng/ml in human plasma. Limit of quantification (LLOQ) was 1 ng/ml. The developed and validated method proved to be very fast and reproducible and was therefore successfully implemented in pharmacokinetic and bioequivalence studies with large number of study samples.
Ključne besede: candesartan, liquid chromatography, tandem mass spectrometry, human plasma
Objavljeno: 17.08.2017; Ogledov: 13; Prenosov: 0
.pdf Polno besedilo (215,54 KB)

Composition of organic compounds adsorbed on PM10 in the air above Maribor
Alen Miuc, Ernest Vončina, Uroš Lešnik, 2015, izvirni znanstveni članek

Opis: Organic compounds in atmospheric particulate matter above Maribor were analysed in 120 samples of PM10 sampled according to the EN 12341:2014 reference method. Organic compounds compositions were investigated together with the primary and secondary sources of air pollution. Silylation as derivatisation method was used for the GC-MS determination of volatile and semi-volatile polar organic compounds. Distribution of fatty acids, n-alkanes and iso-alkanes, phthalate esters, siloxanes, different sterols, various sugars and sugar alcohols, compounds of lignin and resin acids, dicarboxylic acids from photochemical reactions, PAHs, organic nitrogen compounds and products from secondary oxi- dation of monoterpenes were determined. The use of silicone grease for the purpose of lubricating the impact surface of the air sampler caused higher values of gravimetric determination. Solid particles may have been bounced from the surface of a greasy impact plate and re-entrained within the air stream and then collected on a sample filter. The carryover of siloxanes was at least from 5% up to 15% of the accumulated particles weight, depending on ambient temperature. This was the reason that the gravimetric results for determination of PM10 according to the standard EN 12341:2014 were overestimated.
Ključne besede: secondary organic aerosol, volatile organic compounds, PM10, EN 1234:2014
Objavljeno: 17.08.2017; Ogledov: 13; Prenosov: 0
.pdf Polno besedilo (676,87 KB)

Chemical modification and characterization of the surface of polysulfone membranes
Irena Kukovičič, Robert Šoster, Milan Brumen, Volker Ribitsch, D. Wiegel, K. Arnold, Črtomir Stropnik, 2000, izvirni znanstveni članek

Opis: Asymmetric porous membranes were prepared from polysulfone by a wet-phase separation procedure. Different chemical modifications were applied to the upper membrane surface, i.e. the surface which was exposed to interaction with nonsolvent (water) in the coagulation bath during the membrane formation. The membrane surface was modified by the series of Friedel-Crafts electrophilic substitutions of aromatic rings in the polysulfone molecules. As a reagent 1-chlorodecane or propylene oxide dissolved in hexane and $AlCl_3$ as a catalyst were used. In the former case a hydrophobic and in the latter one a hydrophilic coating was achieved, respectively. The membrane surface was also modified by sulfonization with sulfuric (VI) acid water solution; in this way negative charges were introduced at the membrane surface. The membranes, unmodified and chemically modified, were characterized by measuring the membrane thickness, the deionized water flux through the membrane, the zeta potential and contact angle. The specific chemical modifications of the membrane surface affect the water flux, the zeta potential and contact angle values whereas the membrane thickness remains unchanged. These effects are interpreted in terms of hydrophilicity and hydrophobicity, changes of the membrane surface charge and the thickness of shear layer at the membrane surface, all with respect to the particular modification applied. Reaction with 1-chlorodecane gave a hydrophobic surface by nonpolar $–(CH_2)_9-CH_3$ groups and reaction with propylene oxide gave a hydrophilic surface with polar group $-CH(CH_3)-CH_2-OH$. The surface of sulfonized polysulfone membranes contained ionizable ($-SO_3H$) functional groups.
Ključne besede: polysulfone, chemical modification, Friedel-Crafts electrophilic substitution, sulfonization, hydrophylicity, hydrophobicity
Objavljeno: 17.08.2017; Ogledov: 11; Prenosov: 0
.pdf Polno besedilo (82,15 KB)

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