Natasa Pejic

University of Belgrade · Department of Physical Chemistry and Instrumetal Methods

A kinetic method for the determination of l-tyrosine (Tyr) by analyte pulse perturbation, caused by different amounts of Tyr, in the Bray–Liebhafsky (BL) oscillatory reaction realized in a continuous-flow stirred tank reactor, is proposed. For such purposes, the BL oscillating reaction was kept in a stable non-equilibrium stationary state close to...

The effect of acetonitrile (ACN) on the micellization of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), in aqueous solutions at different temperatures was studied. The critical micellar concentration (CMC) as well as the degree of counter ion dissociation (a) of CTAB in aqueous ACN mixtures (10-20 % v/v) at various temperatures (291....

The physicochemical properties of initial formulation, that is anionic/amphoteric surfactants mixture SLES/AOS/CAB (sodium lauryl ether sulfate (SLES), α-olefin sulfonates (AOS) and cocamidopropyl betaine (CAB) at ratio 80 : 15 : 5) with nonionic surfactant of amine oxide type (lauramine oxide (AO)) in various concentration (1–5%) were studied. To...

The physicochemical properties of initial formulation, that is anionic/amphoteric surfactants mixture SLES/AOS/CAB (sodium lauryl ether sulfate (SLES), α-olefin sulfonates (AOS) and cocamidopropyl betaine (CAB) at ratio 80 : 15 : 5) with nonionic surfactant of amine oxide type (lauramine oxide (AO)) in various concentration (1–5%) were studied. To...

In this paper, we intend to show the importance of the bifurcation analysis in understanding of an oscillatory process. Hence, we use the bifurcation diagram of the Bray–Liebhafsky reaction performed in continuous well-stirred tank reactor under controlled temperature variations for the determination of the activation energies as well as rate const...

An undergraduate electrical conductivity measurement experiment in a physical chemistry lab and basic fitting procedures are presented that allow a characterization of micellar system of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTAB) in binary mixture of water and acetonitrile (ACN) as a cosolvent (10%, v/v) at 30.0 °C. C...

The temporal dynamics of the Bray–Liebhafsky reaction (iodate-based catalytic decomposition of hydrogen peroxide in an acidic aqueous solution) was experimentally characterized in a continuous stirred tank reactor by independently varying the temperature and the mixed inflow hydrogen peroxide concentration. When the temperature was the bifurcation...

Performance and efficiency of anionic [sodium lauryl ether sulfate (SLES) and sodium α-olefin sulfonate (AOS)] and amphoteric [cocamidopropyl betaine (CAB)] as well as nonionic [cocodiethanol amide (DEA), various ethoxylated alcohols (C12–C15–7EO, C10–7EO and C9–C11–7EO) and lauramine oxide (AO)] surfactants in various dishwashing liquid mixed mice...

In stoichiometric network analysis (SNA) the instability condition is calculated by the current rates. Recently, we have shown that in the final result the current rates can be substituted by reaction rates, which is a more appropriate value for the examination of instability from experimental point of view. Here, we elaborate the problem of whethe...

Conductivity of two micellar systems was measured in order to determine critical micelle concentration (CMC) of cetyltrimethylammonium bromide (CTAB). Those systems were: CTAB in water and CTAB in binary mixture acetonitrile (ACN)water. Conductivity (κ)-concentration (c) data were treated by four different methods: conventional method, differentia...

Perturbation of the BrayLiebhafsky non-oscillating subsystem (mixture of KIO3 and H2SO4), i.e., Dushman reaction (DR), by piroxicam (PX), was observed in an open reactor, i.e., in the continuously fed well-stirred tank reactor (CSTR). Monitoring the response of DR to perturbations by different concentrations of PX allows developing a simple procedu...

Micellization of hexadecyltrimethylammonium bromide (syn. cetyltrimethylammonium bromide, CTAB) in propylene glycol-water (30% v/v) binary mixture, as well as the thermodynamic properties of the resulting micelles, were investigated by electrical conductivity measurements. The conductivity data were used to determine both the critical micellar conc...

Export Date: 18 October 2014

In this study, in order to evaluate the quality and safety of selected commercial spices brands, contents of moisture and minerals, as well as the concentration of certain heavy metals (As, Hg and Pb) were determined in oregano, sweet basil, parsley and celery. The spice samples were subjected to microwave digestion, and were analyzed by atomic abs...

Simple and reliable novel methods for the determination of uric acid (UA) are proposed and validated. For quantitative determination of UA, two matrices were used: the Bray-Liebhafsky (BL) oscillatory reaction in a stable non-equilibrium stationary state close to the bifurcation point (method A) as well as, the BL non-oscillating subsystem (mixture...

Simple and reliable novel methods for the determination of uric acid (UA) are proposed and validated. For quantitative determination of UA, two matrices were used: the Bray-Liebhafsky (BL) oscillatory reaction in a stable non-equilibrium stationary state close to the bifurcation point (method A) as well as, the BL non-oscillating subsystem (mixture...

A simple, rapid and reliable direct spectrophotometric method for the determination of hesperidin is proposed and validated. The influence of wavelength, solvent, the ionic strength, pH and temperature on hesperidin determination were investigated. Under the optimum conditions, λ = 283 nm, 60% methanol as the solvent, ionic strength, I = 2.5 × 10-5...

Novel analytical methods for quantitive determination of analytes based on perturbations of oscillatory chemical reactions realized under open reactor conditions (continuosly fed well stirred tank reactor, CSTR), have been developed in the past twenty years. The proposed kinetic methods are generally based on the ability of the analyzed substances...

A simple and reliable novel kinetic method for the determination of piroxicam (PX) was proposed and validated. For quantitative determination of PX, the Bray-Liebhafsky (BL) oscillatory reaction was used in a stable non-equilibrium stationary state close to the bifurcation point. Under the optimized reaction conditions (T = 55.0°C, [H2SO4]0 = 7.60×...

The effect of cosolvent (propylen glycol, PG) on micellization of an cationic surfactant, hexadecyltrimethylammonium bromide (hereinafter cetylecyltrimethylammonium bromide, CTAB) in aqueous solution was studied. The thermodynamic of micellization and the aggregation behaviour of CTAB in PG-water mixture at different temperatures (from 298.2 K to 3...

The non-periodic, periodic and chaotic regimes in the Bray–Liebhafsky (BL) oscillatory reaction observed in a continuously fed well stirred tank reactor (CSTR) under isothermal conditions at various inflow concentrations of the sulfuric acid were experimentally studied. In each series (at any fixed temperature), termination of oscillatory behavior...

The Bray-Liebhafsky (BL) oscillatory reaction generated in the batch reactor at 62-68 o C was perturbed by cobalt(II)-nitrate, supported on the macroreticular copolymer of poly-4-vinylpyridine with divinylbenzene (Co-PVPDVB). The kinetic data was analyzed of the complex pathways of the hydrogen peroxide decomposition in the examined BL reaction. Th...

A novel procedure for kinetic determination of some water-soluble vitamins of the B-group (thiamine (B-1), riboflavin (B-2), niacin (B-3) and pyridoxine (B-6)) by the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory chemical system involving the catalytic decomposition of hydrogen peroxide in the presence of both hydrogen and iod...

This paper gives some recently published data of our research group related to application of the Bay-Liebhafsky (BL) oscillatory reaction (the reaction of catalitic decomposition of hydrogen peroxide in presence of both H(+) i IO(3)(-)) in analytical purposes. Regarding the extreme sensitivity of nonlinear chemical systems on small changes of exte...

The kinetic investigations of the malonic acid decomposition (8.00 × 10−3 mol dm−3 ≤ [CH2(COOH)2]0 ≤ 4.30 × 10−2 mol dm−3) in the Belousov-Zhabotinsky (BZ) system in the presence of bromate, bromide, sulfuric acid and cerium sulfate, were performed in the isothermal closed well stirred reactor at different temperatures (25.0°C ≤ T ≤ 45.0°C). The fo...

Dynamic behavior of hydrogen peroxide decomposition catalyzed by iodate and hydrogen ions (the Bray-Liebhafsky reaction), in a continuous stirred tank reactor is investigated. The experimental results are obtained at one operational point in concentration phase space by varying mixed inflow concentrations of the sulfuric acid. The experimental evid...

The infuence of poly-4-vinylpyridine-co-divinylbenzene-Co2+ catalyst on the Bray-Liebhafsky (BL) oscillator used as the matrix for establishing catalyst’s activity was analyzed. The addition of the catalyst do not change the dynamics of the reaction in the BL matrix, but the periods of the oscillatory evolution as well as the preoscillatory period...

The influence of the initial malonic acid concentration [MA]0 (8.00 x 10(-3) < or = [MA]0 < or = 4.30 x 10(-2) mol dm(-3)) in the presence of bromate (6.20 x 10(-2) mol dm(-3)), bromide (1.50 x 10(-5) mol dm(-3)), sulfuric acid (1.00 mol dm(-3)) and cerium sulfate (2.50 x 10(-3) mol dm(-3)) on the dynamics and the kinetics of the Belousov-Zhabotins...

A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state close to the bifurcation point. The response of the Bray-Liebhafsky (BL) oscillatory reaction as...

A pulse perturbation technique was applied to the Bray–Liebhafsky (BL) oscillatory reaction system in a stable nonequilibrium stationary state close to the bifurcation point, to determine micro-quantitatively 6-O-acetylmorphine (6-O-AM). The proposed method, in optimized reaction conditions ([KIO3]0 = 5.9×10−2 M, [H2SO4]0 = 5.5×10−2 M, and [H2O2]0...

A novel kinetic method for micro-quantitative determinations of morphine (MH) is proposed and validated. The method is based on the potentiometric monitoring of the concentration perturbations of the oscillatory reaction system being in a stable non-equilibrium stationary state close to the bifurcation point between stable and oscillatory state. Th...

A rapid and sensitive assay for quantitative determination of rutin in oral dosage forms based on isocratic reversed phase high performance liquid chromatography (RP-HPLC) was developed and validated. Using a C(18) reverse-phase analytical column, the following conditions were chosen as optimal: mobile phase methanol-water 1:1 (v/v), pH 2.8 (adjust...

Cited By (since 1996):25, Export Date: 18 October 2014

Some new experimental evidence of complex irregular oscillations in the Belousov–Zhabotinsky reaction realized in a batch reactor is presented. The results were obtained under relatively low cerium and malonic acid concentrations. One-dimensionalmaps were used for general discussion, and, particularly, for the influence of noise on the evolution of...

A new procedure for kinetic determination of paracetamol in pharmaceuticals is proposed. The method is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system being in a stable non-equilibrium stationary state close to the bifurcation point. In the case considered as the matrix system, the Bray-Liebhafsky...

Macroporous cross-linked copolymer of 4-vinylpyridine and 25% (4:1) divinylbenzene is analyzed under open conditions, that is in a continuous well-stirred tank reactor (CSTR). With this aim the appropriate bifurcation diagram is found and the behavior of the system with and without polymer in the vicinity of the bifurcation point is used for the po...

Asimple, rapid and accurate procedure for the quantitative determination of quercetin in its pure form and in formulations has been developed. The method is based on the spectrophotometric determination of a complex formed between quercetin and potassium titanyloxalate in 50 % ethanolic solutions. To characterize the quercetin titanyloxalato comple...

A simple and reliable kinetic method for the determination of hesperidin (Hesp) is developed. It is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system which is in a stable non-equilibrium stationary state close to the bifurcation point. The Bray-Liebhafsky oscillatory reaction is used as the matrix s...

A simple, rapid and accurate procedure for the quantitative determination of quercetin in its pure form and in formulations has been developed. The method is based on the spectrophotometric determination of a complex formed between quercetin and potassium titanyloxalate in 50 % ethanolic solutions. To characterize the quercetin titanyloxalato compl...

Dynamics of the Bray-Liebhafsky (BL) oscillatory reaction is analyzed in a Continuously-fed well-Stirred Thank Reactor (CSTR). Deterministic chaos is found under different conditions, when temperature and acidity are chosen as control parameters. Dynamic patterns observed in real experiments are also numerically simulated.

The current research provides a simplified sample preparation procedure for the accurate estimation of quercetin in pure and in the pharmaceutical dosage form. Direct spectrophotometric method for the determination of quercetin in the presence of ascorbic acid was established. The influences of medium, wavelength, pH, temperature and the ionic stre...

A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open re...

The kinetics of the Belousov-Zhabotinsky (BZ) oscillatory reaction was analyzed. With this aim, the time evolution of a reaction mixture composed of malonic acid, bromate, sulfuric acid and cerium(III) was studied at 298 K. Pseudo-first order kinetics with respect to malonic acid as the species undergoing decomposition with a corresponding rate con...

A new method applying a non-linear chemical system under conditions far from thermodynamic equilibrium in microvolume/microconcentration quantitative analysis is described. The chemical system used as a matrix is the Bray–Liebhafsky reaction in a non-equilibrium stationary state close to a bifurcation point. The method is based on monitoring the re...