Chemistry Journal of Moldova

Analytical chemistry

DETERMINATION OF COPPER AND ZINC IN MINERAL WATERS BY ATOMIC ABSORPTION SPECTROPHOTOMETRY

Author(s):

Tatiana Mitina, Nadejda Bondarenko, Oxana Bunciuc


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.2
Pages: 45-47
Keywords: mineral waters, microelements, atomic absorption spectrometry.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(2).10

Graphical Abstract: 
The content of copper and zinc in mineral waters were determined by atomic spectroscopy with preliminary extraction of metals. Validation of the technique was carried out by the method of standard additions and proved the reliability of analytical data.

Downloads: 42

PHYSICOCHEMICAL PROPERTIES OF THE GASOLINE AND ALCOHOL BIOFUEL MIXTURES

Author(s):

I. Povar, V. Cerempei and B. Pintilie


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.2
Pages: 48-52
Keywords: alcohol, biofuel, distillation curves, gasoline, Reid saturated vapour pressure, specific gravity.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(2).11

Graphical Abstract:
 The influence of added alcohols, ethanol and butanol, on the main biofuel properties, such as the specific gravity, Reid saturated vapour pressure and distillation curves have been investigated. These properties are intimately related to the fuel composition and their prediction relies on the knowledge of its components characteristics. This research proves the possibility of obtaining fuels with different levels of resistance to detonation, using gasoline with different chemical components and various fractions of alcohols.

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PHASE STABILITY OF MONOATOMIC ALCOHOL-GASOLINE MIXTURES FOR DIFFERENT COMPOSITIONS AND HYDRODYNAMIC CONDITIONS

Author(s):

Valerian Cerempei


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 73-76
Keywords: butanol, ethanol, gasoline, mixtures, phase stability.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(1).08

Graphical Abstract:
 The article investigates phase stability for the mixtures of monoatomic alcohols (ethanol, butanol) with gasoline in the presence of water. There have been determined the optimal storage conditions of mixtures depending on their composition and mixing conditions. The positive influence of butanol on the phase stability of ethanol-gasoline mixtures was detected.

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VOLTAMMETRIC CHARACTERIZATION OF THE BEHAVIOR OF BIOLOGICALLY ACTIVE COMPOUND ENOXIL IN VARIOUS MEDIA

Author(s):

Gheorghe Nemţoi, Tudor Lupaşcu, Alexandra Ciomaga, Alexandru Cecal


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 62-68
Keywords: complex biologically active compound Enoxil, cyclic voltammetry, standard redox potential, dosage of pharmaceuticals.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(1).09

Graphical Abstract:
 This paper presents the results of scientific research related to the electrochemical behavior of the complex preparation Enoxil. It was established that the oxidation-reduction process of Enoxil is quasireversible. The reactivity of Enoxil obtained from alcohol soluble enotannins is more pronounced, compared to that obtained from standard enotannins. The dependence of cathodic current intensity on Enoxil concentration is linear. This can be used to establish Enoxil concentration in solution. Cyclic voltamograms were used to establish reduction and oxidation potential and the formal redox potential on platinum electrode in sodium perchlorate aqueous environment. These features can be used for identification and determination of Enoxil in pharmaceuticals.

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TEMPERATURE INFLUENCE ON PHASE STABILITY OF ETHANOL-GASOLINE MIXTURES

Author(s):

Valerian Cerempei


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 69-72
Keywords: composition, ethanol, gasoline, mixtures, phase stability, temperature.
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Abstract (JPEG)

DOI:
dx.doi.org/10.19261/cjm.2011.06(1).10

Graphical Abstract:
 The article investigates phase stability of ethanol-gasoline mixtures depending on their composition, water concentration in ethanol and ethanol-gasoline mixture and temperature. There have been determined the perfect functioning conditions of spark ignition engines fueled with ethanol-gasoline mixtures.

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TO THE EQUILIBRIUM MODEL CHOICE IN HETEROGENEOUS AQUEOUS SYSTEMS. 1. THEORETICAL BASIS IN THE CASE OF TWO COEXISTING SOLID PHASES

Author(s):

I. Povar, Nina Timbaliuc, Tatiana Cazac, Diana Shepel, Oxana Spinu and Ludmila Chiriac


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 57-61
Keywords: equilibrium model, heterogeneous system, solubility product, pH value, solid phase.
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DOI: dx.doi.org/10.19261/cjm.2011.06(1).11

Graphical Abstract:
An approach has been developed to determine the equilibrium model in heterogeneous aqueous systems containing a mixture of solid phases from the initial composition of the heterogeneous mixture and the equilibrium values of the pH. This approach allows to significantly reduce the quantity of measured data, properly for solubility measurements. By using the new deduced equations it is possible to determine the solubility products of precipitates on the basis of the known composition of initial mixtures and pH values of saturated solutions avoiding some difficult experimental solubility measurements. The derived relations are useful for solving both direct and indirect equilibrium problems.

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THE INFLUENCE OF THIOSEMICARBAZONE 2,3-DIHYDROXYBENZALDEHYDE ON CATALYTIC CURRENTS IN THE SYSTEM MOLYBDENUM (VI) – POTASSIUM CHLORATE IN ACID SULFATE SOLUTIONS

Author(s):

Ludmila Chiriac, Tatiana Cazac, I. Povar and M. Revenco


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 52-56
Keywords: voltammetry, catalytic current, molybdenum, thiosemicarbazone 2,3-dihydroxybenzaldehyde, chlorate of potassium.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(1).12

Graphical Abstract:
The polarographic catalytic current in acid solutions of Mo(VI), thiosemicarbazone 2,3-dihydroxybenzaldehyde (TSC 2,3-DHBA) and chlorate ions has been investigated. The scheme of reactions, taking place in the solutions and on the electrode, has been proposed. The increase of the catalytic current is explained by the formation of an active intermediate complex [Mo(V)×TSC 2,3-DHBA (ClO-3)]. The rate constant of this complex formation K = 2.56 × 106 mol-1×dm3×s-1, the activation energy Ea = 15.9 kcal×mol-1 and the reaction activation entropy ∆Sa¹ = -23.5 e.u. have been calculated.

Downloads: 22

VOLTAMMETRIC BEHAVIOR OF SOME STEELS IN AQUEOUS SOLUTIONS OF HNO3

Author(s):

Gheorghe Nemtoi, Liliana Airinei, Tudor Lupascu and Alexandru Cecal


Field: Analytical chemistry
Type: Research paper
Issue: 2011 Volume 6, no.1
Pages: 45-51
Keywords: corrosion, electrochemical parameters, nitric acid, steels, voltammograms.
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DOI:
dx.doi.org/10.19261/cjm.2011.06(1).13

Graphical Abstract:
The corrosion process of some steels immersed in HNO3 solutions of different concentrations by means of voltammetric measurements was investigated. For different values of the corrosion potential, or of the contact time: solid steel-aggressive medium, several equations of the type: I = f (E) were proposed, only for linear domains of the voltammograms.

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ADSORPTION WAVE OF VANADIUM COMPLEX WITH 2,3–DIHYDROXYBENZALDEHYDE

Author(s):

Ludmila Kiriyak, Natalia Cecoi, Tatiana Cazac, Mihail Revenco


Field: Analytical chemistry
Type: Research paper
Issue: 2009 Volume 4, no.2
Pages: 24-27
Keywords: Voltammetry, 2,3–dihydroxybenzaldehyde, vanadium.
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DOI:
dx.doi.org/10.19261/cjm.2009.04(2).16

Graphical Abstract:
 The polarographic behavior of the complex formed by V(V) and 2,3–dihydroxybenzaldehyde (2,3–DHBA) in the solution containing acetate buffer (pH 5,2) has been investigated. By means of a.c. polarography, chronovoltammetry and other techniques, it has been shown that the electrode process is complicated by the adsorption of 2,3-DHBA and its vanadium complex. The kinetic and adsorption parameters of the electrode process have been determined: adsorption equilibrium constant B= 1,32⋅105 mol-1⋅dm3, the attraction constant γ = 1,2, the maximum surface concentration Гmax = 9,10⋅10-11 mol⋅ cm-2; the share of the electrode surface occupied by one particle of the adsorbed complex S = 1,81 nm2 and the free adsorption energy ΔG = - 39,1 kJ· mol-1.

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FLOW INJECTION ANALYSIS SYSTEM COUPLED WITH ICP-EOS FOR DETERMINATION OF SOME METALLIC ELEMENTS IN DRINKING WATER

Author(s):

Cristina Dinu, Gabriela Vasile, Liliana Cruceru, Jana Petre


Field: Analytical chemistry
Type: Research paper
Issue: 2009 Volume 4, no.1
Pages: 66-71
Keywords: drinking water, As, Se, hydride analyses, ICP-EOS.
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DOI:
dx.doi.org/10.19261/cjm.2009.04(1).11

Graphical Abstract:
 The European Drinking Water Directive (98/83/EC), transposed in Romanian Legislation as Low 458/2002, amended by Low 311/2004, imposes the limit of concentration for metallic elements in water intended for human consumption. The toxic metals arsenic and selenium are among these elements and the limit value is 10 μg/L. In the paper there are presented the working conditions for determination of As and Se from drinking water using modern techniques based on the fl ow injection-hydride generation with the inductively coupled plasma atomic emission spectrometry (FIAS-ICP-EOS). The analyses were performed on Optima 5300 DV Perkin Elmer equipment with FIAS 400 Flow Injection System, Perkin Elmer type. For the hydride generation two types of solution were used: 10% (v/v) HCl as a carrier solution and 0.2 % NaBH4 in 0.05%NaOH solution as a reducing agent [1]. The treatment step of the samples and standard solutions consisted in reducing with mixed solutions of KI and ascorbic acid in acidic condition (HCl) for As and only with HCl and high temperature for Se [2,3]. The paper contains the characteristic parameters of the methods, such as: low detection limit, quantifi cation limit, repeatability, precision, recovery, which were evaluated using Certifi ed Reference Materials for each element.

Downloads: 19