Spectrophotometry determination of metronidazole and tinidazole by their complexation with copper(II)

It is shown that the treatment of chloroform solutions of drugs of the nitroimidazole series (NIm) with crystalline copper(II) acetate gives colored chloroform-soluble adducts of the general formula [Cu(CH₃COO)₂NIm]₂, which can be used as analytical forms in the spectrophotometry determination of metronidazole and tinidazole. The respective analytical methods are developed and certified.     

Kinetic study of nickel(II) complexation by pteroylglutamic acid

The kinetics of the complexation of NiII by pteroylglutamic acid have been studied in the 545 ∘C range, the ionic strength (0.6 M) being regulated with KNO3, in the 5.5–7.0pH range, using the stopped-flow method. Under the experimental conditions two processes were observed. The faster process was detected in the millisecond range and is associated with the reaction between NiII and the ligand. The slower is observed within a few seconds. Complementary equilibrium studies were made at 25 ∘C. The results are consistent with the formation of a 1:1 complex between the reactants, and a mechanism is proposed to account for the observed behaviour. Equilibrium constants for the NiII plus pteroylglutamic acid system, as well as activation parameters, are reported. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spectrophotometric determination of microamounts of quercetin based on its complexation with copper(II)

The complexation process of the transition metal Cu(II) with quercetin was studied. The investigation was conducted spectrophotometrically in ethanol at the maximum absorption wavelength of 458.5 nm. Cu(II)—quercetin complex composition (1: 1) was determined using the Job, Harvey—Manning, and mole ratio methods. Complex stability constant was calculated by the Job and mole ratio methods and the respective logarithm values were 7.53 ± 0.25 and 7.44 ± 0.03. A new method for quantitative determination of the quercetin content in solution was developed in this work. At the optimal conditions quercetin was determined in concentrations ranging from 0.202 to 1.006 μg cm⁻³ with relative standard error of 2.5 % to 5.5 %. The lower detection limit was 0.067 μg cm⁻³. The method was found very accurate, reproducible, and sensitive, capable to determine microamounts of quercetin in pharmaceutical preparations.     

Spectrophotometric determination of copper(II) with 3-thianaphthenoyltrifluoroacetone

Summary Two visible spectrophotometric methods are described for the determination of Copper(II) with 3-thianaphthenoyltrifluoroacetone at a pH of 4.0. The effect due to pH, time, solvents, reagent concentration and diverse ions are reported. Beer's law is obeyed in both cases and the molar extinction coefficients at 410 and 430 nm are 9.3·10² and 2.9·10² respectively.

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Zusammenfassung Zwei spektrophotometrische Verfahren zur Bestimmung von Kupfer(II) mit 3-Thianaphthenoyltrifluoraceton bei pH 4,0 wurden beschrieben. Der Einfluß von pH, Zeit, Lösungsmitteln, Reagenskonzentration und von diversen Fremdionen wurde ermittelt. Das Beersche Gesetz ist in beiden Fällen erfüllt. Der molare Extinktionskoeffizient beträgt bei 410 bzw. 430 nm 9,3·10² bzw. 2,9·10².

     

Reversed phase liquid chromatographic determination of organic acids using on-line complexation with copper(II) ion

We describe a simple and sensitive liquid chromatographic method for the analysis of organic acids using on-line complexation with copper(II) ion. Organic acids complexed with copper(II) ion were separated on a reversed-phase C18 column and detected by UV absorption at 240 nm. The copper(II) ion concentration in the mobile phase had a great influence on separation and sensitivity. A mobile phase consisting of 10 mM copper(II) sulfate in 5 mM sulfuric acid (pH 2.3) was used to separate nine organic acids (tartaric, malic, malonic, lactic, acetic, citric, maleic, succinic and fumaric acids). The detection limits of the examined organic acids calculated at S/N = 3 ranged from 0.6 to 100 μM. The detector signal was linear over three orders of magnitude of organic acid concentration. The method successfully measured organic acids in juice and vinegar samples.     

Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of alpha-(2-benzimidazolyl)-alpha-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.     

On the complexation of copper (II) ion with 2-hydroxybenzamide

The complexation of the Cu2+ ion with 2-Hydroxybenzamide (salicylamide, HL) has been studied, at 25 degrees C, by potentiometric measurements with a glass electrode in NaCIO4 media for ionic strength ranging from 0.5 to 3 mol/dm3. The data are consistent with the formation of the complexes CuH(-1)(HL)+, CuH(-2)(HL)2, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL). The minor species, Cu2H(-2)(HL)2(2+) and CuH(-2)(HL), amount to at least 20% of the total copper. Elaboration of the data according to the Specific Interaction Theory yields the constants valid in the infinite dilution reference state: [formulas: see text] and the interaction coefficients (kg/mol) of complex species with medium ions: b(L-,Na+) = 0.11 +/- 0.03; b(CuH(-1)(HL)+,NaClO4) = 0.17 +/- 0.05; b(CuH(-2)(HL)2,NaClO4) = 0.11 +/- 0.05; b(Cu2H(-2)(HL)2(2+),NaClO4) = 0.2(7) +/- 0.1; b(CuH(-2)(HL),NaClO4) = -0.0(3) +/- 0.1.     

Determination of copper(I) and copper(II) ions after complexation with bicinchoninic acid by CE

A facile, sensitive, and selective method was developed for the simultaneous separation and determination of copper(I) [Cu(+)] and copper(II) [Cu(2+)] ions using CE with direct UV detection. The copper ions were complexed with a 1.5 mM bicinchoninic acid disodium salt solution at pH 8.7 prior to analysis. Acetate buffer (2 mM) was used as the CE running buffer. Parameters affecting CE separation such as sample pH, applied voltage, concentration of complexing agent, nature of the buffer solution, and interferences by other metal ions, were evaluated. The LODs for Cu(+) and Cu(2+) were 3.0 and 2.5 microg/mL (S/N = 3), respectively. The developed method allows the simultaneous determination of Cu(+) and Cu(2+) in less than 5 min with RSDs of between 5.3 and 9.5% for migration time and between 3.4 and 9.7% for peak areas, respectively. At optimum conditions, the percentage recoveries of Cu(+) and Cu(2+) were found to be 99.4 and 99.5%.     

Dissociation and complexation ofN-m-tolyl-p-methoxybenzohydroxamic acid with manganese(II), nickel(II), copper(II) and zinc(II)

Summary The thermodynamic ionisation and formation constant at different ionic strengths of some divalent metal ions ofN-m-tolyl-p-methoxybenzohydroxamic acid at 25 and 35° were determined in several dioxanwater media. The solid complexes of Cu^II, Ni^II and Mn^II withN-m-tolylbenzo-,N-m-tolyl-p-methylbenzo- andN-m-tolyl-p-methoxybenzohydroxamic acids were prepared and their magnetic susceptibilities measured at room temperature.     

Artificial neural networks study of the catalytic reduction of resazurin: stopped-flow injection kinetic-spectrophotometric determination of Cu(II) and Ni(II)

An artificial neural network (ANN) procedure was used in the development of a catalytic spectrophotometric method for the determination of Cu(II) and Ni(II) employing a stopped-flow injection system. The method is based on the catalytic action of these ions on the reduction of resazurin by sulfide. ANNs trained by back-propagation of errors allowed us to model the systems in a concentration range of 0.5-6 and 1-15 mg l⁻¹ for Cu(II) and Ni(II), respectively, with a low relative error of prediction (REP) for each cation: REP_Cu(II) = 0.85% and REP_Ni(II) = 0.79%. The standard deviations of the repeatability (s_r) and of the within-laboratory reproducibility (s_w) were measured using standard solutions of Cu(II) and Ni(II) equal to 2.75 and 3.5 mg l⁻¹, respectively: s_r[Cu(II)] = 0.039 mg l⁻¹, s_r[Ni(II)] = 0.044 mg l⁻¹, s_w[Ni(II)] = 0.045 mg l⁻¹ and s_w[Ni(II)] = 0.050 mg l⁻¹. The ANNs-kinetic method has been applied to the determination of Cu(II) and Ni(II) in electroplating solutions and provided satisfactory results as compared with flame atomic absorption spectrophotometry method. The effect of resazurin, NaOH and Na₂S concentrations and the reaction temperature on the analytical sensitivity is discussed.     

Semimicro determination of mercaptans with copper(II)

A rapid and precise titrimetric method for the determination of mercaptans on the semimicro scale is described. Samples dissolved in water, methanol. dimethylformamide or acetonitrile are treated with a measured excess of cupric sulphate. After 1 min, the excess of copper(II) is back-titrated with standard mercaptoacetic acid solution. At the end-point the violet complex first formed changes to a permanent yellow. The method is applicable to a variety of mercaptans and accurate to 0.2%. It is relatively free from interferences.     

Study of kinetics of complexation reaction of Co with 2-benzoylpyridine-4-phenyl-3-thiosemicarbazone and kinetic-spectrophotometric determination of cobalt

Kinetics of the complexation reaction of Co²⁺ with 2-benzoylpyridine-4-phenyl-3-thiosemicarbazone (BPPT) was spectrophotometrically examined at 421 nm. The ligand that was developed for a simple kinetic-spectrophotometric determination of Co²⁺ was based on 1:2 complex formation between Co²⁺ and BPPT. The complexation reaction was carried out in ethanol-water medium at 25 °C. Kinetic and activation parameters of the complexation reaction were calculated, and the rate equation and the reaction mechanism were proposed. The calibration graph is linear in the concentration range of 0.10−2.91 mg·L⁻¹ for the tangent method. The species that caused interference were investigated.     

Spectrophotometric determination of trace amount of copper(II) ion based on complexation with an anthraquinone derivative.

The spectrophotometric determination of Cu(II) with an anthraquinone derivative (Alizarin Red S) has been investigated. The experimental conditions, such as the pH of the sample and concentration of ligand, were optimized. This method is simple and sensitive for determination of Cu(II) ion. The interfering effects of diverse ions were investigated. Copper ion was determined by measuring the absorbance of the Cu(II)-ARS complex at 510 nm. Beer's law was obeyed over the concentration range of 0.011 - 0.320 mmol dm(-3) and the detection limit (S/N = 3) was 0.038 microg cm(-3). The relative standard deviation at 20 microg cm(-3) was 1.02% (n = 5). The method was applied for real samples.     

Kinetic study of the oxidation of catechol by aqueous copper(II)

The kinetics of the oxidation of catechol by aqueous copper(II) have been studied as a function of reactant concentrations at pH 6.4-7.2. To follow the reaction, a spectrophotometric method has been developed that circumvents the problem of precipitation of decomposition products of the initial o-quinone oxidation product. The rate law shows that the reactive species is the monocatecholate complex of Cu(II), and that this species undergoes rate-limiting intramolecular electron transfer with k = 1.9 x 10(-5) s(-1) (22 +/- 1 degrees C, mu = 0.125 M NaClO(4)). The results have allowed a reanalysis of previous work on the autoxidation in the aqueous Cu(II)-catechol-dioxygen system, and comparisons to mechanisms of copper(II) oxidases.     

Adsorption of lead(II) and copper(II) on activated carbon by complexation with surface functional groups

The adsorption of lead(II) and copper(II) on an activated carbon (Filtrasorb 300, Chemviron) was characterized assuming that it takes place by formation of complexes with functional groups, present in the activated carbon. Their concentration and conditional adsorption coefficients were determined for each metal by titration of the carbon in suspension in aqueous phase, at constant acidity, with the metal itself. For each titration point, the concentration of the metal in the solution phase after equilibration was determined, and the data were processed by the Ruzic linearization method, to obtain the concentration of the active sites involved in the sorption, and the conditional constant. The effect of the pH was also examined, in the range 4-6, obtaining that the adsorption increases at increasing pH. The protonation and adsorption constants were determined from the conditional adsorption coefficients obtained at the different acidities. The concentration of the active sites is 0.023 and 0.042 mmol g⁻¹, and the protonation constants are 1.0×10⁶ and 4.6×10⁴ M⁻¹ for Pb(II) and Cu(II). The corresponding adsorption constants are respectively 1.4×10⁵ and 6.3×10³ M⁻¹. All the parameters are affected by a large uncertainty, probably due to the heterogeneity of the active groups in the activated carbon. Even if so, these parameters make it possible a good prediction of the adsorption in a wide range of conditions. Other sorption mechanism can be set up at different conditions, in particular at different pH, as it has been demonstrated in the case of copper(II).     

1,6-Bis(hydrazidomethylsulfinyl)hexane: the solution state and complexation with copper(II)

Russian Chemical Bulletin - The solution state of a new antituberculosis drug 1,6-bis(hydrazidomethylsulflnyl)hexane (L) and its complexation with copper(II) were investigated by spectrophotometry,...     

Gravimetric determination of copper(II) with p-aminobenzoic acid

A method has been developed for the gravimetric determination of 20-100 mg of copper(II) with p-aminobenzoic acid. Ag, Hg(II), Pb, Al, Fe(II), Bi, Sb(III) and Sn(II) interfere, but Zn, Co(II), Ni and Cd do not. The precipitate can be weighed after drying at 80-100 degrees , or can be ignited to copper(II) oxide at temperatures above 400 degrees , and weighed in this form.