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The protonation constants of ten Schiff's bases synthesized by the condensation of 2-hydroxy-1-naphthaldehyde with aniline and o-, m-, and p-substituted methylanilines, ethylanilines and methoxyanilines in various dioxan-water mixtures have been determined potentiometrically using an electrode system calibrated in concentration units of the hydrogen ion. The influence of substituents in the molecular...
The potentiometric determination of the protonation constant of 2-chlorophenol in NaCl media at different ionic strengths and its distribution coefficient between these media and two organic solvents at 25 o C are presented. An automated potentiometric system was used, and the determination of the constants was carried out using both graphical and numerical methods. A thermodynamic model...
The complex formation between pyrophosphate (P 2 O 4-7 ) and protonated methylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine, has been studied potentiometrically, in aqueous solution, at 25°C. It was found that the species ALH q (A = amine, L = P 2 O 4-7 ) are formed withq...
Acid-base equilibria in aqueous solutions of cis-bis(trimethylphosphine)platinum(II) dinitrate at 25°C, 0.2 M ionic strength (KNO 3 ), have been investigated by potentiometry with a glass electrode. The procedure consisted of multiple addition of the investigated analyte to a supporting electrolyte solution ( multiple sample addition ) and subsequent titration with strong base. For the...
A new suite of 10 programs concerned with equilibrium constants and solution equilibria is described. The suite includes data preparation programs, pretreatment programs, equilibrium constant refinement and post-run analysis. Data preparation is facilitated by a customized data editor. The pretreatment programs include manual trial and error data fitting, speciation diagrams, end-point determination,...
The Briggs-Rauscher reaction is known as a nonlinear and non-equilibrium chemical oscillation reaction. The reaction solution is composed of malonic acid as organic substrate, hydrogen peroxide and iodate in sulphuric acid as oxidizing agent, and manganese (II) as metal catalyst. The calorimetric behaviour, in terms of the total heat Q and the heat evolving rate q for each chemical oscillation, was...
Autoprotolysis constants of acetonitrile, propionitrile, nitromethane, ethylene carbonate and dimethyl sulphoxide were determined using a coulometric-potentiometric method with a hydrogen/palladium electrode as generator. The method is based on the titration of a strong base, tetrabutylammonium hydroxide, with H + ions generated by anodic oxidation of hydrogen dissolved in palladium. The...
The application of SQUAD to the refinement of formal potentials from potentiometric or coulometric steady-state and spectrophotometric measurements was tested. The formal potential thus obtained for the Fe(CN) 3-6 /Fe(CN) 4-6 couple in 0.5 M H 2 SO 4 agreed with published data. This method was found to be satisfactory for the determination of typical...
The reaction between tetrabutylammonium periodate and phenothiazine in the presence of the strong acids in chloroform was studied by potentiometry and the reaction pathways were determined. The oxidimetric titration conditions of phenothiazine derivatives using a standardized chloroform solution of tetrabutylammonium periodate were optimized and a potentiometric detection of end points was utilized...
The protonation constants of five Schiff base and two benzothiazoline type ligands and stability constants of their complexes with six lanthanide ions were determined by potentiometrically in ethanol-water solution (1:1, v/v) at 25 ± 0.1°C. The Schiff base-type ligands were salicylidene 2-iminopyridine (SAPy), salicylidene-5-methyl-2-iminopyridine (SAPyMe), salicylidene-5-chloro-2-iminopyridine (SAPyCl),...
A coated graphite-epoxy ion-selective electrode for bismuth(III), based on the ion-pair between the [Bi(EDTA)] - anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated onto a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) or ortho-nitrophenyloctylether (o-NPOE) in PVC was deposited directly onto a Perspex tube...
A new method for the determination of ion exchange equilibrium constants is developed. A technique based in the application of potentiometric titrations is used in the study of non selective strong acidic resins. Potentiometric titrations are carried out without constant ionic strength, so a mathematical treatment is developed in order to take into account the estimation of the activity coefficients...
Potentiometric pH sensors based on polymer film were prepared by electropolymerization of the monomer nickel(II)-4,4 ,4 ,4 -tetraaminophthalocyanine (NiTAPc) or copper(II)-4,4 ,4 ,4 -tetraaminophthalocyanine (CuTAPc) on glassy carbon (GC) electrodes. The polymer of metal tetraaminophthalocyanine (p-MTAPc) film coated electrodes show a slope of 55 ± 1 mV/pH (at 20°C) and nearly Nernstain...
The protolytic behavior of d-gluconic-δ-lactone acid has been studied by means of automated potentiometric titrations at different ionic strengths in the range 0.1≤I≤3.0 mol dm -3 in NaClO 4 at 25°C. This study reveals a protolytic equilibrium of gluconic acid as well as a distribution equilibrium between gluconic acid (HG) and its lactone form (L). The values of the stoichiometric...
The copper (II) or nickel (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5 10 5 and 3 10 6 ) was investigated in aqueous dilute solution (NaNO 3 0.1 mol l -1 ; 25°C). Potentiometric titrations were carried out, first to precise the acid-base properties of the two polymers, and secondly to determine the stability constants of...
A novel iodide ion-selective electrode has been produced based on a molecular deposition technique in which water-soluble porphyrin was alternatively deposited with water-soluble polypyrrole on a 2-aminoethanethiol modified silver electrode. The potentiometric response is independent of pH of the solution between pH 1 and 7, while it is dependent on the nature of the medium. The electrode has a linear...
Cesium ion-selective PVC membrane electrodes based on anilino-(1,3-dioxo-2-indanylidene) acetonitrile derivatives as a novel class of neutral ionophores were examined. The ionophores were p-methoxyanilino-(1,3-dioxo-2-indanylidene) acetonitrile, p-methylanilino-(1,3-dioxo-2-indanylidene) acetonitrile and p-N,N-dimethylanilino-(1,3-dioxo-2-indanylidene) acetonitrile. The anilino-(1,3-dioxo-2-indanylidene)...
A PVC membrane electrode for lead ions based on 5,5′-dithiobis-(2-nitrobenzoic acid) as membrane carrier was prepared. The electrode exhibits a Nernstian response for Pb2+ over a wide concentration range (1.0×10−2–4.0×10−6 M). It has a relatively fast response time and can be used for at least 3 months without any divergence in potentials. The proposed electrode revealed good selectivities for Pb2+...
We examined the variation with ionic strength (I, adjusted with KCl, KNO3, KBr, NaCl or NaClO4) of the formal potential (Econst) for glass electrodes exhibiting a Nernstian response (i.e. Ecell=Econst−slog[H+]). For this purpose, we investigated the different factors included in the formal potential, so we obtained reported values for the liquid junction potential as a function of ionic strength and...
A flow injection potentiometric method for the rapid determination of paraquat in herbicide formulations and biological samples is described. It is based on the utilization of a flow-through potentiometric detector containing polyvinyl chloride-immobilised octamethylcyclotetrasiloxane, a lipophilic plasticizer (tetra-n-undecyl 3,3′,4,4′-benzophenone tetracarboxylate) and membrane additive potassium...
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