Potentiometric pKa determination of standard substances in binary solvent systems

Wrobel, Roman; Chmurzyński, Lech

doi:10.1016/s0003-2670(99)00737-0

Cited by 48 publications

(28 citation statements)

References 16 publications

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“…Dissociation constants of many other acids and bases in organic solvents have been determined by potentiometric titration using a glass electrode calibrated with buffers prepared from picric acid or 2,6-dinitrophenol (see, e.g. [21,22,31,32,[34][35][36][37][38][39][40][41][42][43][44] and references cited therein). Typically, a one-point calibration has been applied and correction for the effect of the ionic strength has been done with the aid of the Debye-Hückel theory.…”

Section: Ph In Non-aqueous Mediamentioning

confidence: 99%

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Porras

Kenndler

2004

Journal of Chromatography A

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Section: Ph In Non-aqueous Mediamentioning

confidence: 99%

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Porras

Kenndler

2004

Journal of Chromatography A

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“…Moreover, UV-Vis absorption spectrometry has still been used widely for the determination of dissociation constants, because of their accuracy and reproducibility. 5 Moreover, the use of computer programs for the refinement of dissociation constants allows the different pK a values of polyprotic substances to be determined, even when they are very close. [6][7][8][9] In the last decade, some alternative techniques have been developed, based on separation methods such as liquid chromatography (LC) and capillary zone electrophoresis (CZE).…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Determination of pKa values of some auxins in methanol-water mixtures by reversed phase liquid chromatography and potentiometric methods

Kelen¹,

Şanlı²

2009

J. Braz. Chem. Soc.

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Os hormônios das plantas são de vital importância para o seu funcionamento normal. As auxinas são uma classe de fito-hormônios envolvidas em muitos aspectos do crescimento. Os ácidos indol-3-acético (IAA), indol-3-pirúvico (IPA) e indol-3-lático (ILA) são auxinas com funções biológicas estimulantes do processo de crescimento, tais como elongação e divisão. Neste estudo, os valores pK a de IAA, IPA e ILA em misturas de metanol-água a 30%, 40% e 50% (v/v) foram determinados usando potenciometria, cromatografia líquida (LC) e metodologia LC-DAD. Valores de pK a em água, preditos pelo método SPARC também foram investigados.Plant hormones are of vital importance for the normal functioning of plants. Auxins are a class of phytohormones involved in many aspects of plant growth. Indole-3-acetic acid, (IAA), indole-3-pyruvic acid (IPA) and indole-3-lactic acid (ILA) are auxins with biological functions stimulating growth processes such as cell elongation and division. In this study, the pK a values of IAA, IPA and ILA in 30%, 40% and 50% (v/v) methanol-water mixtures were determined using potentiometry, liquid chromatography (LC) and LC-DAD methodology. Also, the pK a values in water predicted by the SPARC on-line calculator have been investigated. Keywords: dissociation constants, LC, LC-DAD, methanol-water mixtures, plant hormones, potentiometry IntroductionDissociation constants are important physicochemical parameters of a substance, and the knowledge of these parameters is of fundamental importance in a wide range of applications and research areas. The chromatographic retention and electrophoretic behaviour of ionizable compounds strongly depend on the pK a of the compound and the mobile phase pH. Therefore, a satisfactory knowledge of the acid-base behaviour of substances in a hydro-organic media such as methanol (MeOH)/water is essential to predict the influence of pH on selectivity and retention in liquid chromatography (LC), and also to optimize analytical procedures for the separation of ionizable compounds by various techniques. [1][2][3] Methanol is one of the most utilized solvents due to its good solvating properties of organic compounds. In addition, due to its relatively high dielectric constant (ε = 32.63) dissolves ionic solutes and prevents ion-pair formation at very high solute concentrations. Among the organic solvents, methanol is the closest one to water in terms of its structure and properties and, therefore, acidic dissociation in methanol occurs in an analogous way to that in aqueous solution. However, methanol can solve a wide majority of organic acids more effectively than water and in many cases it is a more suitable solvent for the determination of the dissociation constants. 4 There are a large spectrum of pK a determination techniques including potentiometry, conductivity, calorimetry, UV-Vis and NMR spectrometry, mass spectrometry, liquid chromatography, capillary zone electrophoresis, and software computational predictions. Among these techniques, the potentiometric titration is most ec...

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“…For this system, over the concentration range studied, there was a linear relationship among the potential difference, E, and the logarithm of the acid/base ratio, {E = f (lg c HA c A − )}; and the slope of the glass electrode response, s, matched that of the theoretical Nernst slope being in the range of 57-62 mV. As the pK a value for the reference compound, 2,6-dinitrophenol, in the mixed solvent system was unknown, it was determined by a previously reported procedure [15].…”

Section: Resultsmentioning

confidence: 99%

“…The results obtained so far for this type of systems are also divergent, some of them demonstrating a linear dependence between pK a and mole fraction, while other are showing non-linear relationships [13,14]. Similar to acidity constants, some authors describe a non-linear nature of variations of the anionic homoconjugation constants as a function of composition of the binary solvent system [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Molecular Heteroconjugation Equilibria in (n-Butylamine + Acetic Acid) Systems in Binary (Dimethyl Sulfoxide + 1,4-Dioxane) Solvent Mixtures

et al. 2007

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The acidity constants of molecular acid, K a (HA), cationic acid, K a (BH + ), as well as the equilibrium constants of anionic homoconjugation, K AHA − , cationic homoconjugation, K BHB + , and molecular heteroconjugation, K AHB , have been determined in (n-butylamine + acetic acid) systems without proton transfer in binary [dimethyl sulfoxide (DMSO) + 1,4-dioxane (D)] solvent mixtures. The constants were determined by using the potentiometric titration method at a fixed ionic strength. It is concluded that the molecular heteroconjugation constants in the mixed solvent systems studied are linearly related to the 1,4-dioxane content. Furthermore, in the (acid + base) systems without proton transfer, the direction of titration (direct B + HA or reverse HA + B) has been found to affect the precision of determination of reliable values of molecular heteroconjugation constants. Moreover, it has been found that the relative dielectric constants of the solvent mixtures studied change linearly as a function of solvent composition, as well as solvent components do not show interactions of solvent-solvent type.

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Potentiometric pKa determination of standard substances in binary solvent systems

Cited by 48 publications

References 16 publications

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Determination of pKa values of some auxins in methanol-water mixtures by reversed phase liquid chromatography and potentiometric methods

Molecular Heteroconjugation Equilibria in (n-Butylamine + Acetic Acid) Systems in Binary (Dimethyl Sulfoxide + 1,4-Dioxane) Solvent Mixtures

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