Reference value standards and primary standards for pH measurements in organic solvents and water + organic solvent mixtures of moderate to high permittivities

Rondinini, Sandra; Mussini, Patrizia R.; Mussini, T.

doi:10.1351/pac198759111549

Cited by 171 publications

(62 citation statements)

References 2 publications

(3 reference statements)

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“…Measurements are performed in a similar way to those performed in water following IUPAC standardization guidelines. 23,24 Potassium hydrogen phthalate solution (0.05 mol kg -1 ) dissolved in the appropriate MeOH/water medium was used as a reference value standard (RVS) for calibration of pH/ion analyzer. 25,26 pH measurements of the mobile phases were performed in triplicate to ensure stability and reproducibility of the potentiometric system.…”

Section: Chromatographic Methodsmentioning

confidence: 99%

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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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Section: Chromatographic Methodsmentioning

confidence: 99%

“…23,24 Carbon dioxide dissolved in titrating solution was purged out with nitrogen gas. The auxin solution was completely mixed with a magnetic stirrer.…”

Section: Procedures Potentiometric Proceduresmentioning

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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“…Whilst this "best" value is an acceptable approach to the "true" E" value, in terms of statistical treatment of errors, it may not exactly coincide with the required E" value consistent with the E p~ measurements leading to pH through eq. When analysing the e m f of cell (6) in terms of the Nernst equation, E" value is ahgain needed. However, this indirect influence is of minor importance.…”

Section: Aggregation and Re-assessment Of Ph Standardsmentioning

confidence: 99%

Reference value standards and primary standards for pH measurements in D2O and aqueousorganic solvent mixtures: New accessions and assessments (Technical Report)

Mussini¹,

Mussini²,

Rondinini³

1997

Pure and Applied Chemistry

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“…The use of Equation 1 requires knowledge of E 0 values, also needed for pH measurements. The relevant E 0 values covering those tetrahydrofuranwater mixtures containing up to 70 % (waw) tetrahydrofuran at 298.15 K were determined in this study, in accordance with IUPAC recommendation [2], from emf measurements of the reversible cell:…”

Section: Introductionmentioning

confidence: 90%

“…This system ensures reliable emf measurements. The functional expression that relates pH and emf, E, is [2]:…”

Section: Introductionmentioning

confidence: 99%

Autoprotolysis Constants and Standardization of pH Measurements in Tetrahydrofuran-Water Mixtures

Barbosa¹,

Barrón

Butí

1999

Electroanalysis

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Standard emf for the cell PtaAgaAgClaHCl in THF-wateraGE (glass electrode) in tetrahydrofuran-water mixtures containing 0±70 % (waw) of tetrahydrofuran and values of the autoprotolysis constants, K ap , of these media were obtained. The in¯uence of variations in the solvent composition on pK ap values was evaluated. The resulting equations enables us to determine pK ap values in any tetrahydrofuran-water mixture, and thus permit one to establish the pH scale in these mixtures. The quasilattice quasichemical (QLQC) theory of preferential solvation was applied to obtain the degree of preferential solvation of hydrogen ions in these media, in order to explain the variation of the pK ap values obtained in the tetrahydrofuran-water mixtures studied.

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Reference value standards and primary standards for pH measurements in organic solvents and water + organic solvent mixtures of moderate to high permittivities

Cited by 171 publications

References 2 publications

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

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

Reference value standards and primary standards for pH measurements in D2O and aqueousorganic solvent mixtures: New accessions and assessments (Technical Report)

Autoprotolysis Constants and Standardization of pH Measurements in Tetrahydrofuran-Water Mixtures

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