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Theparambil SM, Begum G, Rose CR. pH regulating mechanisms of astrocytes: A critical component in physiology and disease of the brain. Cell Calcium 2024; 120:102882. [PMID: 38631162 DOI: 10.1016/j.ceca.2024.102882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Revised: 03/28/2024] [Accepted: 03/28/2024] [Indexed: 04/19/2024]
Abstract
Strict homeostatic control of pH in both intra- and extracellular compartments of the brain is fundamentally important, primarily due to the profound impact of free protons ([H+]) on neuronal activity and overall brain function. Astrocytes, crucial players in the homeostasis of various ions in the brain, actively regulate their intracellular [H+] (pHi) through multiple membrane transporters and carbonic anhydrases. The activation of astroglial pHi regulating mechanisms also leads to corresponding alterations in the acid-base status of the extracellular fluid. Notably, astrocyte pH regulators are modulated by various neuronal signals, suggesting their pivotal role in regulating brain acid-base balance in both health and disease. This review presents the mechanisms involved in pH regulation in astrocytes and discusses their potential impact on extracellular pH under physiological conditions and in brain disorders. Targeting astrocytic pH regulatory mechanisms represents a promising therapeutic approach for modulating brain acid-base balance in diseases, offering a potential critical contribution to neuroprotection.
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Affiliation(s)
- Shefeeq M Theparambil
- Faculty of Health and Medicine, Department of Biomedical and Life Sciences, Lancaster University, Lancaster, LA1 4YW, Lancaster, UK.
| | - Gulnaz Begum
- Department of Neurology, The Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA, USA
| | - Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
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2
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Szyszkiewicz-Warzecha K, Wilczek-Vera G, Lewenstam A, Górska A, Tarasiuk J, Filipek R. The Influence of Chemical Activity Models on the Description of Ion Transport through Micro-Structured Cementitious Materials. MATERIALS (BASEL, SWITZERLAND) 2023; 16:1116. [PMID: 36770123 PMCID: PMC9920105 DOI: 10.3390/ma16031116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 01/20/2023] [Accepted: 01/21/2023] [Indexed: 06/18/2023]
Abstract
The significance of ion activity in transport through a porous concrete material sample with steel rebar in its center and bathing solution is presented. For the first time, different conventions and models of ion activity are compared in their significance and influence on the ion fluxes. The study closes an interpretational gap between ion activity in a stand-alone (stagnant) electrolyte solution and ion transport (dynamic) through concrete pores. Ionic activity models developed in stationary systems, namely, the Debye-Hückel (DH), extended DH, Davies, Truesdell-Jones, and Pitzer models, were used for modeling the transport of ions driven through the activity gradient. The activities of ions are incorporated into a frame of the Nernst-Planck-Poisson (NPP) equations. Calculations were done with COMSOL software for a real concrete microstructure determined by X-ray computed tomography. The concentration profiles of four ions (Na+, Cl-, K+, OH-), the ionic strength, and the electric potential in mortar (with pores) and concrete samples (with aggregates and pores) are presented and compared. The Pitzer equation gave the most reliable results for all systems studied. The difference between the concentration profiles calculated with this equation and with the assumption of the ideality of the solution is negligible while the potential profiles are clearly distinguishable.
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Affiliation(s)
- Krzysztof Szyszkiewicz-Warzecha
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
| | - Grażyna Wilczek-Vera
- Department of Chemistry, McGill University, 845 Sherbrooke Street West Montreal, Montreal, QC H3A 0G4, Canada
| | - Andrzej Lewenstam
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
| | - Anna Górska
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
| | - Jacek Tarasiuk
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
| | - Robert Filipek
- Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland
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Goldberg RN, Giessmann RT, Halling PJ, Kettner C, Westerhoff HV. Recommendations for performing measurements of apparent equilibrium constants of enzyme-catalyzed reactions and for reporting the results of these measurements. Beilstein J Org Chem 2023; 19:303-316. [PMID: 36960304 PMCID: PMC10028569 DOI: 10.3762/bjoc.19.26] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 02/15/2023] [Indexed: 03/17/2023] Open
Abstract
The measurement of values of apparent equilibrium constants K' for enzyme-catalyzed reactions involve a substantial number of critical details, neglect of which could lead to systematic errors. Here, interferences, impurities in the substances used, and failure to achieve equilibrium are matters of substantial consequence. Careful reporting of results is of great importance if the results are to have archival value. Thus, attention must be paid to the identification of the substances, specification of the reaction(s), the conditions of reaction, the definition of the equilibrium constant(s) and standard states, the use of standard nomenclature, symbols, and units, and uncertainties. This document contains a general discussion of various aspects of these equilibrium measurements as well as STRENDA (Standards for Reporting Enzymology Data) recommendations regarding the measurements and the reporting of results.
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Affiliation(s)
- Robert N Goldberg
- Biosystems and Biomaterials Division, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA
| | - Robert T Giessmann
- Institute for Globally Distributed Open Research and Education (IGDORE), Berlin, Germany
| | | | - Carsten Kettner
- Beilstein-Institut, Trakehner Straße 7–9, 60487 Frankfurt am Main, Germany
| | - Hans V Westerhoff
- Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
- Molecular Cell Biology, Faculty of Science, Free University Amsterdam, The Netherlands
- School of Biological Sciences, Faculty of Biology, Medicine, and Health, University of Manchester, Manchester, UK
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Single ion activity coefficients of chloride ions in aqueous sodium chloride and magnesium chloride estimated potentiometrically based on ionic liquid salt bridge at 298 K. Electrochem commun 2021. [DOI: 10.1016/j.elecom.2021.106953] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Badocco D, Pedrini F, Pastore A, di Marco V, Marin MG, Bogialli S, Roverso M, Pastore P. Use of a simple empirical model for the accurate conversion of the seawater pH value measured with NIST calibration into seawater pH scales. Talanta 2020; 225:122051. [PMID: 33592773 DOI: 10.1016/j.talanta.2020.122051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 12/17/2020] [Accepted: 12/22/2020] [Indexed: 10/22/2022]
Abstract
The seawater pH measurement is usually quite complicated because that matrix is characterized by a high ionic strength leading to calibration errors if NIST standards are used. For this matrix, different pH scales like the "total hydrogen ion concentration scale" (TOT) and the "seawater scale" (SWS), are defined, and suitable synthetic seawater solutions must be prepared according to standard procedures to calibrate the glass electrode. This work provides a new approach to make seawater pH measurements by using the glass electrode calibrated with the NIST standards (pHNIST) converting the pHNIST into the right TOT or SWS scales by using empirical equations derived from theoretical thermodynamic data: pHTOT=pHNIST+0.10383+4.33⋅10-5TS+3.633⋅10-5T2-4.921⋅10-5S2, and pHSWS=pHNIST+0.097733+4.1059⋅10-5TS+3.5437⋅10-5T2-4.941⋅10-5S2, for the TOT and SWS scales, respectively. These equations are functions of two simple experimental parameters, namely, T = temperature (°C) and S = salinity (PSU, (g/L), Practical Salinity Units). These equations were experimentally validated and the uncertainty of pHTOT and pHSWS was demonstrated to have no statistical difference with the corresponding values obtained following the standard operative procedure (SOP) using commercially unavailable seawater-like buffers. The proposed method has therefore the same performances and it is largely preferable as it avoids long and tedious procedures of the synthetic seawater preparations.
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Affiliation(s)
- Denis Badocco
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Filippo Pedrini
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Andrea Pastore
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Valerio di Marco
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Maria Gabriella Marin
- Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35121 Padova, Italy
| | - Sara Bogialli
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Marco Roverso
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy
| | - Paolo Pastore
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy.
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Ràfols C, Beltrán JL, Rosés M, Bosch E. Ionic equilibria in aqueous organic solvent mixtures. Speciation of hydrofluoric acid in several ethanol/water solutions. J Electroanal Chem (Lausanne) 2019. [DOI: 10.1016/j.jelechem.2019.113318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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High throughput method to characterize acid-base properties of insoluble drug candidates in water. J Pharm Biomed Anal 2018; 154:404-412. [PMID: 29573736 DOI: 10.1016/j.jpba.2018.03.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Revised: 03/03/2018] [Accepted: 03/04/2018] [Indexed: 10/17/2022]
Abstract
In drug design experimental characterization of acidic groups in candidate molecules is one of the more important steps prior to the in-vivo studies. Potentiometry combined with Yasuda-Shedlovsky extrapolation is one of the more important strategy to study drug candidates with low solubility in water, although, it requires a large number of sequences to determine pKa values at different solvent-mixture compositions to, finally, obtain the pKa in water (pwwKa) by extrapolation. We have recently proposed a method which requires only two sequences of additions to study the effect of organic solvent content in liquid chromatography mobile phases on the acidity of the buffer compounds usually dissolved in it along wide ranges of compositions. In this work we propose to apply this method to study thermodynamic pwwKa of drug candidates with low solubilities in pure water. Using methanol/water solvent mixtures we study six pharmaceutical drugs at 25 °C. Four of them: ibuprofen, salicylic acid, atenolol and labetalol, were chosen as members of carboxylic, amine and phenol families, respectively. Since these compounds have known pwwKa values, they were used to validate the procedure, the accuracy of Yasuda-Shedlovsky and other empirical models to fit the behaviors, and to obtain pwwKa by extrapolation. Finally, the method is applied to determine unknown thermodynamic pwwKa values of two pharmaceutical drugs: atorvastatin calcium and the two dissociation constants of ethambutol. The procedure proved to be simple, very fast and accurate in all of the studied cases.
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McGuigan JA, Kay JW, Elder HY. Ionised concentrations in calcium and magnesium buffers: Standards and precise measurement are mandatory. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017; 126:48-64. [DOI: 10.1016/j.pbiomolbio.2017.03.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Revised: 01/20/2016] [Accepted: 03/10/2016] [Indexed: 11/16/2022]
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Tupys A, Kalembkiewicz J, Bazel Y, Zapała L, Dranka M, Ostapiuk Y, Tymoshuk O, Woźnicka E. 1-[(5-Benzyl-1,3-thiazol-2-yl)diazenyl]naphthalene-2-ol: X-ray structure, spectroscopic characterization, dissociation studies and application in mercury(II) detection. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2016.07.119] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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10
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McGuigan JAS, Kay JW, Elder HY. Ionised concentrations in calcium and magnesium buffers: Standards and precise measurement are mandatory. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 121:195-211. [PMID: 26975789 DOI: 10.1016/j.pbiomolbio.2016.03.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Revised: 01/20/2016] [Accepted: 03/10/2016] [Indexed: 06/05/2023]
Abstract
In Ca(2+) and Mg(2+) buffer solutions the ionised concentrations ([X(2+)]) are either calculated or measured. Calculated values vary by up to a factor of seven due to the following four problems: 1) There is no agreement amongst the tabulated constants in the literature. These constants have usually to be corrected for ionic strength and temperature. 2) The ionic strength correction entails the calculation of the single ion activity coefficient, which involves non-thermodynamic assumptions; the data for temperature correction is not always available. 3) Measured pH is in terms of activity i.e. pHa. pHa measurements are complicated by the change in the liquid junction potentials at the reference electrode making an accurate conversion from H(+) activity to H(+) concentration uncertain. 4) Ligands such as EGTA bind water and are not 100% pure. Ligand purity has to be measured, even when the [X(2+)] are calculated. The calculated [X(2+)] in buffers are so inconsistent that calculation is not an option. Until standards are available, the [X(2+)] in the buffers must be measured. The Ligand Optimisation Method is an accurate and independently verified method of doing this (McGuigan & Stumpff, Anal. Biochem. 436, 29, 2013). Lack of standards means it is not possible to compare the published [Ca(2+)] in the nmolar range, and the apparent constant (K(/)) values for Ca(2+) and Mg(2+) binding to intracellular ligands amongst different laboratories. Standardisation of Ca(2+)/Mg(2+) buffers is now essential. The parameters to achieve this are proposed.
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Affiliation(s)
- John A S McGuigan
- Medical, Veterinary and Life Sciences Faculty, University of Glasgow, G12 8QQ, UK.
| | - James W Kay
- Medical, Veterinary and Life Sciences Faculty, University of Glasgow, G12 8QQ, UK
| | - Hugh Y Elder
- Medical, Veterinary and Life Sciences Faculty, University of Glasgow, G12 8QQ, UK
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Gagliardi LG, Tascon M, Castells CB. Effect of temperature on acid–base equilibria in separation techniques. A review. Anal Chim Acta 2015; 889:35-57. [DOI: 10.1016/j.aca.2015.05.053] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2014] [Revised: 05/16/2015] [Accepted: 05/22/2015] [Indexed: 10/23/2022]
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12
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Longitudinal meta-analysis of NIST pH Standard Reference Materials(®): a complement to pH key comparisons. Anal Bioanal Chem 2014; 407:3193-203. [PMID: 25450053 DOI: 10.1007/s00216-014-8326-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 11/01/2014] [Accepted: 11/06/2014] [Indexed: 10/24/2022]
Abstract
This meta-analysis assesses the long-term (up to 70 years) within-laboratory variation of the NIST pH Standard Reference Material® (SRM) tetroxalate, phthalate, phosphate, borate, and carbonate buffers. Values of ΔpH(S), the difference between the certified pH value, pH(S), of each SRM issue and the mean of all pH(S) values for the given SRM at that Celsius temperature, t, are graphed as a function of the SRM issue and t. In most cases, |ΔpH(S)| < 0.004. Deviations from the nominal base:acid amount (mole) ratio of a buffer yield t-independent, constant shifts in ΔpH(S). The mean ΔpH(S) characterizes such deviations. The corresponding mole fraction of impurity in the conjugate buffer component is generally <0.3 %. Changes in the equipment, personnel, materials, and methodology of the pH(S) measurement yield t-dependent variations. The standard deviation of ΔpH(S) characterizes such changes. Standard deviations of ΔpH(S) are generally 0.0015 or less. The results provide a long-term, single-institution complement to the time-specific, multi-institution results of pH key comparisons administered by the Consultative Committee for Metrology in Chemistry and Biology (CCQM).
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Acquaviva A, Tascon M, Padró J, Gagliardi L, Castells C. Automatized measurements of dihydrogen phosphate and Tris(hydroxymethyl) aminomethane in acetonitrile/water mixtures from 20 to 60°C. Talanta 2014; 127:196-203. [DOI: 10.1016/j.talanta.2014.04.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 04/09/2014] [Accepted: 04/09/2014] [Indexed: 11/26/2022]
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Zapała L, Woźnicka E, Kalembkiewicz J. Tautomeric and Microscopic Protonation Equilibria of Anthranilic Acid and Its Derivatives. J SOLUTION CHEM 2014; 43:1167-1183. [PMID: 25067861 PMCID: PMC4074347 DOI: 10.1007/s10953-014-0190-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 04/04/2014] [Indexed: 10/25/2022]
Abstract
The acid-base chemistry of three zwitterionic compounds, namely anthranilic (2-aminobenzoic acid), N-methylanthranilic and N-phenylanthranilic acid has been characterized in terms of the macroconstants Ka1, Ka2, the isoelectric point pHI, the tautomerization constant Kz and microconstants k11, k12, k21, k22. The potentiometric titration method was used to determine the macrodissociation constants. Due to the very poor water solubility of N-phenylanthranilic acid the dissociation constants pKa1 and pKa2 were determined in MDM-water mixtures [MDM is a co-solvent mixture, consisting of equal volumes of methanol (MeOH), dioxane and acetonitrile (MeCN)]. The Yasuda-Shedlovsky extrapolation procedure has been used to obtain the values of pKa1 and pKa2 in aqueous solutions. The pKa1 and pKa2 values obtained by this method are 2.86 ± 0.01 and 4.69 ± 0.03, respectively. The tautomerization constant Kz describing the equilibrium between unionized form ⇌ zwitterionic form was evaluated by the Kz method based on UV-VIS spectrometry. The method uses spectral differences between the zwitterionic form (found at isoelectric pH in aqueous solution) and the unionized form (formed in an organic solvent of low dielectric constant). The highest value of the Kz constant has been observed in the case of N-methylantranilic acid (log10Kz = 1.31 ± 0.04). The values of log10Kz for anthranilic and N-phenylanthranilic acids are similar and have values of 0.93 ± 0.03 and 0.90 ± 0.05, respectively. The results indicate that the tested compounds, in aqueous solution around the isoelectric point pHI, occur mainly in the zwitterionic form. Moreover, the influence of the type of substituent and pH of the aqueous phase on the equilibrium were analyzed with regard to the formation and the coexistence of different forms of the acids in the examined systems.
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Affiliation(s)
- Lidia Zapała
- Department of Inorganic and Analytical Chemistry, Faculty of Chemistry, Rzeszow University of Technology, 6 Powstańców Warszawy Ave., 35-959 Rzeszow, Poland
| | - Elżbieta Woźnicka
- Department of Inorganic and Analytical Chemistry, Faculty of Chemistry, Rzeszow University of Technology, 6 Powstańców Warszawy Ave., 35-959 Rzeszow, Poland
| | - Jan Kalembkiewicz
- Department of Inorganic and Analytical Chemistry, Faculty of Chemistry, Rzeszow University of Technology, 6 Powstańców Warszawy Ave., 35-959 Rzeszow, Poland
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Shibata M, Kato M, Iwamoto Y, Nomura S, Kakiuchi T. Potentiometric determination of pH values of dilute sulfuric acid solutions with glass combination electrode equipped with ionic liquid salt bridge. J Electroanal Chem (Lausanne) 2013. [DOI: 10.1016/j.jelechem.2013.07.024] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Affiliation(s)
- Dan Fraenkel
- Eltron Research & Development Inc., 4600 Nautilus Court South, Boulder, Colorado 80301-3241, United States
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Roy RN, Roy LN, Henson IB, Stegner JM, Dinga JJ, Summers CE, Suhrheinrich GL, Veliz JA, Dieterman LA. Buffer Standards for the Physiological pH of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine (TRICINE) from T = (278.15 to 328.15) K. THE JOURNAL OF CHEMICAL THERMODYNAMICS 2012; 52:11-15. [PMID: 22745513 PMCID: PMC3381610 DOI: 10.1016/j.jct.2012.02.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The pH values of two buffer solutions without NaCl and seven buffer solutions with added NaCl, having ionic strengths (I = 0.16 mol·kg(-1)) similar to those of physiological fluids, have been evaluated at 12 temperatures from T = (278.15 to 328.15) K by way of the extended form of the Debye-Hückel equation of the Bates-Guggenheim convention. The residual liquid junction potentials (δE(j)) between the buffer solutions of TRICINE and saturated KCl solution of the calomel electrode at T = (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. For the buffer solutions with the molality of TRICINE (m(1)) = 0.06 mol·kg(-1), NaTRICINE (m(2)) = 0.02 mol·kg(-1), and NaCl (m(3)) = 0.14 mol·kg(-1), the pH values at 310.15 K obtained from the extended Debye-Hückel equation and the inclusion of the liquid junction correction are 7.342 and 7.342, respectively. These are in excellent agreement. The zwitterionic buffer TRICINE is recommended as a secondary pH standard in the region for clinical application.
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Affiliation(s)
- Rabindra N. Roy
- Corresponding author. Tel.: 1 + 417 873 7247; fax: 1 + 417 873 7856, (R. Roy)
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Padró JM, Acquaviva A, Tascon M, Gagliardi LG, Castells CB. Effect of temperature and solvent composition on acid dissociation equilibria, I: Sequenced pssKa determination of compounds commonly used as buffers in high performance liquid chromatography coupled to mass spectroscopy detection. Anal Chim Acta 2012; 725:87-94. [DOI: 10.1016/j.aca.2012.03.015] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2011] [Revised: 02/18/2012] [Accepted: 03/05/2012] [Indexed: 10/28/2022]
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20
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Roy LN, Roy RN, Allen KA, Mehrhoff CJ, Henson IB, Stegner JM. Buffer standards for the physiological pH of the zwitterionic compound of 3-(N-morpholino)propanesulfonic acid (MOPS) from T = (278.15 to 328.15) K. THE JOURNAL OF CHEMICAL THERMODYNAMICS 2012; 47:21-27. [PMID: 22247568 PMCID: PMC3254115 DOI: 10.1016/j.jct.2011.09.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
This paper reports the pH values of five NaCl-free buffer solutions and eleven buffer compositions containing NaCl at I = 0.16 mol·kg(-1). Conventional pa(H) values are reported for sixteen buffer solutions with and without NaCl salt. The operational pH values have been calculated for five buffer solutions and are recommended as pH standards at T = (298.15 and 310.15) K after correcting the liquid junction potentials. For buffer solutions with the composition m(1) = 0.04 mol·kg(-1), m(2) = 0.08 mol·kg(-1), m(3) = 0.08 mol·kg(-1) at I = 0.16 mol·kg(-1), the pH at 310.15 K is 7.269, which is close to 7.407, the pH of blood serum. It is recommended as a pH standard for biological specimens.
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Affiliation(s)
- Lakshmi N. Roy
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
| | - Rabindra N. Roy
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
| | - Kathleen A. Allen
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
| | - Casey J. Mehrhoff
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
| | - Isaac B. Henson
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
| | - Jessica M. Stegner
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, MO 65802, USA
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Fraenkel D. Effect of Solvent Permittivity on the Thermodynamic Behavior of HCl Solutions: Analysis Using the Smaller-Ion Shell Model of Strong Electrolytes. J Phys Chem B 2011; 115:14634-47. [DOI: 10.1021/jp207878f] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Dan Fraenkel
- Eltron Research & Development Inc., 4600 Nautilus Court South, Boulder, Colorado 80301-3241, United States
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Evaluation of the Standard Potential of the Ag/AgCl Electrode in a 50 wt-% Water–Ethanol Mixture. J SOLUTION CHEM 2011. [DOI: 10.1007/s10953-011-9758-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Ferse A, Müller HO. Factorizing of a concentration function for the mean activity coefficients of aqueous strong electrolytes into individual functions for the ionic species. J Solid State Electrochem 2011. [DOI: 10.1007/s10008-011-1413-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Kakiuchi T. Salt bridge in electroanalytical chemistry: past, present, and future. J Solid State Electrochem 2011. [DOI: 10.1007/s10008-011-1373-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Zapała L. Potentiometric Studies on the Equilibria of Flufenamic Acid in Aqueous Solutions and in Two-phase Organic Solvent + Water Systems. J SOLUTION CHEM 2011. [DOI: 10.1007/s10953-010-9642-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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26
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Bodendorfer BM, Harmon MA, Henson IB, Martin MS, Roy LN, Roy RN, Stegner JM, Wollen JT. Calculation of the pH of Buffer Solution of 2-[<i>N</i> -Morpholino]ethanesulfonic Acid (MES) from 5°C to 55°C. ACTA ACUST UNITED AC 2011. [DOI: 10.4236/ojpc.2011.13011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Haya L, Sayago FJ, Mainar AM, Cativiela C, Urieta JS. Quantum-chemical predictions of redox potentials of carbamates in methanol. Phys Chem Chem Phys 2011; 13:17696-703. [DOI: 10.1039/c1cp21576k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Roy LN, Roy RN, Wollen JT, Harmon MA, Stegner JM, Shah AA, Henson IB. Buffer Standards for the Biological pH of the Amino Acid N-[2 hydroxyethyl]piperazine-N'-[3-propanesulfonic acid], HEPPS, From (278.15 to 328.15) K. JOURNAL OF CHEMICAL AND ENGINEERING DATA 2011; 56:4126-4132. [PMID: 22096257 PMCID: PMC3215147 DOI: 10.1021/je200629y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
For the HEPPS buffer under investigation, there are seven buffer solutions without NaCl and eight buffer solutions that contain Cl(-) and have an ionic strength (I = 0.16 mol·kg(-1)), which is similar to that of blood plasma. These buffer solutions have been evaluated in the temperature range of (278.15 to 328.15) K using the extended Debye- Hückel equation and the Bates-Guggenheim convention. The previously determined E(j) values have been used to determine the operational pH values of HEPPS buffer solutions at (298.15 and 310.15) K. These are recommended as secondary standard reference solutions for pH measurements in saline media with an isotonic ionic strength of I = 0.16 mol·kg(-1).
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Affiliation(s)
- Lakshmi N Roy
- Hoffman Department of Chemistry, Drury University, 900 N. Benton Ave., Springfield, Missouri 65802, USA
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Spitzer P, Pratt KW. The history and development of a rigorous metrological basis for pH measurements. J Solid State Electrochem 2010. [DOI: 10.1007/s10008-010-1106-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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31
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Partanen JI, Salmimies RK, Partanen LJ, Louhi-Kultanen M. Prediction of Activity Coefficients for Uni-univalent Electrolytes in Pure Aqueous Solution. Chem Eng Technol 2010. [DOI: 10.1002/ceat.200900617] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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SHIBATA M, YAMANUKI M, IWAMOTO Y, NOMURA S, KAKIUCHI T. Stability of a Ag/AgCl Reference Electrode Equipped with an Ionic Liquid Salt Bridge Composed of 1-Methyl-3-octylimidazolium Bis(trifluoromethanesulfonyl)-amide in Potentiometry of pH Standard Buffers. ANAL SCI 2010; 26:1203-6. [DOI: 10.2116/analsci.26.1203] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Ferra MIA, Graça JR, Marques AMM. Application of the Pitzer Model to Assignment of pH to Phthalate Standard Buffer Solutions. J SOLUTION CHEM 2009. [DOI: 10.1007/s10953-009-9421-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Buffer Standards for the Physiological pH of the Zwitterionic Compound, HEPPSO from 5 to 55 °C. J SOLUTION CHEM 2009. [DOI: 10.1007/s10953-009-9442-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Roy LN, Roy RN, Denton CE, LeNoue SR, Roy CN, Ashkenazi S, Fuge MS, Wollen JT, Stegner JM, Allen KA, Harmon MA. Buffer Standards for the Biochemical pH of 3-(N-morpholino)-2-hydroxypropanesulfonic Acid from (278.15 to 328.15) K. JOURNAL OF CHEMICAL AND ENGINEERING DATA 2009; 54:1860-1864. [PMID: 20160876 PMCID: PMC2771950 DOI: 10.1021/je800983y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The values of the second dissociation constant pK(2) and related thermodynamic quantities of the ampholyte 3-(N-morpholino)-2-hydroxypropanesulfonic acid (MOPSO) have been previously determined at temperatures from (278.15 to 328.15) K. In this study, the pH values of two buffer solutions without NaCl and three buffer solutions with NaCl having ionic strengths (I = 0.16 mol·kg(-1)) similar to those in blood plasma, have been evaluated at 12 temperatures from (278.15 to 328.15) K using an extended form of the Debye-Hückel equation, since the Bates-Guggenheim convention is valid up to I = 0.1 mol·kg(-1). The liquid junction potentials (E(j)) between the buffer solutions of MOPSO and saturated KCl solution of the calomel electrode at (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. These values of E(j) have been used to ascertain the operational pH values at (298.15 and 310.15) K. Three buffer solutions of MOPSO are recommended as useful reference solutions for pH measurements in saline media of ionic strength I = 0.16 mol·kg(-1).
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Affiliation(s)
- Lakshmi N. Roy
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Rabindra N. Roy
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Cole E. Denton
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Sean R. LeNoue
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Chandra N. Roy
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Shahaf Ashkenazi
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Michael S. Fuge
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Joshua T. Wollen
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Jessica M. Stegner
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Kathleen A. Allen
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
| | - Meagan A. Harmon
- Hoffman Department of Chemistry, Drury University, Springfield, MO 65802
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Roy RN, Roy LN, Ashkenazi S, Wollen JT, Dunseth CD, Fuge MS, Durden JL, Roy CN, Hughes HM, Morris BT, Cline KL. Buffer Standards for pH Measurement of N-(2-Hydroxyethyl)piperazine-N'-2-ethanesulfonic Acid (HEPES) for I = 0.16 mol.kg from 5 to 55 degrees C. J SOLUTION CHEM 2009; 38:449-458. [PMID: 20161485 PMCID: PMC2794207 DOI: 10.1007/s10953-009-9378-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The values of the second dissociation constant, pK(2) of N-(2-hydroxyethyl) piperazine-N'-2-ethanesulfonic acid (HEPES) have been reported at 12 temperatures over the temperature range 5 to 55 degrees C, including 37 degrees C. This paper reports the results for the pa(H) of eight isotonic saline buffer solutions with an I = 0.16 mol*kg(-1) including compositions: (a) HEPES (0.01 mol*kg(-1)) + NaHEPES (0.01 mol*kg(-1)) + NaCl (0.15 mol*kg(-1)); (b) HEPES (0.02 mol*kg(-1)) + NaHEPES (0.02 mol*kg(-1)) + NaCl (0.14 mol*kg(-1)); (c) HEPES (0.03 mol*kg(-1)) + NaHEPES (0.03 mol*kg(-1)) + NaCl (0.13 mol*kg(-1)); (d) HEPES (0.04 mol*kg(-1)) + NaHEPES (0.04 mol*kg(-1)) + NaCl (0.12 mol*kg(-1)); (e) HEPES (0.05 mol*kg(-1)) + NaHEPES (0.05 mol*kg(-1)) + NaCl (0.11 mol*kg(-1)); (f) HEPES (0.06 mol*kg(-1)) + NaHEPES (0.06 mol*kg(-1)) + NaCl (0.10 mol*kg(-1)); (g) HEPES (0.07 mol*kg(-1)) + NaHEPES (0.07 mol*kg(-1)) + NaCl (0.09 mol*kg(-1)); and (h) HEPES (0.08 mol*kg(-1)) + NaHEPES (0.08 mol*kg(-1)) + NaCl (0.08 mol*kg(-1)). Conventional pa(H) values, for all eight buffer solutions from 5 to 55 degrees C have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 degrees C have been determined based on the NBS/NIST standard between the physiological phosphate standard and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH 7.3 to 7.5 at I = 0.16 mol*kg(-1).
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Box K, Völgyi G, Ruiz R, Comer J, Takács-Novák K, Bosch E, Ràfols C, Rosés M. Physicochemical Properties of a New Multicomponent Cosolvent System for the pKa Determination of Poorly Soluble Pharmaceutical Compounds. Helv Chim Acta 2007. [DOI: 10.1002/hlca.200790161] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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A Determination of Standard Potentials and Related Primary pH Standards in the 50 Mass Percent (N-Methyl-2-Pyrrolidinone + Water) Mixture at Various Temperatures. J SOLUTION CHEM 2007. [DOI: 10.1007/s10953-007-9162-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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41
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Gagliardi LG, Castells CB, Ràfols C, Rosés M, Bosch E. δ Conversion Parameter between pH Scales ( and ) in Acetonitrile/Water Mixtures at Various Compositions and Temperatures. Anal Chem 2007; 79:3180-7. [PMID: 17358047 DOI: 10.1021/ac062372h] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The SSpH in acetonitrile/water mixtures at different temperatures cannot be directly measured because of the lack of calibration buffers in these hydroorganic media at most temperatures different from 25 degrees C. In this paper, the delta parameter has been determined for acetonitrile/water mixtures from 0 up to 90% acetonitrile at different temperatures from 15 to 60 degrees C, and the values were fitted to a very simple simultaneous function of composition and temperature. The delta values allow conversion of the SWpH scale (pH measured in acetonitrile/water with electrodes calibrated in water) to the SSpH scale (pH measured in acetonitrile/water with electrodes calibrated in the same acetonitrile/water mixture). The practical determination of SWpH is direct because the calibration of the electrodes is carried out with commercial aqueous standard buffers. Thus, the SSpH value of any buffered acetonitrile/water mobile phase used in reversed-phase liquid chromatography, which is directly related to the ionized fraction of analyte and, therefore, to its average retention, can be easily known at any temperature from the measured SWpH and the corresponding delta value.
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Affiliation(s)
- Leonardo G Gagliardi
- Departament de Química Analítica, Facultat de Química, Universitat de Barcelona, Barcelona, Spain
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Affiliation(s)
- Frank J Millero
- Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA.
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Prenesti E, Fisicaro P, Berto S, Ferrara E, Daniele PG. Monitoring the traceability of the pH of a primary tetraborate buffer: comparison of results from primary and secondary apparatus. Anal Bioanal Chem 2007; 387:2595-600. [PMID: 17245528 DOI: 10.1007/s00216-007-1117-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2006] [Revised: 12/22/2006] [Accepted: 01/05/2007] [Indexed: 10/23/2022]
Abstract
This paper reports evaluation of the behaviour of different combined glass electrodes applied to measurement of the pH of a primary, 0.01 mol kg(-1), tetraborate buffer. Measurements were first performed by use of a primary Harned cell (at 15, 25, and 37 degrees C); these results were then compared with those obtained for the same solution by use of three combined glass electrodes (25 degrees C) with different membranes and liquid-junction designs, calibrated by use of commercial pH-metric buffers. The pH of the same solution was also measured in terms of the molal concentration of hydrogen ions, using acid-base titration to evaluate the formal potential difference K of each cell at fixed ionic strength, I, adjusted by addition of KCl or Et4NI (tetraethylammonium iodide). The reference value from primary measurement, paH = 9.171, was slightly closer to the mean value obtained by determination of concentration, rather than that obtained by direct measurement of activity; the differences were smaller than the extended uncertainty characteristics of the secondary measurements. The importance of evaluation of the ionic strength of the solution under study is emphasised. We verified that for tetraborate buffer slight modification of the value of I used to calculate gamma (i) (the activity coefficient of a single ion) in the calculation of paH from the acidity function at zero molality of chloride can significantly affect the reference value of the calibrator tool. This is true, in general, for low values of the ionic strength, such as those considered in this work; an approximate value of I can then cause distortions along the pH traceability chain. Application of the concepts of thermodynamics to this traceability chain is discussed.
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Affiliation(s)
- Enrico Prenesti
- Dipartimento di Chimica Analitica, Università di Torino, via Pietro Giuria 5, 10125, Torino, Italy.
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Longhi P, Mussini T, Rondinini S. An Analysis of Operational Conditions for the Double Addition Method of Determining Ions From Electromotive Forces of Ion-Selective Electrode Cells. ANAL LETT 2006. [DOI: 10.1080/00032718208064450] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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45
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Lito MJGHM, Camões MF, Viçoso CM. Effect of condensation phenomena on potentiometric measurements. Anal Chim Acta 2006; 575:45-51. [PMID: 17723570 DOI: 10.1016/j.aca.2006.05.078] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2005] [Revised: 05/22/2006] [Accepted: 05/23/2006] [Indexed: 11/20/2022]
Abstract
Results of potentiometric analysis, namely those of pH measurements, depend on temperature control of the experimental setup, as it is expressed in the analytical law, the Nernst equation, starting from the primary level, where reference values are conventionally assigned to standard solutions, through the whole traceability chain, down to the service laboratory. Fundamental studies of pH standards, based on the measurement of the potential of an electrochemical cell without transference, known as Harned cell, containing a platinum-hydrogen electrode and a silver-silver chloride reference electrode, refer condensation phenomena on the portions of the cell walls which are not immersed in the thermostatic bath, as one of the major sources of error in the assessment of both the silver-silver chloride electrode standard potential and on pH values. In this work such effect, which is bound to happen due to significant temperature differences between the ambient air temperature and the water bath, has been quantified, presenting an original contribution to the improvement of the quality of potentiometric analysis results. This was possible due to the availability of a climatic cabin "WALKIN" with a temperature control of +/-0.01 degrees C, which permitted that temperature gradients were built between the thermostat water bath (controlled to +/-0.005 degrees C) where cells filled to about 2/3 full were immersed up to 90% of their height, and the surrounding environment.
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Second Dissociation Constant of Bis-[(2-hydroxyethyl)amino]acetic Acid (BICINE) and pH of Its Buffer Solutions from 5 to 55 °C. J SOLUTION CHEM 2006. [DOI: 10.1007/s10953-005-9009-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Buffer Standards for the Physiological pH of the Zwitterionic Compound, TAPS, From 5 to 55 ∘C. J SOLUTION CHEM 2006. [DOI: 10.1007/s10953-005-9010-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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48
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Fisicaro P, Ferrara E, Prenesti E, Berto S. Role of the activity coefficient in the dissemination of pH: comparison of primary (Harned cell) and secondary (glass electrode) measurements on phosphate buffer considering activity and concentration scales. Anal Bioanal Chem 2005; 383:341-8. [PMID: 16142421 DOI: 10.1007/s00216-005-3417-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2005] [Revised: 06/20/2005] [Accepted: 06/25/2005] [Indexed: 10/25/2022]
Abstract
Despite recent efforts devoted to assessing both the theoretical rationale and the experimental strategy for assignment of primary pH values, these have not yet been accomplished satisfactorily. Traceability and comparability of pH values are achieved only within the constraints of internationally accepted conventions and predefined conditions that cannot account for all possible situations when pH is measured. Critical parameters to be defined are, in particular, the activity coefficients (gamma (i)) of the ionic species involved in the equilibrium with the hydrogen ions in the solution, which are usually estimated with the approximation typical of the Debye-Hückel theoretical model. For this paper, primary (Harned cell) measurements (traceable to the SI system) of the pH of a phosphate buffer have been considered and the results have been compared with secondary (glass electrode) measurements obtained by considering either the activity (paH) or concentration (pcH) scale of the hydrogen ions. With conventional approaches based on measurements related to activity or concentration scale, discrepancies emerge which have been assigned to incomplete inferences of gamma (i) arising from chemical features of the solution. It is shown that fitting and comparable paH and pcH results are attainable if evaluation of gamma (i) is performed using better estimates of the ionic strength, according to an enhanced application of the Debye-Hückel theory.
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Affiliation(s)
- Paola Fisicaro
- Istituto Elettrotecnico Nazionale Galileo Ferraris, Strada delle Cacce 91, 10135, Torino, Italy.
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Gagliardi LG, Castells CB, Ràfols C, Rosés M, Bosch E. Effect of temperature on the chromatographic retention of ionizable compounds. J Chromatogr A 2005; 1077:159-69. [PMID: 16001552 DOI: 10.1016/j.chroma.2005.04.070] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The retentive behavior of weak acids and bases in reversed-phase liquid chromatography (RPLC) upon changes in column temperature has been theoretically and experimentally studied. The study focuses on examining the temperature dependence of the retention of various solutes at eluent pH close to their corresponding pKa values, and on the indirect role exerted by the buffer ionization equilibria on retention and selectivity. Retention factors of several ionizable compounds in a typical octadecylsilica column and using buffer solutions dissolved in 30% (v/v) acetonitrile as eluent at five temperatures in the range from 25 to 50 degrees C were carefully measured. Six buffer solutions were prepared from judiciously chosen conjugated pairs of different chemical nature. Their pKa values in this acetonitrile-water composition and within the range of 15-50 degrees C were determined potentiometrically. These compounds exhibit very different standard ionization enthalpies within this temperature range. Thus, whenever they are used to control mobile phase pH, the column temperature determines their final pH. Predictive equations of retention that take into account the temperature effect on both the transfer and the ionization processes are evaluated. This study demonstrates the significant role that the selected buffer would have on retention and selectivity in RPLC at temperatures higher than 25 degrees C, particularly for solutes that coelute.
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Affiliation(s)
- Leonardo G Gagliardi
- Departament de Química Analítica, Facultat de Química, Universitat de Barcelona, Barcelona, Spain
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50
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Porras SP, Kenndler E. Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte. J Chromatogr A 2004; 1037:455-65. [PMID: 15214682 DOI: 10.1016/j.chroma.2003.07.018] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although the establishment of a pH scale and the determination of the pH in water is not problematic, it is not a straightforward task in non-aqueous solvents. As capillary zone electrophoresis (CZE) in organic solvents has gained increasing interest, it seems to be valuable to re-discuss the concept of the pH in such media, especially pointing to those aspects, which make pH measurement uncertain in non-aqueous solvents. In this review, the relevant aspects when dealing with primary standard (PS) and secondary standard (SS) as recommended by the International Union of Pure and Applied Chemistry (IUPAC), and the usage of the operational pH are discussed with special emphasis to non-aqueous solvents. Here, different liquid junction potentials, incomplete dissociation of the electrolytes (especially in solvents with low or moderate relative permittivity) and the occurrence of homo- and heteroconjugation must be taken into account. Problems arising in capillary zone electrophoresis practice are addressed, e.g. when the background electrolyte (BGE) consists of organic solvents, but the measuring electrode (normally the glass electrode) is calibrated with aqueous buffers, and the liquid junction potentials between the solvents do not cancel each other. The alternative concept of establishing a certain pH is described, using mixtures of reference acids or bases with known pKa in the organic solvent, and their respective salts, at a certain concentration ratio, relying to the Henderson-Hasselbalch equation. Special discussion is directed to those organic solvents most common in capillary zone electrophoresis, methanol (MeOH) and acetonitrile (ACN), but other solvents are included as well. The potential significance of small amounts of water present in the organic solvent on changes in pKa values, and thus on the pH of the buffering components is pointed out.
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Affiliation(s)
- Simo P Porras
- Institute for Analytical Chemistry, University of Vienna, Wahringerstrasse 38, A-1090 Vienna, Austria.
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