Potentiometric titrations using Gran plots: A textbook omission

Rossotti, F. J. C.; Rossotti, Hazel

doi:10.1021/ed042p375

Cited by 624 publications

(268 citation statements)

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“…The ionic strength of all working solutions was kept constant at 1.00 M by the addition of NaCl (Ajax, Australia, 99.9 %). Concentrations of H + and OH  were cross-checked by acid-base titrations using Gran plots 30 . Alkali solutions were discarded after two weeks.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

“…The middle portion was used for titration while the first and last portions were analysed for [Cu(I)] T , where the subscript T indicates the total or analytical concentration, by aerial oxidation to Cu(II) followed by titration against standard EDTA using fast sulfon black indicator 33 . Concentrations of H + were determined from Gran plots of titrations with NaOH solution 30 . Stock solution concentrations were determined to  0.1 % and were found to drift only very slowly (ca.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

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Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Königsberger

Hefter

et al. 2015

Dalton Trans.

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Protonation constants for the biologically-important thioamino acids cysteine (CSH), penicillamine (PSH) and glutathione (GSH), and the formation constants of their complexes with Cu(I), have been measured at 25 C and an ionic strength of 1.00 mol dm 3 (Na)Cl using glass electrode potentiometry. The first successful characterisation of binary Cu(I)CSH and Cu(I)GSH species over the whole pH range was achieved in this study by the addition of a second thioamino acid, which prevented the precipitation that normally occurs. Appropriate combinations of binary and ternary (mixed ligand) titration data were used to optimise the speciation models and formation constants for the binary species. The results obtained differ significantly from literature data with respect to the detection and quantification of protonated and polynuclear complexes. The present results are thought to be more reliable because of the exceptionally wide pH and concentration ranges employed, the excellent reproducibility of the data, the close agreement between the calculated and observed formation functions, and the low standard deviations and absence of numerical correlation in the constants. The present formation constants were incorporated into a large Cu speciation model which was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye. This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, which is known to occur as a consequence of Wilson's disease.

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Section: Experimental and Computational Methodsmentioning

confidence: 99%

Section: Experimental and Computational Methodsmentioning

confidence: 99%

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Königsberger

Hefter

et al. 2015

Dalton Trans.

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“…The number of potentiometric data for each defined pH region is given in Tables 1 and 2. For computing the protonation constants of ligands [33][34][35] (log K) and the formation constants of Al(III) complexes (log b) data were utilized in the pHϭ1.5-3.88 range. The hydrolysis of Al(III) ion was completely neglected in this pH range, but above pH 4.0 the existence of hydroxo complexes was considered.…”

Section: Methodsmentioning

confidence: 99%

“…32) To determine the stoichiometries of possible complexes, the degree of formation of Al(III) chelates n ᎐ was calculated from the formation curves employing the method of Irving and Rossotti. [35][36][37][38] The species distribution diagrams 39) …”

Section: Methodsmentioning

confidence: 99%

Potentiometric and Spectroscopic Studies on Aluminium(III) Complexes of Some Catechol Derivatives

Türkel

Berker

Özer

2004

CHEMICAL & PHARMACEUTICAL BULLETIN

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The aqua Al(III) ion is the "hardest" of the trivalent ions commonly found in the environment and in biological systems. Its effective ionic radius is 54 Å, which is smaller than other commonly encountered trivalent metal ions. Therefore the aqua Al(III) ion has the highest charge/size ratio and high affinity for hard anions. As a result, it has a strong tendency to hydrolyze in aqueous solution and its coordination equilibria contain rather complicated hydroxo complexes. 1 2,5) investigated the relations between the basicities of these oxygen donors and the stabilities of their Al(III) complexes. They concluded that the logarithm of protonation constants of monodentate donors and pK sum of bi-or terdentate donors provide a quantative measure for the hardness of each donor. The order of decreasing basicities along with the summation of their approximate logarithms of protonation constants are proposed to be: (catecholate ca. 22)Ͼ(aliphatic monohydroxy acid anion ca. 18) Ͼ(aromatic hydroxy acid anion ca. 16)Ͼ(alkoxide ca. 14)Ͼ(phenoxide ca. 10)Ͼ(carboxylate ca. 4). Therefore the complexes of Al(III) ion that are sufficiently stable to hydrolytic reactions and consequent precipitation in aqueous solution should contain ligands with the highest pK sum.The complexes of catechol derivatives with Al(III) ion including metal ions such as Fe(II), Fe(III), Mg(II), Ca(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II), UO 2 (II), and VO(II) were studied by various researchers. 1,2,5-26) They determined that two or three moles of catechol derivatives are coordinated with one mole of these metal ions in their complexes. In particular, the constants of formation equilibria of Al(III) complexes of catechol derivatives have been the subject of a number of investigations. 1) Some of the hydroxy aromatic ligands are interesting three-protic ligands (H 3 L), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), 3,4-dihydroxyhydrocinnamic acid (3,4-DHHCA), and 3,4-dihydroxyphenylacetic acid (3,4-DHPA) are typical examples and they have affinities for metal ions to form stable complexes. 19,20,21,26) Some of their complexes do not hydrolyze and precipitate in aqueous solution, since 3,4-DHBA, 3,4-DHHCA, and 3,4-DHPA have one carboxylate binding site besides the catecholate sites that are in chelatable positions. 2,3-DHBA contains three potential binding sites on three adjacent ring carbons. It is a good model of the competitive salicylate (COO Ϫ , O Ϫ ) and catecholate type (O Ϫ , O Ϫ ) chelation in the same molecule. 5) Kennedy and Powell 7) investigated Al(III): catechol and 3,4-DHBA complexes using potentiometry in aqueous solution in Iϭ0.1 mol · l Ϫ KCl ionic medium at 25°C. They reported the stability constants for the mononuclear diphenolate complexes of Al(III) with catechol such as AlL, AlL 2 , and AlL 3 . They also indicated that monoand bis-complexes of catechol become hydrolyzed and then AlL(OH) Ϫ , and AlL 2 (OH) 4Ϫ hydroxo complexes formed. In the case of 3,4-DHBA, the existence of Al(HL)...

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“…A more elaborate discussion involving a statistical analysis about the advantages and limitations of this method can be found in the literature. 4 The functions of Gran's method, using pH or mV reading, and in-depth coverage of the calculations involved 5 as well as the uncertainty of the equivalence point 6 may be found in the literature. The case to handle other simple types of one-step precipitation, complexometric and redox titrations is reported.…”

Section: Introductionmentioning

confidence: 99%

Four Points Function Fitted and First Derivative Procedure for Determining the End Points in Potentiometric Titration Curves: Statistical Analysis and Method Comparison

Kholeif

2001

ANAL. SCI.

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IntroductionFor determining the inflection point or end point in potentiometric titration curves by the "parent" of the differential category, the regular first derivative (RFD) or second derivative (RSD) method is simple and straight forward, but lacks the accuracy of the end point calculated under the influence of certain factors. This category of methods depends on the presence of an inflection point to function properly, but does not require any prior information about the nature of the analyte. The end point can be located in this case if two sequential titrant additions result in a change of at least 0.3 pH unit (17.7 mV at 25˚C) in the titration curve. Programmable versions of the RFD and RSD methods locate the end point using inverse parabolic interpolation 1 and Neville inverse interpolation 2 algorithms, respectively. Variable deviations of the calculated end point using the RFD method in comparison with the true end point arise from a plot of dy/dx (x = ml of titrant and y = response; either mV or pH) against the quantity (xi+1 + xi)/2 or the mean of two successive titrant volume additions, as described by Gran. 3A similar situation is also found with the RSD method.The equivalence point category of methods are usually specific for the type of analyte and/or shape of titration curve. In most cases, they involve a derived equation for each analyte and titration types considered without the necessity of the presence of an inflection point in the titration curve. The Gran's plot 3 is one example known since 1950. A more elaborate discussion involving a statistical analysis about the advantages and limitations of this method can be found in the literature. 4 The functions of Gran's method, using pH or mV reading, and in-depth coverage of the calculations involved 5 as well as the uncertainty of the equivalence point 6 may be found in the literature. The case to handle other simple types of one-step precipitation, complexometric and redox titrations is reported. 7 Each type of analyte and titration requires a specific derived function based on prior knowledge about the stoichiometry of the reactants in a way that the method cannot be easily generalized. In the same equivalence point category, Fortuin's method 8 is generally applied to symmetrical potentiometric titration curves with equidistant titrant volumes in the region of inflection, and is based on a derived equation. The method uses four data points in the region of inflection to calculate two parameters related to the transition in this region. The limitations and conditions were also stated 8 in relation to calculations of the two parameters.In the present work, a new method with a programmable algorithm is presented. It is demonstrated here using the sigmoid and cumulative functions implemented in the algorithms sigmoid first derivative (SFD) and cumulative first derivative (CFD) and compared together with the results obtained from the RSD method as the "parent" of the differential category. The work also includes graphical and statistical analys...

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Potentiometric titrations using Gran plots: A textbook omission

Abstract: Describes Gran's graphical method of end point determination for the precise analysis of acids and bases.

Cited by 624 publications

References 1 publication

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Potentiometric and Spectroscopic Studies on Aluminium(III) Complexes of Some Catechol Derivatives

Four Points Function Fitted and First Derivative Procedure for Determining the End Points in Potentiometric Titration Curves: Statistical Analysis and Method Comparison

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