Potentiometric colloid titration

In most applications we want to know the charge density of dispersed systems. To determine the surface charge of dispersed particles, titration methods can be used. Before we can do a quantitative titration experiment we need to know the specific surface area, that is the total 

To verify that the salt is really indifferent and no specific binding of the ions occurs, the experiment can be repeated with a different salt. If titration curves measured at the same ionic strength are identical we have good evidence for the absence of specific binding. 

In potentiometric colloid titration the amount of potential-determining ions in solution is measured by an appropriate electrode. For oxides, where mainly the pH determines the potential, a glass electrode is a suitable detector. For Agl we could use an Agl electrode etc. 

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Potentiometric colloid titrations can also be carried out on colloids having a fixed number of certain dissociable groups, (say latlces with carboxylic or sulfate groups, proteins) or heterogeneous systems such as clay minerals. When there is only one tj je of group, l.e. in the case of so-called monqfunctional surfaces, the... 

Hattori T, Katai K, Kato M, Izume M, Mizuta Y. Colloidal titration of chitosan and critical unit of chitosan to the potentiometric colloidal titration with poly(vinyl sulfate) using toluidine blue as indicator. Bull Chem Soc Jpn 1999 72 37-41. 

With the above In mind, a° can be determined by colloid titrations, as described In sec. I.5.6e. To review the experimental ins and outs, consider (insoluble) oxides, subjected to potentiometric acid-base colloid titration. Basically the procedure Is that o° (at say pH , and c ) Is related to a° at pH" and the same Salt adding acid or base. The titration Is carried out in an electrochemical cell In such a way that not only pH" is obtainable, but also the part of the acid (base) that is not adsorbed and hence remains In solution. Material balance then relates the total amount (of acid minus base) adsorbed, a°A (where A is the interfacial area) at pH" to that at pH. By repeating this procedure a complete relative isotherm a°A as a function of pH Is obtainable. We call such a curve "relative" because it Is generally not known what <7° was In the starting position. 

Polymer-polymer complexation is generally detected via conductometric or potentiometric titrations. Colloid titration represents an inverse-system where a polymer with known characteristics, such as potassium poly (vinylalcohol-sulfate) or poly(diallyldimethylam-moniumchloride), are used to quantify the concentration of polycation or polyanion, hence relying on a 1 1 stoichiometry. Using the cationic dye, tol-uidine blue, as an indicator, a metachromatic end point is detected. Both methods are volumetric. 

Colloid Titration A method for the determination of charge, and the zero point of charge, of colloidal species. The colloid is subjected to a potentiometric titration with acid or base to determine the amounts of acid or base needed to establish equilibrium with various pH values. By titrating the colloid in different, known concentrations of indifferent electrolyte, the point of zero charge can be determined as the pH for which all the isotherms intersect. See also Point of Zero Charge. 

Background. Another form of colloid titration for estimating cationic (quaternary ammonium) compounds is based on a potentiometric procedure and utilizes an eleetrode that is specific to the titrating anionic surfactant chosen. The theory is that the cationic material complexes stoichiometrically with the anionic surfactant. 

GC, MGC, and PVSK were the reagents for colloidal titration (Wako Pure Chemical Industry, Ltd., Osaka). DTPA was purchased from Aldrich Chemical Company, Inc., Milwaukee. The other chemicals were of reagent grade. For the potentiometric titration, deionized water (0.3 pS/cm) was used. 

Pyman, M.A.F. Posner, A.M. (1978) The surface areas of amorphous mixed oxides and their relation to potentiometric titration. J. Colloid Interface Sci. 66 85-93 Pyzik, A. Sommer, S.E. (1981) Sedimentary iron monosulfides kinetics and mechanism of formation. Geochim. Cosmochim. Acta 45 687-698... 

B. Momstam, K.-G. Wahlund, and B. Jonsson, Potentiometric Acid-Base Titration of a Colloidal Solution, Anal. Chem. 1997,69, 5037. For titration of entire cell surfaces, see L Sokolov, D. S. Smith, G. S. Henderson, Y. A. Gorby, and F. G. Ferris, Cell Surface Electrochemical Heterogeneity of the Fe(III)-Reducing Bacteria ShewaneUa putrefaciens," Environ. Sci. TechnoL 2001,35, 341. 

The second type of potentiometric titration curves are shown in Figures 3.36b and c. Figure 3.36b shows that the crossover point of the same colloid system as in Figure... 

James, R. O., Davis, J. A., and Leckie, J. O. (1978). Computer simulation of the conductometric and potentiometric titrations of the surface groups on ionizable latexes. J. Colloid Interface Sci. 65, 331-343. 

Due, M., Gaboriaud, R, and Thomas, F., Sensitivity of the acid-base properties of clays to the methods of preparation and measurement. Evidence from continuous potentiometric titrations, J. Colloid Intetf. Sci., 289, 148, 2005. 

Skartsila, K. and Spanos, N., Surface characterization of hydroxyapatite Potentiometric titrations coupled with solubihty measurements, 7. Colloid Interf. Sci., 308, 405, 2007. 

Spadini, L. et al., Hydrous ferric oxide Evaluation of Cd-HFO surface complexation models combining Cd EXAFS data, potentiometric titration results and surface site structures identified from mineralogical knowledge, J. Colloid Interf. Sci., 266, 1, 2003. 

Spanos, N., Georgiadou, 1. and Lycourghiotis, A., Investigation on rutile, anatase, and industrial titania/water solution interfaces using potentiometric titration and microelectrophoresis, J. Colloid Interf. Sci.. 172. 374, 1995. 

Establishment of solid/solution equilibria was followed as a function of time. Resulting equilibrium solutions were filtered through 0.45 pm filters, which might not have been sufficiently effective to retain small colloids. On the other hand, concentrations of dissolved Zr in the equilibrium solutions were determined by complexometry, which wouid not detect colloidal Zr. The solubility data were interpreted by presence of the dominant solution species Zr(OH)j and Zr2(OH) with complexation constants determined from the potentiometric titrations, using solubility constants of Zr(OH)4 as the only fitting variable. However, as can be seen in Figures D-6 to D-9 the experimental data can be equally well fitted by presence of polymeric species, for example by the presence of the two tetramers Zr (OH) and Zr4 (OH) 5. The results were not substantially influenced by NO3 complexation. In most cases, the contribution of NOj complexes represented less than 1% of the total speciation. A maximum of 17% N07 complexes is predicted for the most acid medium in 2 M NaN03. 

Among the six interfacial variables discussed in this section, the surface charge density oo, the surface potential (fo, and the potential at the OHP fd (usually called the diffuse layer potential), are most important in characterizing interfacial properties. The three remaining variables (i.e., ap, /p, and Od) can be estimated using Eqs. (5), (7), and (8) if oo, and /rf are known exactly. ao can be determined experimentally by the potentiometric titration method, and detailed explanation of the potentiometric titration is given, for example, by Yates [10]. The estimate of fo for the ceramic powder/aqueous solution interface is discussed in the next section, yd is perhaps the most important interfacial electrochemical parameter since it is closely correlated with the kinetic stability of a given colloidal suspension and it can be conveniently determined (approximately) experimentally. 

Fig. 12. Number of acidic groups determined from Boehm titralion vs potentiometric titration. Reprinted with permission ftom LI. Sakme and T.J. Bandosz, J. Colloid Interf Sci. 240 (2001) 252...

Iso- and Hetero-polyanions. Potentiometric titrations of H against WO ions have shown that the product formed in the first 0.01 s of reaction is not paratungstate A, [HW Oji] ", nor any other discrete ion intermediate between this and WO , but is a mixture of a number of ill-defined products. These may be colloidal hydrated W oxides formed very rapidly in local regions of high acidity before complete mixing can occur and which are converted into [HW602i] in ca. 1 s. Steps in the aggregation of [M04] (M = Mo or W) ions have also been studied by cryoscopy, spectrophotometry, and pH measurements. ... 

FIGURE 5.18 The determination of proton surface charge from potentiometric data by comparing a titration of the colloidal suspension (squares) with one of the support electrolyte alone (circles). 

FIGURE 5.26 Potentiometric titration curves of Mn02 (3.33 g L 214 g"i) in the presence of different concentrations of phosphate. The pH was initially adjusted to 3.0 with HNO3. (Reprinted from J. Colloid Interface Sci., 301, Mustafa, S. et al., pH effect on phosphate sorption by crystalline Mn02, 370-375. Copyright 2006, with permission from Elsevier.)... 

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