Colloid titration

Ueno, K. Kina, K. Colloid Titration—A Rapid Method for the Determination of Charged Colloid, /. Chem. Educ. 

The reaction of a positively charged polyelectrolyte with a negatively charged polyelectrolyte produces a precipitate, forming the basis for a precipitation titration. This paper provides an overview of colloid titrations, discussing... 

The extent of hydrolysis of the copolymers was determined by conductometric titration. The increase in carboxylate content was determined by difference, before and after hydrolysis. (The AMPS content of the polymers, where measured, was determined by colloid titration with poly [diallyl dimethyl ammonium chloride].)... 

Colloid (or polyelectrolyte) titration . Charge may also be measured volumetrically using the principle of colloid titration which relies upon the fact that polymers of opposite charge can be stoichiometric-ally charge titrated in aqueous solution. A cationic polyelectrolyte (C) can be titrated with an anionic polyelectrolyte in the presence of an appropriate indicator (I) as follows ... 

Wang, L.K. Process Control Using Zeta Potential and Colloid Titration Techniques, PB87-179099/ AS US Department of Commerce, National Technical Information Service Springfield, VA, 1984,... 

Ionic charges of the polymers were determined by photometric colloid titrations in some instances. A known amount of poly(diallyldimethylammonium chloride) was added to the polymer solution at a pH of 2.5. The excess poly(diallyldimethylammonium chloride) was titrated by poly(vinylsulfate) using the adsorption indicator methylene blue. The end point was detected by the photometric detector as the color of the solution changes from blue to violet. For anionic copolymers the colloid titration was conducted at pH values of 2.5 and 10.0 to determine the extent of modification. 

The reaction of acrylamide copolymers and taurine was studied at temperatures between 125° and 200° C, reaction time 2-7 hours, and taurine charge 10-100 mol% based on polymer. The substituted amide formation was determined by NMR and colloid titration. The C-13 NMR of the product exhibits carbonyls consistent with the formation of a secondary amide. The spectrum also exhibits two new methylene signals for the incorporated taurine at chemical shifts slightly different from the starting taurine. Additionally, the chemical shifts for the signals of taurine are pH dependent, whereas little change in chemical shift is observed for the signals of the incorporated taurine. The presence of sulfonate incorporated into the polymer was detected and quantitatively determined by colloid titration at pH 2.5. 

Mizote, A., Odagiri, H., Toei, K., and Tanaka, K. 1975. Determination ofcarboxylicacids(mainly galacturonic acid ) and their degree of esterification in industrial pectins by colloid titration with Cat-Floc. Analyst 100 822-826. 

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. 

Potential-determining ions are those whose equilibrium between two phases, frequently between an aqueous solution and an interface, determines the difference in electrical potential between the phases. Consider a Agl dispersion in water. There will exist some concentrations of Ag+ and I" such that the surface charge of the Agl particles is zero. This is called the point of zero charge (pzc). It is usually determined by a titration method (called a colloid titration). 

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. 

Figure 3.28. Illustration of a seminal colloid titration result obtained after pioneering work by E.J.W. Verwey and H. de Bruyn. Silver iodide in (l-l) electrolytes drawn curves 7 1 KNOg + NaNOg mixture, O NaClO, A NaNOg. The surface charge could not be exactly established because the surface area was not well known. pAg and units are convertible because Nemst s law applies. The (7 l)-KNOg + NaNOg mixture was chosen to suppress the liquid Junction potential (sec. F5.5d) with the salt bridge. Source Redrawn from data by J.A.W, van Laar, PhD Thesis. State Unlv. Utrecht (1952) E.L. Mackor. Rec. Trau. Chim. 70 (1951) 763, as collated by J.Th.G. Overbeek In Colloid Science Vol. 1, H.R. Kruyt, Ed., Elsevier (1952) 162. Older references include E.J.W. Verwey, H.R. Kruyt, Z. Phys. Chem. A167 (1933) 149 E.J.W. Verwey. Rec. Trav. Chim. 60 (1941) 887 and H. De Bruljn. Rec. Trav. Chim. 61 (1942) 5, 21.

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... 

Although colloid titration is the most usual and general method of measuring the surface charge as a function of pH, pAg, temperature, concentration of organic additives, etc.. It Is not the only one. A few alternatives are ... 

Electrokinetic charges (o ) can, under a number of conditions, be obtained from one of the electrokinetic techniques, as detailed in chapter 4. For simple surfaces (flat, homogeneous, no hairs) is probably close to o. Electrokinetics are therefore not alternatives to colloid titrations but rather serve as additional means of establishing the (counter-) charge distribution. Only in media of very low dielectric permittivity, where Stem layers are absent, is CT = (j -CT° a good approximation. 

Figure 3.32. Electrical double layer on silver iodide in IO m Na or K (1-1) salts. Comparison of results obtained by different authors, different techniques and different sols. Curves 1-5, potentlometric colloid titration curve 6, capacitance method for electrodes. References 1) E.L. Mackor, Rec. Trav. Chim. 70 (1951) 763 2) J.A.W. van Laar, PhD. Thesis, State Unlv, of Utrecht. NL (1952) 3) J. Lyklema, Trans. Faraday Soc. 59 (1963) 418 4) B.H. Bljsterbosch. J. Lyklema. J. Colloid Set 20 (1965) 665 5) B.H. Bljsterbosch, unpublished 6) J.H.A. Pleper, D.A. de Vooys. J. Electroanal. Chem. 53 (1974) 243. (Redrawn from B.H. Bljsterbosch, J. Lyklema, Adv. Colloid Interface Set 9 (1978) 147).

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. 

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