Colloidal titration method

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

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). 

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 ... 

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 J. Colloid Set 20 (1965) 665 5) B.H. Bljsterbosch, unpublished 6) J.H.A. Pleper, D.A. de Vooys.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. 

Terayama H. Method of colloid titration (a new titration between polymer ions). J Polym Sci 1952 8 243-253. 

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. 

Analytical Methods. Historically, the copolymer composition of cationic acrylic polymers has been measured by conductiometric (28), silver nitrate (29), or colloid titration (52, 53). Chromatographic methods have been reported for acrylamide monomer (54-56) however, no such methods have been employed for quaternary ammonium monomers. In this chapter, a new HPLC method (Nalco) is described for the simultaneous determination of both comonomers. Colloid titration is described in the next paragraph and was used only for comparison purposes. 

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. 

The results are given in Table 11.8. The table gives silica particle diameter calculated from the specific surface area obtained by the Sears titration method after soluble silica correction. Values obtained at 0.3% SiOa are subject to more error due to higher amount of silica monomer present relative to colloidal silica. Results obtained by electrodialysis nucleation and by acidification with H2SO4 are included for comparison. 

Materials. Dodecylpyridinium bromide was synthesized by treating fractionally distilled 1-dodecane bromide in dry pyridine for 12 hr. The crude surfactant was recrystallized twice from acetone followed by decolorization with active charcoal in methanol solution. The resulting white crystal is a monohydrate of DoPBr. The critical micelle concentration (CMC) in aqueous solution as determined by electric conductivity method is 17.4 mM at 30°C in agreement with literature. Calf thymus DNA (sodium salt, SIGMA) was used as received. Residual (nucleotide) concentration was determined by a colloid titration using poly(potassium vinyl sulfate) as a titrant and Toluidine Blue as an indicator. 4 Propionyl- a-cyclodextrin (prop- a-CD) used as a neutral carrier was prepared by esterification of a-cyclodextrin (Tokyo Kasei Co.) with propionic anhydride in dry pyridine at room temperature for 12 hr. The reaction mixture was poured onto ice to obtain a gummy product which was then dissolved in acetone and precipitated in cold water. The dissolution-precipitation was repeated three times. The hydrophobicized oc-CD is a white powder. 

FIGURE 6.51 Surface charge density for A-300 in the aqueous suspension (CsiO2=0.2 wt%) at 0.001 M NaCl as a function of pH (measured by titration method). (Adapted from J. Colloid Interface Sci., 260, Gun ko, V.M., Mikhailova, I.V., Zarko, V.I. et al.. Study of interaction of proteins with fumed silica in aqueous suspensions by adsorption and photon correlation spectroscopy methods, 56-69,2003c, Copyright 2003, with permission from Elsevier.)... 

Goddard ED. Substantivity through cationic substitution. Cosmet Toilet 1987 102 71-80. Hutter JM, Clarke MT, Just EK, Lichtin JL, Sakr A. Colloid titration a method to quantify the adsorption of cationic polymer by bleached hair. J Soc Cosmet Chem 1991 42 87-96. Aruchami M, Gowri N, Sundara-Rajulu G. Chitin deacetylases in invertebrates. In MuzareUi R, Jeuniaux C, Gooday GW, eds. Chitin in Nature and Technology. New York Plenum Press, 1986 263-268. 

Her has carried out a hitherto unpublished investigation of the rates at which extremely small particles of colloidal silica depolymerize to monomer both directly in the molybdic acid reagent and in dilute alkali in which the monomer is determined on separate samples by reaction with molybdic acid. The size of the particles was estimated from the specific surface area, which was determined by the Sears alkali titration method corrected for monomer. The measurements were made as the particles grew in size at pH 8.5 and also as they became aggregated at pH 5.9. 

Similarly, the basicity can be defined when an acid is converted by its conjugated base. This allows to define acidity and basicity in the same scale. A similar expression can be proposed for interaction of bases with Lewis sites. The amine titration method, described by Tanabe et al. [33], consists of titrating a solid acid suspended in benzene with -butylamine using an indicator. Although this technique is widely applied in the fields of colloids and soil sciences [31], it has many limitations to deduce gas-solid phenomena, the surface Hammett acidity function also having doubtful physical meaning [6]. 

Hydrolysis degree This is the proportion of acrylate monomer in the chains. This characteristic plays a key role in the viscosification mechanism, the adsorption and the precipitation behavior. Method colloidal titration. 

Initially used by Terayama for measuring the concentration of polyions in aqueous media [15], the method of colloid titration is based on complexation between oppositely charged polyions. For example, the titration of a polyanion with a polycation is ... 

More recently, McLean et al. [20] determined the pKa of individual fatty and resin acids by titration using a similar titration method to that of Kanicky and Shah [19]. The values, which they termed colloidal p/fa-values , were slightly lower than those obtained by Kanicky and Shah, especially for the unsaturated C-18 acids. The differences were, however, not discussed. Resin acids gave pKa-values of 6.2-13, values that are in the range of earlier reported values [21-23]. 

EXPERIMENTAL PROCEDURES AUTOMATED TURBIDIMETRIC TITRATION. A method for the automated aqueous turbidimetric titration of surfactants has been published (10) in which anionic surfactants are titrated against N-cetylpyridinium chloride to form a colloidal precipitate near the equivalence point. N-cetylpyridinium halides have a disadvantage in that they have the tendency to crystallise out of solution (15), consequently the strength of the solution may alter slightly without the knowledge of the operator, also the crystals suspended in solution may cause damage to the autotitrator. In view of these drawbacks hyamine was preferred as the titrant. 

EMULSION MECHANISM. The above results show that the indicator was unnecessary because the method is essentially a turbidimetric one. However, the occurence of a sharp minimum in the titration curve at low salt concentrations, suggests that the formation of a colloidal precipitate is not the underlying mechanism for the turbidity. Consequently, efforts were made to clarify the underlying physico-chemical mechanism of the titration. 

Ruzic [278 ] considered the theoretical aspects of the direct titration of copper in seawaters and the information this technique provides regarding copper speciation. The method is based on a graph of the ratio between the free and bound metal concentration versus the free metal concentration. The application of this method, which is based on a 1 1 complex formation model, is discussed with respect to trace metal speciation in natural waters. Procedures for interpretation of experimental results are proposed for those cases in which two types of complexes with different conditional stability constants are formed, or om which the metal is adsorbed on colloidal particles. The advantages of the method in comparison with earlier methods are presented theoretically and illustrated with some experiments on copper (II) in seawater. The limitations of the method are also discussed. 

Many of the studies, from which our current understanding of reactions at the oxide-electrolyte interface has developed, were based on titrations of colloidal suspensions of oxides. The key to resolving questions left open by this work lies in the study of better defined oxide surfaces, the examination of a particular interface by many different experimental methods, and the development of mathematical methods for interpreting the data. 

A rapid method of dealing with the precipitated selenium is to wash it and dissolve it in a cold saturated solution of sodium sulphide. The red colloidal solution obtained can be titrated with a standard potassium cyanide solution,7 the end-point being marked by a change of colour from red to yellow ... 

In volumetric analysis, hydrophilic colloids alter the end point, e.g., in a titration of HC1 and NaOH, the amount of deviation in the end point is increased with increasing amounts of colloids. In the volumetric estimation of silver by Mohr s method, the phenomenon of adsorption comes into being. 

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