Colloidal titration method determination

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). 

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. 

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. 

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. 

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]. 

Lin, X.Y. Farhi, E., and Arribart, H., Determination of the isoelectric point of planar oxide surfaces by a particle adhesion method, J. Adhesion, 51, 181, 1995. McCafferty, E. and Wightman, J.P., Determination of the surface isoelectric point of oxide films on metals by contact angle titration, J. Colloid Interf. Sci., 194, 344, 1997. 

Finally pH, ionic thorium species and colloids were found to approach a steady state which is comparable to the solid-liquid equilibrium of amorphous Th(IV) hydroxide determined in [2002NEC/MUL] with the coulometric titration-LIBD method. 

Figure A-45 Experimental data determined in [2000BUN/1CNO], [2003NEC/ALT] for TI1O2 colloids using the titration-LlBD method. The solubility from oversaturation after precipitation of microciystalline Th02(cr, hyd) and from imdersaturation with crystalline Th02(cr) are compared to the solubility curves calculated for Th02(cr) and Th(OH)4(am) (from [2003NEC/ALT]).

Figure A-45 Experimental data determined in [2000BUN/KNO], [2003NEC/ALT] for Th02 colloids using the titration-LlBD method.676...

Similar to solid particles, colloidal dissolved substances, too, build up an ion cloud corresponding to the double layer model. In the case of colloidal dissolved substances, it is extremely difficult to shift the ion cloud in a reproducible manner for subsequent charge determination. This is why another method, the so-called charge titration, has been established in the paper industry. 

Pseudo steady-state titration was found to be a valuable method for the determination of stability of colloidal nanocrystals upon change of the pH in the solutions [56]. CdSe nanocrystals coated with hydrophilic deprotonated thiol (thiolate) ligands were studied systematically. For comparison, CdTe and CdS nanocrystals coated with the same types of ligands were also examined. The results showed... 

An alternative to standard acid-base titration is the mass titration, originally proposed by Noh and Schwarz (1989), consisting in the addition of the solid colloid to an electrolyte solution. As the solid is added, the solution pH changes, until it reaches a limiting value pH if the sample is pure, then this value corresponds to pH. o. However, if it contains acid or base impurities, these get dissolved and affect pH , which no longer is equal to pHg. Later on, Kallay and coworkers (Zalac and Kallay 1992 Preocanin and Kallay 2006) extended the method to account for the presence of impurities, combining the mass titration with a following acid-base titration in principle, both the pH g and the amount of impurities can be determined. 

There are many different ways to determine the size of colloidal silica. Surface titration by aqueous 0.10 M NaOH solution has been used since the 1950s Sears titration [10], and has become an industrial standard method to determine the surface area, and thereby particle size, of silica sols. 

For unmodified silica dispersions, the surface charge is the main stabilizing factor. Surface charge of colloidal siUca dispersions can be measured by cationic polyelectrolyte titration [54], The surface charge of two unmodified silica dispersions and the corresponding silane-modified siHca dispersions were made by titration of the said dispersions with a Polybrene solution, 4 g per liter. All silica dispersion had a concentration of 5 g SiO per liter. To compensate for the presence of soluble silicate species in the silica dispersions, the latter were quantitatively determined by using the ammonium heptamolybdate method [55]. 

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