Potentiometric titrations technique

The experimental approaches used to characterize ion-pair partitioning are cyclic voltammetry and potentiometric titration. Cyclic voltammetry is overall more powerful, but requires special instrumentation which is not commercially available as a ready-to-use set-up. For this reason the potentiometric titration technique has been more widely used. 

Tab. 4.1 Partitioning of ionizable drugs (see pKa) into small unilamellar vesicles (SUVs) of DOPC and into octanol for uncharged and charged species, determined by the potentiometric titration technique, compared with their intestinal absorption (%) at the doses indicated. (Adapted from Tab. 2 of ref. 16)... 

In contrast to direct potentiometry, the potentiometric titration technique offers the advantage of high accuracy and precision, although at the cost of increased time and increased consumption of titrants. Another advantage is that the potential break at the titration endpoint must be well defined, but the slope of the sensing electrode response need be neither reproducible nor Nernstian, and the actual potential values at the endpoint are of secondary interest. In many cases, this allows for the use of simplified sensors. 

The different fractions obtained in this way may be analysed later by various methods. Liquids, sealed in sample tubes, and gases may be analysed by glc or GSC gases such as halogens, hydrogen halides or CO2 may be absorbed on various solids and subsequently analysed quantitatively by potentiometric titration techniques. Alternatively, analysis may be carried out in situ or small samples withdrawn for direct GLC or Gsc analysis. These techniques will be discussed in detail later. 

Lutzerrkirchen. J. et al. Limitations of the potentiometric titration technique in determining the proton active site density of goethite surfaces, Geochim. Cosmochim. Acta. 66. 3389. 2002. 

By the systematic work on the complexation equilibrium analyses of both weak acidic and weak basic polyelectrolytes, the Gibbs-Donnan approach is validated to provide deep insights into the complexation behaviors of linear polymer ligands. This concept does not need any adjustable parameter it only uses the logic of phase separation of polyelectrolyte aqueous solutions. The electrostatic nonideality (polyelectrolytic effect) observed in the acid dissociation equilibria of a polyion can directly be used to correct for the electrostatic nonideality for metal complexation. The potentiometric titration technique with concurrent measurements of pH and pM is most suit-... 

The solubilities of metal-oxides in molten chloride mixtures with addition of Ba2+ cations were determined by the potentiometric titration technique in Refs. [193, 194], The solubility products of MgO, NiO, CoO, MnO, ZnO and CdO in the BaCl2-KCl-NaCl (0.43 0.29 0.28) melt were found to be considerably higher than those in the molten KCl-NaCl equimolar mixture. The titration of Ca2+ cations with KOH in the said melt did not result in CaO precipitation, although according to the titration data Ca cations possessed appreciable oxoacidic properties. 

As mentioned in Section 3.7.1.2, there is a considerable scatter of solubility product values obtained in the molten KCl-NaCl eutectic using different methods of solubility determination. This disagreement in the solubility parameters may be explained by differences in the sizes of oxide particles whose solubility is to be determined. The difference in size causes the scatter of the solubility data according to the Ostwald-Freundlich equation and the employment of the isothermal saturation method, which implies the use of commercial powders (often pressed and sintered), leads to values which are considerably lower than those obtained by the potentiometric titration technique where the metal-oxides are formed in situ. Owing to this fact, the regularities connected with the effect of physico-chemical parameters of the oxides or the oxide cations should be derived only from solubility data obtained under the same or similar experimental conditions. However, this does not concern the dissociation constants of the oxides, since homogeneous acid-base equilibria are not sensitive to the properties of the solid phase of... 

Some features of potentiometric titration techniques in molten salts have been discussed. The automatic potentiometric titration described in details consists of the following. A rod, prepared as frozen K2Cr207 solution in the melt, was immersed into the melt containing a base with the constant rate, e.m.f data were recorded by die recording potentiometer. Such a routine may be used only for the detection of equivalence points in melts (with accuracy of 3.5 %). 

Citric acid complexes are soluble in water, but exist also water-insoluble complexes, their speciation and properties are depending on the oxidation state of metal cation, ionic strength, pH and temperature. Citrate complexes were investigated by a variety of experimental methods but evidently the potentiometric titration technique and spectroscopic methods prevailed. Available in the hterature investigations were directed mainly to citrate complexes with alkali metals and alkaline earth metals, Na, K+Ca and Mg % considering that they are major components of natural waters and biological fluids. Other important group of complexes is these with divalent and trivalent metal cations (Cu Ni +, Cu, Ni, Fe % Tl ). 

In response to the growing demand for an accurate interpretation of the complex multi-component equilibria involved in these systems, an extensive investigation was conducted using the potentiometric titration technique. The... 

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