Potentiometric behaviour titration

Anomalous titration curves for PLL in pure water are observed as illustrated by Figure 1 which shows the effect of various counterions on the potentiometric behaviour of PLL [12, 14]. A conformational change between a very compact form (stable at low a values) and an extended coil-like form clearly appears. Stabilization of the compact conformation is found to be more pronounced as the length of apolar chains of tetraalkylammonium counterion chains increases. The transition between the two forms, which is initiated at a critical oc of 0.15-0.20 (in the presence of Na" or K ), is shifted to higher values of a in the presence of tetraalkylammonium counterions attaining an of about 0.7 with bulky (and hydrophobic) N-tetrabutylammonium ions (Bu4N ). 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

Their electrochemical properties serve to regulate the coagulation rates, catalysis behaviour and electron transfer reactions of iron oxides (Mulvaney et ah, 1991). Two major methods of characterizing electrochemical behaviour are potentiometric titration and electrophoresis. 

V Surface Characterisation, A quantitative analysis of the amounts of PAA associated with the latices was obtained by conductometric titration and a qualitative analysis of its behaviour by potentiometric titration. Titrations were performed under a nitrogen atmosphere using a Radiometer Autoburette system and a M64 pH meter together with a Wayne Kerr B642 Bridge. 

Most polymers belonging to this class are water-soluble only in their protonated form. As a consequence, most potentiometric titrations of these polymers have been performed with OH starting from their hydrochlorides, either in water or in mixed solvents, such as water/dioxane, water/sulfolane, water/acetonitrile 64). Many poly[thio-l-(N,N-dialkyl-aminomethyl)ethylene]s are optically active, and in these cases ORD and CD techniques may be used to study their protonation behaviour, in addition to potentiometric techniques. 

The partitioning behaviour of an ionisable compound can also be followed directly using a two-phase potentiometric titration using commercial instrumentation (Sirius analytical Instruments) as shown by Avdeef et al. (1998). 

Thus, the highest oxides or chromium(VI) and molybdenum(VI) were established to destroy molten KN03 with subsequent evolution of N02 termination of this destruction resulted in stabilization of the pO values of the melt [67], This value determined by the method of potentiometric titration was found to reduce as the temperature of the melt was elevated considerably. Such a behaviour of the acidic solution in the nitrate melt was explained by the formation of nitrogen pentoxide, N2Os, or nitronium cation, NOj, in the acidic solution, together with the corresponding oxoanions of Cr(VI) and Mo(VI). Since the added acids are very strong, their reaction with the melt... 

The potentiometric titration routine is now considered to be the easiest way to obtain a lot of information on the behaviour of metal oxides in... 

The first section corresponds to the non-saturated solution characterized by a sharp pO decrease at small initial concentrations of a base-titrant the behaviour of the potentiometric titration curves under these conditions is dependent on the magnitude of the dissociation constant of the formed oxide. 

We shall now analyse some consequences of the obtained formula, which describes the behaviour of the E-pd dependence in different sections of the potentiometric titration curve. The first consequence concerns the onset of the metal-oxide precipitation the condition... 

One of the most probable reasons for such a behaviour of strongly acidic solutions in iodide-melts, under the potentiometric titration conditions is transfer of oxygen through the solid electrolyte membrane to the iodide-melt. The following processes could be assumed to occur in the said system. 

The fluoride complexes of the divalent ions from Mn(II) to Zn(Il) have been studied by potentiometric titration, using a fluoride selective electrode at 298.15 K and I = 1.0 M NaC104. Under the experimental conditions employed (25 cm 0.05 M metal(II) perchlorate solution was titrated by 10 cm 0.004 M NaF solution), only monofluoride complexes are formed but in rather low concentrations (at the end of titrations [NiF ] 2.2x10 M can be calculated). This yielded only a moderate effect (1-2 mV) in the measured electrode potential, therefore we estimate higher uncertainty in K ((2.2 1.0) for NiF in the present review, than suggested by the authors. The authors reported an anomalous stability sequence in the Mn(II)-Zn(II) series which does not fit an Irving-Williams type trend. This behaviour was later confirmed by several authors (see e.g., [83SOL/BON]). 

Baes and Mesmer s [1976BAE/MES] comprehensive survey and critical review of the hydrolysis of cations is the most frequently cited standard book on metal ion hydrolysis and widely accepted to represent the state of the art for long time after its publication. The authors have in most cases made their own analysis of previously published data and tested a number of different equilibrium models. The choice of models is based on the standard deviation of the experimental average number of coordinated hydroxide ions 0H However, one should complement this method by a calculation of the speci-ation in the various test solutions as done in the present review. Species that occur in low concentrations should be looked upon with suspicion as gradual changes in diffusion potentials and changes in the ionic medium may be erroneously interpreted as minor complexes. The discussion of the hydrolytic behaviour of thorium(IV) is based on the following potentiometric titration studies which are also included in the data evaluation of the present review ... 

Triblock and random polyampholytes based on DMAEM-MMA-MAA were examined for their phase separation behaviour [52]. Triblock polyampholytes have a much broader phase separation region than the random ones. The specific structure of PMAA-fc-PlM4VPCl with the excess of cationic or anionic blocks at the lEP is close to the structure of non-stoichiometric IPC. It is suggested that its nucleus consists of intraionic IPC surrounded by cationic blocks protecting it from precipitation [53]. ABC triblock copolymers of polystyrene-b/ock-poly(2-(or 4)vinylpyridine)-fc/ock-poly(methacrylic acid) were synthesized by living anionic polymerization [53 a]. Interpolymer complexation of the polyvinylpyri-dine and poly(methacrylic acid) blocks in the micellar solution was studied in relation to pH in solution by potentiometric, conductimetric and turbidimetric titration and in bulk by FTIR spectroscopy. 

As shown in Figure 5, in 40 and 50% methanol-water mixtures, the behaviour of PMA solutions becomes similar to that of PAA, i.e. there is no longer a detectable discontinuity in both potentiometric and viscosity titrations. It can thus be admitted that hydrophobic interactions are virtually destroyed and therefore the conformational behaviour of PMA follows directly the electrostatic repulsions between the carboxylic groups [10],... 

That the pyrimidine nucleus is linked to the thiazole nucleus through the nitrogen atom of the latter soon became apparent. A comparison of the behaviour of thiamine and its thiazole moiety towards certain chemical reagents indicated the presence of a quaternary nitrogen in the former. Moreover, upon potentiometric titration of thiamine with alkali it behaved exactly as an addition product (VIII) of VII and methyl iodide. 

In an attempt to clarify the effects of ionic and hydrophobic substituents on the polyelectrolytic behaviour of polysaccharides, potentiometric titrations and activity measurements of the counter-ions have been conducted on carboxy-methyldextrans containing either substituted carboxy-groups or benzyl groups. Dextran glass (10 M, dextran) attached to an alkylamine-bonded phase of glass has been used for the hydrophobic immobilization of enzymes. ... 

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