Potentiometric properties

The acid-base properties of isoxazole and methylisoxazoles were studied in proton donor solvents, basic solvents or DMSO by IR procedures and the weakly basic properties examined (78CR(Q(268)613). The basicity and conjugation properties of arylisoxazoles were also studied by UV and basicity measurements, and it was found that 3-substituted isoxazoles were always less basic than the 5-derivatives. Protonation increased the conjugation in these systems (78KGS327). 

The ligand pATa values and transition metal chelate stability constants of arylisoxazoles were detected photometrically and the stability of the complexes studied (79JlCi25i). 

The pKa values of a number of isoxazoles have been reported and again the weakly basic nature of the ring, being less than oxazole, is demonstrated (see Table 3) (7iPMH(3)i. p. 23). 

Aminoisoxazoles can be determined photometrically by reaction with sodium 1,2-naph-thoquinone-4-sulfonate and selective extraction of the resulting dye into CCI4 for absorbance measurements. This class of compound can be determined in the presence of sulfonamides, sulfanilamides, hydroxylamines and other select amines (74MI41610). 

Polarographic studies on haloisoxazoles in anhydrous DMF containing R4N were performed and the magnitude of the half-wave potentials were recorded. Cleavage of the C—X bond was faster in phenylhaloisoxazoles than in halobenzenes. Substitution patterns affected the reduction (79ZOB1322). 

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When we previously investigated the potentiometric properties of carefully purified plasticizers of low polarity, no EMF responses were observed, whereas for a more polar solvent (nitrobenzene), transient EMF responses were obtained [55,59]. Because of this large difference, we were also interested in the combined SHG and EMF response of more polar ion-exchanger membranes. As previously, we used nitrobenzene for this purpose. 

There is experimental evidence to support the estimate that t/H = t/Na in this system. In the research of Travers and one of the present authors (2), a study of the complexation of divalent metal ions by poly-methacrylic acid (PMA) showed that deviation from ideality with a of the divalent ions exposed to the same potential as the H+ ion was described exactly by the deviation term deduced from the potentiometric properties of the PMA. Additional evidence for this estimate is available in the ion-exchange literature (3,4,5). At a relatively low cross-linking percentage (2 wt % divinyl benzene) j/h is about equal to t/Na> as evidenced by the ion-exchange distribution of Na+ and H+ between a polystyrene sulfonate-based resin and a simple dilute electrolyte mixture of Na+ and H+ (Na H+, X"). The selectivity coefficient measured over the complete composition range of the resin deviates very little from unity to demonstrate this as an experimental fact (KHNa = 1.02 zt 0.02... 

Since Merle s data indicate that deviation from ideality of the charged species is negligible in the gel, contrary to expectations derived from the preceeding analysis, we reexamined the potentiometric properties of the flexible carboxymethyldextran gel system (Sephadex CM-50) studied by Merle. We also carried out a parallel investigation of the much more rigid PM A resin (IRC-50) cross-linked with approximately 5 wt % divinyl benzene. The titrations of these polymers with standard b,ase were made in the presence of sodium polystyrene sulfonate. The pH and pNa of the solution phase and the volume (Vp) of the gel (resin) phase were measured at selected a values covering the complete neutralization range. 

To assist computation of the degree of dissociation of the Sephadex and IRC-50 at the lower pH values, the activity coefficient of hydrogen ion in the presence of the polystyrene sulfonate was determined by examining the potentiometric property of 0.001M reagent-grade acetic acid from Fisher in the presence of 0.03, 0.06, and 0.09M NaPSS (mol wt 500,000). At each polystyrene sulfonate concentration a unique activity coefficient (0.300, 0.290, and 0.290, respectively, in 0.03, 0.06, and 0.09M NaPSS), essential for the resolution of the acid dissociation constant, was resolved by this approach. 

Dutton and co-workers 20,4 ) detected, in addition to cytochromes b and 6t, a cytochrome b-like species with the a band at 558 nm at room temperature having the Eo value of about -f-130 mV at pH 7.2 in beef heart mitochondria and submitochondrial particles from pigeon heart. Berden and co-workers (43,46) also reported type b cytochrome with the Eo of -)-154 mV at pH 7.2 in beef heart mitochondria, but the absorption maximum was at 562 nm instead of 558 nm. It is not known whether these two are the same species and/or identical with the reported type b cytochrome in complex II or chromophore 558 in complex III (24). A summary of the spectral and potentiometric properties of type b cytochromes proposed to exist in mitochondria is given in Table III. 

Q7. Zotti, G., S. Zecchin, and G. Schiavon. 1999. lonochromic and potentiometric properties of the novel polyconjugated polymer from anodic coupling of 5,5 -bis(3,4-ethylenedioxy)thien-2-yl)-2,2 -bipyridine. Chem Mater 11 3342-3351. 

Cosofret W, Erdosy M, Raleigh JS, Johnson TA, Neuman MR, Buck RP. Aliphatic polyurethane as a matrix for pH sensors effects of native sites and added proton carrier on electrical and potentiometric properties. Talanta 1996 43(1) 143-51. 

Amides can be titrated direcdy by perchloric acid ia a nonaqueous solvent (60,61) and by potentiometric titration (62), which gives the sum of amide and amine salts. Infrared spectroscopy has been used to characterize fatty acid amides (63). Mass spectroscopy has been able to iadicate the position of the unsaturation ia unsaturated fatty amides (64). Typical specifications of some primary fatty acid amides and properties of bisamides are shown ia Tables 5 and 6. 

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

In cases where it proves impossible to find a suitable indicator (and this will occur when dealing with strongly coloured solutions) then titration may be possible by an electrometric method such as conductimetric, potentiometric or amperometric titration see Chapters 13-16. In some instances, spectrophotometric titration (Chapter 17) may be feasible. It should also be noted that ifit is possible to work in a non-aqueous solution rather than in water, then acidic and basic properties may be altered according to the solvent chosen, and titrations which are difficult in aqueous solution may then become easy to perform. This procedure is widely used for the analysis of organic materials but is of very limited application with inorganic substances and is discussed in Sections 10.19-10.21. 

Electrochemical sensors play a crucial role in environmental and industrial monitoring, as well as in medical and clinical analysis. The common feature of all electroanalytical sensors is that they rely on the detection of an electrical property (i.e., potential, resistance, current) so that they are normally classified according to the mode of measurement (i.e., potentiometric, conductometric, amperometric). A number of surveys have been published on this immense field. The reader may find the major part of the older and recent bibliography in the comprehensive reviews of Bakker et al. [109-111]. Pejcic and De Marco have presented an interesting survey... 

SECM employs a mobile UME tip (Fig. 3) to probe the properties of a target interface. Although both amperometric and potentiometric electrodes have found application in SECM, amperometry - in which a target species is consumed or generated at the probe UME - has found the most widespread use in kinetic studies at liquid interfaces, as... 

The design of bioeompatible (blood compatible) potentiometric ion sensors was described in this chapter. Sensing membranes fabricated by crosslinked poly(dimethylsiloxane) (silicone rubber) and sol gel-derived materials are excellent for potentiometric ion sensors. Their sensor membrane properties are comparable to conventional plasticized-PVC membranes, and their thrombogenic properties are superior to the PVC-based membranes. Specifically, membranes modified chemically by neutral carriers and anion excluders are very promising, because the toxicity is alleviated drastically. The sensor properties are still excellent in spite of the chemical bonding of neutral carriers on membranes. 

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