Dielectrometric titrations: nonquantitative reactions

Abstract

terminated prepolymer when this material was found to react with ethanol during the capping operation. This reaction caused a shift in elution volume of the material, confirming the presence of reactive end groups as opposed to unreacted polyol.The chromatogram of the prepolymer, shown as composite Peak C in Figure 4, was obtained by fractionation on the high permeability limit columns. The long tail in the high molecular weight region indicates that the prepolymer had an extremely broad molecular weight distribution. Although no suitable calibration of elution volume in terms of absolute molecular weight was obtained for this polyurethane, ratios of i V w / J T n and iVz/iRw could be estimated from a polystyrene calibration. By this means it was estimated nw/nn to be 15 and Rz/Rw to be 4.6 where ivn is the number average molecular weight, ,Vw is the weight average molecular weight and Rz is the "z" average molecular weight. ACKNOWLEDGEMENTThe authors acknowledge Hans W. Osterhoudt for his valuable guidance and the work of the Analytical Department of Armstrong Cork Company for its supplementary analyses of materials.

Nonlinear regression model for the representation of dielectric constants for binary aprotic solvents

“…Tommila and Murto (7) find that the rate of hydrolysis of ethyl acetate under acidic conditions reaches a maximum when dimethyl sulfoxide, used as a solvent, is present in a 1:2 molar ratio with water. Rammler and Zafforoni (8), studying the enzymic activity of trypsin in protein degradation, found similarly that the activity changes abruptly when the molar ratio of dimethyl sulfoxide to water reaches 1:2 and also that the loss of activity becomes irreversible at a lower ratio of 1:2.9. Jezorek and Mark (11) have measured the decay of anthracene and naphthalene anion radicals, prepared by polarographic reduction of the parent hydrocarbons, when water functions as a proton donor in the presence of various solvents, including dimethyl sulfoxide and dimethylformamide.…”

“…In addition the e value of a medium is one of the primary properties to be considered in selecting a solvent for potentiometric titrations in a nonaqueous medium (7). Similarly, by monitoring the changes in dielectric constant it is possible to determine the end point in titrations involving reactants and products with differing dipole moments, and this technique has been thoroughly explored by Megargle et al (8).…”

“…A variety of methods have been used to evaluate the interaction between dimethyl sulfoxide and water. These range from determining heats of mixing (2), viscosities of mixtures (2), and the velocity of sound in paper treated with mixtures of water and dimethyl sulfoxide (3) to measuring effects on the infrared (4) and nuclear magnetic resonance (1, 4-6) spectra of the water and rates of reactions, involving water as a reagent (7)(8)(9)(10)(11), when increasing amounts of dimethyl 1 Present address: Instito de Química, University Estadual de Campinas, Campinas, Sao Paulo, Brazil.…”

“…The kinetic methods (7)(8)(9)(10)(11) gave a direct indication of the effect of dimethyl sulfoxide on the reactivity of water in specific circumstances.…”

Hue‐shifting for accurate and precise quantification of biochemical substances using diagnostic test strips

“…However, they do not indicate the accuracy of regression models. To date, in the quantification of the chemical substances in samples relying on regression analysis, NMAE (or a similar error statistic as the indicator of accuracy) has seldom been considered 34‐36 . Nevertheless, as Table 1 and Figure 5 show, the statistics that indicate the reliability of coefficients and constants help users to find the most reliable and accurate measures consisting of a constant and coefficients.…”