Capillary Electrophoresis and its Basic Principles in Historical Retrospect. Part 4. Svante Arrhenius´ Electrolyte Dissociation. From 56 Theses (1884) to Theory (1887)

Since the main interest of Svante Arrhenius, a student at Uppsala University, was the electrical conductivity of highly dilute electrolyte solutions, which had not yet been determined at the beginning of the 1880s, he decided to determine experimentally the molecular conductivities of aqueous solutions of about fifty electrolytes and their dependence on the dilution. In his dissertation, which he began in the winter of 1882/1883, he summarized his results and considerations in 56 "theses". He observed that strong acids had a high molecular conductivity, which increased only slightly with increasing dilution. Weak acids, in contrast, had low molecular conductivities, but these increased abruptly above a certain dilution. Arrhenius' innovative hypothesis was that electrolyte molecules are composed from two parts, "an active (electrolytic) and an inactive (non-electrolytic) part," with the proportion of the active part increasing with increasing dilution at the expense of the inactive part. Moreover, the electrically active part, which conducts electricity, was also the chemically active part. Arrhenius introduced the activity coefficient, later quoted as the degree of dissociation, which indicated the proportion of active molecules to the sum of active and inactive molecules. He tentatively related activity coefficient to molecular conductivity. He assumed that the higher the activity coefficients of different acids at the same equivalent concentrations, the stronger they are. Arrhenius tested his hypothesis taking the heat of neutralization of acids with a strong base measured by Thomsen and Berthelot. Strong acids developed the highest neutralization heats, i.e., the activation heat of water, since they consisted entirely of active H+ and OH- ions, which combined to inactive H2O. Weak acids developed correspondingly less. The established parallelism between the molecular conductivities of acids and their heats of neutralization was the first proof of Arrhenius' hypothesis. He relied on thermochemistry and completed his dissertation. He presented his dissertation in June 1883 and published it in 1884 to obtain his doctorate. At that time, Wilhelm Ostwald was investigating the affinities of acids to bases, i.e. the intensity of the effects of acids on the rates of reactions they cause. He took the rate constants as a measure of the relative strength of the acids. After receiving Arrhenius' thesis, he measured the acid´s molecular conductivities and found a remarkable proportionality to the reaction rate constants of the hydrolysis of methyl acetate and the inversion of cane sugar caused by them. This was the second proof of Arrhenius' hypothesis, based on the results of chemical kinetics. A memoir presented in 1885 by J. H. van 't Hoff on the analogy between the osmotic pressure of a highly dilute solution separated from the pure solvent by a semipermeable membrane and the pressure of an ideal gas containing the same number of particles as the solution led to probably the most convincing proof of the Arrhenius hypothesis. This analogy corresponded to Avogadro's well-known law, which is PV=RT. He found that the pressure for non-conductors such as glucose followed this law, but was higher for electrolytes. This deviation was accounted for by the van 't Hoff factor i, which indicates into how many particles the solute - at least partially - has dissociated, so that the modified law is PV=iRT. The factor i could be deduced from Raoult's freezing point depression, and could also be calculated using Arrhenius' degree of dissociation α. The degree of dissociation, in turn, was determined from the ratio of the conductivity of a dilute electrolyte solution and that under limiting conditions. The agreement found between the factors i determined by the two independent methods was the third proof of the Arrhenius hypothesis. There was a fourth proof, namely the additivity of physical properties. With these four nonelectrical and independent proofs, the 56 theses of Arrhenius' dissertation became the groundbreaking theory of dissociation of substances dissolved in water, which he published in 1887. In 1903 the Nobel Prize in Chemistry was awarded to him "in recognition of the extraordinary services he has rendered to the advancement of chemistry by his electrolytic theory of dissociation”

Gas Chromatography and Analysis of Binding Media of Museum Objects: A Historical Perspective

This contribution covers the major historic milestones of the evolution of gas chromatography (GC) from its beginnings to its current status as one of the most powerful analytical separation techniques, and demonstrates simultaneously how this technique has enabled and continuously improved the analysis of organic binding media in objects of cultural heritage. After an introduction into the basics of chromatography, the development of GC is traced from its emergence in the late 1800s as a mere preparative technique through a period of relative stagnation into the mid of the 20th century. Then, the 1950s are covered by highlighting the major advances in theory and technology within this decade, all of which contributed to firmly consolidate the status of GC as a modern analytical separation technique. From there the maturing of GC is followed through the 1960s up to the present days, a period being marked by the transition from packed to capillary columns; the essential adaptation of injection and detection devices; the replacement of glass by fused silica as column material; major progresses in stationary phase chemistry; and, finally, the advent of the hyphenation of GC with mass spectrometric detection devices. Throughout this survey, examples of applications of contemporary GC techniques to binding media analysis are discussed to provide an illustrative historic record of the continuous improvements achieved. The account will be closed with critical reflections on GC’s current relevance to and future role in the analysis of binding media in objects of cultural heritage.

Solubility of Tris(hydroxymethyl)aminomethane in Methanol + 1-Propanol Mixtures at Various Temperatures

Article on the solubility of tris(hydroxymethyl)aminomethane in methanol + 1-propanol mixtures at various temperatures

Solubility of Tris(hydroxymethyl)aminomethane in Water + Methanol +1-Propanol Mixtures at Various Temperatures

Article on the solubility of tris(hydroxymethyl)aminomethane in water + methanol + 1-propanol mixtures at various temperatures

Solubility of Sodium Acetate in Ternary Mixtures of Methanol, 1-Propanol, Acetonitrile, and Water at 298.2 K

Article on the solubility of sodium acetate in ternary mixtures of methanol, 1-propanol, acetonitrile, and water at 298.2 K

Temperature Dependence of Acidity Constants, a tool to affect separation selectivity in capillary electrophoresis

The mathematical models of migration and dispersion in capillary zone electrophoresis of small molecules form a sound basis for separation strategies of complex mixtures. It turned out that the key property is the effective mobility of the sample ions. To tune resolution parameters such as pH, complexation constants and ionic strength are widely used; temperature however is not although mobilities and pKa values depend in a more or less degree on temperature. From the temperature dependences of pKa values of a number of compounds listed in the literature a general rule can be derived: for carboxylic and inorganic acids dpKa/dT values are very small and the pKa values change less than ±0.05 units/10 K. Thermodynamically speaking, these compounds exhibit dissociation enthalpies close to zero. Phenols and amines, on the other hand, have systematically larger dpKa/dT values of about −0.1 to −0.2 units per 10 K (the results of dissociation enthalpies of 20–70 kJ/mole). Based on this classification, a distinction can be made between different situations in capillary electrophoresis: (i) selectivity changes with temperature are largely due to the temperature dependence of the pKa of the buffering compound in the background electrolyte, (ii) selectivity changes mainly result from the temperature dependence of the pKa of the sample ions, and (iii) temperature effects on the pKa values of both, sample and buffer play a role. This work demonstrates such effects on selectivity in capillary electrophoresis highlighting the fact that in some instances temperature can be used to fine-tune separations.Fil: Reijenga, Jetse C.. Eindhoven University of Technology; Países BajosFil: Gagliardi, Leonardo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Viena; AustriaFil: Kenndler, Ernst. Universidad de Viena; Austri