The effect of solvents on the extraction of lanthanoids with 18-crown-6 and trichloroacetate

The effect of solvents on the extraction of lanthanoids with 18-crown-6 and trichloroacetic acid was investigated for the solvents, 1,1,-dichloroethane, 1,2-dichloroethane, 1,1, 2,2-tetrachloroethane, chloroform, di-2-chloroethyl ether, and methylene chloride. Distribution coefficients (25 °C) normalized to the water solubility (wt./vol.) in the solvents correlated to the polarizability index (^*) for La³⁺, Ce³⁺, Pr³⁺, and Nd³⁺ with r values=0.93,0.93,0.95, and 0.98, respectively. The distribution coefficients for Nd³⁺ also correlated with the Hildebrand solubility parameter () (r=0.98). These correlations agree with the literature that for large ions, the extraction thermodynamic properties correlate with the polarizability index and Hildebrand solubility parameter.     

A Titration Microcalorimetric Study of the Effects of Halide Counterions on Vesicle-Forming Aggregation in Aqueous Solution of Branched-Chain Alkylpyridinium Surfactants

Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains. Copyright 2000 Academic Press.     

The development and application of capillary electrophoresis methods for food analysis

Capillary electrophoresis (CE) offers the analyst a number of key advantages for the analysis of the components of foods. CE offers better resolution than, say, high-performance liquid chromatography (HPLC), and is more adept at the simultaneous separation of a number of components of different chemistries within a single matrix. In addition, CE requires less rigorous sample cleanup procedures than HPLC, while offering the same degree of automation. However, despite these advantages, CE remains under-utilized by food analysts. Therefore, this review consolidates and discusses the currently reported applications of CE that are relevant to the analysis of foods. Some discussion is also devoted to the development of these reported methods and to the advantages/disadvantages compared with the more usual methods for each particular analysis. It is the aim of this review to give practicing food analysts an overview of the current scope of CE.