The equilibrium constants, K, and enthalpy changes, // 0. for the 1:1 association reaction between chloride ion and a variety of proton donors, HR, have been determined at 30°C in sulfolane. Thermodynamic data for the association of Clwith substituted acetic acids as HR were also obtained at 25°C in acetonitrile, dimethylformamide, and dimethyl sulfoxide. The experimental methods used involved solubility and vapor-pressure measurements, proton NMR, and calorimetry. The order of increasing donor strength of HR based on 2/ (1) (kcal mol-1) in sulfolane is HCCI3 (-2.1) < HOH (-2.6) < HCH3O ~HCH3CO2 (-3.2) < HC6H50 (-3.6) < HCO2H ~HCF3CO2 (-4.0) « HC1 (-8.1). The enthalpy changes, A//S(HR), for the process HR(g) -» HR(1) were also determined. Comparisons of our // 1) and A//S(HR) data with reported AHr(g) values for the gas-phase reaction Cl-(g) + HR(g) -ClHR-(g) permit a complete analysis of the solvent effect on this hydrogen-bonding reaction. Both the change in the order of donor strength and the widening of donor strength range on passing from sulfolane to the gas phase are accounted for by differences in the solvation enthalpies AHS of both HR(g) and ClHR-(g). The calculated enthalpy change for Cl-(I) + HR(g) -C1HR-(1) appears to vary only slightly with the three solvents studied. This agrees with findings for other anion-molecule reactions with dipolar aprotic solvents.

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An electrochemical detector was designed and constructed, based upon a thin-layer cell with a working electrode prepared from carbon paste modi®ed with copper-(or silver-) exchanged zeolite particles. This electrode was then evaluated as a sensor for nonelectroactive cations in an electrolyte-free¯ow injection system and as an amperometric detector for suppressed ion chromatography. In the absence of supporting electrolyte, a higher signal-to-background ratio enhanced by about two order of magnitude the response obtained in electrolytic medium. Peak currents resulted from an important faradic component which was due to the electrochemical activity of the mediatorcontaining zeolites, while the capacitive counterpart was much lower. When applied to the analysis of alkali, alkaline earth metal and ammonium ions, in combination with a suppressed ion chromatography system, the zeolite-modi®ed detector gave rise to reproducible amperometric responses. This resulted in chromatograms comparable to those obtained simultaneously by using a conductivity detector in series, and any extra-column effects were never observed. The most sensitive responses were achieved when using zeolites displaying the largest pore size, the highest ion exchange capacity, and the most mobile mediator, to ensure the highest exchange rates for the analytes within the zeolite framework.