Alkali halide—acid amide interaction in gas chromatographic stationary phases

Abstract

Specific interaction occuring between an alkali-metal halide and an acid amide in a gas chromatographic stationary phase has been investigated by using nine alkali-metal-halide-containing polyethylene glycol stationary phases and nine aliphatic acid amides as samples solutes. The magnitude of the interaction is evaluated in terms of excess free energy of transfer ▪ for each combination of halide and amide used. A discussion is presented of the dependence of ▪ on the change in ( i) the polarity of the stationary phase, ( ii) the concentration of the halide in the stationary phase, ( iii) the ionic radii of the cations and anions of the alkali-metal halides, and ( iv) the chemical structure of the amide molecule. It is suggested that the solubility of an alkali-metal halide in the stationary phase and the dipole moment of the amide molecule contribute to the change in solute retention in alkali-metal-halide-containing columns. The utility of the findings is demonstrated by the fact that diacetamide and butyramide are eluted from a column of polyethylene glycol 20,000 containing lithium chloride in the reverse order of their elution from an analogous, but salt-free, column.