Description
Methods of estimation of the system void volume in liquid-liquid chromatography are considered. Several well-established techniques for doing so that are widely recommended for reverse-phase HPLC are applied; however, none provides an unambiguous result. It is concluded that generalized conventions regarding the definition and determination of the void volume are required. For the systems in question in this work, the void volume was taken as that which gave an activity coefficient of unity for the mobile phase (here, methanol) in itself. infinite-dilution activity coefficients of aliphatic aldehydes, ketones, esters, and alcohols in methanol, water, and in mixtures of the two, were determined at 298 K by a combination of GLC and LLC techniques. Retentions of members of homologous series as a function of the number of carbon atoms and the mobile-phase composition were examined next, and a connection between retention behavior, the properties of the solutes, and the mobile phase was demonstrated. The relative contributions of the mobile and stationary phases to the LC separation of polystyrene oligomers was also studied; at least 17 homologs of 680M polystyrene were resolved. The preparation and chromatographic properties of a commercial silica LC packing, LiChrosorb SI 60, modified by surface incorporation of the individual cations H⁺, Li⁺, Cs⁺, NH₄⁺, Ag⁺, Mg²⁺, Co²⁺, Cd²⁺, and AI³⁺ , were examined. The test solutes were N,N-dimethylaniline, N-methylaniline, o-chloroaniline, o-nitroaniline, 2,4-dimethylaniline, m-chloroaniline, and 4-chloroaniline, for which the elution order varied substantially depending upon the cation-form silica employed. There was found to be some correlation between metal-ligand complexation constants and retentions for species for which the relevant data were available.
