Studies on the separation of hydronium ion using surfactant-modified reversed-phase stationary phases and eluents containing an acidified electrolyte

Abstract

A further investigation of a chromatographic system allowing determination of hydrogen ions is reported. For this purpose an octadecylsilica column dynamically modified with sodium dodecylsulfate (SDS) or lithium dodecylsulfate (LDS) was used as stationary phase and a slightly acidified electrolyte (usually KCl)–SDS solution was used as the eluent. The concentration of SDS, KCl and the acidity of the eluent affected the structure of aggregates formed by the molecules of dodecylsulfate at the surface of the stationary phase. These aggregates of dodecylsulfate were found to be responsible for the appearance of a chromatographic peak attributed to the presence of H 3O + ions in a sample. Other cations in the sample could be separated in the same manner, permitting the simultaneous separation of monovalent cations from H 3O +. The detection limit for H 3O + ions was 2.25·10 −6 M using an eluent comprising 0.3 m M LDS, 50.0 m M KCl and 0.10 m M H 2SO 4. The proposed method is shown to be applicable for the determination of free H 3O + ions in aqueous solutions of strong acids.