Untersuchungen zum Retentionsmechanismus von Anionen in der zwitterionischen Ionenchromatographie

The subject of this work is ion chromatography with zwitterionic functionalization of the stationary phase, called zwitterionic ion chromatography (ZIC). After giving a first and clear definition of the method, a certain choice of analytes, eluent species and eluent concentration range is made. A high capacity, sulfobetaine functionalized material is synthesized and used as a stationary phase for zwitterionic ion chromatography. Systematic variation of these parameters succeeds in an extensive collection of retention data, which is used for the subsequent development of a retention model. The retention times of all analytes increase with increasing eluent concentration, regardless of the eluent species used. After standardization, the majority of the analytes show an almost identical dependence of the retention on the eluent concentration. The selectivity of the system is subject to only slight changes within the parameter variation. Overall, the system exhibits a high constancy in the elution order, while also showing a clear correlation to the Hofmeister series and the hydration properties of the analytes. Based on the results, previously postulated models describing the mechanism of zwitterionic ion chromatography are abandoned. An alternative proposal for a novel retention mechanism for the separation of ionic analytes using a ZIC system is elaborated. The retention behaviour of anions in ZIC systems is described best by assumption of a partitioning mechanism, where water plays a crucial role due to the dependence of the partitioning coefficients of the analytes on their hydration. In the following, this special mechanism will be called "ion partitioning chromatography".