Development of system suitability tests for ion-interaction chromatography of colorants on reversed-phase packing materials

Ion-interaction reagent (IIR) chromatography has been established as a highly selective and sensitive method for studies on ionic solutes in environmental and food analysis. This technique makes use of a mobile phase containing an ion-interaction reagent (alkylammonium phosphate) which, flowing in isocratic conditions, induces a modification of the stationary phase surface. The formation of an electrical double-layer adsorbed onto the original RP packing material permits the separation of anionic and/or cationic species. As an essential requirement for transferring of IIR methods, it is necessary to devise suitable conditions for validation of the methods. The present work describes the development of system suitability tests (SSTs) based on a group of red dyes as a model system, where the influence of a number of parameters has been examined, including: organic modifier percentage, mobile phase pH, alkylamine chain length, IIR concentration, column temperature, flow-rate, sample composition. Some factors affecting sample stability have also been explored. To extend the results, two yellow dyes were added to the mixture, to provide a group of peaks characterized by critical resolution. Standardized conditions are proposed to assess the suitability of a new column packing material for adequate resolution of the proposed system.