We present ITP-ESI-MS as a powerful tool for selective and sensitive analyses of anionic analytes. Our extended concept of ITP includes besides regular and freeacid ITP also self-maintained ITP in moving boundary systems. Easy theory describes the system properties including their stacking-window diagrams. Simple ESIcompatible electrolyte systems allow flexible tuning with very satisfactory results as demonstrated on the example of analysis of pharmaceuticals in waters.