Electrolyte system strategies for anionic isotachophoresis with electrospray‐ionization mass‐spectrometric detection. 1. Regular isotachophoresis and free‐acid isotachophoresis

The subject of this work is the definition of a simple model based on general ITP theory that allows describing and predicting the behavior of ITP systems compatible with ESI ‐ MS detection. The model is exemplified by anionic ITP of weak acids that represent an interesting potential application field of ITP ‐ ESI ‐ MS . Suitable ESI ‐compatible electrolyte systems of very simple composition are proposed including a special free‐acid ITP arrangement. The properties of these systems are discussed using illustrative diagrams of their stacking windows. The use of anionic ITP ‐ ESI ‐ MS in negative‐ion ESI mode is reported for the first time and its suitability for sensitive trace analysis is demonstrated. The presented ITP ‐ ESI ‐ MS application example comprises a free‐acid ITP system formed of formic and propionic acids and direct injection analysis of ibuprofen and diclofenac in waters with quantitation limits of the order 10 −10 M.