Capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI-MS) as a powerful tool for trace element speciation

The on-line coupling of capillary electrophoresis (CE) and electrospray ion ization mass spectrometry (ESI-MS) for speciation analysis is entailed with a number of difficulties due to technical and methodical reasons. The opti mization of several parameters in order to provide stable operating conditi ons are illustrated in detail: the positioning of the CE capillary, the CE buffer system, the concentration sensitivity and the detection mode. Additi onally, off-line ESI-MS investigations of metal species with different stab ilities were carried out in order to assess the influence of the ESI-proces s on the analyzed samples. It turned out, that metal ions and weak metal co mplexes may undergo gas-phase ligand replacement and intramolecular charge transfer reactions. Therefore, the structure of species will be altered. Co valent organometallic compounds and strong metal complexes, on the other ha nd, will not be altered and will be detected as charged molecular ions and/ or as charged ion-solvent clusters. Examples of different compounds illustr ate this fact.