Separation and quantitation of metal ions by 4-(2-pyridylazo)resorcinol complexation in capillary electrophoresis–electrospray ionisation mass spectrometry

The possibility of using capillary electrophoresis–electrospray ionisation (ESI)/MS to separate and quantify cobalt and iron was explored. It was necessary to tackle and overcome problems from different sources, some of them being rather unpredictable. The results obtained suggest the occurrence of oxidation processes of metal ions during the formation of the electrospray. The quantitative oxidation of cobalt(II) to cobalt(III), a process at our knowledge never described before, appears particularly interesting. The results obtained, though not optimised for sensitivity appear promising, since a limit of detection of the order of tenths of picograms was obtained. Further, from the comparison with the results obtained by optical detection, the use of CE–ESI/MS appears advantageous.