Electrolytic corrosion of a stainless-steel electrospray emitter monitored using an electrospray–photodiode array system

Abstract

An electrospray–photodiode array (ES-PDA) system provides a useful alternative to ES-MS for the study of the electrolytic reactions that occur at the point of high voltage (or ground) contact in an ES ion source emitter. These electrolytic reactions charge-balance the loss of an excess of ions of one polarity in the charged ES droplets. This ES-PDA approach is particularly useful when the redox products are either neutral or difficult to detect in the gas phase unaltered. The latter is the case for the multiply charged metal ions derived from ES emitter corrosion. In this study, the anodic corrosion of iron in a stainless-steel ES emitter, detected optically as tris(1,10-phenanthroline)iron(II), [Fe(phen)₃ ]²⁺ , was found using the ES-PDA system to account for the majority of the charge-balancing current under the conditions used. The metal ions derived from emitter corrosion may be produced at levels sufficient to cause chemical background problems in ES-MS. Probably because of the relatively high concentration detection limits of ES-MS for multiply charged inorganic species, this problem has not yet been a major issue. One expects further use of ES as a nebulization source for ICP-AES and ICP-MS, because of the much better concentration detection limits of these techniques, to bring this issue to the forefront.