A comparison of the electrochemical stabilities of metal, polymer and graphite coated nanospray emitters

Abstract

Chronoamperometry (CA) and cyclic voltammetry (CV) were used to compare the electrochemical behavior of metal, polymer and graphite coated nanospray emitters. It is shown that electrochemical reactions occurring at the emitter surface limit the lifetime of the noble metal coated nanospray emitters while the graphite coated nanospray emitters show good electrochemical stabilities. Although the surface of the graphite coated emitters may be passivated at positive potentials, the conductive coating is not lost as for the noble metal coated nanospray emitters. The graphite coated nanospray emitters still produced a stable nanospray signal despite the presence of a passivated surface. The polymer (i.e. polyaniline) coated nanospray emitters showed very low electrochemical activity and could not be thoroughly tested by CA. The relative short lifetimes seen in the electrochemical tests are qualitatively comparable with those obtained in nanospray experiments, in which only the outmost tip of the emitter is electrochemically active. However, the electrochemical stress during CA far exceeds the stress during ESI, which implies that CA can be used to perform quick and simple estimates of emitter stabilities. To our knowledge, this is the first time the electrochemical behavior of metal, polymer and graphite coated nanospray emitters has been compared.

Electrochemical Aspects of Mass Spectrometry: Atmospheric Pressure Ionization and Ambient Ionization for Bioanalysis

“…As such, careful selection of emitter material, which might include noble metal‐, graphite‐, and polymer (i.e. polyaniline)‐ coatings, should be made such that emitters are stable and do not degrade in the range of solvent oxidation potentials ,. To minimize unintended consequences, coated capillaries can be avoided altogether and can be replaced with fused silica emitters with an upstream electrical contact .…”

“…polyaniline)-coatings, should be made such that emitters are stable and do not degrade in the range of solvent oxidation potentials. [77,78] To minimize unintended consequences, coated capillaries can be avoided altogether and can be replaced with fused silica emitters with an upstream electrical contact. [79] By accounting for inherent electrochemical processes of ESI, electrolysis properties can be either avoided or exploited.…”

A soft on‐column metal coating procedure for robust sheathless electrospray emitters used in capillary electrophoresis‐mass spectrometry

“…The latter methods produce very stable sheathless ESI emitters with exceptional lifetimes of over 300 h of continuous use [27]. Thin, smooth metal films facilitate the electrospray process by creating a high surface tension at the very small contact area of the eluent with the electrode.…”

“…The high electric field strength leads to sputtering of the coating, as well as electrochemical reactions at the interface, mainly electrolysis of water in the positive spray mode. The use of sheathless electrospray emitters is therefore limited by short lifetimes that are typically up to 100 h for standard electrospray and 6 h for nanospray [26,27]. In addition, gas formation caused by solvent oxidation and corrosion of the conductive metal surface can result in mechanical and oxidative stress on the coating.…”

Electrochemical ionization and analyte charging in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source

“…For the case of electrochemical reactions occurring at the electrodes, transport processes become important to deliver the ions from the surface to the bulk reservoir where adducts are formed. Several investigations into the importance of electrochemistry in ESI have been presented in the literature [10,15–18,22–23], in which the ion source is treated as a controlled current electrochemical flow cell [16,18,24–26]. In this electrolytic cell, an oxidation/corrosion reaction is occurring at the electrode surface, consuming electrons and producing positive ions.…”