Protein-Glass Surface Interactions and Ion Desalting in Electrospray Ionization with Submicron Emitters

  • Zije Xia
  • Evan R. Williams
Research Article


Theta glass electrospray emitters can rapidly mix solutions to investigate fast reactions that occur as quickly as 1 μs, but emitters with submicron tips have the unusual properties of desalting protein ions and affecting the observed abundances of some proteins as a result of protein–surface interactions. The role of protein physical properties on ion signal was investigated using 1.7 ± 0.1 μm and 269 ± 7 nm emitters and 100 mM aqueous ammonium acetate or ammonium bicarbonate solutions. Protein ion desalting occurs for both positive and negative ions. The signal of a mixture of proteins with the 269 nm tips is time-dependent and the order in which ions of each protein is observed is related to the expected strengths of the protein–surface interactions. These results indicate that it is not just the high surface-to-volume ratio that plays a role in protein adsorption and reduction or absence of initial ion signal, but the small diffusion distance and extremely low flow rates of the smaller emitters can lead to complete adsorption of some proteins and loss of signal until the adsorption sites are filled and the zeta potential is significantly reduced. After about 30 min, signals for a protein mixture from the two different size capillaries are similar. These results show the advantages of submicron emitters but also indicate that surface effects must be taken into account in experiments using such small tips or that coating the emitter surface to prevent adsorption should be considered.

Graphical Abstract


nanoESI Submicron emitters Ion desalting Protein absorption Theta emitters Protein ion signal, Time dependence 



This material is based upon work supported by the National Science Foundation Division of Chemistry under grant number CHE-1609866. The authors also thank Dr. Anna Susa and Dr. Daniel Mortensen for helpful discussions.

Supplementary material

13361_2017_1825_MOESM1_ESM.pdf (1.1 mb)
ESM 1 (PDF 1172 kb)


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Copyright information

© American Society for Mass Spectrometry 2017

Authors and Affiliations

  1. 1.Department of ChemistryUniversity of CaliforniaBerkeleyUSA

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