The Story

Calin Znamerovschi joined my group to do a mass spectrometry study of the crown complexes of silver ion. He was using electrospray ionization, a rather new ionization method we had just installed on our triple quad. The responses for the silver ion and complexes did not match predictions from the complex formation constant by several orders of magnitude, assuming the peak areas were any indication of abundance.

If the discrepancy was due to difference in response factors, i.e. ionization efficiency, between the metal ion and the complexed metal ion, they were remarkably large. That intrigued me and stimulated my inquiry into why that should be the case.

In electrospray, the sample solution is formed into tiny, charged droplets. As they evaporate, the droplets release charge in the form of atmospheric ions—some of which, hopefully, are the material you would like to detect.

The analogies between these droplets and the mercury droplets I studied in graduate school, gave me some insight into how the response factor could be related to the surface activity of the ions in solution. This distinction between the ions on the droplet surface and those in the interior is shown in the illustration you selected for this category.

I used my proposed mechanism for ion formation to predict some response data published by Kebarle and Tang. The fit was excellent, and I had some great years refining our understanding of this, now indispensable process. Papers by Nadja Cech and Terri Quenzer further developed the ramifications of the “surface equilibrium” theory of ion formation. Recognition of these contributions came in the form of invitations to provide chapters in several books. They are among my most widely cited papers.

Papers and a patent regarding electrospray ionization

Coauthors and co-inventors involved in our work in electrospray ionization are Terri Constantopoulos (Quenzer), George Jackson, Ma’an Amad, Nadja Cech, Juan Fernandez de La Mora, Gary Van Berkel, Richard Cole, Manuel Martinez-Sanchez, John Fenn, and Jennifer Krone.

1997 A Predictive Model for ESI
1999 Effects of Salt Concentration
1999 Electrical Equivalence of ESI Needles
2000 Challenges Achieving Model
2000 Effect of Proton Affinities
2000 Relating Response to Nonpolar character
2000 Electrochemical Processes in ESI
2001 Detecting Epoxides
2001 Effect of Surface Affinity
2001 Practical Implications of ESI Studies
2001 Predicting Response from Retention Time
2002 Patent, Resistive stabilization of ESI
2006 ESI, How & When It Works