Journal of Analytical & Bioanalytical Techniques
Open Access

Research Article

Unusual Post-Spray Proton Transfer to Protein Using Acetone Spray in Desorption Electrospray Ionization

Anna Warnet^1*, Nicolas Auzeil² and Jean-Claude Tabet¹

¹CSOB-Institut Parisien de Chimie Moléculaire (UMR 8232-UFR 926), CNRS, Université Pierre et Marie Curie, Paris, France

²EA4463: Laboratoire de chimie et toxicologie analytique et cellulaire, Université Paris Descartes, Faculté des Sciences Pharmaceutiques 4 avenue de l’Observatoire, Paris, France

*Corresponding Author:

Anna Warnet
CSOB-Institut Parisien de Chimie Moléculaire (UMR 8232-UFR 926)
CNRS, Université Pierre et Marie Curie (UPMC), 75005 Paris, France
Tel: 33-0-1-44-27-518
E-mail: anna.warnet@upmc.fr

Received date: August 26, 2015; Accepted date: October 01, 2015; Published date: October 07, 2015

Citation: Warnet A, Auzeil N, Tabet JC (2015) Unusual Post-Spray Proton Transfer to Protein Using Acetone Spray in Desorption Electrospray Ionization. J Anal Bioanal Tech 6:283. doi:10.4172/2155-9872.1000283

Copyright: © 2015 Warnet A, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Although acetone, in DESI ionisation generally leads to protein aggregation, in this study we report unexpected multi-proton transfers to lysozyme using this aprotic solvent as a charged spray. The DESI/acetone mass spectrum of lysozyme displays (i) a significant increase in the average charge state (Zav) and (ii) an incomplete H+/Ca2+ exchange, even though the overall contribution of cationised species is high, relative to those from spraying with a methanol/water solvent. This behavior is contrary to that expected from gas phase basicity, because GBacetone >GBmethanol. Decreasing the amount of sample deposited on the target (from 50 to 0.050 pmole) leads to a charge state increase, as seen in ESI, but not in the extent of cationisation. Moreover, the DESI signal duration is extended with sprayed acetone even though the total ionic current is significantly lowered. With a d6-acetone spray, no incorporation of a deuteron occurs, and the ionization yield is strongly decreased for multi-protonated lysoi+ lysozyme. This is in contrast to that observed with a d4-methanol spray, which displays a distribution of 48 deuterons in the lyso9+ ion as shown in high resolution with a LTQ/Orbitrap instrument. This unexpected behavior of the (CD3)2CO spray suggests that protons do not originate from acetone. Furthermore, dry argon post-flow on the target surface results in the lysozyme signal suppression, whereas with a humid argon flow, the signal is regenerated. On the other hand, an argon stream bubbling in heavy water, yields incorporation of several deuterons. The interpretation of this behavior is explained by considering the acetone radical ions at the surface of the primary droplets (and/or offspring droplets and/or at the wet sample surface), being able to react with ambient moisture (or with traces of water adsorbed at liquid phase). Under these conditions, enough protons are produced to generate multi-charged solvated lysozyme aggregates which then become desolvated in the reduced pressure in the skimmer area.

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