The Addition of Polar Organic Solvent Vapors During the Analysis of Proteins by DESI-MS
- PDF / 1,364,250 Bytes
- 5 Pages / 595.276 x 790.866 pts Page_size
- 48 Downloads / 172 Views
J. Am. Soc. Mass Spectrom. (2019) DOI: 10.1007/s13361-019-02345-w
SHORT COMMUNICATION
The Addition of Polar Organic Solvent Vapors During the Analysis of Proteins by DESI-MS Roshan Javanshad, Tara L. Maser, Elahe Honarvar, Andre R. Venter Department of Chemistry, Western Michigan University, Kalamazoo MI 49008-5413, USA
Abstract. Exposure of electrospray droplets to organic vapors was shown to dramatically reduce alkali-metal adduction on protein ions and shift protein charge states. Since DESI-MS is affected by similar adduct species as ESI-MS and shares similar ionization mechanisms, polar organic vapor additives should likewise also improve the DESI-MS analysis of proteins. Here the DESI spray was exposed to a variety of polar organic vapor additives. Head space vapors of polar organic solvents were entrained in nitrogen gas and delivered to the atmosphere inside a semi-enclosed plastic enclosure surrounding the spray plume. The vapors of acetone, acetonitrile, ethyl acetate, methanol, and water were investigated. Vapor dependent effects were observed with respect to changes in protein charge state distributions and signal intensities. With ethyl acetate vapor addition, the signal intensities of all proteins investigated were significantly increased, including proteins larger than 25 kDa such as carbonic anhydrase II and bovine serum albumin. Keywords: DESI, Protein, Vapor, Polar organic vapor, Ambient ionization, Imaging, Ethyl acetate, ESI, Desorption, Electrospray ionization Received: 2 July 2019/Revised: 23 September 2019/Accepted: 25 September 2019
Introduction
I
mplementations of desorption electrospray ionization mass spectrometry (DESI-MS) have been disproportionately in favor of direct/ambient analysis of smaller molecules such as metabolites and lipids, since analysis of larger molecules such as proteins by DESI-MS has been challenging [1, 2]. However, with the continuous efforts towards improving DESI-MS of proteins, this technique is rapidly becoming a powerful tool for direct analysis of large proteins (> 25 kDa) from complex mixtures. Solvent additives such as ammonium bicarbonate [3] and serine [4], or delayed-desorption-DESI [5] and combinations of these approaches have aimed to address supposed problems with the slow kinetics of protein dissolution during the analysis of proteins by DESI. Roshan Javanshad and Tara Maser contributed equally to this work.
Correspondence to: Andre Venter; e-mail: [email protected]
Another powerful approach entails coupling of DESI-MS to ion mobility which now allows for imaging of small proteins and peptides directly from tissue samples [6, 7]. The addition of polar organic vapors into the spray chamber or curtain gas during ESI analysis was shown to enhance electrospray ionization of proteins and peptides. Under such conditions, a reduction of alkali metal adduction was observed together with changes in protein charge states typically to lower charge values [8–10]. The addition of polar organic vapors such as acetonitrile, acetone, ethyl acetate, wate
Data Loading...