[ASAP] Proton Transfer Reactions for the Gas-Phase Separation, Concentration, and Identification of Cardiolipins

4 years ago

[ASAP] Proton Transfer Reactions for the Gas-Phase Separation, Concentration, and Identification of Cardiolipins

Caitlin E. Randolph, Kimberly C. Fabijanczuk, Stephen J. Blanksby, Scott A. McLuckey

Cardiolipin (CL) analysis demands high specificity, due to the extensive diversity of CL structures, and high sensitivity, due to their low relative abundance within the lipidome. While electrospray ionization mass spectrometry (ESI-MS) is the most widely used technology in lipidomics, the potential for multiple charging presents unique challenges for CL identification and quantification. Depending on the conditions, ESI-MS of lipid extracts in negative ion mode can give rise to cardiolipins ionized as both singly and doubly deprotonated anions. This signal degeneracy diminishes the signal-to-noise ratio, while in addition (for direct infusion), the dianion population falls within a m/z range already heavily congested with monoanions from more abundant glycerophospholipid subclasses. Herein, we describe a direct infusion strategy for CL profiling from total lipid extracts utilizing gas-phase proton-transfer ion/ion reactions. In this approach, lipid extracts are ionized by negative ion ESI generating both singly deprotonated phospholipids and doubly deprotonated CL anions. Charge reduction of the negative ion population by ion/ion reactions leads to an enhancement in singly deprotonated [CL – H]⁻ species via proton transfer to the corresponding [CL – 2H]^2–̅ dianions. To concentrate the [CL – H]⁻ anion signal, multiple iterations of ion accumulation and proton-transfer ion/ion reaction can be performed prior to subsequent interrogation. Mass selection and collisional activation of the enriched population of [CL – H]⁻ anions facilitates the assignment of individual fatty acyl substituents and phosphatidic acid moieties. Demonstrated advantages of this new approach derive from the improved performance in complex mixture analysis affording detailed characterization of low abundant CLs directly from a total biological extract. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.analchem.0c02545. Scheme S1: proton-transfer reaction scheme; Figure S1: product ion spectrum of [CL 16:0/18:1/16:0/18:1 – 2H]^2–; Figure S2: product ion spectrum of [PA 16:0/18:1 – H]⁻; Figure S3: pre- and post-ion/ion reaction negative nESI mass spectra of E. coli extract; Table S1: cardiolipin profile for E. coli extract; Figure S4: demonstration of selective transfer of charge-reduced [CL – H]⁻ product ions to the LIT for storage following the proton-transfer ion/ion reaction; Figure S5: product ion spectrum of the mass-selected product ion observed at m/z 673; Figure S6: product ion spectrum of the mass-selected product ion observed at m/z 699; Figure S7: CID spectrum of the charge-reduced [CL 70:3 – H]⁻ ion that has not been concentrated in Q3 using a refill experiment (PDF) This article has not yet been cited by other publications.

Publisher URL: http://feedproxy.google.com/~r/acs/ancham/~3/ZUHMVJGXh9k/acs.analchem.0c02545

DOI: 10.1021/acs.analchem.0c02545