Charge Retention/Charge Depletion in ESI-MS: Experimental Evidence

Abstract

The effects of liquid and gas phase additives (chemical modifiers) on the ion signal distribution for Substance P (SP), recorded with a nanoelectrospray setup, are evaluated. Depletion of the higher charge state of Substance P ([SP+3H]3+) is observed with polar protic gas phase modifiers. This is attributed to their ability to form larger hydrogen-bonded clusters, whose proton affinity increases with cluster size. These clusters are able to deprotonate the higher charge state. “Supercharging agents” (SCAs) as well as aprotic polar gas phase modifiers, which promote the retention of the higher charge state of Substance P, do not form such large clusters under the given conditions and are therefore not able to deprotonate Substance P. Both SCAs and aprotic modifiers form clusters with the higher charge state, leading to stabilization of the charge. Whereas supercharging agents have low vapor pressures and are therefore enriched in late-stage electrospray droplets, the gas phase modifiers are volatile organic solvents. Collision induced dissociation experiments revealed that the addition of a modifier significantly delays the droplet evaporation and ion release process. This indicates that the droplet takes up the gas phase modifier to a certain extent (accommodation). Depending on the modifier’s properties either charge depletion or retention may eventually be promoted.

Nested-channel for on-demand alternation between electrospray ionization regimes

“…This would reduce proton transfer from analytes ions to neutral gas phase solvent clusters. This kind of charge retention 47,48 would lead to the observed higher charge states without denaturing the proteins.…”

The Charge-State and Structural Stability of Peptides Conferred by Microsolvating Environments in Differential Mobility Spectrometry

“…The detection of fragile charge states was accompanied by an increase in peak area of all ions by a factor of ∼2 in DMS environments seeded with aprotic modifiers compared to pure N 2 . No charge reduction was observed in DMS environments seeded with aprotic modifiers, which is consistent with observations made by Seale et al 74 and Thinius et al 83 This appears counterintuitive in light of the enhanced GPB of the free molecules of ACE (782 kJ mol −1 ) and MeCN (748 kJ mol −1 ) relative to EtOH (746 kJ mol −1 ), 85 which depleted the [MP1 + 3H] 3+ species under most experimental conditions. To explore the observed charge reduction observed with protic modifiers and the stabilization afforded by aprotic modifiers, the thermochemistry of cluster formation and the feasibility of proton transfer pathways was evaluated using computational chemistry.…”

Simple, Rapid Lipidomic Analysis of Triacylglycerols in Bovine Milk by Infusion‐Electrospray Mass Spectrometry

“…Signal suppression in biological samples has a variety of sources: ionization suppressing species such proteins and salts (Annesley, 2003; King et al, 2000), lipid aggregation (Koivusalo et al, 2001), or charge carrier depletion (Thinius et al, 2020). These phenomena affect signal intensity in manner independent of acyl carbon number and desaturation level.…”