Current Electrospray Mass Spectrometry: an Overview. Part A. Analyte Atomization

Abstract

Electrospray ionization (ESI) is an atomization and ionization method through which a solution‐phase analyte can be transferred via minute charged droplets into the gas‐phase as an ion. The first part of this two‐part review on electrospray mass spectrometry considers the formation of these minute charged droplets. Atomization of liquids can take place through mechanical or electrostatic breakup of a liquid jet. In the absence of an electric field, charged droplets of both polarities are formed because of the disruption of the electrical double layer at the air–water interface. Addition of an electric field results in the formation of charged droplets of a single polarity. At sufficiently high electric field strength, mechanical jet disruption is replaced by electrostatic jet disruption giving the highest yield of charged droplets; this is the commonly used conductive DC electrospray. More recent means of forming charged droplets by DC or AC electric fields are discussed in the following sections. Mechanisms for reducing the droplet electrostatic stress such as droplet fragmentation are reviewed in the final section. These processes form the basis for the creation of charged gas‐phase analytes that is described in Current Electrospray Mass Spectrometry: an Overview. Part B. Analyte Charging.

Conformational effects in protein electrospray‐ionization mass spectrometry

“…In particular, protein charging seems to be heavily affected by the specific structural features and not merely interpretable as a reflection of droplet charging. Furthermore, droplet charging itself is affected by solvent composition in a very complex way (Grimm & Beauchamp, 2010;Verkerk, 2014a). The calculations described above offer a possible alternative interpretation.…”

“…However, it is interesting to ask whether a similar correlation holds for gas-phase structures. To test this hypothesis, structural models for desolvated protein ions produced by ESI are needed (Verkerk, 2014a;Verkerk, 2014b). As discussed in the following sections, development of such models is complicated by the extraordinary large number of different patterns of ionized residues (protomers) corresponding to a given value of net charge.…”