Controlling gas-phase reactions for efficient charge reduction electrospray mass spectrometry of intact proteins

The scope of gas-phase ion/ion chemistry accessible to mass spectrometry is largely defined by the available tools. Due to the development of novel instrumentation, a wide range of reaction phenomenologies has been noted, many of which have been studied extensively and exploited for analytical applications. This perspective presents the development of mass spectrometry-based instrumentation for the study of the gas-phase ion/ion chemistry in which at least one of the reactants is multiply charged. The instrument evolution is presented within the context of three essential elements required for any ion/ion reaction study: the ionization source(s), the reaction vessel or environment, and the mass analyzer. Ionization source arrangements have included source combinations that allow for reactions between multiply charged ions of one polarity and singly charged ions of opposite polarity, arrangements that enable the study of reactions of multiply charged ions of opposite polarity and, most recently, arrangements that allow for ion formation from more than two ion sources. Gas-phase ion/ion reaction studies have been performed at near atmospheric pressure in flow reactor designs and within electrodynamic ion traps operated in the mTorr range. With ion trap as a reaction vessel, ionization and reaction processes can be independently optimized and ion/ion reactions can be implemented within the context of MS n experiments. Spatial separation of the reaction vessel from the mass analyzer allows for the use of any form of mass analysis in conjunction with ion/ion reactions. Time-of-flight mass analysis, for example, has provided significant improvements in mass analysis figures of merit relative to mass filters and ion traps. The development and evaluation of new tools has clearly been a central activity and contributor to the dramatic advances in the capabilities of mass spectrometry over the past several decades. In this perspective, we relate the evolution of instrumentation for research activities focused on the study and use of ion/ion reactions and offer it as one example of many where progress in an area of science is intimately related to and dependent on the development of instrumentation. It is provided in appreciation for the inspirational example of creativity in instrumentation development [1] provided by Cooks over the years. Electrospray ionization (ESI) [2], among its many contributions, enabled the development of macro-molecule ion/ ion chemistry as a research area. The multiple-charging phenomenon associated with electrospray makes possible the generation of multiply charged reactant ions. This capability leads to the possibility that at least one ion/ion reaction product can retain charge, which makes such a product directly amenable to study with mass spectrometry. In the past two decades, significant progress has been made in understanding and exploring the gas-phase ion/ion chemistry of high mass multiply charged ions. A variety of potential analytical applications have been developed accordingly. Co...

Section: Atmospheric Pressure Ion/ion Reactions Followed By Mass Analmentioning

confidence: 99%

Section: Atmospheric Pressure Ion/ion Reactions Followed By Mass Analmentioning

confidence: 99%

Evolution of instrumentation for the study of gas-phase ion/ion chemistry via mass spectrometry

Xia

McLuckey

2008

“…In subsequent work, we were able to employ a corona discharge source to produce reagent ions in place of the 210 Po source [5,6]. This eliminated the regulatory and practical issues associated with obtaining and using radioactive materials, and in our most recent design the corona reduction chamber is quite small, efficient, and easy to put together [6].Now, that is all a very nice background, but it does not address the question posed in the title of this article: "Is Charge Reduction Necessary?" This begs the question "Necessary for what?"…”

mentioning

confidence: 99%

“…It has been in routine use in the atmospheric science community for particle analysis applications for decades [1]. In the last decade it has been developed in the field of biological mass spectrometry in two primary forms: at reduced pressure, typically inside of an ion trap mass spectrometer [2], and at atmospheric pressure, to reduce the charge of electrospray-generated ions before their entry into a mass spectrometer [3][4][5][6]. The latter approach has been developed primarily by our group at the University of Wisconsin-Madison, and it will serve as the principal subject of the present discussion.…”

mentioning

confidence: 99%

Is charge reduction in ESI really necessary?

Smith

2008

Self Cite

The technique of charge reduction electrospray mass spectrometry (CREMS), which can reduce the charge state complexity produced in electrospray ionization (ESI), is discussed. (J Am Soc Mass Spectrom 2008, 19, 629 -631) © 2008 American Society for Mass Spectrometry C harge reduction in the gas-phase occurs whenever oppositely charged ions combine. It has been in routine use in the atmospheric science community for particle analysis applications for decades [1]. In the last decade it has been developed in the field of biological mass spectrometry in two primary forms: at reduced pressure, typically inside of an ion trap mass spectrometer [2], and at atmospheric pressure, to reduce the charge of electrospray-generated ions before their entry into a mass spectrometer [3][4][5][6]. The latter approach has been developed primarily by our group at the University of Wisconsin-Madison, and it will serve as the principal subject of the present discussion.We coined the acronym CREMS, for charge reduction electrospray mass spectrometry, for the approach. The nominal rationale for developing CREMS was to achieve complexity reduction in mass analyzing mixtures of many different molecules. The two main methods for producing gas-phase ions from macromolecules (e.g., proteins, nucleic acids, synthetic polymers) are matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). For reasons that are not yet entirely clear [7], MALDI produces primarily singly charged ions, whereas ESI produces a distribution of multiply charged ions in various charge states. Thus, whereas MALDI produces relatively simple mass spectra from mixtures of different molecules, with one major peak per analyte species, an ESI analysis of the same mixture may give an unresolved composite of many overlapping peaks. Charge reduction offered the potential of being able to have the simplicity of MALDI spectra while maintaining the advantages of ESI with respect to its real-time capability and gentler ionization.We have developed two approaches to CREMS, differing in how reagent ions are generated. In the first approach [3, 4], we employed a 210 Po source of ␣-particles to create "air ions" in a chamber placed between the ESI capillary and the mass spectrometer inlet. We were able to show effective charge reduction of ESI-generated ions down to the singly charged state, with the desired reduction in charge state complexity and concomitant expansion of the m/z range (lower z ϭ Ͼgreater m/z). This yields "MALDI-like" ESI mass spectra from mixtures of proteins or nucleic acids. Figure 1 shows an example of the spectral simplification afforded by CREMS on a mixture of seven proteins (reproduced from reference [4] with permission). In subsequent work, we were able to employ a corona discharge source to produce reagent ions in place of the 210 Po source [5,6]. This eliminated the regulatory and practical issues associated with obtaining and using radioactive materials, and in our most recent design the corona reduction chamber is quite small, ...

“…The second approach is to admit the ions of opposite polarity into an electrodynamic ion trap for subsequent mutual storage and reaction. The former approach has employed a spray ionization method as one of the ion sources and either a discharge [12][13][14], radioactive source [15,16], or another spray ionizer [17] as the second ion source. In this approach, the ion sources have been operated simultaneously and, in general, continuously.…”

mentioning

confidence: 99%

A pulsed triple ionization source for sequential ion/ion reactions in an electrodynamic ion trap

Liang

Han

Xia

et al. 2007

A pulsed triple ionization source, using a common atmosphere/vacuum interface and ion path, has been developed to generate different types of ions for sequential ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The triple ionization source typically consists of a nano-electrospray emitter for analyte formation and two other emitters, an electrospray emitter and an atmospheric pressure chemical ionization emitter or a second nano-electrospray emitter for formation of the two different reagent ions. The three emitters are positioned in a parallel fashion close to the sampling orifice of the tandem mass spectrometer. The potentials applied to each emitter are sequentially pulsed so that desired ions are generated separately in time and space. Sequential ion/ion reactions take place after analyte ions of interest and different set of reagent ions are sequentially injected into a linear ion trap, where axial trapping is effected by applying an auxiliary radio frequency voltage to the end lenses. The pulsed triple ionization source allows independent optimization of each emitter and can be readily coupled to any atmospheric pressure ionization interface with no need for instrument modifications, provided the potentials required to transmit the ion polarity of interest can be synchronized with the emitter potentials. Several sequential ion/ion reactions examples are demonstrated to illustrate the analytical usefulness of the triple ionization source in the study of gas-phase ion/ion chemistry. . Electron-transfer reactions appear to be a highly useful means for deriving the primary structure information of peptides and proteins [7][8][9][10][11].Most ion/ion reaction studies involving biomolecules are conducted in one of two ways. The first approach is to mix the oppositely charged reactant ions at or near atmospheric pressure before sampling ions into a mass spectrometer. The second approach is to admit the ions of opposite polarity into an electrodynamic ion trap for subsequent mutual storage and reaction. The former approach has employed a spray ionization method as one of the ion sources and either a discharge [12][13][14], radioactive source [15,16], or another spray ionizer [17] as the second ion source. In this approach, the ion sources have been operated simultaneously and, in general, continuously. This approach avoids the need for instrument modification to accommodate an additional ion source interface but it is not conducive to MS n studies. In the latter approach, electrodynamic ion traps, either a quadrupole ion trap or a linear ion trap (LIT), are used as reaction vessels for ion/ion reactions due to their ability to store oppositelycharged ions simultaneously [18] as well as their ion isolation and MS n functionalities [19].Sequential ion/ion reactions have been found to be useful in a number of applications in the analysis of peptides and proteins. One example is the increase of the absolute charge state of a polypeptide ion, which has been achieved via two sequential i...