Valeriy V. Raznikov

Decomposition of charge-state distributions for a better understanding of electrospray mass spectra of bioorganic compounds. Part 1: basic formalism.

Further development in our approach for the interpretation of a mass spectral peak series resulting from unique modifications at a number of molecular sites is described and its application for the analysis of electrospray mass spectra of multiply-charged ions of biopolymers is specified. This method was based initially on the assumption that the modifications are mutually independent. The output is a set of modification probabilities for the considered molecular sites, which explains the observed peak intensity distribution with the best accuracy. It is shown here that the method is also applicable, in some cases, to the strong interaction between modified sites. This is important for the formation of multiply-charged ions, at least in the gas phase, since it should be significantly influenced by the internal electric fields. The capabilities and limitations of this approach are discussed. One limitation is that only unimodal distributions (those having only one maximum) are possible in the considered model. Another is that relatively large biomolecules may not be suitable for this type of analysis. Some experimental results of the application of this method are described in Part 2 of this work.

Decomposition of charge-state distributions for better understanding of electrospray mass spectra of bioorganic compounds. Part 2: application of the method.

The results of the analysis of electrospray mass spectra of β-endorphin and chicken egg lysozyme in different conditions of data acquisition using the method described in Part 1 of the work are reported. At least partial unfolding during the process of ion formation in the electrospray ion source of an initially native biomolecule of lyzozyme in solution should supposedly explain the received set of probabilities of proton retention by basic and acidic residues of this molecule for all considered conditions of data acquisition.

A new method to study the kinetics of ion decay in a radio frequency quadrupole with resonance rotational excitation

A new method to study the kinetics of ion decay reactions in a radio frequency quadrupole (RFQ) with resonance rotational excitation is described. The decay reaction occurs while ions move through the RFQ and the resulting precursor-ion consumption, as well as the appearance of fragment ions, are monitored using high-resolution orthogonal time-of-flight mass spectrometry (o-ToF MS). The developed method enables one to extract absolute values of the decay rate constants using the ion drift motion under the uniform DC electrical field along the RFQ created by the segmented structure. The ion dwell time, as well as its internal temperature are calculated using the ion mobility measured under the same experimental conditions as the kinetic investigations. The values of the decay rate constants, activation energies and preexponential factors for three substances under investigation are reported.

Possibilities for Energy Transport into a Radio-Frequency Quadrupole by a Shifted Supersonic Gas Jet. Part II. Accumulation and Heating of Ions

The aim of this work was the assessment of the ability of a supersonic jet to accumulate sufficiently dense ion clouds inside the quadrupole, the ion cloud being “heated” to a relatively high temperature under a relatively low density of the residual gas (pressure lower than 10–4 Torr). Kinetic measurements gave an estimate of the number of accumulated ions at the beginning of the quadrupole of about 2 × 107 and their internal temperature of 6000 K.

Possibilities for Energy Pumping in a Radio-Frequency Quadrupole by Shifted Supersonic Gas Jet. Part I: Accelerated and Excited Atom Transmission

Generation of an ion beam and its transmission into a mass analyzer is one of central problems in mass spectrometry. The use of a narrowly directed supersonic gas jet has a number of advantages in comparison with other sampling methods. The aim of this work was to confirm the declared earlier properties of the jet formed at the outlet of a cylindrical channel when the free path length of gaseous atoms at the beginning of the channel is comparable with the channel diameter. The paper describes the ability of such a supersonic jet to conserve an additional energy of jet gas atoms. A significant influence of the temperature of the gas flow on the yield of cyclohexane fragment ions was found, cyclohexane being an admixture in the noble gas jet passing through an electron ionization ion source. A possibility of obtaining a flow of metastable electronically excited atoms inside the jet is also shown. The results of the work confirm the availability of the supersonic gas jet for the design of a high efficiency ion source inside the radio-frequency quadrupole at the input of the mass analyzer.

Disentangling of Information About the Structure of Biomolecules Based on the Decomposition and Separation of Two-Dimentional Charge Distributions of Ions

Electrospray ionization mass spectra of biomolecules typically consist of a series of multiply charged ions because of the transfer of protons or other charge carriers between ions of biomolecules and the surrounding liquid or gas. The distribution of intensities of ions retained charge carriers contains information about the spatial structure of biomolecules. A new method is developed for the separation and decomposition of multidimensional charge distributions of ions bearing other charge carriers, such as alkali metal ions, along with protons. The proposed method ensures the estimation of the probability of charge carrier retention by separate functional groups for the selected conformations of biomolecules. The paper describes the application of this method to the analysis of a two-dimensional charge distribution of horse heart cytochrome C, resulting in the revelation of at least two its structural forms under the studied conditions.

Two possible improvements for mass spectrometry analysis of intact biomolecules.

The goals of our study were to investigate abilities of two approaches to eliminate possible errors in electrospray mass spectrometry measurements of biomolecules. Passing of a relatively dense supersonic gas jet through ionization region followed by its hitting the spray of the analyzed solution in low vacuum may be effective to keep an initial biomolecule structure in solution. Provided that retention of charge carriers for some sites in the biomolecule cannot be changed noticeably in electrospray ion source, decomposition and separation of charge-state distributions of electrosprayed ions may give additional information about native structure of biomolecules in solution.