Alexander F. Dodonov

Heating of Ions Moving in a Gas Under the Influence of a Uniform and Constant Electric Field

A simple model for estimation of the internal temperature of ions, moving in a monoatomic gas under the influence of an electric field, is considered. The basic assumption of the model is formation of ion-atom complexes in a quasi-equilibrium state for some of the ion-atom collisions, and other collisions are considered as elastic in which no energy is transferred to the internal energy of the ion. For Langevin collision cross sections, the model allows coinciding equations to be obtained for internal and translational or effective temperatures of ions, in cases where the polarization energy of the atom in the local electric field of the ion is not taken into account. The influence of this polarization energy leads, in the context of the model considered here, to an increase of internal ion temperature by a factor of 1.3‐1.5 compared to its effective temperature (which coincides with the buffer gas temperature for zero external electric field). Using this result the significant discrepancies in activation energies for dissociation of protonated leucine enkephalin, measured by different methods, are qualitatively explained. Copyright # 1999 John Wiley & Sons, Ltd.

Multichannel extraction of charged species from liquid with use of track membranes

Abstract An extraction of negative charged species under electric field from liquid solutions into vacuum by use of poly(ethylene terephialate) track membranes has been investigated. The measurements of a total current at different voltages, applied between a liquid sample and a electrode in vacuum, has been carried out. In addition, an influence of an electrolyte concentration on the total current for the KI solution in glycerol has been studied. It is shown that a special feature of extraction of charged species from the channels of dielectric membranes is connected largely with on accumulation of charges on the vacuum surface of the polymer membrane. So, the current from dielectric membrane is controlled by several processes including formation of strong electric field near the liquid-vacuum interface, transport of ions along the channels to the interface and the field-assisted transition of charged species into vacuum.

New Method for Ion Mobility Determination by Stability Threshold Measurement in Gas Filled Radio Frequency Quadrupoles

A new method is proposed for determining ion mobility by use of a RF-only quadrupole equipped with a longitudinal electrical field along its axis (RFQLEF). This method is based on measuring the transmission threshold for the ions of interest as a function of the RF voltage and frequency. The method is based on the analysis of the equation of the motion of ions under the RF-only quadrupolar electrical field and the friction force due to collisions of the ions with the buffer gas molecules. The stability diagram for this equation was found numerically by a modified matrix method. According to the stability diagram the threshold values of the RF voltage and frequency determine the mobility coefficient for the ions of interest. Mobility coefficients for electrosprayed ions of several substances (bradykinin 2a, gramicidin S 2a and 1a, multicharged ions of apomyoglobin and cytochrome c) were measured and compared with literature values. # 1998 John Wiley & Sons, Ltd.

Extraction pulse generator for time‐of‐flight mass spectrometry

We describe an extraction pulse generator for time‐of‐flight mass spectrometry. It has an improved pulse shape, flat top and bottom, and suppressed tail after switching.

Design and performance of an electrospray ionization time-of-flight mass spectrometer

In order to circumvent the limitations of a quadrupole mass filter, which so far has been the most common mass analyzer for use with electrospray ionization, a mass spectrometer coupling electrospray with time-of-flight mass analysis has been constructed. The design of this spectrometer, including a simple electrospray ion source, an atmosphere–vacuum interface without a rf-only quadrupole/multipole that discriminates against low mass ions which can be used for internal calibration, orthogonal extraction, and a reflectron, is presented together with its performance characteristics. A resolving power of 7500 was obtained for the +5 ion of bovine insulin and the detection limit for the same molecule was shown to be 1 f mol. Mass accuracy using a conventional two-point calibration is 60 ppm for internal calibration on low mass ions and better than 100 ppm for external calibration on peptide ions. An improved mass accuracy equal to 10 ppm was achieved using internal three-point calibration on low mass ions naturally present in the spectra. The dynamic range of a single sample was found to be at least 400:1.

Polymer track membranes for extraction of ions from aqueous solutions at atmospheric pressure

The possibility of the application of the electromembrane technique for production of ions of biological molecules at atmospheric pressure is demonstrated. This technique has previously only been used for extraction of ions from liquids directly into vacuum. The membrane technique for ion extraction at atmospheric pressure was tested with both time-of-flight and Fourier transform ion cyclotron resonance mass spectrometers. The mass spectra of intact molecular ions obtained from aqueous solutions of peptides and proteins are presented. The possible mechanisms of non-destructive ion extraction are discussed. The new technique is promising for achieving absolute sensitivity (charging every analyte molecule) and for performing spatially-resolved analysis of liquid biological samples.

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.

Mass Spectrometric Studies of Physical, Thermochemical and Reactive Properties of Xenon Fluorides, Xenon Oxides and Xenon Oxyfluorides

Using a reactor with a flowing diffusion cloud coupled to a high-resolution, low-energy electron-impact ionization mass spectrometer, mechanistic, kinetic and thermochemical characteristics of gas-phase reactions with the participation of charged and neutral xenon oxides, xenon fluorides and xenon oxyfluorides have been investigated. Ionization energies for XeF, XeF2, XeF4, XeO3, XeO4, XeOF4 molecules and appearance energies for the ions formed from these molecules were obtained. Based on experimental and reference data, the enthalpies of XeO3 and XeOF4 formation were refined and a number of binding energies in the parent and fragment ions were calculated. For electron-impact ionization, the ionization cross-sections for Xe, XeF2, XeF4 and XeOF4 proved to correlate with a semi-empirical principle of full ionization. Based on the temperature dependencies of saturated vapor pressures for XeO4, XeOF4 and XeO2F2, their enthalpies of evaporation, sublimation and melting were determined. The mechanisms of gas-phase reactions between H atoms and neutral XeF2, XeF4, XeF6, XeO4 and XeOF4 were studied.

Rate measurements for the reaction of H-atoms with the xenon and krypton fluoride molecules.

Abstract Elementary strongly exothermic reactions of H-atoms with the F 2 , KrF 2 , XeF 2 , XeF 4 , XeF 6 molecules useful for chemical lasers have been investigated by mass-spectrometric probing of the diffusion cloud in flow [1] . Some ionisation and appearance potentials were defined [2] from experimental ionization efficiency curves. Arrhenius expressions were obtained for the rate constants between 298–505 K. They correspond to an activation energy of 8.9± 0.6; 11.3±0.2; 21.8±2; 22.6±5; 28.5±3.8 kj/mol for the H + F 2 , KrF 2 , XeF 2 , XeF 4 , XeF 6 reactions respectively, with the preexponential factor near 10 −10 cc/molec-c for all rate constants. It was established that HF product of the H+F 2 “model” reaction is excited up to 8-th vibrational level while such one of the H+ KrF 2 reaction is not vibrationally excited. Thus a second product of H+KrF 2 reaction may be eximer KrF(B 2 Σ) with the energy excitation 481.3 kJ/mol which corresponds to sum of the reaction heat and activation energy.