Monopole Mass Spectrometer Research Articles

Mass Spectrometric Studies of Valine Molecules by Electron Shock in the Gas Phase

Relevance. Valine is one of the eight amino acids not synthesised by the human body, necessary for the synthesis and growth of body tissues, muscle coordination; regulation of nervous processes, nitrogen metabolism, and stabilisation of the hormonal background. Since α-amino acids contain an asymmetric carbon atom, they can exist as optical isomers (mirror antipodes) that play an essential role in protein biosynthesis. The structure of matter and the physical processes that occur in it are studied using the method of mass spectrometry and spectral analysis. This indicates the relevance of the problem that was studied in this paper. Purpose. Mass spectrometric studies of the formation of ionic products of single and dissociative ionisation of the valine molecule (C5 H11NO2) with electrons according to the method of beams intersecting within the energy range of bombarding electrons 6-70 eV. To consider the mechanisms of formation of the most intense ion fragments during dissociative ionisation by electron shock. Methods. The experiment was conducted on an installation with a monopole mass spectrometer of the MX-7304A type, which belongs to the class of dynamic mass analysers with electron shock ionisation in the range of mass numbers 0-120 Da. The mass spectra of molecules were investigated at different temperatures of the source of molecules in the range of 300-600 K. Results. The obtained results are compared with the mass spectra of the D-, L-, and DL-enantiomeric forms of the valine molecule with data from the NIST and SDBS databases. The features of the processes of formation of ion fragments of valine molecules by electronic shock are analysed in detail, and the dynamics of the yield of ion fragments in the range of evaporation temperatures of the initial substance of 300-440 K is also studied. The total relative ionisation cross-section of the molecule under study was measured according to mass spectrometric method with an ionising electron energy of 5-60 eV. Based on the results of experimental studies, a threshold section of the dependence of the total relative cross-section of valine ionisation is determined and given in this paper. Conclusions. A detailed analysis of the processes of formation of fragment ions in the mass spectra allows demonstrating the influence of the structural forms of valine enantiomers on the redistribution of relative intensities of product ions

Mass Spectrometry of Glutamic Acid and Glutamine in the Gas Phase

We report on the method and results of a mass-spectrometric investigation of the yield of positive ions formed as a result of the dissociative ionization of glutamic acid and glutamine by electron impact in the gas phase. The measurements were performed at various temperatures using a monopole mass spectrometer of MX-7304A type in a range of ion masses within 10–150 Da. Peculiarities of the formation of molecular fragment ions of glutamic acid and glutamine by electron impact were studied in detail and the dynamics of fragment ion yield was measured at various temperatures of evaporation of the initial substances within 310–430 K.

Mass spectrometric research glutamine molecule

Background : Amino acids are molecules of vital organic compounds, which simultaneously contain amino (-NH 2 ) and carboxyl (-СООН) groups. Currently, a large number of amino acids are found in interstellar clouds, meteorites. This contributes to the propagation of the hypothesis of the extraterrestrial origin of life on Earth. In general, the penetration of physical methods of research into the study of complex organic molecules is predicted and promises many discoveries in the path of knowledge of the mystery of living matter. Methods : One of the important methods of studying the structure of matter and physical processes that occur in it is mass spectrometry and spectral analysis. The experiment was performed on a monopole mass spectrometer (MX) type MX-7304A, which belongs to the class of dynamical mass spectrometers with ionization by electron impact The monopole mass analyzer, in contrast to the quadrupole, divides the ions not only orthogonally, but also in the direction of the input of particles into the analyzer. Thus, a bundle of ions at the outlet of the ion source should be parallel, monokinetic and directed along the axis of the analyzer. A bundle of investigated glutamine molecules was obtained using an effusion source whose temperature could vary widely. This made it possible to investigate the temperature dependence of the formation of various fragments of the investigated molecule. Measurements of mass spectra were carried out in such a way as to ensure accuracy of 3-5%. Temperature dependences of the formation of positive ions of fragments were measured using a special precision feedback device, which allowed maintaining the temperature of the molecules in the gas phase with an accuracy of ±0,05K. Results : Mass spectrometric studies of glutamine have been carried out by the method of bundles, which are transformed in the range of bombarding electrons energy 6-70 eV and at temperatures of 340-460 K. The dominant mass spectrum is the peak that corresponds to the ion-fragment with m / z = 84 a.o.m., which corresponds to the fragment C 3 H 2 NO 2 + . The smallest energy is the C-C, N-C, C-O bonds, which leads to the fragmentation of the glutamine molecule by electron impact and the appearance of a carboxylic, amino group in the mass spectrum of the ion-fragments. Conclusions: The high efficiency of the occurrence of ionic fragments of glutamate molecules and the strong temperature dependence of their formation in interaction with electrons indicate a very complex mechanism of electronic fragmentation of the glutamine molecule, which in turn significantly influences the composition of fluorophores.

Ionization of glycerin molecule by electron impact

The methods and results of studying the yield of positive ions produced due to direct and dissociative electron impact ionization of the glycerin molecule are described. The experiment is carried out using two independent setups, namely, a setup with a monopole mass spectrometer employing the method of crossing electron and molecular beams and a setup with a hypocycloidal electron spectrometer with the gas-filled cell. The mass spectra of the glycerin molecule are studied in the range of mass numbers of 10–95 amu at various temperatures. The energy dependences of the effective cross sections of the glycerin molecular ions produced by a monoenergetic electron beam are obtained and analyzed; using these dependences, the appearance energies of fragment ions are determined. The dynamics of the glycerin molecule fragment ions formation is investigated in the temperature range of 300–340 K.

A pulse generator for feeding mass spectrometers

A small-size high-frequency rectangular alternating-voltage pulse generator is designed for energizing a cylindrical electrode of a monopole mass spectrometer. Amplitudes of positive and negative pulses linearly increase from zero to +150 V/−180 V for ∼10 min and the frequency simultaneously linearly decreases from 2.0 to 1.4 MHz. A negative-polarity direct component, which is required for operation of the mass spectrometer, is formed due to unequal positive and negative amplitudes with respect to the ground. Spectra of residual gases with atomic mass numbers of 1–130 amu are obtained.

Mass-spectrometric investigation of coal gases from samples with a low and high degree of coalification

The methods and results of experimental investigation into the composition of gases by mass spectrometry with electron impact ionization are described. Experiments are performed on a crossed-beams setup with ion separation and detection using a monopole mass spectrometer with an upgraded ion source. Emphasis is on determination of the molecular composition of gases, including methane, liberating from the coal material as a function of temperature.

Mass-spectrometric study of coal gases

Experimental techniques and results of an investigation of the composition of coal gases by electron-impact ionization mass spectrometry (EIMS) are described. Then EIMS measurements were performed on a setup with intersecting beams, ion separation and detection by monopole mass spectrometer, and modified source of ions. The main attention is devoted to the method of determining the temperature-dependent molecular composition of gases (including methane) evolved from carbonaceous rock.

Electron impact-induced ionization and dissociation of the freon-12 molecule

An experimental technique is described, and the relative cross sections of the single and dissociative electron-impact ionizations of the freon-12 molecule (CCl2F2) in the near-threshold energy range are obtained. The experiment is performed on a device that provides the mass separation and recording of ions with a monopole mass spectrometer. The mass spectrum of the freon-12 molecule is measured at various ionizing-electron energies, and the relative cross sections of dissociative ionization are measured for the most intense ion fragments, including isotope-containing fragments. The threshold dependences of these cross sections are used to determine the appearance potentials of the ion fragments. The isotope shift in the thresh-old appearance energies of ion fragments [C35ClF2]+ and [C37ClF2]+ is measured for the first time.

Electron-impact fragmentation of ascorbic acid

The processes of ascorbic acid total and dissociative ionization by 6 to 100 eV electrons in the temperature interval 360–460 K are studied with an MX-7304A monopole mass spectrometer. A scheme of ascorbic acid fragmentation due to electron-impact-induced ionization is suggested, and possible channels of producing the most intense fragment ions in the mass spectrum are indicated. The energy dependences and thresholds of fragment ion formation are determined for the first time in the incident electron energy range 7–30 eV.

Optimizing the energy filter of the “dihedral angle with end-face diaphragms” type

The 3D problem of determining the parameters of a charged particle energy filter for a monopole mass spectrometer is solved. Optimal geometry and operating conditions making it possible to raise the transmission of the instrument by an order of magnitude are found. Such an energy filter is intended for secondary ion (or atomic) mass spectrometry installations built around a monopole mass analyzer.

Ion-optical system with energy filtering for a monopole mass spectrometer

An electrostatic ion-optical system providing angular focusing of the beam and its monochromatization at the entrance to a monopole mass spectrometer is suggested and analyzed. The system uses a funnelshaped extracting electrode and a cylindrical energy filter with a flat electrode in its meridional plane. The geometry of the system and the supply voltage can be varied in proportion to the aperture radius and anode potential, respectively.

Peculiarities of the MX7304A monopole mass spectrometer performance in pulse counting mode

The peculiarities of the performance of the MX7304A monopole mass spectrometer in the pulse counting mode are considered. The advantages and drawbacks of the counting mode are discussed. A method for selecting the optimal voltage of a secondary-electron multiplier is described. A technique for correcting the detector signal in view of counting loss at high signal rates is proposed.

ION SOURCE FOR MONOPOLE MASS SPECTROMETER

The results of simulation of an industry monopole mass-spectrometer ion source with SIMION 3D software are described. Construction imperfections are disclosed. The results of the analysis are checked experimentally by the ion source modifica­tion for a МХ7304АМ monopole mass-spectrometer. A new construction of the ion grid source is proposed with better characteristics and operating parameters.

Secondary ion mass spectrometer based on a high-dose ion implanter

A secondary ion mass spectrometer built around a modified high-dose ion implanter is used to study secondary ion emission in metals over a wide range of primary beam energies. The implanter generates ion beams with energies of up to 150 keV and a substrate current to 30 μA. A modified MX7304A monopole mass spectrometer is applied as an analyzer of secondary ions with mass numbers of up to 400 with a resolution of 1 M at a level of 10% of the peak height. The detection limit for iron is 6.5 ppm. The analyzer is equipped with a small-size filter separating secondary ions in energy. The relative emission intensities of the secondary monatomic and cluster ions of copper for different primary ion beam parameters are studied.

Dynamic mass spectrometer for studies of organic and inorganic molecules

Experimental technique is described and relative cross-sections of direct and dissociative ionization of CO 2, C 4H 9OH, C 2H 5OH, CH 3OH, C 6H 12O 6 and C 7H 8 molecules by electron impact in the near-threshold energy range are obtained. The experiment is performed on a setup with ion mass separation based on a monopole mass spectrometer which is proved to be successful for such a sort of experiments. For the incident electron energy range from 7 to 35 eV the energy dependences of cross-section of appearance of the main molecule ions and the fragment ions formed due to its dissociation are given.

Dissociative ionization of ethanol, methanol and butanol molecules

We measured direct and dissociative ionization functions for ethanol, methanol and butanol molecules, and determined relative cross sections. The experiment was carried out by means of a crossed electron and molecular beam method at the setup equipped with a monopole mass spectrometer. The ions were detected by a secondary electron multiplier. The mass spectra for butanol molecule as well as the energy dependence of the ionization cross section for the initial molecules and the dissociative ionization cross sections for the fragment ions from 5 eV to 60 eV are presented.

Ionization of water and carbon dioxide molecules by electron impact near threshold

A measurement technique is described and relative cross-sections for direct and dissociative ionization of H 2O and CO 2 molecules by electron impact near the threshold are obtained. The experiment is performed by a setup with mass separation of the ions by a monopole mass spectrometer and their detection by a secondary electron multiplicator. The energy dependencies of the cross-sections for the formation of the main molecule ions and fragment ions resulting from dissociation are given in the incident electron energy range from 7 to 35 eV.

Ionization of Nitrogen, Oxygen, Water, and Carbon Dioxide Molecules by Near-Threshold Electron Impact

An experimental technique for measuring the cross sections of direct and dissociative ionization of N2, O2, H2O, and CO2 molecules by electron impact in the near-threshold energy range is described. The setup used in the experiments allows mass separation of ions with a monopole mass spectrometer. It is shown that such a setup can be used to advantage in separation experiments. For incident electron energies between 7 and 35 eV, the energy dependences of the cross sections of generation of parent ions and ion fragments due to parent molecule dissociation are obtained.

A new monopole mass-analyzer based on a hyperboloid electrode system

A new version of the monopole mass spectrometer with improved characteristics, which advances the idea of the quadrupole analyzer, is described.

Optimum analysing electrode radius for a fourfold monopole mass spectrometer

Values are presented for the optimum radius of curvature of the analysing electrode in a fourfold monopole mass spectrometer. Computer simulation of the operation of the device demonstrates that residual field non-linearity present, even when using an opti-mum radius, does not impair device operation and peaks are well formed. Half-peak-height resolutions in excess of 200 are shown to be possible at 100% transmission. Experimental results reported previously support the values of electrode radius given.