Comparison of mass spectra characteristics using statistical analysis methods for the case of ionisation of organic molecules by electron impact with different electron energies

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Abstract

The sensitivity and accuracy of volatile organic compound (VOC) identification can be enhanced through the manipulation of ionisation energy in electron impact ionisation mass spectrometric gas analysers. This is achieved by modulating the number of ions formed in the ion source. This paper presents a comparison of data obtained by electron impact ionisation at electron energy (EE) values in the range of 25–105 eV for a number of organic substances belonging to different classes of organic compounds. In order to interpret the dynamics of changes in the peak intensities of fragment ions, an analysis was conducted using similarity matrices based on different similarity metrics. This analysis demonstrated the influence of electron energy (EE) on the probability of formation of the main fragment particles of the studied substances, and consequently, on the similarity of the recorded mass spectrum with the reference mass spectrum from the database.

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About the authors

S. V. Silkin

Moscow Institute of Physics and Technology

Email: e.nikolaev@skoltech.ru
Russian Federation, Dolgoprudny

A. V. Sakharov

Moscow Institute of Physics and Technology

Email: e.nikolaev@skoltech.ru
Russian Federation, Dolgoprudny

S. I. Pekov

Skolkovo Institute of Science and Technology; Siberian State Medical University

Email: e.nikolaev@skoltech.ru
Russian Federation, Skolkovo; Tomsk

V. A. Eliferov

Moscow Institute of Physics and Technology

Email: e.nikolaev@skoltech.ru
Russian Federation, Dolgoprudny

V. G. Tkachenko

Moscow Institute of Physics and Technology

Email: e.nikolaev@skoltech.ru
Russian Federation, Dolgoprudny

D. V. Kolesnik

Moscow Institute of Physics and Technology

Email: e.nikolaev@skoltech.ru
Russian Federation, Dolgoprudny

E. N. Nikolaev

Skolkovo Institute of Science and Technology

Author for correspondence.
Email: e.nikolaev@skoltech.ru
Russian Federation, Skolkovo

I. A. Popov

Moscow Institute of Physics and Technology; Siberian State Medical University

Email: popov.ia@mipt.ru
Russian Federation, Dolgoprudny; Tomsk

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Supplementary files

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2. 1. Mass spectra of isopropanol obtained by electron impact ionization. (a) at 70 eV in comparison with the spectrum from the NIST database; (b) at 25 eV in comparison with the spectrum obtained at 70 eV; (c) at 105 eV in comparison with the spectrum obtained at 70 eV.

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3. Fig. 2. THF mass spectra obtained by electron impact ionization (a) at 70 eV in comparison with the spectrum from the NIST database; (b) at 25 eV in comparison with the spectrum obtained at 70 eV; (c) at 45 eV in comparison with the spectrum obtained at 70 eV; (d) at 105 eV in comparison with the spectrum obtained at 70 eV.

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4. Fig. 3. Mass spectra of ethyl acetate obtained by electron impact ionization (a) at 70 eV in comparison with the spectrum from the NIST database; (b) at 90 eV in comparison with the spectrum obtained at 70 eV.

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5. 4. Ionization efficiency curves for the main fragmentary ions (a) n-hexane, (b) 2,2,4-trimethylpentane.

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6. 5. Ionization efficiency curves for the main fragmentary ions (a) ethylformate, (b) butyl acetate.

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7. Fig. 6a. The matrix

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8. Fig. 7. Matrix of cosine measures

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