SU834493A1 - Method of mass-spectrometric analysis - Google Patents

Description

(54) METHOD OF MASS SPECTROMETRIC ANALYSIS OF SUBSTANCES

one

The invention relates to mass spectrometry, primarily for the qualitative and quantitative analysis of individual substances and their mixtures, and can be used for soft, i.e. non-destructive ionization of molecules and radikёshovs, especially those that do not contain molecular ions in the mass spectrum during electron impact ionization.

Methods are known for analyzing substances in the gas or vapor phase, based on inelastic processes between atomic particles, namely, recharging reactions or on ion-molecular reactions, chemical ionization 1.

The analyte is present as an impurity to a known basic substance and when the initial mixture is irradiated with electrons, the main form is formed14, the positive burden of this substance which then reacting with the molecules of the analyte, produces the ions characterizing this analyzed substance. The ions characterizing the analyte are formed due to different ion-molecular reactions, resulting from repeated interactions between the molecules of the analyte and the ions of the main substance, as well as the ions resulting from such interactions. The analysis is carried out by measuring the intensity of the ions characterizing the analyte.

Disadvantages of the method — a special pressure zone (1 mm Hg) is required in the ion source, where ion-bottle reactions occur, and, therefore, additional relatively powerful and expensive pumping means, the method does not always ensure sufficiently soft ionization, those. obtaining of the scaled mass spectra; polyatomic compounds are used as the main substance.

The closest to the proposed is a method of mass spectrometric analysis of substances in the gas phase, according to which the test substance is ionized by highly excited atoms with the formation of associative ions with subsequent separation according to

Im / e. Sh.

 However, this method uses atoms with high ionization potentials, 410 has a number of drawbacks. Firstly, to obtain highly excited atoms, the excitation energy of which is near their ionization potentials, relatively high energy electrons are needed, and such electrons will also lead to ionization and further decomposition of the analyzed molecules. Secondly, atoms with a high ionization potential are practically difficult to excite with cheap and affordable light sources. Third, when a highly excited atom interacting with a high ionization potential with a molecule, the ionization potential of which is lower, a decomposition of the molecule can occur with the formation of fragment ions in the mass spectrum. The purpose of the invention is to obtain few linear mass spectra. The goal is achieved by the fact that in mass spectrometry analysis of substances in the gas phase by which the test substance is ionized by highly excited atoms with the formation of associative ions and then separated by t / e in the analyzer, atoms with low ionization potentials, for example alkali and alkaline earth metals. In order to produce ions that characterize the U5IX source analyte, associative ionization is used, which results in the formation of complex ions, which are ionized compounds of atoms with low ionization potentials, with the atoms or molecules of the analyte. The availability and amount of the analyte is judged by the intensity of such complex ions. The reactions of associative ionization occur between highly excited atoms A of a known element of the periodic table, with an ionization potential lower than the potential of the analyte M under the scheme, according to the scheme.

7-10 410 5-CHO ZCHO-

55 43 51 40 А + М- АМ + е, where AM is a complex ion, is characteristic; the current analyzed substance; e is an electron. Highly excited atoms A can be obtained by the action of electrons, photons, in discharge or in some other way. . In the mass spectrum, in addition to AM ions, only A and A ions are contained if the energy of electrons or photons, under the action of which highly excited atoms are formed, is less than the ionization potential of the analyte. As atoms A, for example, alkali metal atoms, alkaline earth atoms, or other atoms having low ionization potentials are used. Ionization of the analyte does not occur, since the ionization potential of element A is lower than the ionization potential of the analyte, and electrons or photons with energy below the ionization potential of the analyte are used to excite atoms. The formation of ions occurs due to the associative ionization of two neutral particles, and not due to ion-molecular reactions. In the proposed method there is no need to create an area with increased pressure in the ion source, the process occurs at pressures in the ion source, mass spectrometer 10 -. 10 mm Hg PRI m. A quartz crucible with metallic potassium is placed on the mass spectrometer through a direct input to the ion source. The temperature of the preheater, the crucible is 150 ° C, the energy of ionizing electrons is b eV, the current of full flow is 3.2 mA. Then, gaseous substances of various chemical nature are injected through the inlet system. The resulting mass spectra and pressures which carry out the inlet of the analyte are given in the table,. -Table

Substance

Pressure, torr

, -6

3-10 5- 101, 5.10

-6

NH.

6-10

-6

CgHjo pair

5-10

The absolute value of the ion current K (CH3) CO. At the input of the multiplier is 1.5; the resolution of the device is 1000. The value of the current of the ions K in all cases at the input of the multiplier is greater than A, which is the upper limit of the measurement. system.

Using the proposed method of mass spectrometric analysis provides the possibility of obtaining low-linear mass spectra, which is extremely important for analyzing complex mixtures of substances, as well as identifying individual substances; due to soft ionization, the possibility of registering radicals formed in various processes; the ability to use light from conventional discharge lamps to obtain mass spectra as well as lasers,.

Claims (1)

1. US patent 355527, cl. 250-41.9, 1970, 0 2, Kuprinov SB, Reactions of electronically excited atolls and molecules, High-energy Chemistry, 197, t.be 4, s, 304 (prototype),