SU1684831A2 - Ion-cyclotron resonance mass-spectrometer - Google Patents

Description

The invention relates to scientific instrumentation, to the technique of mass spectrometry and can mainly be used in the technique of studying the mechanisms and kinetics of ion-molecular reactions, precision measurement of ion masses, analysis and identification of substances and their mixtures,

The aim of the invention is to increase the sensitivity and resolution and to improve the reproducibility of the results, as well as to simplify the interpretation of mass spectra,

FIG. 1 shows a general view of the proposed device; FIG. 2 shows the cross section of the measuring cell of the spectrometer (in the plane perpendicular to the magnetic field B power lines), as well as the junction of side-electrode electrodes (for the case of n 24).

The measuring cell of the spectrometer contains end plates 1.2 of ion confinement, side-shaped excitation and detection electrodes 3, source of 4 ions; input terminals 5.6 of the excitation circuit, output terminals 7.8 of the detection circuit,

The device works as follows.

The ion source 4 creates an ion bundle located in the center of the measuring cell. A constant potential is applied to the ion confinement plates 1, 2 to keep the ions in the cell. The input terminals 5.6 of the excitation circuit are connected to an alternating voltage generator g with a frequency equal to the cyclotron count of the SOS of the ions under study. In response, the action of the variable radio; l-1. auxiliary voltage in a cell kgkgoms-tra obO5 00 4

00 GS

Yu

A rotating ion bundle that creates an induced charge in a detection circuit is pleased. The induced charge during the movement of the ion bundle is redistributed over the system of side electrodes, which leads to the presence of an output alternating current with a frequency of n / 4 times greater than the cyclotron frequency of the ions. The output current is removed from the detection circuit terminal 7.8 and goes into an electronic data processing system.

Such an arrangement of the detecting and exciting electrodes, as well as their electrical connection, allows to improve the reproducibility of the results and simplify the interpretation of the mass spectra, since this eliminates the asymmetric harmonic components in the ICR signal

The presence of an excitation circuit in the device, consisting of n / 2 side electrodes, makes it possible to create an electric field that provides uniform unwinding of ions in the entire volume of the measuring cell. With such excitation, it is possible to obtain a rotating non-deformed bundle of ions for rotational radii comparable to the cell radius, which increases the resolution of the instrument. In this case, it becomes necessary to keep the rotating bundle of ions on the periphery of the cell. Such confinement is possible only in the absence of noticeable sagging of the electric fields created by the side electrodes and end retention plates on the path of movement of the ions.

 - g

where D is the distance between the electrodes;

g is the radius of rotation of the ion bundle.

An increase in the radius of the cyclotron motion causes a sharp increase in the ICR signal, and consequently, the sensitivity, then when the distance to the detection electrodes is smaller than their transverse dimensions R-rc and, where | the transverse size of the electrodes.

Increasing the sensitivity of the instrument requires unwinding of the ions to the peripheral areas of the cell of the spectrometer and determines the requirement for its design.

D with R-rmax:.

Example, consider the proposed device with eight side electrodes (p 8). In order to clarify and optimize the basic metrological characteristics of the device (resolution, sensitivity), electric fields were simulated on a computer. In order to excite the cyclotron motion of ions, an alternating radio frequency voltage is applied to the terminals of the exciting circuit, resulting in an electric field, determined by the boundary conditions on the electrodes of the cell and the Lachlass equation,

The efficiency of the excitation field is determined by the amount of energy gained by the ions during the treatment period and

W (r) | (grad Cf dl),

About where integration is done by

Cr, Numerical modeling shows that the amount of energy acquired by the ion over a period of 10% does not depend on the radius of rotation of the ions g (when g varies from 0 to 95% of the cell radius R) and p therefore, in the proposed device unwind the ions to orbits with a radius of rotation close to the cell radius.

The movement of ions at the periphery of the cell was also simulated numerically on a computer in order to improve the retention properties of the measuring cell and, consequently, increase the resolution of the device, while varying the dimensions of the side electrodes. It is shown that an increase in resolution leads to a condition on the distance between the electrodes D. 5A R-rma,)

where is the maximum ion radius.

Thus, the proposed device allows the cyclotron movement to be biased to radii close to the cell radius and to effectively hold the rotating bundle of ions.

Consider now the process of registering the signal of the ICR,

the ion bundle is a redistribution of charges on the detecting electrodes, which causes a current in the circuit, coming from the terminals to the electron5

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experimental control and data processing system. The detected current is determined from the condition that the potentials on the side electrodes of the spectrometer are equal and oscillates at a frequency that is a factor of 1 times the cyclotron frequency.

KO sin (2coet + q, g "with R,

where Q is the total charge of ions in the bundle.

For the amplitude of the recorded signal, the following estimate is valid:

t 49We ESh1 J-tlu / f 1- (r / R)

max

from which it can be seen that the amplitude of the recorded signal (a, consequently, and the sensitivity of the device) increases sharply with an increase in the radius of rotation of the ions: g R. The maximum allowable radius of retention of the ions of a defined condition

AtR - rmay ± 8.

An improvement in the reproducibility of the results is achieved due to the fact that during the registration of the ICR signal, the distribution of charges on the detecting and exciting electrodes satisfies the group of symmetry transformations Cuh (i.e., symmetrically with respect to the rotations through 90 °). During one revolution of the ion bundle around the axis, charge redistribution between the detection and excitation electrodes occurs four times, which corresponds to a doubling of the recorded frequency in the proposed device, without harmonic components in the ICR signal associated with the asymmetry of the detecting and exciting electrodes and the dependent from a particular cell design.

The increased sensitivity and resolution achieved in the proposed device will allow

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five

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to expand the field of application of ion-cyclotron resonance mass spectrometry, to study the little-studied and total molecular reactions with the participation of intermediate excited particles, to conduct preparative rest and energy of stable and unstable nuclei. Improving the reproducibility of results simplifies the procedure for interpreting mass spectra, since it allows you to create standard library catalogs of mass spectra, as well as to use existing ones.

Claims (1)

Invention Formula Ion cyclotron resonant mass spectrometer auth.St. No. 1307492, characterized in that, in order to increase the sensitivity and resolution and improve the reproducibility of the results, the excitation electrodes are located between the detection electrodes and connected in two diametrically symmetric groups, the number of excitation electrodes is equal to the number of detection electrodes, while in the detection circuit between the two detecting electrodes electrodes from one group have two exciting and one detecting electrode from another group, and in the excitation circuit between two excitations One detecting electrode is located by the waiting electrodes from one group, and the distance between the electrodes satisfies the condition A Ј R-r wav about rDD R Raus cell distance (m); mGX maximum radius of cyclotron motion of ions (m); Ј is the transverse size of the detecting and exciting electrodes (m). Compiled by N. Katinov Editor N. Kamenska Tehred A. Kravchuk Proofreader M.Samborsk Order, 3510 CirculationSubscription VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moskvl, Zh-35, 4/5 Raushsk nab. Production and Publishing Combine Patent, Uzhgorod, st. Gagarin, 101 eight FIG. g