SU1218426A1 - Method of measuring mass spectra in magnetic resonance machines spectrometer - Google Patents

Abstract

This invention relates to the field of mass spectrometry. The purpose of the invention is to increase the accuracy of the measurement of the ion current ratio of the known peaks of the mass spectrum and to simplify the measurement of the mass spectrum over a wide range of mass numbers. Adjustment is made to the reference peak of one of the multiplets. For this, the magnetic field and the modulation voltage frequency are simultaneously changed. The product of the multiplet mass number by the value of the modulation voltage frequency is measured. In the process of unfolding the multiplet mass spectrum ... by changing the magnetic field of the mass analyzer, this product is kept constant. In the description of the device that implements the method. The device contains a source 1 with a slit 5, a modulator 2 with a slit 6, a drift slit 7 and a lead capacitor 4 with a slit 8. 3 pcs. i (LU 00 4 GS O5 (rig. /

Description

The invention relates to mass spectrometry and can be used in various magnetic resonance mass spectrometers used in scientific and practical purposes for mass spectrometric analysis of substances in the gas phase.

The aim of the invention is to improve the accuracy of measuring the ion current ratios of known mass spectrum peaks and to simplify the measurement of the mass spectrum in a wide range of mass numbers by pre-tuning the studied peaks of the complex polyharmonic spectrum of the magnetic resonance mass spectrometer by controlling the generator frequency and magnetic field.

FIG. 1 shows schematically the MRMS analyzer placed in the electromagnet gap, an option; figure 2 - polyharmonic multiplet spectrum; Fig. 3 shows the dependence of the output current for ions of one mass on the change in the magnetic field.

In Fig. 1, source 1, modulator 2, generator 3, view capacitor 4 and slots 5, 6, 7 and 8 of the source, modulator, drift space and high-capacitor, respectively, are indicated.

The ions leaving the slots 8 and 5 of source 1 are separated by mass to charge ratio as in a conventional .180-degree magnetic static mass spectrometer (first stage of ion separation). The ions identified by slit 6 and modulator 2 lie in a narrow mass range. The equation of motion of ions in a uniform magnetic field is determined by the extrusion

pV 2U

J

(one)

Where

M

e

n and

R

-the ratio of the mass of the ion M to its charge e;

- magnetic strength, o floor; i

accelerating stress;

radius of a circular path.

The second stage is a magnetic resonance analyzer, in which the separation of the ions of the mass multiplet occurs according to the time of their flight through a circular trajectory in a uniform magnetic field.

x

I2i84262

The time span of the TC of one circle is

22 I (N. s

(2)

o

five

0

The ions trapped in modulator slit 6 are exposed to the high-frequency sinusoidal voltage of generator 3. Some of the ions that received a sufficient increment of energy in the modulator pass through the drift slot 7 and re-enter the modulator slit 6.

The second time, the ions are passed to the modulator in the form of short ion packets cut by slit 7. The ion current meter through slit 8 and step capacitor 4 gets% 1, again accelerated in the modulator. Due to the difference in the time of flight along the drift orbit and the large steepness of the change in the high-frequency field of the modulator, ions even with a small difference in mass (small difference in the time of flight) are obtained after the energy increment, as a result of which they move along circular trajectories with different radii.

The frequency of the voltage, the modulator voltage, is related to the ratio of the length of the circumference of the drift orbit to the geometric dimensions of the modulator by the ratio

(3)

0

five

Where

L

R

S

0

five

- voltage frequency of the generator feeding the modulator;

TC - cyclotron period of K ions - harmonic number / integer

the number in the resonant mode of operation and K K, t ei, with compensation; 1 is an integer, ni 0,25. The setting for a peak of a certain mass in MRMS, in contrast to static mass spectrometers, depends on the ratio of the parameters t, U, H, and.

From expressions (1), (2), (3) with a constant ion energy (11 const) and a constant radius of their trajectory in a drey4 orbit (Pz const: fig, 1),

tj 4Fo;

-2

1n

ko-b

where A and B are constant values;

M-, NdI Kg- is the mass of ions, the intensity of the magnetic field and the number of the harmonic corresponding to the joint fulfillment of the conditions of CM and (5).

Therefore, choosing a certain number of harmonic K and determining the product A experimentally for any known mass, it is possible for ions with any other known mass from the tables to calculate the values of the corresponding frequencies.

If at a certain value of i, the magnetic field is changed, then the dependence of the output current for ions of one mass on the change in the magnetic field will look, as shown in Fig. 3, because when H changes, as follows from (2),

Tc lf K changes as H decreases, the set constant frequency coincides with the resonant frequencies of peaks with ever increasing numbers of harmonics.

The fall in the intensity of the output currents when H varies relative to Nd, corresponding to conditions (4) and (5) is due to the fact that in the first stage of the device the ion beam descends from the slit 6 of the modulator (Fig. 1).

Thus, at moles of smaller H and large H, the current of ions with mass Mj does not appear.

i

The greater the resolution of the first stage R (the less & H Hg-Hg H. Therefore, to obtain an unambiguous adjustment of the device to the selected compensation peak with the Hp field, a sufficiently large R is necessary. The minimum value resolving ability of the first stage of the device meets this condition can be obtained if -rr - v (the expression .K

neither (5), but AK (from expression 3). Since of (1)

 2ip,

HO R

p l J l .PI

where R is resolution

on the base of the peak of the first stage, then for an unambiguous adjustment on H to a peak with a given mass that meets the conditions (41 and (5) it is necessary to have R. 4 К „

This condition is technically feasible as is usually K 20-100. Figure 2

 5 shows the polyharmonic spectrum of the multiplet at P, 4 K o and the unambiguous spectrum at R, 4K ,.

Thus, if condition (b) is satisfied, the unfolding

20 of the spectrum for given masses is reduced to calculating the corresponding values of f by changing the magnetic field so that it passes the field Hd for the ions under study. Wherein

25, it is not necessary to measure or calculate exact H values, which is technically difficult.

I

Claims (1)

; Claim 30 A method for measuring mass spectra in a magnetic resonant mass spectrometer, which is used to scan the multiplet mass spectrum by changing the magnetic field of a mass analyzer, which is designed to improve the accuracy of measuring ion current ratios of known mass spectrum peaks. Qa and simplifying the measurement of the mass of the spectrum in a wide range of mass numbers, tuning to the reference peak of one of the multiplets by simultaneously changing the magnetic field and the modulation voltage frequency, measuring the product value and the multiplet mass number per modulation voltage frequency value and support this work 35 45 50 in the process of unfolding the mass spectrum. / L / x