SU1051618A1 - Method of positioning mass spectrometer having double focusing - Google Patents

Abstract

A METHOD FOR TUNING A MASS SPESTROMETER WITH DOUBLE FOCUS on the maximum resolution, consisting in a cyclically sequential change in the spatial position of the ion source, object gap, electrostatic analyzer, its aperture and energy gap relative to each other and simultaneously register the mass spectrum on the detector and choosing the smallest width of the mass lines for the optimum mutual arrangement of the elements of the ion-optical circuit1, which so that, in order to improve the accuracy of the adjustment, the mutual spatial position of the ion-optical axis of the mass spectrometer and the ion beam in the region of the electrostatic analyzer is determined by changing the potential distribution between its plates while maintaining the potential differences between them and the spatial position of the aperture, and energy cracks. 1, SL 35 00

Description

This invention relates to methods for adjusting a dual-focusing maos spectrometer to a maximum resolution and can be used in mass spectrometry.

Methods are known for increasing the resolution of double-focusing mass spectrometers based on the correction of aberrations.

First-order aberrations and dual-focusing mass spectrometers are eliminated by appropriately selecting the parameters of the instrument's ion-optical scheme, under which the conditions of double-focusing are performed in the electric and magnetic sector fields. Second-order aberrations are partially compensated for by appropriate selection of the boundaries of the electric and magnetic fields l.

The disadvantage is that the choice of the parameters of the ion-optical scheme and the calculation of second-order aberrations is based on the assumption that the central trajectory along which the ion moves with a radial divergence ot, O and an energy spread of L5 O in an electric field has zero potential. With this assumption, the electrodes of the electrostatic analyzer are usually fed with the same magnitude and opposite sign voltages that are applied between the plates, the analyzer and its body. In this case, the focus conditions of the first order are collapsing.

The closest to the present invention is a method for adjusting a double-focusing mass spectrometer by mechanically adjusting in a certain sequence the mutual spatial arrangement of the ion source, the object slit, the ion detector, the electric and magnetic fields, and the mass spectra on the detector.

The order of operations, as a rule, is not strictly regulated, however, upon the completion of the cycle of operations, they again can be repeated cyclically. If optimal is achieved

2oeWt H4.,. H,.,

In the expressions (2-4) i, (, 4, 5Cfe, the new coefficients of the polynomial decomposition of the trajectory of the ion motion, and i. Ieij. Are their derivatives.

the position of one of the objects, in the next cycle, the operation for its adjustment is eliminated, i.e. as the optimum resolution value is reached, in each subsequent cycle, the number of operations may decrease. In this case, naturally, the initially indicated sequence of operations also changes.

The disadvantages of this method are the long duration of the alignment cycle and the greater complexity of the process of adjusting the mass spectrometer for maximum resolution

It is known 3 that the presence of a potential at the point of entry of an ion beam leads to the refraction of the latter. This alters the form of the coefficients of the polynomial decomposition of the trajectory of the ion motions, by which the aberration characteristics of the instrument are determined. Taking into account the influence of the refraction of the ion trajectory at the boundary of the electric field, the condition of first-order focusing along the angle of radial divergence changes

(one)

tgWVe

with

,, Dgo (- 1 where g is the angle of the sector electric field; CJ is the coefficient of the electric

floor; ODI ° h output shoulders

sector floor, referred to the radius of the average trajectory of the ion hop,;

O is the ion trajectory potential; .V (j is the ion acceleration voltage. The presence of a potential at the point of entry of the ion beam into the electric field is taken into account in the expressions for the spherical aberration of the second order of 5, and the energy dispersion Dp

I-iT

8n-h „(. ()

(2)

Ve

(3)

e (

Uo

Vn

)

Analyzing expressions (1–4) can be done, but conclude that changing Uo will lead to a violation of the first-order focusing condition with respect to the angle of radial divergence, a change in the spherical aberration of the second order 5 (j, and energy dispersion Dg, which, in turn, will cause a decrease in the resolution of the mass spectrometer. Thus, the refraction of the ion beam trajectory at the boundaries of the electric field imposes on etije more stringent requirements on the mechanical alignment of the entire ion-optical scheme, the optimal beam will lead to a violation of the focusing conditions already in the first approximation. Experimental verification of the theory showed that when the potential changes on the central trajectory of the electrostatic analyzer with an arbitrary input of the ion beam, the electric field is observed to linearly shift the mass spectrum along the focal plane of the magnetic analyzer instrument resolution (by a factor of 2–3). It was also established that, simultaneously with a change in aberrations, the fraction of the multiple x ions while the ion current at the maximum of one shot dnyh ions and resolution to n mnogozar dnyh: ions is reduced, which simplifies the mass spectrum of the multicomponent sample in the analysis. This improves the accuracy of the analysis, since in this case the imposition of the LIVII of multiply charged ions onto the analytic lines is reduced. The purpose of the invention is to improve the accuracy of the adjustment of adjustment due to a more accurate selection of the optimal potential in the ion beam trajectory in the field of the electrostatic analyzer. I. , The goal is achieved. According to the method of adjusting the mass spectrometer with double focusing to the maximum resolution, which consists in cyclically changing the spatial position of the ion source, the object slit, the electrostatic analyzer, its aperture and energy slits, the OTHOCit magnetic detector and the ion detector with the simultaneous registration of the mass spectrum at the detector and the choice of the most optimal mutual arrangement of the elements of the ion-optical This scheme, the mutual position of the ion-optical axis of the mass spectrometer and the ionic one in the region of the electrostatic analyzer, establishes a measured potential distribution between its plates, while maintaining the potential differences between them and the spatial space anbi. turn and energy cracks. FIG. Figure 1 shows the mass spectrometer circuits, with the help of which the proposed method is implemented in Figures 2 and 3. The diagrams illustrating the method. The scheme contains a focusing system for sources 1 and 2 of ions, an object slit 3J aperture slit 4, an electrostatic energy analyzer 5, an energy slit b, a slit 7 for measuring the ion beam charge (monitor slit) 7, a magnetic mass analyzer 8, sensitive detector 9, device 10 for moving the magnet, device 11 for turning the magnet. The method is carried out as follows. First, an object slit 3 is installed in the center of the ion beam of the ion source. Then, the aperture and energy slits 4 and 6 are set in the radial direction to the position corresponding to the maximum charge rate on the slit 7 of the monitor. Their optimal position is monitored according to the indications of the integrator connected to the slit 7. Thereafter, the magnetic analyzer 8 is adjusted in the region of medium and heavy masses, for which a series of mass spectra for different angles of entry of the ion beam into the magnetic field. The installation of angles is performed by rotating the magnetic analyzer 8 around the point of entry of the ion beam into the magnetic field with the help of a magnet rotating device 11. By the smallest width of the arcing on the detector, the most optimal angle is selected and fixed. Similarly, adjustment is made in the light mass region by moving the magnetic analyzer B in the direction perpendicular to the ion-optical axis of the instrument. The movement of the magnetic analyzer is carried out using the device 10 movement. Figure 2 shows the variation of the width of the mass lines of tin and lead & 6rj and ypb for ions of different aaridities as a function of the UQ potential as a result of photometry of photographic plates. Here l-iPb npH Wo-10 kV, 2-4РЬ at 10 kV, 3-4РЬ at УО 17,5 kV, 4-4РЬ at, 5 кВ, on fig. 26 1-eSn at kV, 2-5 5п at 0 10 KB, 3rd-5п at Vo 17,5 kV, 4-А5п at Ve 17,5 kV. Fig. 3 shows the change in the log-ichma of the blackening of mass-mass EgJ ions of different charges of lead Pb and tin 5p as a function of potential.

.ASC at accelerating voltage V

 HERE - Pb., 2-Pb-. 3- P, 4-Pb "in FIG. Sv 1-L, 2-Sn% 3-Sn 4-5h4

As seen in FIG. 2 and 3, with a linear potential change, a linear displacement of the mass lines is observed along the focal plane of the magnetic analyzer with a significant drop in the resolution of the device {on the order of 200300%). At 9toM, the maximum of the logarithm of one-charge ion ions coincides with the maximum of the resolution of the instrument, while the fraction of multi-ion ions is reduced.

As the accelerating voltage Vo increases, the resolution of the device increases, and the range of permissible values of o also increases.

Thus, the method of adjusting the ass-spectrometer by changing the potential lia on the central path of the electrostatic analyzer with a constant voltage,

acting between its plates, it allows to replace part of the process of mechanical adjustment of the mass spectrometer with an electric one, which reduces the time of adjustment of the device, simplifies its process.

  ISO 200 25B call UoB

-f 0-2 d-3.-4

t 150 200 250 t UoB

but

6)

Faye. 2

-to -sh ff ff w m 150 too zsB

Claims (1)

METHOD OF ADJUSTING A MASS SPECTROMETER WITH DOUBLE FOCUSING to the maximum resolution, which consists in cyclically sequentially changing the spatial position of the ion source, the object of the other gap, the electrostatic analyzer, its aperture and energy gaps, the magnetic analyzer and the ion detector relative to each other with simultaneous registration of the mass spectrum on the detector and the choice of the smallest width of the mass lines of the optimal mutual arrangement of the elements of the ion-optical circuit, characterized in that that, in order to increase the accuracy of adjustment simplification, the mutual spatial position of the ion-optical axis of the mass spectrometer and the ion beam in the region of the electrostatic analyzer is established by changing the potential distribution between its plates while keeping the potential difference between them and the spatial position of the aperture and energy gaps unchanged.