DE1498971A1 - Method for the separation or the separate detection of ions with different specific charges - Google Patents

Description

SIEMENS-SCHUCKERTWERKE. . -. Erlangen, the

Aktiengesellschaft Werner-von-Siemens-Str.

PLA 62/8201

Method for the separation or for the separate detection of ions with different specific charges

The known method for separating ions of different mass and charge in temporally periodic electric fields, the potential of which is a square function of the spatial coordinates (DBP 9hk 900), is based on the following principle: The ions are brought into a temporally periodic electric field, whose Potential <p (x, y, z) is a quadratic function of the spatial coordinates x, y, ζ of the general

2 2 2

mean the form φ = * f (t) fax. + fly -χζ) is lind where f (t) is any periodic function of time t.

In ^! In such a field, ions can perform two types of movements1 Either the ions carry out oscillations around the center of symmetry of the field, the amplitudes of which vary from ion to ion

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Do not exceed the maximum value (stable trajectories), or the amplitudes increase over time, so that the particles, after a sufficient residence time in the field, hit the field-generating electrodes or other Limitations of the apparatus fly and are excreted as a result (unstable trajectories).

With a given field it depends solely on the specific charge of the ion whether it is stable or unstable in this sense Orbit describes. For a given field, there are stable or unstable ones Areas for ions of the specific charge e / m. The position and breadth of these areas allows itself through within very wide limits Variation of amplitude, frequency * or waveform of the [field-generating Change tensions.

From this it follows that it is necessary for the excretion of unstable ions requires a certain minimum time during which the ions remain in the separating field. It showed in our own theoretical investigations that for the separation quality or the so-called resolving power, of such fields, it is not the absolute dwell time that is decisive, but the number η of periods of the function f (t) during which the ions are in the separating field. In particular, the experimental investigation on a cylindrically symmetrical field (A = O, ß = / = lj, shows that

ρ in this case is proportional to the achievable resolution η grows. In practically all applications of these fields, efforts will therefore be made to make η as large as possible, which in principle can be done in three ways possible are: " -

1. Using a high frequency at which f (t) oscillates;

2. Use of long and extensive fields; _: 5 · Use of slow ions. '- ·'

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The disadvantages of these routes are discussed below:

1. Theoretical and experimental studies showed that the The high-frequency power required to operate such a mass filter increases extremely sharply with the frequency, in some cases of the symmetrical field with the fifth power of the frequency. Therefore, there are practically very narrow limits to an increase in the frequency.

2. It is evident that the use of very long fields is significant means expenditure on equipment and thus excludes a whole range of theoretically possible applications of these fields in practice, For example, for precision atomic mass determinations would be according to this method fields the length of about 10 m with an accuracy of the apparatus structure of 1/100 mm is required.

3. The use of slow ions "means first of all that the acceleration voltage, with which the ions are extracted from the ion source must be low. But this also makes the extracted Ion current small. This difficulty can be partially avoided by first applying a high extraction voltage for the Ions used, but before they are injected into the separating field * decelerates again. The disadvantage of this method is that after decelerating the ions at considerable angles to the given direction of injection enter the separation field and are for the most part not "captured" by it, i.e. ions with theoretical

'' stable tracks are excreted on the field electrodes, because the maximum value of their oscillation amplitudes is greater than the distance between the field electrodes and the field axis.

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PLA 62/8201

Mass filters have been built in which to achieve a appropriate compromises of the methods according to 2) and>) were used for a given resolution.

The invention relates to a method for separating or separately detecting ions of different specific charges in a temporally periodic field, the potential of which is a square puncture of the coordinates χ ,, γ, ζ of the general form f - ^ f ₁ (t) (αχ + ßy - ^ z) + f _g (t) and f, (t) and f ₂ (t) are arbitrary periodic functions of time. According to the invention, the ions to be separated are then decelerated again after the acceleration, in the ion source after entering the electrical separation field Potential ψ ^ 0 and the potential of the separating field can have the form (äx + Sy - / a) - {ff _Tr , where φ ^ _{ν is} a time constant

Means braking potential for the trapped ions. The bullet aperture of the cannula through which the ions enter the separating field can be at a potential Ψ- ^ Φ and the potential of the separating field

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can have the form f. (t) (c (x + ßy - ^ z). Also can, in particular when using electron impact ion sources, the envelope of the ionization space in which the atoms to be separated are ionized, lie on earth potential. Furthermore, the position and width of the stable or unstable areas by changing the amplitude, frequency and / or waveform of the field-generating voltages will. By superimposing further alternating voltages small amplitude narrow unstable areas are embedded in a stable area, '

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The method according to the invention has the following advantages over the previous one: The ions enter the separating field as a well-focused bundle with fluted !: Radial energies. In the course of their deceleration? '3 ■. The focussing forces of the mass filter are already reduced, so that "capture" in the separating field takes place with a significantly better degree of efficiency than with. the method known from Lusher * This results in a very strong increase in the separate ion flow, which is always more than an order of magnitude greater than the range of values obtained with the previous methods.

Is maxi on one? Increasing the currents is not of interest, then it is possible to analyze ^{belli much slower ions than previously 3.} Dada, "? A is öaa ed sungsverraögen w ^ d ^ ritlieh increased the erfindungsgemfißen to Verwirkliohung eqv method erforc'erlichen constructive measures ailgdE ^ l£.se@n in & af yet h perform for existing devices *?" .. ''"

In particular, it is also possible to use combinations of those described Set options and thereby increase the resolution of the Trenafeldea while at the same time increasing the Strem *

The Varfahrer * is also applicable to the considerable Energieinhomogenität benut & tetO ions and therefore restricts ¹ dis applicability of the general separation process nipht "

Dio Grrreiehten improvements are achieved with eefez * little additional outlay on equipment. >'

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For constructive implementation of the invention, care must be taken that dxs average potential of the separation panel ψ ^ only eineii small amount below is dsm * in which the ions are formed ■ "-, _T /> ■ * Embodiments of the srfindüngsgemäBen solution are in. The Sfv shown in FIGS. 1 and 9 shows:
ο ? g .. i the ElBf Vußraum a Maasenfiltsrs - with associated Pofcentiaibildern, "

. Fig. 2 diagrams vut ät roiwersorgung sines Massenrilters, 3 .gibt measuring Ungar "of the collector current (in ivillkürlichea Eit ^ IOE, · - - ■ ^'5'."

and de « kai 1ύmir: gsyenüogena (m / Am)" again *

In the Fig.la to Ic three possibilities according to the invention are outlined. In the upper part of FIG. 1 a, the electrodes of a measuring filter are shown schematically. The ionization space, which has an exit diaphragm 2, is denoted by 1. In the direction of the exiting ion beam, there are two intermediate diaphragms 3 and the insert diaphragm ² I, which also serves as an extraction diaphragm. The analyzer rods are marked with 5. Fig. 1a shows the case in which the insertion diaphragm is earthed, the formation of the ions takes place at a high positive potential and the entire separating field is also high to slow down the ions.

Fig. Ib shows the case "that the formation of ions of a weak positive potential j ^ ₀ is carried out, and the partition box is driven symmetrically as in the previous method to ground. But then the bullet aperture must be at a strong negative potential f _Ε ^.

In FIG. 1c, the ions are formed at zero potential, acceleration against the strongly negatively biased bullet aperture and braking on daa saw awake negative potent; | §1 of the separating field. 909805/0 887. BAD ORFGLNAL "

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The potential distribution, as it is required by Fig. La and Ic, is easy to achieve because the · DC voltage component U der Function f (t) not fed to the mass filter symmetrically with respect to earth becomes, but asymmetrical. This can be done, for example, by means of a suitable preload (Fig.2a) or by an asymmetrical earth (Fig.2b). The measurement results given later are obtained by this latter method. In the Flg. 2a and 2b are the analyzer rods marked with 11, they are powered by a high frequency voltage source 12 and a · DC voltage source 1. "5 with the required Tensions pass. In FIG. 2a, the voltage divider 14 tapped in the middle is connected to ground via a DC voltage source 15. In Fig. 2b, however, omitting the DC voltage source by shifting the tap of the voltage divider from the In the middle position, the potential shift desired according to the invention takes place. With l6 blocking circles are designated.

The experimental results £ R of an arrangement according to FIG. 1 a are shown in FIG. A cylindrically symmetrical arrangement (^ »(U + V.eostu.t) (x -y ~ * / r ~) was used. The ions are formed in a normal electron impact source at a potential φ ~ and against the Grounded bullet screen accelerates ₍ step through this

■ they enter the separating field with an energy of 70, 20 or 17.5 eV. The braking potential ψ _ is superimposed on the separating field itself, so that the ions with an energy eü _fi «« ^ (ψΎ _Ο "Ϋψ _τ ) pass through the separating field (e =» unit charge). The ion current of 132γ + was measured at the collector and the resolution achieved as a function of U

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It can be seen that to achieve a resolution of about 4000 in this case the energy of the ions in the separating field must not exceed 20 eV. If it is increased to 70 eV, the resolution m / dm drops to 2000. If the ion source itself is operated at 20 V, the ion current obtained is a factor of 8.6 below that obtained when the ions are decelerated according to of the invention from 70 eV down to 20 eV. If one compares these values at 17.5 V, the gain in intensity is even a factor of 12. It is important that the same resolving power is achieved experimentally within the measurement accuracy as In the previous method, the same energy of the ions in the separating field is assumed. (The fact that the curves do not have a completely monotonic course is due to the special construction of the apparatus used.) - Furthermore, the energy homogeneity of the ions is not significantly changed by the braking according to the invention has been proven by measurements.

The method according to the invention is therefore suitable for the performance to significantly increase the mass filter, especially in cases where small dimensions of the apparatus are desired, since then reaching the necessary number η is difficult,

6 claims

3 figures "*

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Claims (1)

PLA 62/8201 Claims i “) Methods for the separation or for the separate detection of ions different specific charges in a temporally periodic field, the potential of which is a quadratic function of the coordinates 2 2 2, Xj, y, z is of the general form ψ = ΐ , (t) (ctx + ßy -fz ) + fo (t) and f ' (t) and fp (fc) are arbitrary periodic functions of time , characterized in that the ions to be separated are decelerated again following the acceleration in the ion source after entering the electrical separation field. 2. The method according to claim 1, characterized in that the Ein-.schußblende or cannula through which the ions get into the separation field, 'is grounded, ie has the potential φ = 0, and that the potential "" ■ · ■■ * "222 tial of the separating field has the form f ^ f ^ t) (λχ + ßy -yz) + f _Tr , in which ^{a ze} M ^ i means constant braking potential for the injected ions. Method according to claim 1, characterized in that the bullet - Diaphragm or cannula through which the ions enter the separating field, 'is at a potential p _Eb f0, and the potential of the separating field has the form, ψ ^ f ^ t) (ax ² + ßy ² - ^ z ² ) H. Method according to Claim 1, characterized in that, particularly when using> electron impact ion sources, the envelope of the ionization space in which the atoms to be separated are ionized is at earth potential. . 9 ... «09805/0887 bad ° original ' PLA 62/8201 Η9897Ί ' 5. The method according to any one of claims 1 to 4, characterized; that the position and width of the stable or unstable areas are changed by changing the amplitude, frequency and / or waveform of the field-generating voltages . 6, method according to one of claims 1 to 5 *, characterized in that by superimposing further alternating voltages of small amplitude . narrow unstable-. Areas are stored in a stable area. 90 9805/088 1 BAD ORIGINAL Pf / Kon