SU1691905A1 - Method of formation of ion mass line in time-of-flight mass spectrometer - Google Patents

Abstract

The invention relates to instrumentation automation and control systems, in particular to the technique of mass spectrometry. The aim of the invention is to reduce the time dispersion of the mass line associated with the dispersion of the initial ion velocities. The method provides space-time focusing of ions with different initial speeds of movement, not exceeding a predetermined value. The device implementing the method contains an ion source with an electron gun 1, a grounded grid 2, an accelerating grid 3, a generator of 4 ejection pulses, a generator of 5 deflecting pulses, deflecting plates 6 of a transverse electric field, a receiver 7 of ions, a pulse amplifier 8 and an oscilloscope 9. In order to eliminate the effect of ions having an initial velocity higher than a given one, their deviation in a bespor-less gap is provided. 4 silt (L S

Description

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figs

1 jubilee refers to the instrumentation rp ° / V in automation and systems of control, in hcpchti to the technique of mlss scrometry

The circuit of the invention is a decrease in the time dispersion of the produced mass line associated with the dispersion of the initial ion velocities.

FIG. 1 shows a geometrical scheme of the time of the final mass spectrometer, the ionization plane; figure 2 is a graph of the dependence of the push pulse of the electric field U (t) - EI (i) (lot - oz); on fmg.Z - the flow diagram of the time-of-flight mass spectrometer that implements the proposed method of forming a mass line; Fig. 4 is a block diagram of an electronic unit with which a pulse U-U (t) is generated in accordance with the time dependence according to the proposed method.

A device that implements the proposed method (FIG. 3) contains an ion source with an electron gun 1, a grounded segment 2, an accelerating grid 3, a generator of 4 ejection pulses, a generator of 5 deflecting pulses, deflecting plates 6 of a transverse electric field, a receiver 7 ions (WPP), pulse amplifier 8, oscillograph 9

The grounded grid 2 is located between the accelerating grid 3 and the receiver 7 io s. The flow of electrons from the electron gun 1 creating an ionization plane in the ion sputum, located between the accelerating 3 and grounded 2 grids. The deflecting plates b are located in a non-floor space near the grid 2 perpendicular to the grid plane 2.

The sync output of the 4 ejecting pulse generator 4 is connected to the synchronization inputs of the electron gun 1, the deflection pulse generator 5, the oscilloscope 9, and the second output is connected to the accelerating grid 3 The ion receiver 7 is connected via the pulse amplifier 8 to the oscilloscope input 9,

The generator of push pulses (figure 4) consists of a quartz resonator 10, a generator 11 trigger pulses, generator 12, counter 13 time, ROM 14, DAC 1b, counter 16 masses, multiplier 17, output amplifier 18.

The generator 11 of the starting pulses is connected to the start input of the time counter 13, to the 16 mage counter input and to the synchronization output of the generator 4, pushing out the pulsator Quartz resonator III is connected to (rnr mount 12, the output of which is connected to in hh by input 13.

The output of counter 3 SORPPSN g of the ROM 14 which is connected to the output of the CLP 15 The output of the DAC 15 is connected to the first input, and the output of the counter 16 mass - to the second input of the multiplier 17. The output of the multiplier 17 is connected to the input of the amplifier 18, the output of which is a functional output of the generator four,

The pulses from the generator 11 start the counter 13, which counts the pulses from the generator 12, the frequency of which is determined by the quartz resonator 10. At the same time, all the ROM cells in which the samples of the signal are recorded that are to be generated at the specified times are searched. Codes arrive at the DAC. which converts them into an analog signal, which is a step function and is fed to the input of multiplier 17 (the multiplication factor is proportional to the code of the mass counter and is equal to the mass number). Passing through the multiplier, the signal is amplified in gain block 18 to the required magnitude and smoothed.

The enumeration of masses is carried out by changing the state of the counter 16 by 1 at the moment of forming the pulse from the generator 11.

The isochronism of the passage of ions with speeds, where Vrp is the limiting velocity of ions, i.e. the speed of the ions flying through the accelerating gap loi during the time to, in the proposed method is ensured by the fact that ions having a higher initial velocity fly out to a weedless space with speeds Vi2 smaller than ions having a lower initial velocity

The time dependence of E (t) is found from the equations of motion of ions in an alternating field and the conditions of isochronism of the passage of ions to the ion receiver.

x CR- "

Initial conditions: when, Ho-0; V (0) - V0

Denote S-fj-® w (t),

m

then

u

(2)

Viz / w (t) dt + V0,

0

where Vi2 is the speed of departure to the floorless space;

u the moment of departure of the ion into the floorless space.

The time ti is determined from the equation

tlT

loi V0ti (t) dt dr (3)

about o Then we get

v / tir

one

W

n (T-tO

The relation (O gives the desired law of acceleration, and also the time dependence for the pulses of the electric field. Since with tr-0 w (0} -. .To, for the physical implementation of this method of ion acceleration during time to, the acceleration WQ must be constant, and then, from time on, change the acceleration w (t) in accordance with the law.

The ions emitted into the zero-free space ahead of time to will be deflected by the transverse field E in the transverse direction and will not participate in the formation of the mass line by the time of the transit mass spectrometer. Thus, in contrast to the known method of forming a mass line, in the proposed method, all ions with initial VoSVrp speeds, where Vrp is the limiting focusing rate, and ions with speeds, are involved in forming the mass line. not possessing isochronism of the span, do not participate in the formation of the mass line The proposed method of forming a mass line completely eliminates the time dispersion of the mass line associated with the dispersion of initial velocities.

When forming the mass line during the transit mass spectrometer, besides reducing the time dispersion of the mass line, it is of fundamental importance that ions with a different mass mi do not participate in its formation.

It can be proved that the proposed method of forming a mass line satisfies this condition.

Let the pushing impulse E (t) be tuned to ions with a mass td. Togtsa equation of motion for an ion with

mass t & td (5)

 + 12 |,

Wto

 H} That -I

will have a look.

(t)

Where

f eo,

E (th.

(.., -, Tcq (Tf) -t) 2

Initial conditions: at, X (0) 0, V (0) Vo.

By integrating the equation of motion (5) and expressing Vo through ti (the moment of flight to a non-floor space with speed Via), we can get an expression for the speed Vi2 as a function of Id

., front V12-, oi - n

The base time of flight T for an isochronous mass of yy is determined by the ratio

112

T 5 YTT: - 7

. 01, W0to 2

(6)

five

0

Thus, the transit time T of ions with mass m will be equal to

. m

I n md t1 12 0to, -. - --....-.

Since the time q depends on the initial speed / o. those. (Vo), then from expression (2) it follows that for ions with a mass t- (T, and vice versa, at.

It can be shown that for ions with a mass time of flight Ti. T.

Ions with a mass that fly out to a no-field space for about time to will deviate from the longitudinal direction by the transverse field EL. acting during this time, they will not get into the ion receiver, which means they will not take part in the formation of a mass line during the transit mass spectrometer.

By changing the parameters of the pushing impulse of the electric field E (t), it is possible to form mass lines with different mass m. Parameters to. Eo affect the value 0 of the limiting velocity Vrp of the time focus, since

v / - o1 m p b (o)

Vrp-75- to tg (o)

to 2t 2

As the duration to increase, the limiting velocity Vrp decreases.

As the initial intensity Eo increases, the limiting velocity Vrp also decreases. A characteristic feature of the time dependence of the push pulse (t) is a jump at time tMQ. Jump size (to) -Ep. If LE is 0 (condition of continuity at the moment), TO is the boundary velocity

Vrp- 0 () 2

Thus, if the function E (t) is implemented in a continuous manner, then the region of ion focusing shifts to the region of negative velocities.

As a specific example implementing the proposed method, the time-of-flight mass spectrometer was used with the following parameters: cm: 1.2–9 cm; 1o 10µs; Tf-IOOmx.

The law of change of the push pulse voltage is

Oh 0 t to

( (9

i d L, the volume number of the ion with the i-th mass, a. eat.,

inn - atomic mass unit; q is the ion charge.

Substituting the selected values of the parameters of the mass spectrometer, we obtain for a hydrogen ion U (to) 3.46 V, for an ion with AgO2 Amu. U (to) 346 V. At the same time, the point of location of the mass line on the time axis will also be equal to Tyo 10 µs.

The formation of the mass line during the transit mass spectrometer is carried out as follows.

In the ion source 1 by the electron flow hV3. formed in a short time (0.05-0.1 ms), ionization of atoms creates ions in a narrow zone (1-2 mm) in the X – Q plane. Ions having an initial velocity VQ are accelerated by a push pulse, which is applied to the grids 2-3 from the push pulse generator, producing a pulse U (t) in accordance with the law of its voltage variation with time proposed in the proposed mass line formation method during the transit mass spectrometer (figure 2). The ions emitted into the no-field space during the time from zero to to are deflected by a transverse field E, which is created by a generator 5 of deflection pulses when a pulse is applied to the deflection plates 6. The deflection pulse has a rectangular shape, an amplitude of 200 V and a duration to.

Moreover, only a given mass comes to the receiver of ions 7 at the estimated time, i.e. the mass line contains one mass, all other masses come sooner or later by pepemen. The ion pulse of the mass under investigation is amplified by the pulse amplifier 8 and recorded by an oscilloscope 9. To study another mass line, it is necessary to change the amplitude of the push pulse, and its dependence on the number of ion masses is linear.

The use of the proposed method of forming a mass line during the time-of-flight mass spectrometer makes it possible to increase the mass resolution regardless of its number and the dispersion of the initial ion velocities, which cannot be achieved by any of the known mass line focusing methods.

Another advantage of the proposed mass line formation method during the transit mass spectrometer is the possibility of compressing the range of voltage variation ij (t) sa by additionally measuring the trough measurement together with the amplitude U (to). It nygakayet of the ratio

UM-PAll (10)

 to (T - to) 2

Where

 V.S2.

TH

TC is the position of the mass line of hydrogen ions H, C;

gpn mass of hydrogen atom, kg, At selected parameters of the mass spectrometer U (to) 346 V

Thus, the deployment of masses in a given mass spectrometer can be carried out as follows.

In the mass range Ai 1-100 amu

U (, 46-346B; T (5r 10 µs const; toH µs. In the mass range of AgOU-10000 amu U (to) 346 B const, TH VAT; toi THVA / 10, T3K that 20 T 5 | 10-1000 µs: to 1-100 µs.

Claims (1)

DETAILED DESCRIPTION OF THE INVENTION A method for forming a mass ion line during a transit mass spectrometer, including ionizing atoms in an ion source, accelerating ions with a pushing pulse of a uniform electric field, drifting ions in a free space, and detecting ions in order to reduce the time dispersion of the mass line, the ions are accelerated by an ejecting impulse of the electric field, the time dependence of which has the form Eo. EW- . "Q t (t - t) 2 parameters E0, to are related by five 0 five 0  g-- 112 loi, q eo to H to five 0 five / 01 Vrp-- V 2 m q Eg t0 2m rqe Eo - electric intensity no-1 / g. V / m; m is the mass of the ion, kg; q- ion charge, K; J T is the location of the mass line on the time axis, s; n is the length of a non-floor space; m; loi distance from ionization to ambient-free space, m; to the duration during which the intensity is constant in time. c; Vrp is the ion velocity, passing the accelerating gap loi during the time t0 (m / s), which characterizes the maximum energy 6) /// 77 // 7-Ч - n-f - М-i- (-t - (- i - (- h Ota -I 7 FIG. 2 CD Fig.4 Compiled by V. Kascheev Editor A. Makovska Tehred M. Morgentel figure 1 U (to} Uo ten -1-1. Iff 7 FIG. 2 Proofreader A.Osaulenko