RU2143110C1 - Mass spectrometer - Google Patents

Abstract

FIELD: technical physics, analysis of composition of materials and substances. SUBSTANCE: given mass spectrometer includes pulse ion source, magnetic analyzer with lateral magnetic field and collector connected to recording device. Collector is position-sensitive and is manufactured in the form of individual electrodes connected to recording device with the aid of commutator of synchronous type. EFFECT: two-fold increase of resolution by mass and enhanced signal/noise ratio in spectrum of masses proportional to number of analyzed masses in sample. 1 dwg, 1 tbl

Description

 The present invention relates to the field of separation of charged particles by mass and can be used for chemical analysis of materials.

 An analogue is the time-of-flight mass spectrometer according to A.S. 1725289, class H 01 J 49/40, 1992. It contains an ion source, a mass analyzer with electrostatic mirrors, a detector and associated power sources. The device operates as follows. Ions from the source in a packet enter the analyzer, in which they are separated by the time-of-flight method and recorded by the detector.

 Known mass spectrometer with spatial separation of ions (Survey information Central Research Institute of Instrument Engineering and Instrumentation 1979 M. TS-4. Issue 1 Pages 26, 28, 33). It is a semicircular analyzer with a continuous ion source and a series of collectors of separated ions. The operation of the device is as follows. Ions from the source enter the analyzing magnet in a continuous stream and, when moving in a magnet, are spatially separated along circular paths so that ions of different masses arrive at different collectors.

 Each of the analogs uses the separation of ions either in time or in space.

 A device is known according to US patent N 4472631, class. B 01 D 59/44, 1984. It consists of an ion source with a chromatograph, a span tube with a collision cell, a magnetic filter, a multi-channel detector, and a self-tuning computer. The device operates in a pulsed mode and is intended for mass spectral analysis of secondary ions in a time-of-flight manner at the level of qualitative resolution of ionized fragments of organic substances (such as pure isopropylene) in the mode of parallel registration of ions at a multichannel detector. The operation of the entire device is automated using the built-in electronic control computer.

 In this device, the angular limitation of the applied magnetic sector reduces the spatial separation of the analyzed particles. As a result, the main separation is carried out on a temporary basis, and the spatial separation is only auxiliary in nature and, accordingly, the increase in resolution is insignificant.

 The second disadvantage of the analogue is the use of a multi-channel output for a magnetic sector filter, which leads to a contradiction to the law of electronic optics, according to which the source, the tip of the sector and the image must be on the same line. As a result, a second reason is created for lower resolution of particles in the device.

 In general, the US patent constructively repeats the experimental setup of Soviet physicists (see Kovalev ND and other ZhTF, 1978, v. 48, pp. 1282 - 1285). American progress is in the power of the applied adaptive computer.

 The prototype is a device according to the patent of the USSR 1699355, class. H 01 J 49/40, 1991. The mass spectrometer contains a pulsed ion source, a magnetic analyzer with poles in the form of a tape helix and with a transverse analysis field, and an ion receiver, which is a common collector mounted in the plane of the output end of the electromagnet and connected to the recording appliance. The primary ion packet is separated spatially along the trajectory and time in the analyzing magnet, and partial ion packets are formed. The recording device records only the temporary separation of ions.

 In this spectrometer, as in all time-of-flight, light ions have a higher velocity than heavy ones. In addition, in a magnetic analyzer, ions are spatially separated so that light ions move along shorter trajectories. This effect enhances the time separation of signals from ions of different masses and increases the resolution compared to a conventional time-of-flight mass spectrometer.

 However, in the prototype, the spatial separation of ions by radial coordinates already achieved by the analyzer is used only to increase the efficiency of separation of signals from ion packets by time, because the capabilities due to the design features of the prototype are not fully realized.

 T. about. the task is to create a mass spectrometer that implements both spatial and time-of-flight techniques for obtaining information about the masses of ions.

 The technical result achieved by the invention will be a twofold increase in mass resolution and an increase in the signal-to-noise factor in the mass spectrum, proportional to the number of analyzed masses in the sample.

 To solve this problem, the mass spectrometer, like the prototype, contains a pulsed ion source, a magnetic analyzer with a transverse magnetic field and an ion receiver, made in the form of a collector associated with a recording device.

 Unlike the prototype, the ion collector is position-sensitive in the form of separate electrodes connected to the recording device through a synchronous type switch.

 As an example in FIG. 1 shows a schematic diagram of a device with an electromechanical type switch.

 The device contains a pulsed ion source 1, an electromagnet with poles 2 creating a transverse magnetic field, an ion receiver 3 made in the form of a position-sensitive collector with separate isolated detectors 4 connected to the recording device 5 through a switch. Detectors 4 are made in the form of plates and are installed in the plane of the output end of the electromagnet and are electrically connected to a switch, which is made on the basis of a plurality of electrical contacts 6 arranged around a circle along which an electric brush 7 moves, the second end of which is connected to a recording device 5.

 The device operates as follows. The primary packet of ions under the action of a pulsed ion source 1 is injected into the magnetic field created by the poles 2 of the electromagnet. In accordance with the laws of electrodynamics, ions of different masses make a circular motion along the trajectory of different radii with different speeds, which are determined by the masses of ions. As a result, the primary ion packet is divided into partial ion packets of the same mass. Partial packets arrive at the output end of the electromagnet at different times and in different places. The packet of the lightest ions comes first and it pours out onto detector 4.1, which is located closest to the source. The next packet comes to detector 4.2 and so on. All subsequent partial packets arrive alternately at respectively more distant detectors. The spatial extent of partial packets is inversely proportional to their own masses. The time duration for all packets is the same and equal to the duration of the injection pulse. The coordinates of the detecting plates and the arrival times of ions on them are determined mathematically. The switching of the detecting plate 4 with the recording device 5 is carried out only during the precipitation of ions of a partial packet on the detecting plate, i.e. synchronously. The ion current of the partial packets in the recording device 5 creates a spectral line.

The electromechanical switch is structurally represented by a ring of insulating material on which contact plates with a width of 0.15 mm are mounted with insulating spacers with a thickness of 0.01 mm. In the center of the ring is a brush that sits on the shaft of a synchronous motor rotating at a speed of 3000 rpm. With a ring radius of 500 mm, the brush contact time with the collector plate will be 0.95 • 10 ^-6 s, which is quite comparable with the injection pulse duration. The device can be equipped with another type of synchronous switch, for example, transistor.

 The noise background in the spectrum of the sample is created by random ions in the interpolar space of the drift. To reduce it, the detecting plates 4 are connected to the recording device 5 only for the time of precipitation of ions of a given partial packet and only to this detecting plate.

,
где r - радиус траектории,
v - скорость иона.The mathematical model of the device in question is formulated as follows. The time of ion motion along a semicircular trajectory from the injector to the detector

,
where r is the radius of the trajectory,
v is the ion velocity.

,
где B - магнитная индукция,
m - масса иона,
u - ускоряющее напряжение,
q - заряд иона.The radius of the trajectory is determined by the well-known formula

,
where B is the magnetic induction,
m is the mass of the ion,
u is the accelerating voltage,
q is the ion charge.

После подстановок получаем, что время движения определяется собственными параметрами иона и магнитным полем

Длительность импульса инжекции ограничивается временем движения самых легких ионов
τ ≤ t₁
Разрешающая способность устройства определяется суммой разрешений в пространстве и во времени
R_Σ = R_r+R_t
Пространственное разрешение определяется формулой

,
которая в данном случае приводится к виду

Временное разрешение соответственно выразится

В итоге получается, что пространствено-временное разделение ионов удваивает разрешение

Результаты расчетов для однократно ионизирующих ионов при индукции 326 гс и ускоряющем напряжении 128 вольт приведены в таблице 1.The ion velocity is expressed by the formula

After substitutions, we obtain that the motion time is determined by the eigenparameters of the ion and the magnetic field

The injection pulse duration is limited by the travel time of the lightest ions
τ ≤ t ₁
The resolution of the device is determined by the sum of the resolutions in space and time
R _Σ = R _r + R _t
The spatial resolution is determined by the formula

,
which in this case is reduced to

Temporary resolution will be expressed accordingly

As a result, it turns out that the spatiotemporal separation of ions doubles the resolution

The calculation results for single-ionizing ions at an induction of 326 gf and an accelerating voltage of 128 volts are shown in Table 1.

 In general, all the numerical data show the feasibility of the proposed device.

 Synchronously with the injection pulses of the primary ion packet, the switch of the recording device 5 is started, and it is triggered by the first detector 4 by the moment the first (lightest) partial ion packet arrives and only for the time of precipitation. With the end of the rash, the switching element turns off the first detector and goes to the next. The operation is repeated with each detector. With the receipt of the spectral line from the last detector, the cycle ends and can be repeated. However, the whole mass spectrum of the test sample can be obtained from one primary pulse. This is a single-pulse analysis mode.

 The sensitivity of the device will also be improved, because the injection is carried out by sufficiently long pulses, the length of which is determined by the transit time of the lightest ions in the packet. A high signal to noise ratio is achieved due to the selective switching of the detector 4 with the recording device 5.

 The device retains all known focusing inherent in magnetic analyzers and allows the use of known focusing on energy in a transverse electric field.

 The device allows you to perform analyzes and well-known traditional methods: only spatial or only temporary. To do this, it is enough to change the operating mode of the injector, i.e. put it in continuous operation, and detectors scan in turn at regular intervals. For the time-of-flight method, the detectors must be connected in parallel.

 Thus, the device has various functional capabilities and can be implemented both for precision scientific research and specialized commercial measurements.

Claims (1)

 A mass spectrometer containing a pulsed ion source, a magnetic analyzer with a transverse magnetic field and an ion receiver, made in the form of a collector connected to a recording device, characterized in that the collector is made position-sensitive in the form of separate electrodes connected to the recording device through a synchronous switch type.

Images