JPH11288684A - Time-of-flight mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion detection system of a vertical acceleration type time-of-flight mass spectrometer in which the loss of data due to the saturation of an ion detector does not occur even if an ion pulse of high ion strength is incident on the ion detector. SOLUTION: A plurality of microchannel plates (or microsphere plates), to which different voltages V1 , V2 , V3 are applied by a power supply 9 so that they have different secondary electron amplification rates, are arranged as ion detectors 8, and the lacking part of data about dead time derived from the saturation of the microchannel plate (or microsphere plate) of the higher amplification rate when an ion pulse of high ion strength is incident thereon is complemented by data obtained from the microchannel plate (or microsphere plate) of the lower amplification rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-of-flight mass spectrometer, and more particularly, to a technique in which a high-voltage pulse voltage is applied to ions introduced from an external ion source into an ion reservoir to intersect the flight direction of the ions. The present invention relates to a vertical acceleration time-of-flight mass spectrometer that analyzes ions by mass-to-charge ratio after accelerating ions in the direction of flight.

[0002]

2. Description of the Related Art Time-of-flight mass spectrometers (TOFMS)
Uses the fact that when the same kinetic energy U is applied to ions, the smaller the mass-to-charge ratio M (= m / z) of the ions, the faster the ions arrive at the ion detector. Assuming that the total time of flight over the flight distance L of the ion is t _TOF and the width of the ion pulse is Δt, the resolution R of the obtained mass spectrum is given by equation (1). R = M / ΔM = t _TOF / 2Δt (1) t _TOF = L√ (m / 2U) If the flight distance L of the ion is constant, according to the equation (1),
The smaller the ion pulse width Δt, the higher the resolution R. For this reason, a so-called pulse ionization method using an ultraviolet laser pulse has been developed as the simplest method for shortening the pulse ion width Δt, whereby an ion pulse of several ns is generated. As a device combining TOFMS as a spectrometer with this pulse ionization method, SIM
S / TOF, SNMS / TOF, and MALDI / TO
There is F.

On the other hand, ionization methods such as EI, CI, ESI, and ICP are called continuous ionization methods in contrast to the above-mentioned pulse ionization method. One of the TOFMSs combined with the continuous ionization method is a vertical acceleration time-of-flight mass spectrometer (Orthogonal Acceleration TO
FMS: OA / TOF) has been proposed (JHJDawson
and Guihause, Rapid commu. Mass Spectrom.,
3, (1989), 155).

FIG. 1 shows a schematic diagram of OA / TOF. When the ion beam 3 introduced from the external ion source 1 into the ion reservoir 2 with the kinetic energy eV ₁ fills the ion reservoir 2 having the length y ₀ , a high-voltage pulse voltage (V ₂ ) is applied to the ion pushing plate 4, The ions are accelerated in the direction perpendicular to the flight direction (the direction of the optical axis of the TOFMS) with kinetic energy eV ₂ , are discharged from the ion reservoir, and fly through the TOFMS spectroscopy unit 5 and reach the ion detection unit 6. The cross-sectional shape of the ion beam reaching the ion detector is a rectangular shape reflecting the shape of the ion reservoir, and has a width of several cm to 10 cm and a width of several mm.

[0005]

An ion detector is usually a surface detector and has a short secondary electron transit time and a microchannel plate (MC) having a secondary electron amplifying action.
P) or one microsphere plate (MSP) is used. However, MCP (or MSP)
When an ion pulse having a high ion intensity (a large number of ions) is incident, saturation occurs as a secondary electron multiplier. The length of time over which this saturation can be resolved depends on the MCP
(Or MSP), but is typically dominated by the microsecond order. For this reason,
Until the saturation of the MCP (or MSP) is eliminated, a dead time as an ion detector occurs, during which spectrum measurement cannot be performed and data is lost.

[0006] If the mass-to-charge ratio (m / z) of an ion pulse having a high ion intensity is known in advance, the MCP (or MCP) can be obtained in a short time immediately before the ion reaches the ion detector.
SP), the voltage applied to the ion detector is reduced and restored, and only when the ion pulse having a high ion intensity arrives, 2
There is a method of lowering the secondary electron gain (MCP gate method). Although this method has the effect of shortening the dead time, it is difficult to predict such time in advance when measuring the spectrum of an unknown sample.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a vertical acceleration time-of-flight mass that does not cause data loss due to saturation of an ion detector even when an ion pulse having a high ion intensity is incident on the ion detector. An ion detection system for an analyzer is provided.

[0008]

In order to achieve this object, a time-of-flight mass spectrometer according to the present invention provides a high-intensity pulse voltage to ions introduced from an external ion source into an ion reservoir. In a time-of-flight mass spectrometer that accelerates ions in a direction that intersects the flight direction of the ions and then flies a certain flight distance to analyze the mass-to-charge ratio of the ions, a plurality of microelectrodes with different secondary electron amplification factors Channel plates (or microsphere plates) are arranged side by side as ion detectors, and the insensitivity resulting from the saturation of the high-amplification microchannel plates (or microsphere plates) when an ion pulse having a high ion intensity is incident. Microchannel plate (or microsphere plate) with low amplification rate for data missing part of time It is characterized in that is complemented by al obtained data.

In addition, after applying a high-voltage pulse voltage to the ions introduced from the external ion source into the ion reservoir, the ions are accelerated in a direction intersecting the flight direction of the ions, and then are made to fly a certain flight distance. In a time-of-flight mass spectrometer for analyzing the mass-to-charge ratio of ions, the spectrum is integrated using a signal averager in order to improve the S / N ratio of the obtained spectrum.

[0010] In addition, after a high-voltage pulse voltage is applied to ions introduced into the ion reservoir from an external ion source to accelerate the ions in a direction crossing the flight direction of the ions, the ions are caused to fly for a predetermined flight distance. In a time-of-flight mass spectrometer for analyzing a mass-to-charge ratio of ions, a plurality of microchannel plates (or microsphere plates) having different secondary electron amplification factors arranged in parallel with the direction of incidence of ions are provided. A plurality of preamplifiers for amplifying the output from the plate for each plate, a plurality of A / D converters for performing an A / D conversion of the output from the preamplifier for each preamplifier, and collectively processing the output from the A / D converter And a data processing system for performing the processing.

[0011] In addition, by applying a high-voltage pulse voltage to the ions introduced from the external ion source into the ion reservoir, the ions are accelerated in a direction intersecting the flight direction of the ions, and then are caused to fly a certain flight distance. In a time-of-flight mass spectrometer that analyzes the mass-to-charge ratio of ions, after the AD converter and before the data processing system,
A plurality of signal averagers for integrating outputs from the plurality of AD converters for each AD converter are provided.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an ion detection system of the vertical acceleration time-of-flight mass spectrometer according to the present invention. The ion pulse 7 is incident on the ion detector 8 while keeping the strip-shaped beam cross-sectional shape. The ion detector 8 has three MCPs (or MSPs) arranged in parallel according to the shape of an ion pulse, and different voltages V ₁ , V ₂ , V ₃ is applied. As a result, 3
Each MCP (or MSP) has a different secondary electron amplification factor. For example, the secondary electron amplification factors are relatively x1, x10, x100, (or x1, x1 respectively).
/ 10, × 1/100). This is, of course, x1 / 3, x1 / 9, x1 / 27 or x1
A setting such as / 5, × 1/10, or × 1/25 may be used. The point is to provide a parallel detection system in which the applied voltage of the MCP (or MSP) is set so as to have a plurality of different secondary electron amplification factors.

A preamplifier 10, an AD converter 11, and a signal averager 12 are connected in series to the three MCPs (or MSPs). And 3
The signal averagers 12 are collectively connected to one data processing system 13.

This ion detection system operates as follows. First, the incident signal of the ion pulse 7 from the ion detector 8 is individually output to three preamplifiers 10 connected to each of the three MCPs (or MSPs), and is amplified by the operation of the preamplifier 10. . The amplified analog incident signal is converted into a digital signal in the AD converter 11. The digitized incident signal is repeatedly integrated in the signal averager 12, and S
/ N ratio is improved. In a time-of-flight mass spectrometer,
Since high-speed measurement of 50 to 100 k times per second is possible, such improvement of the S / N ratio by integration is very effective.
The incident signal with the improved S / N ratio is taken into the data processing system 13 and subjected to various data processing.

The countermeasures against dead time due to saturation of the ion detector itself are as follows. In FIG. 2, for example, when the MCP (or MSP) having the maximum secondary electron amplification factor is saturated by a strong ion pulse, the spectrum of the portion missing in the dead time becomes the MCP having the lower secondary electron amplification ratio.
(Or from MSP). That is, since the spectrum observed with the MCP (or MSP) having a lower secondary electron amplification factor has no data loss due to saturation, multiply the ratio of the secondary electron amplification factor between the two MCP (or MSP). This is because the data portion lost due to the saturation can be reproduced, and almost complete spectrum can be reconstructed by the processing of the data processing system 13.

This method has further advantages in the case of MSP. Since the linearity of the secondary electron gain in the MSP is 10 ³ to 10 ⁴ , having an ion detection system having a plurality of secondary electron gains has the advantage that the total dynamic range of the ion detector can be expanded. is there.

[0017]

As described above, the use of the vertical acceleration time-of-flight mass spectrometer of the present invention makes it possible to easily compensate for the lack of data due to the saturation of the ion detector. Even when measuring a mass spectrum, the measurement can be performed without worrying about saturation of the ion detector.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional vertical acceleration time-of-flight mass spectrometer.

FIG. 2 is a diagram showing an ion detection system of the vertical acceleration time-of-flight mass spectrometer of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... External ion source, 2 ... Ion pool, 3 ... Ion beam, 4 ... Ion extrusion plate, 5 ... TOFMS spectroscopy part, 6 ... Ion detection part, 7 ... Ion pulse, 8 ...
Ion detector, 9: MCP power supply (or MSP power supply), 10: Preamplifier, 11: AD converter, 1
2 ... Signal averager, 13 ... Data processing system.

Claims (4)

[Claims] 1. A high-voltage pulse voltage is applied to ions introduced from an external ion source into an ion reservoir to accelerate the ions in a direction crossing the flight direction of the ions.
In a time-of-flight mass spectrometer that analyzes a mass-to-charge ratio of ions by flying over a certain flight distance, a plurality of microchannel plates (or,
A microsphere plate) is arranged side by side as an ion detector, and a microchannel plate with a high amplification factor when an ion pulse with a strong ion intensity is incident (or
A time-of-flight mass spectrometer characterized in that data missing from the dead time due to saturation of the microsphere plate is complemented by data obtained from a microchannel plate (or microsphere plate) having a low amplification factor. 2. The method according to claim 2, wherein a high-voltage pulse voltage is applied to the ions introduced into the ion reservoir from an external ion source to accelerate the ions in a direction intersecting the flight direction of the ions.
In a time-of-flight mass spectrometer that analyzes a mass-to-charge ratio of ions by flying over a certain flight distance, the spectrum is integrated using a signal averager in order to improve the S / N ratio of the obtained spectrum. The time-of-flight mass spectrometer according to claim 1, wherein: 3. A high-voltage pulse voltage is applied to ions introduced from an external ion source into an ion reservoir to accelerate the ions in a direction crossing the flight direction of the ions.
In a time-of-flight mass spectrometer that analyzes the mass-to-charge ratio of ions by flying over a certain flight distance, a plurality of microchannel plates with different secondary electron amplification factors arranged in parallel with the direction of ion incidence (Or microsphere plate), a plurality of preamplifiers for amplifying the output from the plate for each plate, a plurality of A / D converters for performing A / D conversion of the output from the preamplifier for each preamplifier, and the A / D converter Time-of-flight mass spectrometer, comprising: a data processing system for batch-processing the output from a computer. 4. A high-voltage pulse voltage is applied to ions introduced from an external ion source into an ion reservoir to accelerate the ions in a direction crossing the flight direction of the ions.
In a time-of-flight mass spectrometer that analyzes a mass-to-charge ratio of ions by flying over a certain flight distance, outputs from the plurality of AD converters are output to each AD converter at a stage subsequent to the AD converter and at a stage preceding the data processing system. 4. The time-of-flight mass spectrometer according to claim 3, wherein a plurality of signal averagers are provided for integrating the signals.