JP2000231901A - Mass spectrometer by image analizing method or mass spectrometry using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the dynamic range of a measurement strength to shorten the measuring time, by transforming the output from an ion detector to a two dimensional light signal by using a flying time spectrometer, by inputting it into a personal computer and applying an image analysis to it to measure its mass spectrum, and by applying a mass analysis to an isotope. SOLUTION: A specimen cell to atomize a specimen, a laser system to ionize the specimen and an accelerating electrode to accelerate the ionized atom are individually disposed at one end in a flight tube(FT). A time-of-flight mass spectrometer in which a micro channel plate(MCP) individually provided with a sweep electrode on its front surface and a fluorescent screen on its rear surface is disposed at other end in the FT is used. An output electron produced by colliding an ion mass-segregated by its flying speed in the FT onto the MCP by the sweep electrode is transformed to a light signal on the fluorescent screen, and a picture processing is applied to it after catching it by a CCD camera. Thereby, isotope compositions of specimen elements can be simultaneously measured even if their abundance differs by five figures or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing mass spectrometry of trace isotopes such as calcium-41, nickel-59, and chlorine-36, which are nuclides having a long half-life, using an image analysis method. It is.

[0002]

2. Description of the Related Art Conventionally, in order to measure a nuclide having a long half-life such as calcium-41 with high sensitivity, it is more advantageous to measure atoms of the nuclide than to measure radiation accompanying its decay. there were.

[0003] Therefore, as a method of measuring atoms of this nuclide, a laser resonance ionization mass spectrometry (RI) has been used until now.
Basic studies have been conducted on high-sensitivity analysis of trace isotopes of nuclide atoms that are not affected by isobaric or molecular ions by using MS).

A typical mass spectrometer used in the RIMS is a time-of-flight mass spectrometer (TOFMS: Time).
-Of-F1right Mass Spectrometer
As shown in FIG. 1 and FIG. 2, it is that the atomized sample is ionized by an ionization laser in an electric field (between the accelerating electrodes), and the obtained ions are drifted into a drift space (electric field or the like). Free space)
In this space, mass discrimination of ions based on flight speed is performed in order of light ions to heavy ions. That is, in this system, the electrons that arrive at the microchannel plate (MCP) via the drift space and collide are multiplied by the MCP, and the output electrons are collected at the anode and detected, as shown in FIG. The output was measured using a digital oscilloscope or the like.

[0005]

In the above-mentioned laser resonance ionization mass spectrometry (RIMS), the ratio of the target isotope to the other isotope is determined in order to quantify the target trace amount of isotope. It was necessary to ask for. However, when measuring the abundance ratio based on the current value obtained from the ion detector of the laser resonance ionization mass spectrometer, the dynamic range of the detector is limited, and isotopes with a high abundance ratio Therefore, the accuracy of current measurement of isotopes having a low abundance ratio immediately after generation of a strong current is low, and the performance of RIMS cannot be fully utilized in many cases.

In the conventional time-of-flight mass spectrometer, ions of each isotope are detected in synchronization with ionization by a laser. For example, calcium is 4
0 to 48 isotopes arrive at the detector with a time lag,
If the ratio of the ion with the highest abundance to the ion with the lowest abundance is 8 bits or more (256: 1 or more), it is impossible to measure both ions because they do not fall within the measurement range. Become. That is, there is a problem that a small signal cannot be measured when trying to see a large one, and a large value becomes a constant value over scale when trying to see a small one. Further, in this conventional analyzer, ions are mass discriminated and fly within a time period of several microseconds, so that accurate measurement is impossible without a nanosecond-level time resolution. With current digital signal processing, products with a time resolution of 0.1 nanosecond can be used, but the resolution of signal strength is said to be the highest at 8 bits due to the limitation of high-speed analog / digital conversion. There are also problems.

[0007]

The present invention solves these problems by using a time-of-flight mass spectrometer and converting the output from the ion detector into a two-dimensional optical signal. The target isotope is taken into a personal computer and subjected to image analysis to measure a mass spectrum to perform mass analysis of a target isotope. That is, by using an anode surface coated with a fluorescent substance on a microchannel plate (MCP) used in a time-of-flight mass spectrometer,
It is possible to convert the isotope ion that has reached the CP into an image waiting for two-dimensional information (positional information and intensity).

[0008] In view of this, the ions that have been mass-discriminated according to their flight speeds are sorted to the position where they reach the MCP by using a sweep electrode, so that the ion amount of the isotope is determined from the intensity of the optical signal on the phosphor screen, and the position is determined. Time, that is, mass information can be obtained from the information. Furthermore, cooling type CC
By using a D camera, in a method of analyzing an image, a dynamic range of 16 bits or more can be used for light intensity, and accurate position information can be handled at the same time.

In the present invention, a pulse triangular wave is applied to the sweep electrode in synchronization with the passage of ions at the stage when mass discrimination based on the velocity is performed, and an electric field change in a direction perpendicular to the traveling direction is given to each of them. The arrival position of the isotope is swept, the output electrons are generated by the ions that have reached the MCP and collided, and the output electrons collide with a phosphor screen arranged behind the MCP to be converted into light spots on the phosphor screen, The light spot is observed with a CCD camera and transferred to a personal computer for image analysis.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of the analysis method of the present invention will be described with reference to FIG. A microchannel plate (MCP), which is often used in a time-of-flight mass spectrometer, uses a readout system with a fluorescent screen, and a positive / negatively charged sweeping electrode is placed in front of the MCP. A CCD camera.

As shown in FIG. 5, isotopes ( ^{nM +} , ^{n + 1} M ⁺ , ^{n + 2} M ⁺ ) ionized by a laser are
, Is mass-discriminated speedily by its difference in mass, and is separated by an electric field in the order of arrival by a sweeping electrode placed in front of the MCP, and the separated isotope ions are doubled by the MCP. It becomes a light spot on the phosphor screen. The light spot is recorded by a CCD camera. As a result, the ion amount of the isotope can be obtained from the intensity of the light spot on the phosphor screen, and the mass information can be obtained from the position information.

In the case of the present invention, as shown in FIG. 6, information of time, that is, mass is converted into position information of a detector, and information of the number of flying ions, that is, information of the abundance of isotopes, is used as the light intensity. (Bright and dark), and these pieces of information can be fixed on the image. Then, by processing the information fixed on the image later, high-speed conversion processing becomes unnecessary, and therefore, the dynamic range can be expanded.

In the above image processing, once the mass to be measured is determined, the conditions of the arbitrary waveform device are determined. Therefore, the mass of the object to be measured is developed better in the image than the mass is examined from the image. That is, for example, if the mass of calcium-40 to 48 is checked, this part of the image is determined in advance as calcium-40, and this part is determined as calcium-42.
In addition, the abundance of sample elements is determined by the intensity of light emission (actually, integrated value).
Can be calculated by image analysis, and the actual operation is performed by analyzing which part shines and how much.

The role of the sweep electrode in the present invention is to change the trajectory of the flying ions in the order of arrival, and the mass discrimination is completely performed on the ions before they reach the position of the sweep electrode. Therefore, in the present invention, it is possible to prevent a decrease in resolution that occurs in signal processing, and to perform more accurate time-of-flight mass spectrometry.

In the present invention, a CCD used for measurement
The camera is capable of measuring the light intensity in 16 bits in 65536 steps, and the resolution of the intensity is at a level of 16 bits or more through processing by image analysis.

The MCP used in the present invention is shown in FIG.
a, b, as shown in FIG.
This is a plate formed by bundling micrometer glass tubes, and using a fluorescent screen as its readout surface.

The structure of the time-of-flight mass spectrometer of the present invention is the same as that of the conventional time-of-flight mass spectrometer before reaching the sweep electrode. It is characterized in that an MCP using a phosphor screen is used for the readout system.

[0018]

EXAMPLE As shown in FIG. 4, a time-of-flight type mass spectrometer was used as the mass spectrometer, and a linear type with a flight tube (drift space) of 2.5 m was used. The analyzer is provided with an accelerating electrode in the flight tube, and an Einzel lens is disposed immediately after and at a position of 1 m from the accelerating electrode, where the ion flow of the isotope is narrowed down sequentially. In addition, a sweep electrode provided with a 3 mm slit is arranged 50 cm before the MCP in the flight tube, and the electrode is connected to a sweep circuit via an introduction terminal.

The sweep circuit comprises an arbitrary waveform generator (Biomation Corporation: 2717A) and a voltage amplifier (Toyo Technica: HVA400). For the detection of ions, an MCP with a fluorescent screen having an effective diameter of 20 mm (manufactured by Hamamatsu Photonics) was used, and the obtained optical signal was recorded by a CCD camera.

Excimer lasers and dye lasers (Lu) are used as resonance ionization lasers for ionizing isotopes.
monicsEX742 and HD300) were used. Alkaline earth or alkali metal such as calcium, or a compound thereof is used for a sample ionized by the laser, and the metal or the compound is used as a Khudsen cell (Omegatron: OM).
K-0102) and heated and ionized.

According to the present invention, calcium is atomized by heating the sample, ionized by laser light, and the resulting isotope ion current is converged by the lens provided in the flight tube, and then is applied to the sweep electrode. After being introduced and swept, the swept ion flow was doubled by the MCP, and then converted into an optical signal as a light spot on the phosphor screen. The amount of ions could be measured from the intensity of light at the light spot on the phosphor screen, and the mass could be measured from that position.

[0022]

According to the present invention, an effect unique to the present invention is obtained in that the dynamic range of the measured intensity of ions flying by mass discrimination is widened. That is, isotopes different in abundance by 5 digits or more can be measured simultaneously. This allows one and 100,000 to be viewed simultaneously. In the conventional method, it is necessary to measure each isotope while switching the range, so that there is an effect that the measurement time is shortened.

Further, there is an effect unique to the present invention that the mass spectrometry capability of the time-of-flight mass spectrometer can be faithfully processed. In other words, there is almost no disturbance of the baseline caused by signal processing, and more specifically, an effect is obtained in which an isotope having a mass close to a large amount of isotope can be accurately measured.

Further, the present invention has an effect that measurement sensitivity is high. That is, in the signal detection of the MCP, it is more sensitive to convert to light, so that one ion
When incident on P, it becomes one light spot. This means that the number of atoms can be measured.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a general signal processing system of a conventional time-of-flight mass spectrometer.

FIG. 3 is a diagram showing the basic principle of a conventional time-of-flight mass spectrometer.

FIG. 4 is a diagram showing a configuration of a time-of-flight type analyzer of the present invention.

FIG. 5 shows the sweep electrode, M, of the time-of-flight analyzer of the present invention.
FIG. 3 is a diagram illustrating an arrangement structure of a CP and a CCD camera.

FIG. 6 is a diagram showing a signal system of the time-of-flight mass spectrometer of the present invention.

FIG. 7 is a diagram showing a structure of a microchannel plate.

Claims (2)

[Claims] At least one end of a flight tube is provided with a sample cell for atomizing a sample, a laser system for ionizing the sample, and an acceleration electrode for accelerating the ionized atoms. In a time-of-flight mass spectrometer in which a microchannel plate (MCP) is arranged at the end, a sweep electrode is arranged in front of the microchannel plate, a fluorescent screen is provided in the rear surface, and mass discrimination is performed in a flight tube by a flight speed in a flight tube. The changed ions are given an electric field change by the sweeping electrode and collide with the MCP, and the output electrons generated at that time are optically converted by the phosphor screen,
An analyzer for measuring the isotope composition of a sample element, wherein the light spot is captured by a camera and then image-processed. 2. A microchannel plate (MCP) having a sweep electrode and a fluorescent screen is provided in a flight tube of a time-of-flight mass spectrometer, and a substance to be measured is heated to be atomized and ionized by a laser. , The ions are discriminated by the flight speed in the tube, the ions are passed through a sweeping electrode to give an electric field, and then collide with the MCP to convert the light. An analytical method for measuring composition.