JP4710710B2 - Time-of-flight mass spectrometer - Google Patents

Description

  The present invention relates to a time-of-flight mass spectrometer such as a matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometer (TOFMS).

  As a time-of-flight mass spectrometer, a mass spectrometer (hereinafter referred to as MALDI-TOFMS) using a matrix-assisted laser desorption ionization method as an ion source is well known. In MALDI, in order to analyze samples that are difficult to absorb laser light and samples that are easily damaged by laser light such as proteins, substances such as sinapinic acid that are easy to absorb laser light and are easily ionized are mixed into the sample in advance as a matrix. A sample is prepared in advance, and the sample is ionized by irradiating it with a laser beam for a short time.

  In general, in MALDI-TOFMS, as shown in FIG. 3, a plurality of (several hundreds if many) specimens (samples) 3 are provided in a spot shape on a thin flat sample plate 2 (see, for example, Patent Document 1). ). Then, the sample plate 2 is set on a horizontal sample stage, and the sample to be analyzed is moved to the laser beam irradiation position by moving the sample stage two-dimensionally in the X-axis direction and the Y-axis direction (see FIG. Position of P in 3). Then, by irradiating the laser beam, the sample component, which is the purpose of analysis in the sample, is ionized, and the generated ions are detected by mass separation with a time-of-flight mass separator. When mass analysis of one sample is completed, mass analysis is performed on a large number of samples by repeating the operation of moving the next sample to be analyzed to the laser light irradiation position P and executing mass analysis in the same manner. Can be executed.

In MALDI-TOFMS, since the distance between the upper surface of the sample at the laser beam irradiation position and the detector is basically the flight distance, the height of each sample 3 mounted on the sample plate 2 varies. causing a calculation error of the flight distance is varied mass (strictly mass-to-charge ratio m / z) and. From such a viewpoint, conventionally, a method of suppressing variation in the height of each sample on the sample plate 2 during sample preparation has been proposed (see Patent Document 2).

However, in the sample plate even aligned the height of each sample actually lag behind mass for the same ionic species by the position of the sample in the sample plate to be analyzed, causing a reduction in quality Ryosei degree There is. In other words, it is desirable that the upper surface of the sample table on which the sample plate is set is completely horizontal, but since the processing cost increases as the flatness increases, it is actually difficult to achieve a flatness of several tens of μm or less. . Further, when the sample stage is attached, adjustment is performed so that the upper surface is horizontal, but it is practically impossible to maintain perfect level due to the limit of adjustment. Further, even if the upper surface of the sample stage is completely horizontal, the height of the upper surface of the sample varies due to deformation such as warpage of the sample plate. Because of these various factors, the vertical fluctuation of the upper surface of the sample at the laser irradiation position when the sample stage is moved may be several tens μm to several hundreds μm.

JP 2002-156382 A JP 2004-347524 A

If there is vertical fluctuations of the upper surface of the sample plate as described above, when measuring a plurality of samples prepared in the one sample plate, so that the deviation occurs in the mass by the flight distance is changed. The ions generated from the sample are extracted by the electric field formed by the ion extraction electrode placed in parallel with the sample plate. However, if the height of the upper surface of the sample varies, the distance from the ion extraction electrode changes. , also it will reduce the quality Ryosei degree by initial kinetic energy imparted to ions varies.

The present invention has been made to solve the above problems, and has as its object to reduce the effect of the limitations of dimensional accuracy and mechanical accuracy of the sample stage or sample plate as described above, mass and to provide a time-of-flight mass spectrometer capable of increasing the accuracy.

The present invention, which has been made to solve the above problems, moves the sample holder in the extending direction of the sample mounting surface for a plurality of samples arranged two-dimensionally on the sample mounting surface of the sample holding unit. The sample to be analyzed is moved to a predetermined measurement position, and the laser component is irradiated with laser light from the laser irradiation unit to ionize sample components in the sample, and various ions generated from the sample are extracted to time-of-flight mass In a time-of-flight mass spectrometer that is introduced into a separator, separated according to the mass of ions and detected by a detector,
a) an ion extracting electrode disposed to face the sample mounting surface of the sample holder;
b) When the sample holder is moved, a laser beam weaker than that during ionization is irradiated from the laser irradiation unit to the sample that has arrived at the measurement position , and reflected light from the sample surface is received by the light receiving unit. Displacement amount detecting means for detecting a displacement amount in the ion extraction direction by the ion extraction electrode on the sample surface or the surrounding sample mounting surface based on the displacement of the position of the light receiving spot ;
c) displacement means for displacing the sample holder in the ion extraction direction;
d) According to the detection result by the displacement detection means, in order to make the flight distance from the sample surface coming to the measurement position to the detector through the time-of-flight mass separator constant, Control means for controlling the displacement means to adjust the position of the sample holder so as to be at a reference position in the ion extraction direction;
It is characterized by having.

Large displacement amount as the displacement means actuator is a useful using because rapidity of high accuracy and response of what is required is required, for example, a piezoelectric element or the like.

  The sample holder is a sample plate when, for example, a plurality of samples are formed in a spot shape on the sample plate as described above, and for example, a flat and wide specimen placed on the sample stage. When a plurality of measurement points (in this case, the measurement points are referred to as samples) are set in a two-dimensional manner, it is a sample stage.

Further, in the mass spectrometer according to the present invention, as a method for ionizing a sample component contained in a sample, in addition to MALDI, a surface-assisted laser desorption ionization method such as a desorption ionization method on silicon, which similarly uses a laser, Various other laser ionization methods can be used.

In the time-of-flight mass spectrometer of the present invention, for example, when an arbitrary sample to be analyzed among a large number of prepared samples is moved to a measurement position, the sample surface on which the displacement amount detection means comes to the measurement position Alternatively, the displacement amount of the sample mounting surface in the vicinity thereof is detected. This amount of displacement can be expressed, for example, as a difference with respect to a preset reference position, or as a distance from the ion extraction electrode. It is desirable that the amount of displacement is constant when any sample on the sample mounting surface comes to the measurement position, but the amount of displacement is not constant due to factors such as low flatness of the sample mounting surface. There is. Therefore, the control means receives the displacement amount detection result and drives the displacement means to change the position of the sample holder in the ion extraction direction so that it comes to the reference position, and between the sample surface at the measurement position and the detector. Adjust the flight distance so that it is almost constant. After such adjustment, for example, a laser beam is irradiated onto the sample at the measurement position, and mass analysis of ions generated from the sample is executed.

According to the time-of-flight mass spectrometer according to the present invention, when performing mass analysis of a sample scattered two-dimensionally in a wide range, the flight distance can be kept substantially constant regardless of the position of the sample. . Further, since the distance from the ion extracting electrode is constant, the ion extracting action by the electric field by the electrode is always in the same state. Thereby, it is reduced variation in flight time for the same quality of the ion, thereby improving the quality Ryosei degree with less error of mass that is calculated based on the flight time.

  Hereinafter, MALDI-TOFMS which is one Example of this invention is demonstrated with reference to drawings. FIG. 1 is an overall configuration diagram of the main part of the MALDI-TOFMS of this embodiment.

  As described above, on the upper surface of the thin flat plate-like sample plate 2, a large number of samples 3 prepared by mixing a matrix are two-dimensionally separated and attached in spots. The method for preparing Sample 3 is not particularly limited. The sample plate 2 is set on a sample table 1 whose upper surface is substantially horizontal. The sample stage 1 can be moved two-dimensionally in the X-axis direction and the Y-axis direction by a sample stage drive unit 4 including a motor and the like.

  A laser beam 7 for ionizing the sample in the sample 3 is emitted from the laser irradiation unit 6 and irradiated to a predetermined position on the sample plate 2 via the reflecting mirror 8. Above the sample stage 1, an ion extraction electrode 9 that forms an electric field for extracting ions generated from the sample 3 at the laser irradiation position upward from the vicinity of the generation position is an upper surface of the sample stage 1 and the sample plate 2. It is arrange | positioned so that it may oppose. Above the ion extraction electrode 9, an ion optical system 10 such as an electrostatic lens for suppressing the spread of ions, a time-of-flight mass separator (TOF) 13 having a flight space for flying ions, and a TOF 13 The detector 14 for detecting the ions separated by mass is arranged on a substantially straight line.

  That is, in this MALDI-TOFMS configuration, the TOF 13 is a linear type, and the flight path of the ions emitted from the sample 3 is set in the vertical direction as indicated by the symbol C in FIG. However, the TOF 13 is not limited to the linear type, and may be another known form such as a reflectron type.

Detector 14 outputs a detection signal corresponding to the amount of ions incident, the data processing unit 15 obtains the flight time of each ion by receiving this detection signal, performs conversion to mass from the flight time. Then, to create a mass spectrum of mass on the horizontal axis, the vertical axis and relative intensity.

  Furthermore, as a characteristic configuration of the MALDI-TOFMS of the present embodiment, a displacement sensor (displacement detecting means in the present invention) 12 for measuring the amount of displacement of the height of the upper surface of the sample 3 at the measurement position, and a sample A displacement drive unit (displacement means in the present invention) 16 for moving the table 1 (or only the sample plate 2) in the minute range (for example, about several hundred μm to several mm at the maximum) in the Z-axis direction (vertical direction in FIG. 1); A displacement correction control unit (control means in the present invention) 17 is provided that receives a measurement value from the displacement sensor 12 and sends a control signal to the displacement drive unit 16.

Displacement sensor 12 is of non-contact, by irradiating the sample 3 with fine weak laser beam to measure the position to receive the laser light reflected from the sample 3 the upper surface by the CCD image sensor via the reflecting mirror 11, the The amount of displacement of the upper surface of the sample 3 in the Z-axis direction is calculated based on the displacement of the position of the laser light receiving spot. This amount of displacement may be determined as a relative amount of displacement relative to the reference position by determining a certain reference position, or may be converted into a distance d between the ion extraction electrode 9 whose position is fixed. Also good. In any case, for example, if the height of the upper surface of the sample 3 that has come to the measurement position changes when the sample stage 1 is moved two-dimensionally, the change is reflected in the displacement amount and sent to the displacement correction control unit 17. It is done.

  Further, as the displacement driving unit 16, a minute displacement is possible and a quick response is required, so that, for example, a piezoelectric actuator or the like can be used. In this case, the amount of displacement of the sample stage 1 in the Z-axis direction by the displacement drive unit 16 is determined by the magnitude of the drive voltage applied by the displacement correction control unit 17. A control unit 18 mainly composed of a CPU has a function of controlling the entire analysis operation, and controls the sample stage driving unit 4, the laser irradiation unit 6, the displacement correction control unit 17, and the like.

  Next, a characteristic operation of the MALDI-TOFMS of this embodiment will be described according to an operation flowchart shown in FIG. It is assumed that the control unit 18 performs analysis of each sample 3 on the sample plate 2 in a predetermined order.

  First, the control unit 18 sends a control signal to the sample stage driving unit 4 so that the sample 3 to be analyzed first comes to the measurement position, that is, the laser irradiation position. As a result, the sample stage drive unit 4 appropriately moves the sample stage 1 in the X-axis direction and the Y-axis direction, and sets the sample 3 to be analyzed at the measurement position (step S1).

  Next, the displacement sensor 12 measures the amount of displacement in the Z-axis direction of the upper surface of the sample 3 existing at the measurement position at that time, and sends the measured value to the displacement correction control unit 17. Here, it is assumed that the displacement measurement value is expressed as a relative amount when a predetermined reference value is zero (step S2). When the displacement correction control unit 17 receives the displacement amount measurement value, the displacement correction control unit 17 calculates a drive voltage for making the displacement amount zero, and applies the drive voltage to the displacement drive unit 16. For example, when the position of the upper surface of the sample 3 is above the reference position, it is defined as a positive displacement amount, and when it is below the negative displacement amount, and when the displacement amount measurement value is now + A, The displacement drive unit 16 is driven so that 1 is lowered by A. By the above driving, the sample stage 1 and the sample plate 2 are slightly moved in the Z-axis direction (step S3).

After performing the displacement correction as described above, the control unit 18 sends a control signal to the laser irradiation unit 6 and irradiates the sample 3 with the laser beam 7 for a short time to generate ions from the sample 3. The generated ions started flight is drawn upward by an electric field formed by the ion extraction electrode 9, it continues to fly being introduced into TOF13 after being throttled by the ion optical system 10, delay depending on the mass Will be separated. The fast as smaller ion mass, mass larger ions are detected to reach the detector 14 with a delay. In this way, mass analysis is performed on the sample 3 at the measurement position (step S4).

  Thereafter, the control unit 18 determines whether or not the analysis of all the samples 3 has been completed (step S5). If the sample 3 to be analyzed still remains, the process returns to step S1, and the sample to be analyzed next. 3 is moved to the measurement position, and the processes of steps S2 to S4 are executed. Such a process is repeated until the analysis of all the samples 3 is completed. When the analysis of all the samples is completed, the process is terminated.

  As described above, when each sample 3 scattered two-dimensionally on the sample plate 2 is analyzed, when the sample 3 comes to the measurement position, the height is corrected according to the amount of displacement of the upper surface of the sample 3. As a result, the distance d between the ion extraction electrode 9 and any sample 3 is maintained substantially constant. The displacement is corrected by the above processing for any factors such as the case where the flatness of the upper surface of the sample table 1 itself is not good, the sample plate 2 is deformed such as warpage, or the swell of the sample 3 is uneven. Is done.

Accordingly, since the variations among samples of flight distance of an ion to reach the detector 14 from the starting is reduced, thereby improving the quality Ryosei degree. Further, since the distance d between the ion extraction electrode 9 and the upper surface of the sample 3 at the measurement position is kept constant, the action of the extraction electric field on the ions emitted from the sample 3 becomes constant, and the initial motion given to the ions I have the energy. Therefore, also contributes to improving the quality Ryosei degree in this regard.

  In the above embodiment, the displacement amount of the upper surface of the sample 3 coming to the measurement position is detected. However, for example, when it is not preferable to directly irradiate the sample 3 with laser light for detecting the displacement amount, the vicinity of the measurement position is detected. The amount of displacement of the upper surface of the sample plate 2 may be detected. In this case, the variation in the swell of each sample cannot be corrected. However, in general, this variation is smaller than the displacement caused by the sample stage 1 or the sample plate 2, and therefore, even if the amount of displacement is obtained by avoiding the sample, it is almost the same. The effect can be achieved.

  In the above embodiment, the sample plate 2 is placed on the horizontally placed sample table 1 and ions are extracted vertically upward. For example, the sample plate 2 is vertically moved by the sample table 1 standing upright. It is good also as a structure which stands up and hold | maintains and pulls out an ion in a horizontal direction.

Moreover, although the said Example applies this invention to MALDI-TOFMS, an ion source is not restricted to MALDI, For example, the desorption ionization method (Desorption / Ionization on (porous) Silicon: DIOS) etc. on silicon | silicone etc. The present invention can also be applied to a known surface assisted laser desorption / ionization (SALDI) method and other known ionization methods using a laser ionization method.

  Further, in other respects, it is obvious that even if changes, corrections and additions are made as appropriate within the scope of the present invention, they are included in the scope of the claims of the present application.

The whole MALDI-TOFMS main part block diagram by one Example of this invention. The flowchart for demonstrating the characteristic operation | movement in MALDI-TOFMS of a present Example. The perspective view of the sample plate used for MALDI-TOFMS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sample stand 2 ... Sample plate 3 ... Sample 4 ... Sample stand drive part 6 ... Laser irradiation part 7 ... Laser beam 8 ... Reflector 9 ... Ion extraction electrode 10 ... Ion optical system 11 ... Reflector 12 ... Displacement sensor 13 ... Time-of-flight mass separator (TOF)
DESCRIPTION OF SYMBOLS 14 ... Detector 15 ... Data processing part 16 ... Displacement drive part 17 ... Displacement correction control part 18 ... Control part

Claims (1)

For a plurality of samples arranged two-dimensionally on the sample mounting surface of the sample holding unit, the sample to be analyzed is moved to a predetermined measurement position by moving the sample holding unit in the extending direction of the sample mounting surface, The sample is irradiated with laser light from the laser irradiation unit to ionize the sample components in the sample, and various ions generated from the sample are extracted and introduced into the time-of-flight mass separator, and separated according to the mass of the ions. In a time-of-flight mass spectrometer that detects with a detector,
a) an ion extracting electrode disposed to face the sample mounting surface of the sample holder;
b) When the sample holder is moved, a laser beam weaker than that during ionization is irradiated from the laser irradiation unit to the sample that has arrived at the measurement position , and reflected light from the sample surface is received by the light receiving unit. Displacement amount detecting means for detecting a displacement amount in the ion extraction direction by the ion extraction electrode on the sample surface or the surrounding sample mounting surface based on the displacement of the position of the light receiving spot ;
c) displacement means for displacing the sample holder in the ion extraction direction;
d) According to the detection result by the displacement detection means, in order to make the flight distance from the sample surface coming to the measurement position to the detector through the time-of-flight mass separator constant, Control means for controlling the displacement means to adjust the position of the sample holder so as to be at a reference position in the ion extraction direction;
A time-of-flight mass spectrometer.

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