JP2000036285A - Spectrum processing method for time-of-flight mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide rapidly a mass spectrum that is not affected by the response of a high-voltage pulse circuit or the aberration of a mass spectrometer by measuring a single mass spectrum and a multi-spectrum and finding a device function for duplicating the multi-spectrum in advance. SOLUTION: In a table setting mode, a calculation by means of Fourier transformation is performed by a Fourier transformation part 13 based on a single mass spectrum obtained from a single pulse and one superimposed multi-mass-spectrum obtained from an n-pulse train by the use of a standard sample or the like. Then, a device function arithmetic processing part 14 memorizes them, calculates a device function and stores it in a device function table 15 as the device function at the time of inverse convolution. In a measurement mode, a reverse Fourier transformation is performed through the device function table 15 and a reverse Fourier transformation part 16 in relation to the multi-mass-spectrum of a sample measured by generating ion pulses as in the case of the standard sample and thereby, the single mass spectrum is found and stored in a spectrum storing part 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrum processing of a time-of-flight mass spectrometer for applying a high-voltage pulse voltage from an ion reservoir to an ion pushing plate to obtain a single-shot mass spectrum of a sample observed based on n pulse trains. About the method.

[0002]

2. Description of the Related Art Time-of-flight mass spectrometers (TOFMS)
Utilizes the fact that when the same kinetic energy U is given, the smaller the mass-to-charge ratio m / e = M of ions, the sooner they reach the ion detector. The flight distance of the ion is L, the total flight time is t _TOF , and the width of the ion pulse is Δt
Then, the resolution R of the obtained mass spectrum is given by the following [Equation 1].

[0003]

R = M / ΔM = t _TOF / 2Δt t _TOF = L√ (m / 2U) If the flight distance L of the ions is constant, the resolution becomes higher as the ion pulse width becomes narrower according to [Equation 1]. Therefore, Δt
There is a so-called pulse ionization method using an ultraviolet laser pulse as the simplest method for shortening the width of the laser beam. This gives the number n
SIMS / TOF, SNMS / TOF, and MALD are typical devices that generate ion pulses of s to 10 ns and combine a time-of-flight mass spectrometer as a spectrometer.
There is I / TOF.

On the other hand, ionization methods such as EI, CI, ESI and ICP are called continuous ionization methods as compared to pulse ionization methods. One of the time-of-flight mass spectrometers combined with such a continuous ionization method is a vertical acceleration time-of-flight mass spectrometer (Orthogonal Acceleration TOF).
MS: OA / TOF) has been proposed. FIG. 7 is a schematic view of a vertical acceleration time-of-flight mass spectrometer, in which 21 is an external ion source, 22 is an ion reservoir, 23 is an ion push-out plate, 24 and 25 are grids, 26 is a drift region (spectroscopy unit), 27 denotes an ion detector.

[0005] In the vertical acceleration time-of-flight mass spectrometer, an external ion source 21 at a kinetic energy eV ₁ as shown in FIG. 7
When the ions introduced into the ion reservoir 22 from the reservoir fill the ion reservoir 22 having the length y ₀ , the ion pushing plate 23
To a high-voltage pulse voltage of amplitude voltage = V ₂ . This high-voltage pulse voltage causes the ion to fly in a direction perpendicular to the flight direction (TOF).
The ions are accelerated in the kinetic energy of eV ₂ in the optical axis direction of the MS (e.g., in the direction of the optical axis of the MS), ejected from the ion reservoir 22, and fly over the drift region 26, which is a TOFMS spectroscopic unit.
Reach 7

The flight velocity v ₁ of ions in a vertical acceleration time-of-flight mass spectrometer is given by the following [Equation 2].
The ion residence time t _ion is given by the following [ _Equation 3].

[0007]

## EQU2 ## v ₁ = 1.39 × 10 ⁴ Ｖ (V ₁ / M) (m / s)

[0008]

T _ion = 0.72√ (V ₁ / M) × y ₀ (μs) where y ₀ : cm, V ₁ : volt, M: Dalton Therefore, as a typical example, V ₁ = 20 volts, M
The flight velocity v ₁ of the ion of = 5000 daltons is v ₁ = 8.8 × 10 ² m / s according to [Equation 2]. The length y ₀ of the ion reservoir 22 of the vertical acceleration time-of-flight mass spectrometer is generally several cm. For example, if y ₀ = 2 cm, the ion residence time t _ion is about 22 μs according to [Equation 3].

The kinetic energy of the ions discharged from the ion reservoir 22 and accelerated is U ₂ = 3000 eV, the maximum ion is M = 5000, and the flight distance of the TOFMS is L = 200 cm.
Then, the flight time of ions of M = 5000 reaches the ion detector 27 after about 186 μs according to [Equation 3]. When ions are measured in this cycle, the ion yield is 12%. This ion yield is also called a duty cycle.

[0010]

As a method of improving this duty cycle, the maximum ion M
There is a method in which a pulse voltage is repeatedly applied to the ion push-out plate for the ions accumulated in the ion reservoir 22 without waiting for the ions to reach the ion detector 27, and a superimposed measurement is performed. The repetitive pulse voltage is composed of an arbitrary pulse train of n pulses in one cycle, and this pulse example is repeatedly applied in a constant cycle. A one-cycle mass spectrum measured with n pulse trains is a superposition of n mass spectra based on the pulse train. The superimposed multiplex mass spectrum is processed as one spectrum obtained by processing the deviation (phase deviation) of each pulse time of the pulse train by the deconvolution method after the measurement. Such deconvolution processing methods include two methods using a correlation method and a Fourier transform method.

A deconvolution method using a Fourier transform has also been proposed. In this method, a pulse sequence given in advance is used as an apparatus function, which is subjected to a Fourier transform, and an observed multiple mass spectrum is subjected to a Fourier transform. And the method of separating. Here, a multiple mass spectrum processing method by Fourier transform will be described here.

Assuming that a single mass spectrum obtained by a single pulse is y (t) and a multiple mass spectrum obtained by n pulse trains is w (t),

[0013]

(Equation 4) Taking the Fourier transform of both sides,

[0014]

(Equation 5) From [Equation 5], from Y (ω) = W (ω) / Hn (ω),
Y (t) is obtained by inverse Fourier transform of Y (ω). However, since Equation 5 cannot be calculated at the point where Hn (ω) = 0, y (t) cannot be completely recovered.

Further, when the n pulse trains are actually applied to the apparatus function Hn (ω) as they are, the delay of the high-voltage pulse circuit, the aberration of the time-of-flight mass spectrometer, the detection system of the ion detector and the preamplifier, etc. Due to the response characteristics and the like, there may be a problem that a time difference from the observed spectrum occurs and the superimposed mass spectrum cannot be completely recovered.

[0016]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and is not affected by the response characteristics of a high-voltage pulse circuit, aberrations of a time-of-flight mass analyzer, response characteristics of a detection system, and the like. It is intended to promptly request the reproduction of multiple mass spectra.

For this purpose, the present invention provides a spectrum processing method for a time-of-flight mass spectrometer for obtaining a single-shot mass spectrum of a sample observed based on n pulse trains,
Single-shot mass spectrum observed based on single-shot pulse and n
Fourier transform is performed on both data of the multiplex mass spectrum observed based on the number of pulse trains to obtain an apparatus function in advance. Next, the Fourier transform is performed on the multiplex mass spectrum of the sample observed based on the n pulse trains. Then, an arithmetic operation with the device function is performed to obtain an added mass spectrum of the sample by inverse Fourier transform.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a spectrum processing method for a time-of-flight mass spectrometer according to the present invention.

In the spectrum processing method for a time-of-flight mass spectrometer according to the present invention, as shown in FIG. 1, first, a single-shot mass spectrum y obtained by a single-shot pulse using a standard sample or the like.
(T) is measured (step S11), and Y (ω) is calculated and stored by Fourier transform (step S12). Subsequently, one multiplex mass spectrum w (t) obtained by n pulse trains using a standard sample or the like is measured (step S13), and W (ω) is calculated and stored by Fourier transform (step S14). . Next, Hn (ω) is calculated based on [Equation 5], and this is stored in a table as a device function (Hn (ω) or 1 / Hn (ω)) at the time of deconvolution (step S15). ).

After the apparatus function (Hn (ω) or 1 / Hn (ω)) is obtained and stored in the table as described above, when performing spectrum processing of the sample, the standard sample is measured in the actual mass spectrum measurement. The same pulse train as in the above case is generated, an ion pulse is generated, the multiple mass spectrum w (t) of the sample is measured (step S16), and W (ω) is calculated by Fourier transform (step S17).
Then, using the device function (Hn (ω) or 1 / Hn (ω)) stored in the table, Y (ω) = W (ω) / Hn
(Ω) is obtained (step S18), and a single-shot mass spectrum y (t) is obtained by inverse Fourier transform of Y (ω) (step S19).

Although there is no theoretical limitation on the number n of pulses in one cycle, the flight time of ions in the ion reservoir (t _ion ) and the flight time of TOFMS of ions (t _TOF ) are actually used. , And fast Fourier transform (FFT) operation speed for Fourier transform,
0 μs. In this way, one cycle / several hundred μ
When the S / N of the multiple mass spectrum obtained by the pulse train of s is not good, in order to obtain an observation spectrum with good S / N, Fourier transform is performed on data obtained by measuring m cycles and integrating (averaging and adding) m times. This is also an effective method.

FIG. 2 is a diagram showing an example of the configuration of a spectrum processing apparatus for a time-of-flight mass spectrometer according to the present invention, in which 11 is a time-of-flight mass spectrometer, 12 is observation spectrum data,
13 is a Fourier transform unit, 14 is a device function operation processing unit, 1
5 is a device function table, 16 is an inverse Fourier transform unit, 17
Indicates a spectrum storage unit. FIG. 3 is a diagram showing an example of one superimposed multiplex mass spectrum w (t) obtained by n pulse trains (one sequence), and FIG. 4 is a single mass spectrum y obtained by a single pulse. FIG. 5 is a diagram showing an example of (t), and FIG.
FIG. 6 is a diagram showing an example of (ω), Y (ω) and a device function H (ω). FIG. 6 is a diagram showing an example of a single-shot mass spectrum y (t) obtained by inverse Fourier transform.

In FIG. 2, the observed spectrum data 12
Is a single pulse, n pulse trains, and an integrated mass spectrum w (t), y (t) of the standard sample or the sample measured by the time-of-flight mass spectrometer 11, and the Fourier transform unit 13 , Observation spectrum data 12
W (ω) and Y (ω) are calculated by the Fourier transform from the mass spectra w (t) and y (t). The device function calculation processing unit 14 performs a calculation process in a table setting mode for a device function using a standard sample or the like and a measurement mode for measuring an unknown sample. In the table setting mode, Y (ω) as shown in FIG. 5B is calculated by the Fourier transform unit 13 from the single-shot mass spectrum y (t) obtained by the single-pulse as shown in FIG. Similarly, from the superimposed multiple mass spectrum w (t) obtained from the n pulse trains as shown in FIG.
When (ω) is calculated, the device function calculation processing unit 14
These are stored, and Hn (ω) as shown in FIG. 5C is calculated based on [Equation 5], and this is calculated as a device function (Hn (ω) or 1 / Hn (ω) at the time of deconvolution. )) Is stored in the device function table 15. On the other hand, in the measurement mode, when W (ω) is calculated by the Fourier transform from the multiple mass spectrum w (t) of the sample measured by generating the same pulse train as in the case of the standard sample and generating the ion pulse, The device function (H
n (ω) or 1 / Hn (ω)) using Y (ω) = W
(Ω) / Hn (ω) is obtained. Inverse Fourier transform unit 16
Is a one-shot mass spectrum y as shown in FIG. 6 obtained by performing an inverse Fourier transform of Y (ω) obtained by the device function operation processing unit 14.
(T), and its single-shot mass spectrum y
The spectrum storage unit 17 stores (t).

Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, a spectrum for calculating an apparatus function is measured by continuously introducing a given amount of a general-purpose arbitrary sample or a sample frequently used for mass construction such as PFK into an ion reservoir. Thus, it is also effective to create a device function table in advance. Also, Duty cyc
Since le varies according to the maximum mass range to be measured, the time for retaining ions in the ion reservoir, and the flight distance of the time-of-flight mass spectrometer, in order to obtain an optimal duty cycle, a plurality of It is also effective to create these in advance.

[0025]

As is apparent from the above description, according to the present invention, a single mass spectrum and a multiple spectrum obtained by a time-of-flight mass spectrometer are measured, and an apparatus function for reproducing a multiple spectrum is obtained in advance. So the electrical response of the high pressure pulse circuit for ion extrusion, mass spectrometer aberrations,
In addition, all the device functions of the ion detection unit can be collectively deleted, and can be easily calculated as one device function. Also, D
Since the duty cycle varies depending on the maximum mass range to be measured, the time for which ions are retained in the ion reservoir, and the flight distance of the time-of-flight mass spectrometer, the optimum duty cycle is determined.
It is also very effective in mass spectrometry to prepare a plurality of pulse trains in advance to obtain cle. Since an apparatus function based on n pulse trains calculated in advance after actual measurement can be used, a multiple spectrum shifted on the time axis based on the n pulse trains can be reproduced as a single-shot spectrum without superimposition.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a spectrum processing method for a time-of-flight mass spectrometer according to the present invention.

FIG. 2 is a diagram showing a configuration example of a spectrum processing device of a time-of-flight mass spectrometer according to the present invention.

FIG. 3 is a diagram illustrating an example of one superimposed mass spectrum w (t) obtained from n pulse trains (one sequence).

FIG. 4 is a mass spectrum y obtained by a single pulse.
It is a figure showing the example of (t).

FIG. 5 shows W obtained by performing fast Fourier transform on each mass spectrum.
It is a figure which shows the example of (ω), Y (ω) and the device function H (ω).

FIG. 6 is a diagram illustrating an example of a mass spectrum y (t) obtained by an inverse Fourier transform.

FIG. 7 is a schematic diagram of a vertical acceleration time-of-flight mass spectrometer.

[Explanation of symbols]

11: Time-of-flight mass spectrometer, 12: Observed spectrum data, 13: Fourier transform unit, 14: Device function operation processing unit, 15: Device function table, 16: Inverse Fourier transform unit, 17: Spectrum storage unit

[Procedure amendment]

[Submission date] September 25, 1998 (1998.9.2)
5)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

FIG. 7

Claims (1)

[Claims] 1. A spectrum processing method for a time-of-flight mass spectrometer for obtaining a single-shot mass spectrum from a multiple mass spectrum of a sample observed based on n pulse trains by applying a high-voltage pulse to an ion pushing plate from an ion reservoir. There, the data of both the single mass spectrum observed based on the single pulse and the multiple mass spectrum observed based on the n pulse trains using the standard sample are Fourier-transformed and the device function is obtained in advance and stored, Then, n
A time-of-flight mass spectrometer characterized in that a Fourier transform is performed on a multiple mass spectrum of a sample observed based on the pulse trains, an operation is performed with the device function, and an added mass spectrum of the sample is obtained by an inverse Fourier transform. Spectrum processing method.