JP2008052996A - Mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that separation of peak degrades due to insufficient frequency band of a preamplifier when a scanning speed is raised, but noises increase and detection sensitivity degrades if the frequency band is expanded. <P>SOLUTION: Feedback resistors R1 and R2 are switched so that the gain of a preamplifier 40 is lowered while frequency band is widened if scanning speed is high, and the gain of the preamplifier 40 is raised and the frequency band is narrowed if the scanning speed is low, depending on the scanning speed set by a user. By switching, in interlocked manner, a value of a multiplier 41 on the next stage of the preamplifier 40, the gain through the preamplifier 40 and the multiplier 41 is kept constant regardless of switching of the feedback resistors R1 and R2, resulting in simple process and configuration of the circuits thereafter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mass spectrometer, and more particularly, to a mass spectrometer that performs mass scanning (scan measurement) over a predetermined mass range.

  In a quadrupole mass spectrometer that uses a quadrupole mass filter as a mass separator, a quadrupole mass filter is applied by a voltage applied to four rod electrodes arranged parallel to each other so as to surround the central axis. The mass-to-charge ratio of the ions that pass through, that is, the ions to be sorted is determined. Specifically, among the four rod electrodes, two rod electrodes facing each other across the central axis are + (U + V · cosωt), and the other two rod electrodes are − (U + V · cosωt). A voltage obtained by superimposing a high frequency voltage (V · cos ωt) on a direct current voltage (U) is applied. In this case, by changing the DC voltage value U and the amplitude value V of the high-frequency voltage, the mass-to-charge ratio of ions that can pass through the space surrounded by the four rod electrodes changes (see Patent Document 1, etc.).

  In order to perform mass scanning over a predetermined mass range, U / V is generally kept constant, and U and V are changed with time. For example, when a mass spectrometer is used as a detector for a liquid chromatograph or a gas chromatograph, mass scanning over a predetermined mass range is repeated in order to detect various components in a sample that are sequentially obtained as time elapses. Done. Based on a detection signal obtained by such mass scanning, that is, scanning measurement, a mass spectrum can be created with the mass-to-charge ratio m / z on the horizontal axis and the ion intensity (signal intensity) on the vertical axis.

  In such a mass spectrometer, a secondary electron multiplier or the like is generally used as a detector and outputs a current signal corresponding to the amount of incident ions. The current signal is subjected to current / voltage conversion and signal amplification by a first-stage amplifier (usually called a preamplifier).

  In recent years, as mass spectrometers become widely used, an improvement in scan measurement speed (scan speed) is required in order to improve processing throughput. However, when the scanning speed is increased, the frequency band of the detection signal output from the detector is also increased, so that there is a problem that the frequency band is insufficient in the analog processing circuit, and the separation of adjacent peaks on the mass spectrum is deteriorated. Since it is mainly the preamplifier that limits the frequency band, in order to avoid the above problem, the frequency band may be widened by reducing the amplification factor of the preamplifier. However, there is a problem that noise increases and detection sensitivity decreases because signal strength decreases. Although it is conceivable to increase the voltage applied to the detector in order to compensate for the decrease in the amplification factor, the life of the detector is shortened and noise generated in the detector is increased.

JP-A-10-27570

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to improve the resolution of peaks when increasing the scanning speed of mass spectrometry and to reduce noise when the scanning speed is slow. An object of the present invention is to provide a mass spectrometer capable of avoiding an increase and a decrease in detection sensitivity.

In order to solve the above problems, the present invention provides a mass separator that selectively separates ions according to a mass-to-charge ratio, and a detector that detects ions that have passed through the mass separator, A mass spectrometer that performs scan measurement that scans the mass of ions that pass through the mass separator in a predetermined mass range,
a) setting means for setting a scanning speed of mass scanning in the scan measurement;
b) a first-stage amplifier having a plurality of feedback resistors switchable to amplify a detection signal from the detector;
c) Control for switching the feedback resistance of the first-stage amplifier so as to widen the frequency band while lowering the amplification factor when the scan speed is fast compared to the slow case according to the scan speed set by the setting means Means,
It is characterized by having.

  That is, in the conventional mass spectrometer, the amplification factor of the first stage amplifier (preamplifier) is constant regardless of the scanning speed, and therefore the frequency band is also constant. On the other hand, in the mass spectrometer according to the present invention, for example, when the user sets a desired scan speed by the setting means, the control means appropriately sets the amplification factor and the frequency band in the first-stage amplifier according to the scan speed. Switch the feedback resistor so that the value is the same. Since the product of the amplification factor and the frequency band, that is, the GB product is constant, the frequency band becomes narrower when the amplification factor is increased. Therefore, when the scanning speed is relatively high, the feedback resistance is determined so as to decrease at the expense of the amplification factor in order to secure a necessary frequency band. On the other hand, when the scanning speed is relatively slow, the frequency band may be relatively narrow, so the feedback resistance is determined so as to increase the amplification factor.

  As described above, according to the mass spectrometer according to the present invention, it is possible to reduce the dullness of the peak waveform in the mass spectrum even when the scanning speed of mass spectrometry is high, and to improve the separability of adjacent peaks. Thereby, the calculation accuracy of the mass based on the mass spectrum is improved, and a plurality of different components with close masses can be reliably captured. On the other hand, when the scan speed is relatively slow, high detection sensitivity can be ensured and noise can be reduced to improve the signal-to-noise ratio of the signal. As a result, the trace component is not overlooked, the peak waveform shape can be stabilized, and the quantitative accuracy can be improved.

  Further, as one aspect of the mass spectrometer according to the present invention, there is further provided a multiplier that is in the next stage of the first stage amplifier and switches the magnification so that the output level becomes constant in conjunction with switching of the feedback resistance of the first stage amplifier. It is preferable to provide a configuration.

  According to this configuration, even if the amplification factor is changed in the first stage amplifier, the level of the output signal of the multiplier is the same when the input signal to the first stage amplifier is the same. For this reason, the difference in amplification factor is not affected at all in the processing circuit subsequent to the multiplier, for example, the amplifier or analog / digital conversion circuit in the subsequent stage, and it is possible to avoid the circuit configuration and processing from becoming complicated.

  In the mass spectrometer according to the present invention, the control means may be configured to switch the feedback resistor so as to lower the amplification factor of the first-stage amplifier regardless of the scan speed when measuring a high concentration sample.

  When measuring a high-concentration sample, if the level of the detection signal from the detector is high and the amplification factor of the first-stage amplifier is large, there is a risk of saturation. According to the above configuration, in such a case, since the feedback resistor is switched so that the amplification factor is lowered, it is possible to satisfactorily analyze even a high concentration component by preventing the signal from being saturated.

  Hereinafter, a mass spectrometer which is an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a mass analyzer of the mass spectrometer, and FIG. 2 is a configuration diagram of a detection signal processing circuit. The mass spectrometer of the present embodiment is a part of LC / MS and uses an electrospray ionization method which is one of atmospheric pressure ionization methods as an ionization part.

  In FIG. 1, an ionization chamber 11 provided with a nozzle 12 connected to a column outlet end of a liquid chromatograph (not shown), a pre-quadrupole mass filter 22, a main quadrupole mass filter 23, and a detector 24 are provided. A first intermediate vacuum chamber 14 and a second intermediate vacuum chamber 18 that are separated from each other by a partition wall are provided between the analysis chamber 21 provided. The ionization chamber 11 and the first intermediate vacuum chamber 14 communicate with each other via a thin solvent removal pipe 13, and the top of the skimmer 16 is between the first intermediate vacuum chamber 14 and the second intermediate vacuum chamber 18. The second intermediate vacuum chamber 18 and the analysis chamber 21 communicate with each other through a small opening provided in the partition wall 20. .

The inside of the ionization chamber 11 as an ion source is in an atmospheric pressure atmosphere (about 10 ⁵ [Pa]) due to vaporized molecules of the liquid sample continuously supplied from the nozzle 12, and the first intermediate vacuum in the next stage. The inside of the chamber 14 is evacuated to a low vacuum state of about 10 ² [Pa] by a rotary pump 27. Further, the inside of the second intermediate vacuum chamber 18 at the next stage is evacuated to a medium vacuum state by about 10 ⁻¹ to 10 ⁻² [Pa] by the turbo molecular pump 28, and the inside of the analysis chamber 21 at the final stage is separated. The turbo molecular pump 29 is evacuated to a high vacuum state of about 10 ⁻³ to 10 ⁻⁴ [Pa]. In other words, a multi-stage differential exhaust system in which the degree of vacuum is increased stepwise from the ionization chamber 11 to the analysis chamber 21 to maintain the inside of the final analysis chamber 21 in a high vacuum state. ing.

  Although the structures of the first intermediate vacuum chamber 14 and the second intermediate vacuum chamber 18 are different from each other, an ion optical system is provided for efficiently transporting ions to the subsequent stage. That is, a first lens electrode 15 in which a plurality of (four) plate-like electrodes are arranged in three rows in an inclined manner is provided in the first intermediate vacuum chamber 14, and the solvent is removed by an electric field formed by the electrodes 15. While helping the drawing of ions through the pipe 13, the ions are converged in the vicinity of the orifice 17 of the skimmer 16. The second intermediate vacuum chamber 18 is provided with an octopole-type second lens electrode 19 in which eight rod electrodes are arranged so as to surround the ion optical axis C, whereby ions are converged and analyzed. Sent to chamber 21.

  A predetermined voltage is applied to the first lens electrode 15, the second lens electrode 19, and the quadrupole mass filters 22 and 23 from the power supply units 32, 33, and 34, respectively, and particularly to the quadrupole mass filters 22 and 23, A voltage ± (U + V · cosωt) obtained by adding the predetermined high-frequency voltage Vcosωt generated by the RF generation unit 36 and the predetermined direct-current voltage U generated by the DC generation unit 35 according to the mass-to-charge ratio to be selected by the combining unit 37. ) Is applied. The operations of the power supply units 32, 33, 34 and the like are comprehensively controlled by a control unit 30 mainly composed of a microcomputer, and analysis conditions for the analysis are set by the user via the analysis condition setting unit 31. Is done. In addition to the one shown in FIG. 1, a predetermined voltage (mainly DC voltage) is applied to each part, but the description is omitted because the drawing becomes complicated.

  The operation of this mass spectrometer will be schematically described. The liquid sample supplied almost continuously is sprayed (electrospray) into the ionization chamber 11 while being charged from the tip of the nozzle 12, and the sample molecules are ionized in the process of evaporating the solvent in the droplets. Fine droplets mixed with ions are drawn into the desolvation pipe 13 by the differential pressure between the ionization chamber 11 and the first intermediate vacuum chamber 14, and further the solvent is vaporized in the process of passing through the heated desolvation pipe 13. Is promoted and ionization proceeds. With the help of the electric field formed by the first lens electrode 15 disposed in the first intermediate vacuum chamber 14, the ions enter the first intermediate vacuum chamber 14, are converged and pass through the orifice 17 to form the second intermediate vacuum chamber. 18 is sent.

  In the second intermediate vacuum chamber 18, ions are further converged and sent to the analysis chamber 21 by the action of the electric field formed by the octopole-type second lens electrode 19. In the analysis chamber 21, only ions having a specific mass-to-charge ratio determined by the voltage applied to each rod electrode pass through the space in the long axis direction of the quadrupole mass filters 22 and 23, and the other mass charges. Ions with a ratio diverge on the way. The ions passing through the quadrupole mass filters 22 and 23 reach the detector 24, and the detector 24 outputs a current signal corresponding to the amount of ions as a detection signal.

  When performing scan measurement that repeatedly scans a predetermined mass range, the analysis condition setting unit 31 sets analysis conditions including a scan speed, a mass range, and the like. The maximum scan speed is 15000 [amu / sec] (amu = atomic mass unit), and the scan speed can be set in multiple stages of 15000 / n [amu / sec] (where n = 1, 2, 3,...). Shall. In accordance with this setting, the control unit 30 maintains a constant U / V relationship of the voltage ± (U + V · cosωt) applied to the quadrupole mass filters 22 and 23, while maintaining the DC voltage value U and the amplitude of the high-frequency voltage. The power supply unit 34 is controlled so that the value V changes within a predetermined range and at a speed. Thereby, the mass-to-charge ratio of ions that can pass through the quadrupole mass filters 22 and 23 changes with time, and mass scanning is achieved.

  As shown in FIG. 2, the detection signal from the detector 24 passes through a preamplifier 40, a first multiplier 41, a level shift circuit 42, a second multiplier 43, and an analog filter 44 in order, and an analog / digital (A / D) converter. 45, and is sampled at a predetermined sampling period and then converted into digital data for each sample. The digital data is processed by the data processing unit 46 and then input to the arithmetic processing CPU 47, and data processing for creating a mass spectrum, for example, is executed.

  The operation of each stage will be described sequentially. The current signal from the detector 24 is converted into a voltage signal (that is, I / V converted) by the preamplifier 40 and amplified with a predetermined gain (amplification factor). This preamplifier 40 has a configuration in which two feedback resistors R1 and R2 can be switched by switches SW1 and SW2. Here, when R = 10 MΩ and R2 = 1 MΩ, SW1 is turned on and SW2 is turned off. The gain is 10 × G, SW2 is on, and SW1 is off, the gain is G. The control unit 30 selects a small gain (that is, gain G) when the scanning speed is equal to or higher than a predetermined value, and a large gain (that is, gain 10 × G) when the scanning speed is less than the predetermined value.

  Here, the meaning of switching the gain according to the scan speed will be described. The analysis conditions here are 10 sampling points per [amu] (atomic mass unit), the signal peak is a Gaussian waveform with a half width of about 1/2 [amu], and the maximum scanning speed is 15000 [ amu / sec]. In this case, the frequency band required for the preamplifier 40 is approximately 50 [kHz] according to the calculation. The faster the scan speed, the wider the frequency band required. On the other hand, since the noise at the preamplifier 40 in the first stage is dominant, it is desirable that the gain at the preamplifier 40 is high in order to reduce the noise level. When the signal intensity of the detection signal is low, it is necessary to increase the gain of the preamplifier 40 in order to increase sensitivity. In order to cope with such a high scanning speed, a wide frequency band is required, and it is desirable to increase the gain in order to reduce noise and improve detection sensitivity. However, since the product of the amplification factor and the frequency band (GB product) is constant in the same amplifier, when the amplification factor is increased, the frequency band becomes narrower in inverse proportion.

  Therefore, when the scan speed is fast, the gain is reduced to emphasize the widening of the frequency band, and when the scan speed is slow, the gain is increased because the frequency band has a margin. Here, when the scan speed is 1250 [amu / sec] or more, the feedback resistor R2 is selected to be the gain G, and when the scan speed is less than 1250 [amu / sec], the feedback resistor R1 is selected to be the gain. Is 10 × G.

According to the calculation of the present inventor, the relationship between the scan speed SP and the frequency band fsp required for processing the detection signal is as follows.
2.25 × SP ≒ fsp
It becomes. The frequency band f in the preamplifier 40 is relative to the feedback resistor Rf and the stray capacitance Cf.
f = 1 / (2π × Rf × Cf)
And it is necessary that f> fsp. Assuming now that the stray capacitance Cf is 2 pF, when Rf is 1 MΩ (that is, when the feedback resistor R2 is selected),
f = 1 / (2π × Rf × Cf) = 79 [kHz]
When Rf is 10 MΩ (that is, when feedback resistor R1 is selected),
f = 1 / (2π × Rf × Cf) = 7.9 [kHz]
It becomes. That is, it can be seen that if Rf is 1 MΩ, a necessary frequency band of 50 kHz can be secured.

  The signal amplified by the preamplifier 40 as described above is input to the next first multiplier 41. The magnification (gain) of the first multiplier 41 is also switched under the control of the control unit 30, and the preamplifier 40 When the gain G is selected, a magnification of 10 is given, and when the gain 10 × G is selected by the preamplifier 40, a magnification of 1 is given. Therefore, the total gain of the preamplifier 40 and the first multiplier 41 does not depend on the scan speed at all. Even if the scan speed is different, the first gain is the same regardless of the level of the input signal of the preamplifier 40. The level of the output signal of the device 41 is the same.

Here, considering the noise in the preamplifier 40 and the first multiplier 41, the resistance noise voltage density En in the preamplifier 40 is:
En = √ (4 · k · T · Rf)
It becomes. k is the Boltzmann constant and T is the absolute temperature. When the frequency band is BW, the noise voltage Vn is
Vn = En × √ (BW)
It becomes. In order to adjust the voltage level as described above, when 1 MΩ is selected as the feedback resistor, the first multiplier 41 gives a gain of 10 times.

If k = 1.38 × 10 ⁻²³ [J / K] and T = 300 [K], then the resistance noise voltage density En at Rf = 10 MΩ and 1 MΩ is En ₁₀ = 407 [nV / √Hz], and En ₁ = 128.7 [nV / √Hz]. Since the noise of the operational amplifier itself used here is about 8 [nV / √Hz], it can be considered that the noise in the preamplifier 40 is almost due to the feedback resistor. After the first multiplier 41, the noise in the previous stage is amplified by the magnification, so that the resistance noise voltage density En ′ at the output of the first multiplier 41 when Rf = 10 MΩ and 1 MΩ is respectively En ₁₀ ′ = 407 [nV / √Hz] and En ₁ ′ = 1287 [nV / √Hz]. That is, it can be seen that noise is reduced in the output stage of the first multiplier 41 when the gain at the preamplifier 40 is large. Further, the level of noise that appears after the output of the preamplifier 40 due to the noise generated before the input to the preamplifier 40 becomes smaller as the frequency band of the preamplifier 40 becomes narrower. Therefore, even if the noise generated in the detector 24 is taken into consideration, the larger the feedback resistance Rf, the more the noise is reduced.

  As described above, the signal whose voltage level has been adjusted in the first multiplier 41 is input to the level shift circuit 42, shifted in a direct current by the offset voltage, and input to the second multiplier 43. The second multiplier 43 is a multiplier that automatically sets the magnification to 1 × or 16 × in accordance with the level of the input signal. That is, when the signal strength of the input signal is not more than a predetermined value, the input signal is multiplied by 16, and otherwise, the input signal is output as it is. Thereby, the noise can be relatively reduced, and the dynamic range can be expanded by effectively using the full scale of the input level in the A / D converter 45.

Now, assuming that the noise on the input side of the second multiplier 43 is Np and the noise between the input end of the A / D converter 45 on the output side is Na, the noise N entering the A / D converter 45 is When the magnification at the 2 multiplier 43 is 1, N ₁ = Np + Na
When the magnification at the second multiplier 43 is 16,
N ₁₆ = 16 × Np + Na
It becomes. The value D obtained by A / D conversion of each of these is
_{D 1 = N 1/1 [} LSB] = (Np / 1 [LSB]) + (Na / 1 [LSB])
_{D 16 = N 16/1 [} LSB] = (16 × Np / 1 [LSB]) + (Na / 1 [LSB])
It becomes. As will be described later, in the data processing unit 46, first, in order to compensate for the difference in magnification in the second multiplier 43 in the multiplier 461, when the previous magnification is 1, an operation of digitally multiplying by 16 is executed. . So in this case the data value is
D ₁ ′ = 16 × D ₁ = (16 × Np / 1 [LSB]) + (16 × Na / 1 [LSB]) = D ₁₆ + (15 × Na / 1 [LSB])
It becomes. This means that the noise is larger by 15 × Na / 1 [LSB] than when the second multiplier 43 sets the magnification to 16 times. In other words, it can be seen that noise that appears after A / D conversion can be relatively reduced by multiplying the signal by 16 when the input signal level is low in the second multiplier 43.

The output of the second multiplier 43 is input to the analog filter 44, where unnecessary frequency components outside the band are removed. The cut-off frequency of the analog filter 44 needs to be equal to or less than ½ of the sampling frequency of the A / D converter 45 (here, 150 [kHz]) according to the Nyquist sampling theorem. Fc = 50 [kHz] from the frequency band to be used. The signal from which unnecessary frequency components have been removed is sampled by the A / D converter 45 at a sampling rate of 300 [kHz], and each sample is converted into 16-bit digital data. Here, it is assumed that the data obtained by the A / D converter 45 is a ₀ , a ₁ , a ₂ , a ₃ ,... In time series order, and this is input to the next data processing unit 46.

In the data processing unit 46, first, in order to compensate for the difference in magnification of 1 or 16 in the second multiplier 43 as described above, when the previous magnification is 1, the multiplier 461 performs A An operation of multiplying the / D value by 16 is executed, and this is expanded to 20-bit data. On the other hand, when the previous magnification is 1, only multiplication to 20-bit data is performed without performing multiplication. If the output data of the multiplier 461 is b ₀ , b ₁ , b ₂ , b ₃ ,... In time series order, when the previous magnification is 1,
b _n = a _n × 16
If the previous magnification is 16,
b _n = a _n
And However, _{a n} 16-bit data, the _{b n} is 20-bit data.

Finally, the data rate required by the arithmetic processing CPU 47 is the same as the scan speed and is a maximum of 150 [kHz]. As described above, the main component of the noise is the thermal noise of the resistor, which is random noise. Therefore, the noise can be reduced by about 1 / √2 by averaging the two samples. Therefore, the thinning processing unit 462 generates a data string having a rate of 150 [kHz] by performing a thinning process by averaging two adjacent data having a sampling rate of 300 [kHz]. Specifically, using data b ₀ , b ₁ , b ₂ , b ₃ ,... Input at a rate of 300 [kHz], the following averaging process is executed to halve the rate: Drop it.
c ₀ = (b ₀ + b ₁ ) / 2
c ₁ = (b ₂ + b ₃ ) / 2
...
c _k = (b _2k + b _{2k + 1} ) / 2
...
As a result, noise is reduced, and the noise level is expected to be about 1 / √2 times.

Next, the data C _k at the rate of 150 [kHz] is filtered by the FIR filter 463 having a sampling frequency of 150 [kHz], a data length of 20 bits, a cut-off frequency of 35 [kHz], and a maximum number of taps of 255. The data string α ₀ , α ₁ , α ₂ , α ₃ ,... Is generated by processing. Thereby, sufficient noise removal can be performed while preserving the shape of the mass spectrometry signal data. Then, α ₀ , α ₁ , α ₂ , α ₃ ,... With a data length of 20 bits are input to the addition processing unit 464, and converted into 31-bit data by adding the designated number of times (up to 2047 times). As for the 32nd bit, 32-bit data is generated by setting “1” when at least one of the data to be added is 1048560 or more, and “0” otherwise. The 32-bit data is sent to the arithmetic processing CPU 47 for processing such as mass spectrum creation.

  When the detection signal processing as described above reduces noise as much as possible, the signal strength is increased when the signal strength is low, and there is a possibility that the scan band is high and the frequency band may be insufficient. Can be expanded to obtain a good signal. In the above description, the feedback resistance in the preamplifier 40 is switched only in accordance with the scanning speed. However, when the level of the detection signal is high, that is, when the concentration of the component in the sample to be analyzed is originally high. If the preamplifier 40 increases the gain too much, it may be saturated and the signal waveform may be distorted. Therefore, when it is known in advance that the component concentration in the sample to be analyzed is high, the control unit 30 may select a small feedback resistor regardless of the scan speed to keep the gain of the preamplifier 40 low.

  In the above-described embodiment, the gain (and frequency band) of the preamplifier 40 is switched to two stages. However, this may be switched to three or more stages. In addition, in other respects, it is obvious that changes, modifications, and additions as appropriate within the scope of the present invention are included in the scope of the claims of the present application.

1 is an overall configuration diagram of a mass spectrometer in a mass spectrometer according to an embodiment of the present invention. The block diagram of the processing circuit of the detection signal in the mass spectrometer of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Ionization chamber 12 ... Nozzle 13 ... Desolvation pipe 14 ... 1st intermediate vacuum chamber 15 ... 1st lens electrode 16 ... Skimmer 17 ... Orifice 18 ... 2nd intermediate vacuum chamber 19 ... 2nd lens electrode 20 ... Partition 21 ... Analysis Chamber 22 ... Pre-quadrupole mass filter 23 ... Main quadrupole mass filter 24 ... Detector 27 ... Rotary pumps 28, 29 ... Turbo molecular pump 30 ... Control unit 31 ... Analysis condition setting units 32, 33, 34 ... Power supply unit 35 ... DC generation unit 36 ... RF generation unit 37 ... synthesis unit 40 ... preamplifier R1, R2 ... feedback resistor 41 ... first multiplier 42 ... level shift circuit 43 ... second multiplier 44 ... analog filter 45 ... A / D conversion Unit 46 ... Data processing unit 461 ... Multiplier 462 ... Thinning processing unit 463 ... FIR filter 464 ... Addition processing unit 47 ... Calculation processing CPU

Claims (3)

A mass separator that selectively separates ions according to a mass-to-charge ratio, and a detector that detects ions that have passed through the mass separator, and a mass of ions that pass through the mass separator In a mass spectrometer that performs scan measurement for scanning in a predetermined mass range,
a) setting means for setting a scanning speed of mass scanning in the scan measurement;
b) a first-stage amplifier having a plurality of feedback resistors switchable to amplify a detection signal from the detector;
c) Control for switching the feedback resistance of the first-stage amplifier so as to widen the frequency band while lowering the amplification factor when the scan speed is fast compared to the slow case according to the scan speed set by the setting means Means,
A mass spectrometer comprising:   2. The mass according to claim 1, further comprising a multiplier that is in a stage subsequent to the first stage amplifier and switches a magnification so that an output level becomes constant in conjunction with switching of a feedback resistor of the first stage amplifier. Analysis equipment. 3. The mass spectrometer according to claim 1, wherein the control unit switches a feedback resistor so as to lower an amplification factor of the first-stage amplifier regardless of a scanning speed when measuring a high concentration sample.

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