JP2009277376A - Mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To electrically compensate for the mass shift accompanying temperature changes, when changing the frequency of a square-wave voltage in a circuit for generating the square-wave voltage applied to a ring electrode of a digital ion trap. <P>SOLUTION: Voltage fluctuations and phase fluctuations that accompany temperature changes, when the frequency is changed are measured, in advance, and based on its measurement result, control information for compensating effect of the fluctuations is stored in a memory part 11. When ion mass exhausted from the ion trap 2 at the time of analysis is changed, a control part 7 predicts the voltage fluctuations and the phase fluctuations, by reading out the control information corresponding to the frequency change from the memory part 11, and adjusts voltages of variable voltage sources 45, 46 via a voltage adjusting part 52, by forming a control signal to compensate its effect. As a result of this, for example, when a voltage drop at switches 43, 44 become large due to the temperature changes, the output voltages of the variable voltage sources 45, 46 are increased, and amplitude of the voltage applied to the ring electrode 21 is maintained substantially constant. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mass spectrometer equipped with an ion optical element such as an ion trap that traps ions or selects ions by the action of a high-frequency electric field, and more specifically, a rectangular wave voltage as a high-frequency voltage applied to the ion optical element. The present invention relates to a mass spectrometer to be used.

  As one of mass spectrometers, ions are captured and confined by the action of a high-frequency electric field, ions having a specific mass (strictly m / z value) are selected, and ions thus selected are selected. A mass spectrometer using an ion trap for cleaving is known. As will be described later, a typical ion trap has a pair of ring electrodes whose inner surface has a rotating one-leaf hyperboloid shape, and a pair of inner surfaces disposed with the ring electrode sandwiched between them. Although it is a three-dimensional quadrupole ion trap composed of an end cap electrode, a linear ion trap composed of four rod electrodes arranged in parallel is also known. In the present specification, the ion trap will be described by taking the former “three-dimensional quadrupole type” as an example.

  In a conventional general ion trap, a high frequency electric field for capturing ions is usually formed in a space surrounded by the ring electrode and the end cap electrode by applying a sinusoidal high frequency voltage to the ring electrode. Confinement while oscillating ions. In such an ion trap, an LC resonance circuit is used to generate a sine wave voltage to be applied to a ring electrode as described in Patent Document 1, and the amplitude of a sinusoidal high voltage generated by the LC resonance circuit is increased. By changing, the mass of ions trapped in or discharged from the ion trap is controlled.

  On the other hand, recently, ion traps that confine ions by applying a rectangular wave voltage to the ring electrode instead of a sine wave voltage have been developed (see Patent Document 2, Patent Document 3, Non-Patent Document 1, etc.). ). This type of ion trap is usually called a digitally driven ion trap or simply a digital ion trap because a rectangular wave voltage having binary levels of high and low is used. In contrast, a conventional ion trap using a sinusoidal voltage is referred to as an analog drive ion trap or an analog ion trap.

  In the digital ion trap described above, the mass of ions trapped in or discharged from the ion trap can be changed by changing the frequency while keeping the amplitude (voltage value) of the rectangular wave voltage applied to the ring electrode constant. Can be controlled. Therefore, in the digital ion trap, the amplitude of the high voltage applied to the ring electrode can be reduced as compared with the analog ion trap. Thereby, the cost of the power supply circuit for generating the high frequency voltage can be reduced. In addition, there is an advantage that undesired discharge between the electrodes by increasing the voltage can be avoided.

FIG. 6 is a schematic configuration diagram of a power supply circuit of a digital ion trap described in Patent Documents 2 and 3 and the like. The ion trap 2 includes one ring electrode 21 and a pair of end cap electrodes 22 and 24 arranged with the ring electrode 21 therebetween. A predetermined voltage (usually a DC voltage) is applied to each of the end cap electrodes 22 and 24 from the auxiliary voltage generator 6. The main voltage generator 4 connected to the ring electrode 21 includes a first voltage source 41 that generates the first voltage V _H , a second voltage source 42 that generates the second voltage V _L , and the first voltage source 41. A first switch 43 and a second switch 44 connected in series between the output and the output of the second voltage source 42, and the output voltage V _OUT is extracted from the connection connecting the switches 42, 44. Applied to the electrode 21.

The first switch 43 and the second switch 44 are driven so as to be alternately turned on by a pulsed drive signal supplied from the control unit 7. Since the first voltage V _H is output when the first switch 43 is turned on and the second voltage V _L is output when the second switch 44 is turned on, the output voltage V _OUT ideally has a high level. V _H is a rectangular wave voltage whose low level is V _L. According to the description of Non-Patent Document 1, the voltage level of the rectangular wave voltage is, for example, ± 250V, ± 500V, ±± 750V, ± 1000V, and the like. The control unit 7 changes the switching drive cycle (frequency) of the first switch 43 and the second switch 44, so that the frequency f of the rectangular wave voltage changes while the amplitude (voltage level) is kept constant.

  While digital ion traps have the advantages described above over analog ion traps, they involve technical difficulties that are different from analog ion traps. This will be described below.

In the power supply circuit as shown in FIG. 6, since the first switch 43 and the second switch 44 are required to have high speed, a semiconductor switching element such as a power MOSFET is usually used. Depending on the on-resistance of the switching element and the accompanying capacitance component, the amount of voltage drop differs depending on the drive frequency. Therefore, even if the output voltages of the first voltage source 41 and the second voltage source 42 are constant, not only the frequency of the output voltage _VOUT changes when the drive frequency changes, but also the amplitude of the wrinkles that are originally constant. Fluctuates slightly. FIG. 7 is a waveform diagram showing an example of a change in the rectangular wave voltage when the drive frequency is changed from f1 to f2. In this figure, the “frequency-dependent voltage change” is the fluctuation mainly due to the difference in voltage drop accompanying the difference in driving frequency described above.

  Since a large current flows when the semiconductor switching element as described above is turned on / off, heat is generated due to a current loss inside the switching element. Therefore, the amount of heat generation is considerably larger than that of a power supply circuit using an LC resonance circuit for an analog ion trap. The device characteristics such as the switching element operating speed (ON → OFF time, OFF → ON time, etc.), ON resistance, switching threshold, etc. are temperature dependent, and therefore change depending on the ambient temperature. If the frequency of the rectangular wave voltage applied to the ring electrode 21 is constant, the amount of heat generation is also stable, and the change in characteristics of the switching element due to the influence of temperature is small. However, for example, when the mass of ions to be selected in the ion trap 2 is changed, the frequency of the rectangular wave voltage changes, so the amount of heat generated in the switching element also changes. Therefore, the temperature changes and the characteristics of the switching element change. Even if the frequency changes, the temperature change due to the change in heat generation is slow and there is also a time delay. Therefore, the change in the characteristics of the switching element due to heat generation is similarly slow and causes a time delay.

  Therefore, as shown in FIG. 7, when the frequency is switched from f1 to f2, immediately after that, the amplitude of the rectangular wave voltage changes depending on the frequency (in this example, the amplitude decreases but increases). In some cases). Further, after that, as the temperature of the switching element changes, the amplitude further changes gradually, and when the temperature becomes stable, the amplitude becomes substantially constant. Further, when the switching element on-off, off-on rise time or switching threshold changes, the phase of the rectangular wave voltage fluctuates, resulting in steps in the rising and falling of the rectangular wave voltage as shown in FIG. Or change takes time. In either case, since the potential that acts on the ions in the ion trap 2 and affects the behavior thereof fluctuates, there arises a problem that, for example, the mass of the selected ions shifts.

  That is, in a digital ion trap that can be expected to have high mass accuracy, the change or switching of the mass of the control target ions as described above results in a decrease in the accuracy of ion mass selection. One method for solving this problem is to use a temperature adjusting means that adjusts the temperature of the power supply circuit with high accuracy. For example, a temperature control means comprising a heat conduction block having a heat capacity sufficiently larger than the heat generation amount of the switching element and a Peltier element for cooling the heat conduction block, etc. The above problem can be solved by reducing the difference in the amount of heat generated in the circuit and keeping the temperature constant. Even if the temperature is stabilized, the voltage change depending on the frequency remains, but this can be compensated relatively easily by mass calibration or the like. However, such a temperature control means requires a large cost, and brings about a large cost increase compared to an analog ion trap. It also contributes to hindering downsizing and weight reduction of the device.

JP 2004-152658 A International Publication No. 01/029871 Pamphlet International Publication No. 2005/083743 Pamphlet Furuhashi, Takeshita, Ogawa, Iwamoto, “Development of Digital Ion Trap Mass Spectrometer”, Shimazu Review, Shimazu Review Editorial Department, March 31, 2006, Vol. 62, No. 3.4, pp. 141-151

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to change the temperature due to heat generation of a circuit including a switching element for generating a rectangular wave voltage without using a highly accurate temperature control means. It is an object of the present invention to provide a mass spectrometer that can reduce the influence of the above and improve the mass accuracy of ion selection in the ion trap.

The present invention made to solve the above problems comprises an ion optical element comprising a plurality of electrodes and controlling the behavior of ions by a high-frequency electric field formed in a space surrounded by the plurality of electrodes, and the high-frequency electric field In a mass spectrometer for controlling the behavior of ions in a high-frequency electric field by controlling a frequency of the rectangular wave voltage as a high-frequency voltage applied to at least one electrode of the ion optical element to form a rectangular wave voltage ,
a) first and second DC voltage sources that are variable in voltage;
b) switching means for switching a DC voltage by the first and second DC voltage sources by a switching element to generate and output a rectangular wave voltage having a high voltage and a low voltage by the DC voltage source;
c) switching control means for generating a drive signal having a frequency corresponding to the mass of ions to be controlled and supplying the driving signal to the switching means;
d) When changing the mass of ions to be controlled, predict voltage fluctuations and / or phase fluctuations of the rectangular wave voltage due to changes in the amount of heat generated by the switching means accompanying changes in the frequency of the drive signal corresponding to the changes. Voltage adjusting means for adjusting the voltages of the first and second DC voltage sources so as to compensate for the influence of the fluctuations;
It is characterized by having.

  Examples of the ion optical element include an ion transport optical element such as an ion lens and an ion guide, and an ion trap that traps ions by a high-frequency electric field. The present invention is particularly useful when high mass accuracy is required. It is. From such a point, it is preferable to apply to a mass spectrometer equipped with an ion trap that controls the behavior of ions so that ions are captured by a high-frequency electric field and ions having a specific mass are selectively left.

  Also applicable to mass spectrometers equipped with a three-dimensional quadrupole ion trap having a ring electrode and a pair of end cap electrodes, which are often used to select ions with a specific mass with high mass accuracy and mass resolution. It is preferable to do. In this case, by applying a rectangular wave voltage to the ring electrode, a high frequency electric field for selectively leaving ions of a specific mass or discharging them in reverse can be formed in the ion trap.

  In the mass spectrometer according to the present invention, when the mass of ions to be controlled is changed in the ion optical element, the voltage adjusting means generates the heat generated by changing the frequency of the drive signal of the switching means corresponding to the change. The output voltage fluctuation and the phase fluctuation of the rectangular wave voltage due to the change of are predicted. Here, the output voltage fluctuation is a fluctuation mainly due to a change in the voltage drop amount in the switching element. On the other hand, the phase fluctuation is a fluctuation mainly due to a change in rise time or fall time of a switching element or a drive circuit that drives the switching element, a change in switching threshold, or the like. In the latter case, even if the voltage (amplitude) itself does not change, the potential acting on the ions in the high-frequency electric field changes as the duty ratio of the rectangular wave voltage changes. This potential change can be compensated for by adjusting the voltage (amplitude) while maintaining the phase variation of the rectangular wave voltage.

  The voltage adjusting means adjusts the voltages of the first and second DC voltage sources based on the prediction so as to compensate the influence of the predicted voltage fluctuation and phase fluctuation. For example, when the voltage of the rectangular wave voltage is predicted to gradually decrease as the mass of ions to be controlled changes, the first and second DC voltage sources are controlled so that the voltage gradually increases from the time of change. Also, when it is predicted that the potential acting on the ions will gradually weaken due to phase fluctuations, the first and second DC voltage sources so that the voltage gradually increases from the time of frequency change, as described above. To control. That is, the DC voltage control performed in the mass spectrometer according to the present invention is feedforward control based on the prediction of fluctuation.

As one embodiment of the present invention, the voltage adjusting means includes:
Control information holding means for previously holding control information reflecting the transient characteristics of the voltage fluctuation and phase fluctuation of the rectangular wave voltage when the frequency of the drive signal is changed in response to the change of the mass of the ion to be controlled When,
When the change of the mass of the ion to be controlled is instructed, the frequency change information of the drive signal corresponding to the change is received, the voltage change of the rectangular wave voltage accompanying the frequency change and the control information holding means, and Signal generating means for generating a control signal for compensating for transient characteristics of phase fluctuations;
It can be set as the structure containing.

  The control information held in the control information holding means is created in advance based on the result of actually measuring the transient characteristics when various frequency changes of the drive signal are applied or on the basis of the result of simulation. And The format of the control information is not particularly limited. For example, when a frequency before and after a frequency change is given, a table format is output in which a parameter of a prediction formula is output, or a voltage value that changes with time is directly indicated. It can be in a tabular format where data is output. In this case, it is preferable that the signal generating means is mainly configured by a computer including a CPU.

As another embodiment of the present invention, the voltage adjusting means includes
Frequency detection means for detecting the frequency of the drive signal generated by the switching control means;
Arithmetic processing means for generating a control signal for compensating for the transient characteristics of the voltage fluctuation and phase fluctuation of the rectangular wave voltage according to the change in frequency detected by the frequency detecting means;
It can be set as the structure containing.

  In this case, the arithmetic processing means may be composed of either a digital circuit or an analog circuit, but is preferably composed of a digital circuit when the transient characteristics of fluctuation are not monotonous and complicated.

As one embodiment of the mass spectrometer according to the present invention,
The DC voltage source comprises a constant voltage source that generates a constant DC voltage and a variable voltage source that is variable in a range lower than the constant DC voltage, and is connected in series.
The voltage by the variable voltage source can be adjusted by the voltage adjusting means.

As another embodiment of the mass spectrometer according to the present invention,
The DC voltage source includes a constant voltage source for generating a constant DC voltage, and a fixed resistor and a variable resistor for dividing and outputting a voltage from the constant voltage source by resistance,
The resistance value of the variable resistor may be adjusted by the voltage adjusting means.

  In general, a constant voltage source is easier to ensure voltage accuracy and stability than a variable voltage source. Therefore, according to the above embodiment, it becomes easy to improve the accuracy and stability of the voltage generated by the DC voltage source.

  According to the mass spectrometer of the present invention, the influence of voltage fluctuation and phase fluctuation of the rectangular wave voltage due to the influence of heat generation of the circuit such as the switching element is electrically compensated. This eliminates the need for temperature control means to achieve high temperature stability. Even if necessary, it is necessary to provide simple heat dissipation means such as a fan. The subsequent mass shift can be suppressed. Thereby, high mass accuracy can be realized at low cost.

  Hereinafter, an ion trap mass spectrometer according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a main part of the ion trap mass spectrometer of the present embodiment. The same components as those already described with reference to FIG.

  This ion trap mass spectrometer includes an ion source 1 that ionizes a target sample, a three-dimensional quadrupole ion trap 2, and an ion detector 3. The ionization method in the ion source 1 is not particularly limited. For example, a matrix-assisted laser desorption ion source (MALDI) that ionizes a sample by irradiating the target sample with laser light can be used.

  The ion trap 2 corresponding to the ion optical element in the present invention includes a ring electrode 21 and a pair of end cap electrodes 22 and 24, and a space surrounded by the electrodes 21, 22, and 24 is an ion trapping region. 26. An ion entrance 23 is formed in the center of the end cap electrode 22 on the entrance side, and ions emitted from the ion source 1 are introduced into the ion trap 2 through the ion entrance 23. On the other hand, an ion exit port 25 is formed in the end cap electrode 24 on the exit side and substantially in line with the ion entrance port 23. The ions discharged from the ion trap 2 through the ion emission port 25 reach the ion detector 3 and are detected. The ion detector 3 includes a conversion dynode 31 that converts ions into electrons and a secondary electron multiplier 32, and sends a detection signal corresponding to the amount of incident ions to a data processing unit (not shown).

The main voltage generator 4 is connected to the ring electrode 21, and the auxiliary voltage generator 6 is connected to the end cap electrodes 22, 24. The main voltage generation unit 4 generates a rectangular wave voltage by switching the first voltage V _H and the second voltage V _L by the first switch 43 and the second switch 44 as in the conventional technique shown in FIG. . The first switch 43 and the second switch 44 are semiconductor switching elements such as power MOSFETs. In the conventional configuration, the voltage sources 41 and 42 are constant voltage sources that generate a constant DC voltage, whereas in the configuration of this embodiment, these are the first variable voltage source 45 and the second variable voltage source 46. Has been replaced.

The first voltage V _H and the second voltage V _L , that is, the high level and low level of the rectangular wave voltage are variable, but their amplitudes (voltage values) are almost the same as in the prior art, for example, about ± 250 V, ± 500 V, ± 750V, ± 1000V, and the like. However, the amplitude is not limited to this. The frequency of the rectangular wave voltage is generally in the range of several tens of kHz to several MHz.

  The digital control circuit 5 is a logic circuit using hardware, and includes a voltage adjusting unit 52 that generates voltage control signals V1 and V2 for controlling output voltages of the first variable voltage source 45 and the second variable voltage source 46, and a first control circuit. And a drive pulse generator 51 that generates pulsed drive signals S1 and S2 for controlling on / off of the first switch 43 and the second switch 44. The control unit 7 is mainly configured by a computer including a CPU, and is connected to an input unit 8 such as operation keys, a frequency information storage unit 10, and a voltage compensation information storage unit 11.

  The frequency information storage unit 10 holds information indicating the relationship between the mass of an ion and the frequency of a rectangular wave voltage for causing resonance excitation vibration of the ion with respect to the ion trapped in the ion trap 2. On the other hand, when the frequency of the rectangular wave voltage is changed so as to change the mass of ions to be resonantly excited and oscillated, the voltage compensation information storage unit 11 has a transient voltage fluctuation or phase fluctuation of the rectangular wave voltage that occurs immediately after the change. Control information for compensating characteristics is held.

  Specifically, voltage transient characteristics when the frequency of the rectangular wave voltage applied to the ring electrode 21 is changed from f1 to f2 are measured for various f1 and f2, and the transient characteristics are determined based on the measurement results. A prediction formula F (t) of voltage fluctuation that can be compensated is obtained. The prediction formula F (t) is a function of time t and includes a plurality of parameters corresponding to the frequency f1 before the change and the frequency f2 after the change. This parameter is stored as control information in the voltage compensation information storage unit 11, and a plurality of parameters are derived from the voltage compensation information storage unit 11 by giving the frequencies f1 and f2, and the control unit 7 determines the parameters as a prediction formula F By setting to (t), the prediction formula F (t) when the frequency is changed from f1 to f2 is determined.

  A simple example will be described with reference to FIG. Assume that the voltage fluctuation when the frequency of the rectangular wave voltage changes from f1 to f2 is a curve shown in [f1 → f2]. That is, the voltage that is Va immediately before the frequency change gradually decreases from the time when the frequency changes (t = 0), and saturates at approximately Vb at time t1. Also assume that the voltage fluctuation when the frequency of the rectangular wave voltage changes from f1 to f3 different from f2 is a curve shown by [f1 → f3]. That is, the voltage of Va immediately before the frequency change gradually decreases at a time larger than [f1 → f2] from the time when the frequency changes (t = 0), and saturates at approximately Vc at time t2. From the curve thus obtained, the prediction formula F (t) and parameters corresponding to each frequency condition (frequency before change and frequency after change) can be obtained.

  However, when the frequency change, that is, the minimum time of mass change is shorter than the time until the voltage is saturated, not only the frequency before and after the frequency change but also the past frequency information, that is, the history of the frequency change. It affects the temperature change of the switching element. Therefore, the curve of the voltage change when the frequency is changed has a complicated shape, and it is necessary to use the frequency history as a parameter.

  In addition, the above description considers only the voltage fluctuation accompanying the frequency change, but as described above, the phase of the rectangular wave voltage fluctuates when the rise time, fall time, switching threshold, etc. of the switching element change. The effective potential acting on the ions fluctuates. If this effect is significant, experimentally determine the voltage fluctuation corresponding to this potential fluctuation, add this to the voltage fluctuation as described above, and create a prediction formula that compensates for both. Is preferred.

  Further, the control information stored in the voltage compensation information storage unit 11 is created based on actually measured data as described above, and may be obtained by, for example, simulation calculation.

  Next, an example of the analysis operation in the mass spectrometer of the present embodiment having the above configuration will be described. Here, ions having various masses emitted from the ion source 1 are introduced into the ion trap 2 through the ion incident port 23, and after these ions are once trapped, ions having a specific mass are selected as a precursor to be ion trapped. 2, a case is assumed in which mass analysis of various product ions generated by cleavage is performed by cleaving the ions in the ion trap 2. In this case, the user sets the mass M of the precursor ion from the input unit 8 as one of the analysis conditions.

  First, various ions emitted from the ion source 1 are introduced into the ion trap 2, and the ions are trapped in the ion trapping region 26. Thereafter, in order to selectively leave a precursor ion having a mass M, ions having other masses are resonantly excited and discharged from the ion trap 2. For this purpose, the control unit 7 reads a frequency corresponding to the mass M from the frequency information storage unit 10 and determines a frequency scan sequence so as to execute a frequency scan in a predetermined frequency range excluding this frequency. In the frequency scan, scanning is performed so that the frequency of the rectangular wave voltage is increased or decreased at a predetermined frequency step. Since the frequency change of the rectangular wave voltage is known in advance by this frequency scan sequence, the control unit 7 uses the control information stored in the voltage compensation information storage unit 11 and the prediction formula F (t) described above, A voltage control sequence for compensating for the influence of voltage fluctuation and phase fluctuation accompanying the change in frequency is determined.

The control unit 7 instructs the drive pulse generation unit 51 to change the frequency of the drive signal so as to execute the frequency scan determined by the frequency scan sequence, and the drive pulse generation unit 51 responds accordingly to the frequency of the drive signal. Are sequentially changed and supplied to the first switch 43 and the second switch 44. As a result, a rectangular wave voltage having the first voltage V _H at the high level and the second voltage V _L at the low level is applied to the ring electrode 21 as the output voltage V _OUT . On the other hand, in parallel with this, the control unit 7 sends a control signal to the voltage adjustment unit 52 based on the voltage control sequence. According to this control signal, the voltage adjustment unit 52 sends the voltage control signals V1 and V2 so as to adjust the output voltages of the first variable voltage source 45 and the second variable voltage source 46 as time elapses. This voltage adjustment increases the output voltages of the first variable voltage source 45 and the second variable voltage source 46 in a situation where the voltage decreases with a change in frequency as shown in FIG. 7, for example. As a result, the high level and low level of the output voltage V _OUT are maintained at substantially the same level as before the frequency change.

  Further, when the duty ratio of the rectangular wave voltage becomes smaller as the frequency changes as shown in FIG. 8B, this reduces the effective potential in the ion trap 2 and compensates for this. Accordingly, the output voltages of the first variable voltage source 45 and the second variable voltage source 46 are increased. As a result, the potential acting on the ions in the ion trap 2 is maintained at substantially the same level as before the frequency change.

  Even if the amount of heat generated by the first switch 43 and the second switch 44 changes due to a change in the frequency of the drive signal and a temperature change occurs, it is applied to the ring electrode 21 so as to compensate for the effect of this temperature change. Since the amplitude of the rectangular wave voltage changes, the behavior of ions in the ion trap 2 is hardly affected by the temperature change. Therefore, ions having a mass corresponding to the frequency of the rectangular wave voltage applied to the ring electrode 21 are resonantly excited in the ion trap 2 and discharged to the outside of the ion trap 2 and removed. In accordance with the frequency scan of the rectangular wave voltage, ions having different masses are sequentially removed from the ion trap 2, and only the precursor ions having the target mass M that are not finally resonantly excited remain in the ion trap 2. . Since each ion can be removed from the ion trap 2 with high mass accuracy, the accuracy of the mass of the finally remaining ions is also high.

  After selecting the target ions with high mass accuracy in this way, a collision-induced dissociation gas is introduced into the ion trap 2 and the remaining precursor ions are excited and vibrated. Then, the ions collide with the collision-induced dissociation gas and cleave to generate various product ions. The product ions are sequentially discharged from the ion trap 2 through the ion outlet 25 and detected by the ion detector 3. Thereby, mass analysis data of product ions can be obtained.

  Here, a configuration example of the first variable voltage source 45 and the second variable voltage source 46 included in the main voltage generator 4 will be described with reference to FIGS. 3 and 4. Since the configuration of the second variable voltage source 46 is the same as that of the first variable voltage source 45 except for the polarity, only the first variable voltage source 45 will be described.

In the example of FIG. 3, the first variable voltage source 45 includes a constant voltage source 451 that generates a DC voltage V _HFIX and a variable voltage source 452 that generates a variable DC voltage in the range of 0 to V _HVIR connected in series. It is. The voltage by the variable voltage source 452 is adjusted by the voltage control signal V1. Therefore, the output voltage of the first variable voltage source 45 can be arbitrarily set in the range of V _{HFIX to} V _HFIX + V _HVIR . As described above, the necessary adjustment range of the voltage accompanying the frequency change of the rectangular wave voltage is much smaller than that of the entire voltage. Therefore, typically V _HFIX >> V _HVIR . In general, a constant voltage source is easier to ensure high voltage accuracy and voltage stability than a variable voltage source. Therefore, if the constant voltage source 451 and the variable voltage source 452 are combined, it is easy to ensure the voltage accuracy and stability of the output voltage.

In the example of FIG. 4, the first variable voltage source 45 includes a constant voltage source 455 generates a DC voltage V _HFIX, variable variable resistor in the DC voltage V a resistance dividing _HFIX, resistance 0 to R _VIR 456 and a fixed resistor 457 whose resistance value is R _FIX , the variable resistor 456 and the fixed resistor 457 are connected in series, and a voltage is taken out from the connection point. The movable terminal of the variable resistor 456 is moved by the voltage control signal V1, and the resistance at both ends changes in the range of 0 to R _VIR . Therefore, the output voltage of the first variable voltage source 45 can be arbitrarily set in the range of V _HFIX · {R _FIX / (R _FIX + R _VIR )} to V _HFIX .

  Next, an ion trap mass spectrometer according to another embodiment of the present invention will be described with reference to FIG. In the mass spectrometer of this embodiment, the configuration of the digital control circuit 5 that provides the voltage control signals V1 and V2 to the main voltage generator 4 is different from that of the above embodiment. In the above-described embodiment, basically, information for voltage compensation accompanying frequency change is created in the control unit 7 configured mainly with the CPU. That is, it can be said that voltage compensation is substantially achieved by the function of software operating on the CPU. On the other hand, in this embodiment, voltage compensation is achieved by a hardware function.

  That is, when the control unit 7 instructs the drive pulse generation unit 51 to change the frequency in accordance with the mass change of ions to be resonantly excited in the ion trap 2, and when a drive signal corresponding to this is output, the frequency detection unit 53 Recognize changes. In response to the recognition of the frequency change by the frequency detection unit 53, the adjustment signal generation unit 54 generates the voltage control signals V1 and V2 based on the control information stored in the voltage compensation information storage unit 55 in advance. For example, the voltage compensation information storage unit 55 stores voltage change data with respect to the passage of time from the frequency change point for each frequency before and after the change, and the adjustment signal generation unit 54 stores the frequency before and after the change in the voltage compensation information storage unit 55. The voltage change data with the passage of time can be sequentially read and output.

  Further, the change as shown in FIG. 5 can be regarded as a kind of step response, and this can be realized by a digital filter having a predetermined parameter. Therefore, the adjustment signal generation unit 54 focuses on the digital filter. The digital filter parameters may be stored in the voltage compensation information storage unit 55.

  In addition, when the voltage fluctuation or phase fluctuation of the rectangular wave voltage accompanying the frequency change is monotonous, the functions of the frequency detection unit 53, the adjustment signal generation unit 54, and the voltage compensation information storage unit 55 are not digital calculations but analog calculations. Can also be realized.

  It should be noted that the above embodiment is merely an example, and it is obvious that modifications, corrections, and additions can be appropriately made within the scope of the present invention, and included in the scope of the claims of the present application.

  For example, the above embodiment is a three-dimensional quadrupole ion trap, but an ion trap (so-called so-called ion trap) comprising a multipole (for example, quadrupole) rod and a pair of end cap electrodes provided on both open end faces. The present invention can also be applied to a linear ion trap. The present invention can also be applied to an ion transport optical element called an ion guide that focuses ions by a high-frequency electric field.

The block diagram of the principal part of the ion trap type | mold mass spectrometer which is one Example of this invention. The block diagram of the principal part of the ion trap type | mold mass spectrometer which is another Example of this invention. The figure which shows the structural example of the variable voltage source contained in the main voltage generation part in the mass spectrometer which is a present Example. The figure which shows the structural example of the variable voltage source contained in the main voltage generation part in the mass spectrometer which is a present Example. Explanatory drawing of the acquisition method of voltage compensation information. The schematic block diagram of the power supply circuit of a conventional common digital ion trap. The wave form diagram which shows an example of the change of a rectangular wave voltage when changing a drive frequency. The wave form diagram which shows an example of the change of a rectangular wave voltage when changing a drive frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ion source 2 ... Ion trap 21 ... Ring electrode 22, 24 ... End cap electrode 23 ... Ion exit port 25 ... Ion exit port 26 ... Ion capture region 3 ... Ion detector 31 ... Conversion dynode 32 ... Secondary electron multiplication Tube 10 ... Frequency information storage unit 11 ... Voltage compensation information storage unit 4 ... Main voltage generation units 43 and 44 ... Switches 45 and 46 ... Variable voltage sources 451 and 455 ... Constant voltage source 452 ... Variable voltage source 456 ... Variable resistor 457 ... fixed resistor 5 ... digital control circuit 51 ... drive pulse generation unit 52 ... voltage adjustment unit 53 ... frequency detection unit 54 ... adjustment signal generation unit 55 ... voltage compensation information storage unit 6 ... auxiliary voltage generation unit 7 ... control unit 8 ... Input section

Claims (7)

An ion optical element comprising a plurality of electrodes and controlling the behavior of ions by a high frequency electric field formed in a space surrounded by the plurality of electrodes, wherein at least one electrode of the ion optical element is formed to form the high frequency electric field. In the mass spectrometer that controls the behavior of ions in a high frequency electric field by controlling the frequency of the rectangular wave voltage as a rectangular wave voltage to be applied,
a) first and second DC voltage sources that are variable in voltage;
b) switching means for switching a DC voltage by the first and second DC voltage sources by a switching element to generate and output a rectangular wave voltage having a high voltage and a low voltage by the DC voltage source;
c) a switching control means for generating a drive signal having a frequency corresponding to the mass of ions to be controlled and supplying the driving signal to the switching means;
d) When changing the mass of ions to be controlled, predict voltage fluctuation and / or phase fluctuation of the rectangular wave voltage due to change in the amount of heat generated by the switching means accompanying the change in the frequency of the drive signal corresponding to the change. Voltage adjusting means for adjusting the voltages of the first and second DC voltage sources so as to compensate for the influence of the fluctuations;
A mass spectrometer comprising:   2. The mass spectrometer according to claim 1, wherein the ion optical element is an ion trap that captures ions by a high-frequency electric field and controls ion behavior so as to selectively leave ions having a specific mass. A mass spectrometer characterized by the above.   3. The mass spectrometer according to claim 2, wherein the ion trap is a three-dimensional quadrupole ion trap having one ring electrode and a pair of end cap electrodes. Analysis equipment. The mass spectrometer according to any one of claims 1 to 3, wherein the voltage adjusting means is
Control information holding means for previously holding control information reflecting the transient characteristics of the voltage fluctuation and phase fluctuation of the rectangular wave voltage when the frequency of the drive signal is changed in response to the change of the mass of the ion to be controlled When,
When the change of the mass of the ion to be controlled is instructed, the frequency change information of the drive signal corresponding to the change is received, the voltage change of the rectangular wave voltage accompanying the frequency change and the control information holding means, and Signal generating means for generating a control signal for compensating for transient characteristics of phase fluctuations;
A mass spectrometer comprising: The mass spectrometer according to any one of claims 1 to 3, wherein the voltage adjusting means is
Frequency detection means for detecting the frequency of the drive signal generated by the switching control means;
Arithmetic processing means for generating a control signal for compensating for the transient characteristics of the voltage fluctuation and phase fluctuation of the rectangular wave voltage according to the change in frequency detected by the frequency detecting means;
A mass spectrometer comprising: A mass spectrometer according to any one of claims 1 to 5,
The DC voltage source comprises a constant voltage source that generates a constant DC voltage and a variable voltage source that is variable in a range lower than the constant DC voltage, and is connected in series.
The mass spectrometer is characterized in that the voltage by the variable voltage source is adjusted by the voltage adjusting means. A mass spectrometer according to any one of claims 1 to 5,
The DC voltage source includes a constant voltage source for generating a constant DC voltage, and a fixed resistor and a variable resistor for dividing and outputting a voltage from the constant voltage source by resistance,
The mass spectrometer is characterized in that a resistance value of the variable resistor is adjusted by the voltage adjusting means.

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