JPH0945278A - Mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the time efficiency of mass spectrometry through the elimination of trial implantation by storing in advance the relation between an excitation voltage and an ion detector gain, and lowering the excitation voltage while correcting an output signal if an output signal of an electron detector exceeds a predetermined value. SOLUTION: A controller 14 is connected to a mass spectrometer, and a storage device 15 and a display device 16 are connected to the controller 14. A standard sample is set in the mass spectrometer, and an output value correcting curve showing the relation between a preset excitation voltage and an ion detector gain that is the ratio of ion flow intensity to an output signal of an electron detector 40 is calculated and stored in the storage device 15, Then an unknown sample is subjected to mass spectrometry. When the output signal of the electron detector 40 exceeds a predetermined value, the excitation voltage is lowered and the output signal form the electron detector 40 is corrected in accordance with the relation between the excitation voltage and the ion detector gain that is stored in the storage device 15. Using the corrected output signal, a correct output result corresponding to a new detector gain is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mass spectrometer.

[0002]

2. Description of the Related Art A mass spectrometer is a device for introducing a sample ionized by an ion source into a mass filter, allowing only ions having a specific mass number to pass therethrough, and detecting them by an ion detector. The analysis sample is first introduced into the ion source, ionized, and then introduced into the mass filter. The mass filter allows only ions having a specific mass number m / z (m: mass, z: charge ratio) to pass therethrough. For example, in the case of a quadrupole type, the mass filters are arranged in parallel and in axial symmetry. It consists of a book electrode rod and a voltage supply device for superimposing a DC voltage U and a high frequency voltage V on each electrode rod. The ions vibrate due to the electric field generated by the electrode rods to which the voltages U and V are applied,
Only ions of a certain mass number can pass through the mass filter, other ions diverge. Ions that have passed through the mass filter are detected by an ion detector. Voltages U and V applied to four electrode rods by a voltage supply device
Can be detected by discriminating ions having different mass numbers depending on time (mass scanning).

FIG. 3 shows an example of an ion detector using a secondary electron multiplier. The function of the ion detector will be described with reference to this figure. The ions 51 that have passed through the mass filter enter the ion acceptor 21. An excitation voltage is applied to the ion acceptor 21 by the voltage controller 22, and the ion 51
Each time is incident, the number of secondary electrons 52 according to the magnitude of the excitation voltage is emitted from the ion acceptor 21. The secondary electrons 52 are accelerated by the voltage applied between the ion acceptor 21 and the secondary electron multiplier 30 and introduced into the secondary electron multiplier 30.

Also in the secondary electron multiplier 30, secondary electron amplifiers 31 to 34 made of a substance having a high secondary electron emission efficiency similar to the ion acceptor 21 are arranged. A potential difference for accelerating the secondary electrons is provided between two adjacent secondary electron amplifying bodies, and the secondary electrons generated in the secondary electron amplifying body in the preceding stage are accelerated and the secondary electrons in the latter stage are accelerated. When incident on the secondary electron amplifying body, the secondary electron amplifying bodies in the subsequent stage generate secondary electrons more than the number of incident electrons. Secondary electron amplifier 3 in the final stage
The secondary electrons 53 generated in 4 are accelerated by the potential difference provided between the secondary electron amplifying body 34 and the electron detector 40, and enter the electron detector 40. The electron detector 40 outputs an electric signal 54 which can be handled by an ordinary electric circuit according to the number of incident electrons.

As can be seen from the above description, the magnitude of the electric signal output from the electron detector corresponds to the number of ions incident on the ion detector per unit time (this is called the ion flow intensity). This ratio of the ion flow intensity and the magnitude of the output electric signal is called the gain of the ion detector.

To convert the output value of the ion detector into the concentration value of the analytical component, a calibration curve must be prepared in advance. In order to create a calibration curve, first, one or a plurality of standard samples containing known concentrations of components are prepared, and this is applied to a mass spectrometer to check the output value of the ion detector. Data representing the relationship between the output value thus obtained and the component concentration is plotted on a graph. The calibration curve is obtained by drawing a line on the graph by the least squares method using these data. After creating the calibration curve in this way, the unknown sample is applied to the mass spectrometer, and the output value of the ion detector is applied to the calibration curve to obtain the concentration of the analysis component.

The number of ions detected by the ion detector is proportional to the concentration of the analysis component. Therefore, if the concentration of the analysis component is high, the intensity of the ion stream becomes higher, and the amount of secondary electrons emitted from the ion acceptor also increases. However, there is a limit value for the secondary electron emission amount of the ion acceptor and the secondary electron amplifier depending on the substance used, and when the analytical component is at a very high concentration, the ion acceptor or the secondary electron amplifier is amplified. The secondary electron emission amount in any one of the bodies may lose the proportional relationship and may eventually be saturated. Correct analysis cannot be performed in such a state.

In such a case, by lowering the excitation voltage of the ion acceptor, it is possible to reduce the amount of secondary electrons generated with respect to the intensity of the ion flow and return the ion detector to a correct operating state. Conventionally, the excitation voltage of the ion acceptor can be changed in several steps, and the excitation voltage is appropriately switched according to the concentration of the analysis component. When the excitation voltage of the ion acceptor is changed, the gain, which is the ratio of the ion flow intensity and the output value of the ion detector, is also changed. Therefore, switching of the excitation voltage was also called gain switching.

[0009]

When an unknown sample is analyzed using a mass spectrometer, the maximum concentration that is considered to be detected from the sample is estimated in advance, and the ion detector is used for the estimated value. The work of setting the excitation voltage of the ion acceptor so that a correct value can be output is performed. However, when the actual maximum concentration is larger than the estimated value, the ion detector cannot output the correct value. When such a situation occurs, conventionally, the analysis was stopped at that point, and the ion acceptor should be able to output the correct value even for the component having a concentration exceeding the previously estimated value. It was necessary to reset the excitation voltage of and to start over from the preparation of the calibration curve.

Incidentally, if an unknown sample is subjected to trial striking prior to the analysis and the peak of the component concentration is investigated in advance, the excitation voltage of the ion acceptor can be set appropriately. However, in this case, the fact that the trial shot must be performed first impairs the analysis efficiency.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a detector gain even when the output of the ion detector reaches a limit when a sample is analyzed. It is an object of the present invention to provide a mass spectrometer in which it is not necessary to reset and re-create the calibration curve and to perform trial striking of the sample before analysis in order to estimate the concentration of the target component.

[0012]

Means for Solving the Problems A mass spectrometer according to the present invention made to solve the above problems is a) a metal body to which an excitation voltage is applied, each time an ion is incident on the surface. An ion acceptor that emits a number of electrons according to the excitation voltage, b) a secondary electron amplifier that emits a number of electrons equal to or more than the number of incident electrons each time an electron is incident on the surface, and c) enters A mass spectrometer equipped with an ion detector having an electron detector that outputs an electric signal according to the number of electrons, and d) a predetermined excitation voltage, ion flow intensity, and output of the electron detector. Correction value storage means for storing the relationship with the ion detector gain, which is the ratio with the electric signal, and e) when the output signal from the electronic detector exceeds a predetermined value, the excitation voltage is lowered and the correction value storage means Based on the above relationship stored in the Characterized in that it comprises a gain control means for correcting the signal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Ions having passed through a mass filter first enter an ion acceptor of an ion detector. The ion acceptor is a metal body to which an excitation voltage is applied, and each time an ion is incident on the surface of the ion acceptor, the ion acceptor emits a number of electrons (secondary electrons) according to the applied excitation voltage. The secondary electrons are incident on the secondary electron amplifying body. The secondary electron amplifying body is made of a material having a high secondary electron emission efficiency, and when an electron enters the secondary electron amplifying body, the secondary electron amplifying body emits a number of secondary electrons equal to or larger than the number of incident electrons. A plurality of such secondary electron amplifying bodies may be provided and the number of secondary electrons may be amplified in several stages. The secondary electrons thus increased in number finally enter the electron detector.

The electron detector outputs an electric signal according to the number of incident electrons. The gain of the ion detector is the ratio of the magnitude of this electric signal to the number of ions that enter the ion acceptor from the mass filter per unit time (this is called the ion flow intensity). In this ion detector, when the secondary electron emission in the ion acceptor or secondary electron amplifier approaches saturation, the output signal from the electron detector will not accurately represent the ion flow intensity. Therefore, the upper limit of the output region in which the output signal from the electron detector correctly represents the ion flow intensity is investigated in advance, and this is set as the set output limit.

The gain control means lowers the excitation voltage of the ion acceptor when the output signal from the electron detector exceeds the set output limit. As a result, the amount of secondary electron emission from the ion acceptor decreases, the saturation state of emitted electrons is eliminated, and the output signal from the electron detector correctly corresponds to the ion flow intensity.

When the excitation voltage of the ion acceptor is changed, the gain of the ion detector also changes. Therefore, the gain control means retroactively corrects the output signal of the electron detector obtained before the change of the excitation voltage of the ion acceptor, based on the relationship stored in the correction value storage means. By using the output signal thus corrected, the correct output result corresponding to the new detector gain can be obtained.

[0017]

According to the present invention, even if the output value of the ion detector for the analysis component exceeds the set output limit, it is not necessary to newly set the gain of the detector and start over from the preparation of the calibration curve. In addition, it is not necessary to carry out a test hitting which has been conventionally performed on a sample whose concentration is difficult to estimate. As described above, the implementation of the present invention has the effect of significantly increasing the time efficiency of mass spectrometry.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic diagram showing the configuration of the mass spectrometer. The ions generated by the ion source 11 are introduced into the mass filter 12, and the mass filter 12 allows only ions having a specific mass number to pass therethrough and diverges other ions. The ions 51 that have passed through the mass filter 12 are detected by the ion detector 13. The mass spectrometer 10 includes a controller 14
Are connected, and each unit of the mass spectrometer 10 can be controlled by the control device 14. A storage device 15 and a display device 16 are connected to the control device 14.

FIG. 3 is a detailed view of the ion detector 13.
The ion detector 13 uses the ion acceptor 21 to generate ions 5
In response to 1, the electronic detector 40 outputs an electric signal 54 corresponding to the ion flow intensity. The electronic detector 40 is the controller 14
The controller 14 receives the electrical signal 54 output by the electronic detector 40. On the other hand, the control device 14 is also connected to the voltage control device 22, and the control device 14 can control the excitation voltage of the ion acceptor 21 (hereinafter simply referred to as the excitation voltage) via the voltage control device 22. The excitation voltage can be switched stepwise from the higher one to V1, V2, V3 ...

Next, the relationship between the excitation voltage and the output value of the ion detector 13 will be examined for the mass spectrometer 10 having the above structure. First, a standard sample A containing components of known concentration is prepared. The excitation voltage is set to the first value V1, the sample A is applied to the mass spectrometer 10, and the ion detector 1
Check the output value of 3 and set it as Y1. Next, the excitation voltage is set to the second value V2, and the sample A is set to the mass spectrometer 10
Check the output value of the ion detector 13 and set the value to Y
Assume 2. Similarly, the sample A is applied to the mass spectrometer 10 under the excitation voltages V3, V4, ... And the output values Y3, Y4 ,. The data of the excitation voltage V and the output value Y of the ion detector 13 thus obtained are plotted on a graph and a line is drawn by the least square method or the like.

The curve thus obtained shows the relationship of how the output value of the ion detector 13 changes when the excitation voltage is changed under the condition that the concentration of the analysis component is constant,
That is, the relationship between the excitation voltage and the gain is shown. This relational curve is called an output value correction curve here. The output value correction curve created in this way is stored in the storage device 15 by the control device 14. The output value correction curve of the mass spectrometer 10 is shown in FIG.

Once the output value correction curve is created, analysis of the unknown sample is started. Here, the set output limit of the ion detector 13 of the mass spectrometer 10 is set to Ym in advance. Also, the excitation voltage at the start of analysis is set to Vk1,
The controller 14 stores this value Vk1 in the storage device 15.

The operation of the controller 14 will be described with reference to FIG. After the analysis is started, first, the first component 60 having a peak at time t1 is detected. The peak of the output value corresponding to the component 60 is Y61, which has not reached the set output limit Ym.

After the detection of the component 60 ends, the second component 70 begins to be detected. However, since the concentration of the component 70 was higher than the estimated concentration in advance, the output of the ion detector 13 reached the set output limit Ym at the time t2. Upon detecting this, the control device 14 promptly reduces the excitation voltage to Vk2 by the voltage control device 22. As a result, the gain of the ion detector 13 decreases, and the output value that has reached the set output limit Ym decreases to Ym2. Thus, the analysis is continued without interruption, and the output of the ion detector 13 reaches the set output limit Ym again at the time t3. Upon detecting this, the control device 14 lowers the excitation voltage to Vk3 this time, and in response to this, the output value also decreases again. After that, the analysis is further continued, and the output value reaches the peak Y73 at the time t4, and thereafter, decreases monotonically.

Each time the detector output reaches the set output limit during the analysis, the controller 14 changes the excitation voltage and, at the same time, stores the changed time t and the changed value of the excitation voltage V in the storage device 15. Store.

The chromatogram of FIG. 4 shows three excitation voltages V
The output values obtained under k1, Vk2, and Vk3 are drawn on the same graph with the output values mixed, and the chromatogram is not correctly represented as it is. Therefore, immediately after changing the excitation voltage, the control device 14 obtains the output value obtained under the excitation voltage before the change under the excitation voltage after the change, based on the output value correction curve. Correct the output value.

FIG. 5 is a chromatogram obtained as a result of correcting the output values shown in FIG. The correction is performed twice when the excitation voltage is changed (Vk1 to Vk2) at time t2 and when the excitation voltage is changed (Vk2 to Vk3) at time t3. Specifically, the output value obtained by the time t2 by the correction at the time t2 is Yk2 / Yk1.
Further, by the correction at time t3, the corrected output value obtained by the correction at time t2 and the output value obtained from time t2 to t3 are compressed to Yk3 / Yk2.

The controller 14 stores all the data (time t, excitation voltage V, output value Y) necessary for creating a chromatogram in the storage device 15 while performing the analysis. Therefore, the correction of the output value and the display of the correction result can be collectively performed after the analysis of the sample has been completed. It is also possible to immediately display the corrected chromatogram every time the device 14 corrects the output value. This allows the user to check the chromatogram having the correct shape on the display device 16 at any time during the analysis.

[Brief description of drawings]

FIG. 1 is a correction curve showing a relationship between an excitation voltage of an ion acceptor and a detector output.

FIG. 2 is a schematic diagram of a mass spectrometer.

FIG. 3 is a detailed view of an ion detector using a secondary electron multiplier.

FIG. 4 is a chromatogram before correction obtained by analyzing a sample.

FIG. 5 is a chromatogram obtained by correcting the chromatogram of FIG.

[Explanation of symbols]

 10 ... Mass spectrometer 11 ... Ion source 12 ... Mass filter 13 ... Ion detector 14 ... Control device 15 ... Storage device 16 ... Display device 21 ... Ion acceptor 22 ... Voltage control device 31-34 ... Secondary electron amplification body 40 ... Electron detector 51 ... Ions that have passed through the mass filter 54 ... Output electrical signal

Claims (1)

[Claims] 1. A) a metal body to which an excitation voltage is applied,
An ion acceptor that emits a number of electrons according to the excitation voltage each time an ion is incident on the surface, and a secondary electron that emits a number of electrons equal to or greater than the number of incident electrons each time an electron is incident on the surface. A mass spectrometer equipped with an ion detector having an amplifier and c) an electron detector that outputs an electric signal according to the number of incident electrons, and d) a predetermined excitation voltage and ions. Correction value storage means for storing the relationship between the ion intensity and the ion detector gain, which is the ratio of the flow intensity to the output electrical signal of the electron detector; and e) When the output signal from the electron detector exceeds a predetermined value, the excitation voltage A gain control unit that reduces the output signal and corrects the output signal from the electronic detector based on the above relationship stored in the correction value storage unit.