JP2015127683A - Method for optimizing ion optical system parameter for improving signal stability against fluctuation during ion beam drawing process from plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve signal stability by reducing amount of signal drift relating to an induction coupling plasma mass spectrometer.SOLUTION: Relating to an induction coupling plasma mass spectrometer, a method is disclosed for improving stability of a detection signal from ion detection means. The method includes in which, 1) a pseudo sample containing at least one kind of element is prepared, 2) the pseudo sample ia introduced into the induction coupling plasma mass spectrometer, and by changing a voltage applied to an ion optical system as time passes, measures the pseudo sample, 3) for the element, the amount of change in detection signal that changes between detections is obtained, 4) based on the obtained change amount, a voltage at which the detection signal is most stable is selected, and is used for analysing the sample.

Description

  The present invention relates to a mass spectrometer using plasma as an ion source, and more particularly, to supersonic molecular beam drawing from plasma, ion beam drawing and ion beam transmission processes.

  FIG. 5 is a schematic diagram showing a basic concept of an exemplary inductively coupled plasma mass spectrometer (hereinafter also simply referred to as an apparatus) 10. FIG. 6 is an enlarged view of an interface unit 30 and an ion lens unit 50 described later. The apparatus 10 includes a plasma torch 20 that generates plasma 22, an interface unit 30 that is placed at a position facing the plasma 22, an ion lens unit 50 that is placed behind the interface unit 30, and an ion guide that is placed behind the ion lens unit 50. And an ion separation unit 80 placed after the ion guide unit 70. The ion guide unit 70 may not be provided in the apparatus 10.

  The plasma torch 20 includes a coil 21 for generating a high-frequency electromagnetic field near the tip, and is placed under atmospheric pressure. The coil 21 is connected to an RF power source (not shown). In the plasma torch 20, a high frequency inductively coupled plasma 22 is generated under atmospheric pressure by a high frequency electromagnetic field generated by the coil 21. In the plasma torch 20, the atomized sample (not shown) is introduced into the plasma 22 from the front of the plasma torch 20 (sample introduction process). The introduced sample (not shown) is evaporated and decomposed by the action of the plasma 22, and in the case of the majority of elements, it is finally converted into ions. An ionized sample (not shown) is included in the plasma 22. In addition, since a gas flow is generated from the rear end toward the front end in the plasma torch 20, the plasma 22 extends toward the sampling cone 31.

  The interface unit 30 is generally provided with two cone members, a sampling cone 31 and a skimmer cone 33. A part of the plasma 32 that has passed through the aperture 37 of the sampling cone 31 that directly faces the plasma 22 reaches a skimmer cone 33 that is positioned after that. Thereafter, a part of the plasma 32 passes through an aperture 38 formed in the skimmer cone 33 and reaches behind it as a supersonic molecular beam (ion beam extraction process). Gas molecules (including neutralized ions) that cannot pass through the skimmer cone 33 are exhausted from the interface unit 30 through the exhaust port 39 by the oil rotary pump RP. In general, RP is often an oil rotary pump, but other types of vacuum pumps may be used. An additional cone may also be used behind the skimmer cone.

  The ion lens unit 50 is provided with a first electrode 53 and a second electrode 54 that mainly constitute an extraction electrode unit, a third electrode 55 that constitutes an ion lens, and a fourth electrode 56 that is located at the subsequent stage. In addition, there may be further electrodes behind it. Since the first electrode 53 or the second electrode 54 constituting the extraction electrode portion has a sufficiently large potential different from that of plasma, ions are extracted from the plasma 52 in the form of an ion beam. The ion beam is guided into the collision / reaction cell 71 of the ion guide unit 70 located at the subsequent stage via the ion lens. The first electrode 53 can have any potential, but typically, the first electrode 53 is often set to a ground potential. Although the main lenses are concentrated on the ion lens portion, there are cases where ion lenses are also present in the ion guide portion 70 and the ion separation portion 80. The electrodes in the ion lens unit 50, the ion guide unit 70, and the ion separation unit 80 that affect the trajectory of the ion beam are collectively referred to as an ion optical system.

  The ion beam guided into the collision / reaction cell 71 of the ion guide unit 70 is guided downstream along the trajectory determined by the electric field generated by the multipole electrode 73. The multipole electrode 73 has, for example, an octupole structure. Further, collision / reaction gas may be introduced into the collision / reaction cell 71 from the introduction port 72. Polyatomic ions that interfere with the mass spectrum, including elements of the carrier gas or auxiliary gas, by causing collision of the molecules of the introduced gas with the various ions contained in the ion beam or reactions involving charge transfer, That is, interfering ions are removed from the ion beam. When collision / reaction gas is not introduced from the inlet 72, the collision / reaction cell 71 serves as an ion guide.

  During operation of the apparatus 10, the ion guide unit 70 is exhausted together with the ion lens unit 50 using a turbo molecular pump (TMP1). Therefore, the molecules contained in the plasma but neutralized in the ion lens unit 50 or the ion guide unit 70 or the collision / reaction gas molecules introduced into the collision / reaction cell are exhausted from the exhaust port 79. Is done.

  The ion beam taken out from the collision cell 71 is introduced into the ion separator 80. A multipole structure 81 which is generally a quadrupole is provided in the ion separator 80, and the multipole structure of the quadrupole is generally called a quadrupole mass analyzer or a quadrupole mass filter. (Hereinafter, the multipole structure 81 is referred to as a mass analyzer 81). The electric field generated by the mass analyzer 81 separates ions in the ion beam based on the mass to charge ratio. Note that an ion separation mechanism other than the quadrupole may be used for the ion separation unit. Typical examples include a magnetic field type using a magnetic field sector, a time-of-flight type that separates by the time of flight of ions, an ion trap type that uses an ion trap such as a three-dimensional quadrupole, and a Fourier that uses ion cyclotron resonance and Fourier transform. There are an orbitrap type using a converted ion cyclotron resonance type and an electric field type Fourier transform. Further, there is a tandem type in which a plurality of the mass analyzers described above are connected in series. Subsequently, the separated ions are guided to the subsequent ion detector 82 and detected. Similarly to the ion guide unit 70, the ion separation unit 80 is also evacuated using a turbo molecular pump (TMP 2), and unnecessary ions and other molecules separated by the mass analyzer 81 are discharged from the exhaust port 84. Exhausted. In addition, regarding TMP1 and TMP2, a type of vacuum pump other than the turbo molecular pump may be used.

The ion detector 82 receives and detects the ions separated in the mass analyzer 81, converts them into electrical signals, and outputs them as measurement signals. For example, an inductively coupled plasma mass spectrometer (ICP-MS) is a device having a large dynamic range, and a detected signal ranges from a very small amount (for example, 0.1 cps) to a main component (for example, 10 ¹⁰ cps). . In general, measurement by ion counting is used when the detected signal is low, and analog measurement is used when the detected signal is high. For example, in the case of ion counting, ions are converted into electrons amplified 10 ⁵ to 10 ⁶ times by being introduced into a secondary electron multiplier. An ion count is obtained by converting such electrons into voltage pulses and counting them for a certain period of time. Further, when the intensity of the detected signal is large, a Faraday cup may be used. An example of the inductively coupled plasma mass spectrometer (ICP-MS) as described above is disclosed in Patent Document 1.

  The apparatus 10 as described above includes a system controller (not shown), and the sample introduction unit including the plasma torch 20, the interface unit 30, the ion lens unit 50, the ion guide unit 70, and the ion separation unit 80 include: It can be controlled by the system controller. The system controller can also be controlled by a computer such as a workstation.

  In the mass spectrometer as described above, a high matrix sample may be analyzed as the sample to be analyzed. A high matrix sample is a sample containing a high concentration of metal salt and other substances in addition to the element to be analyzed. Typical high matrix samples include metal solutions, non-metallic material solutions, soil extracts, mineral water and seawater. For example, when analyzing a high matrix sample such as a metal solution, simple substances, salts, and oxides are generally deposited and deposited on the sampling cone 31 and the skimmer cone 33 described above. Due to this deposition, for example, the properties of the sampling cone 31 and the skimmer cone 33 change. Therefore, the generation of supersonic molecular beams at the sampling cone 31 and the skimmer cone 33, fluctuations or fluctuations in the ion beam extraction process at the extraction electrode section, and fluctuations in ion transmission efficiency in the subsequent ion optical system occur. Therefore, the sensitivity of the measurement signal generally varies with time even without changing the measurement conditions and the like. Such a change in sensitivity of the measurement signal is called signal drift.

  In order to correct such signal drift, a specific element having a known concentration is added to the sample to be measured, and the rate of change in signal drift of this specific element that changes with time is obtained. In general, the measurement result of the element to be analyzed is computationally corrected using the change rate. However, the amount of signal drift often varies depending on the element, and even if such a calculation correction is performed, it is not sufficient. In addition, the above method may not be applicable depending on the analysis method.

  Further, in order to reduce such signal drift, the plasma temperature of the plasma torch 20 is increased to promote the decomposition of the sample, and the temperature of the tip of the sampler cone and skimmer cone is kept at a high temperature to reduce the amount of precipitation. Reduction and dilution of the sample (causing a decrease in sensitivity) were also performed. However, even if this is done, it is not sufficient to cope with the problem of signal drift, or the sensitivity has been greatly reduced. For example, Patent Document 2 and Patent Document 3 disclose diluting a high matrix sample, and Patent Document 4 describes controlling the plasma temperature.

Japanese Patent No. 5308641 JP 2008-045901 A JP 2008-275372 A JP 2008-1111744 A

  Accordingly, an object of the present invention is to improve signal stability by reducing the amount of signal drift in an inductively coupled plasma mass spectrometer.

  According to one aspect of the present invention, plasma means for generating plasma for ionizing a sample to be introduced, interface means for drawing a part of the plasma into a vacuum and generating a supersonic molecular beam, and drawing into the vacuum Extraction electrode means for extracting ions from the generated plasma as an ion beam, ion lens means for separating the ion beam and photons and transmitting them backward, and an ion guide for removing interfering ions installed if necessary An inductively coupled plasma mass spectrometer comprising: means; an ion separation means for separating ions according to a mass-to-charge ratio; and a detection means for detecting ions separated by the ion separation means and outputting a detection signal. A method is provided for increasing the stability of the detection signal. The method includes 1) preparing a pseudo sample containing at least one element (this element may be mixed in the process of introducing the sample), and 2) introducing the pseudo sample into the inductively coupled plasma mass spectrometer. The ions of the element are detected while changing at least one of the voltages applied to the ion optical system including the extraction electrode unit, the ion lens unit, the ion guide unit, and the ion separation unit over time. 3) Obtain the amount of change of the detection signal during each detection at each voltage, and 4) select the voltage at which the detection signal is most stable based on the obtained amount of change, and select the voltage as a sample. Including use for analysis.

  The sample can be a high matrix sample. The pseudo sample can be a high matrix sample having a composition similar or not similar to the sample, and can be a plurality of different types of pseudo samples. When measuring a pseudo sample, the operating conditions of the plasma means, the operating conditions of the interface means, the concentration of the pseudo sample, and the introduction amount can be changed in order to promote the change of the detection signal. Determining the amount of change includes using statistical processing. Statistical processing is linear fitting. The number of elements is plural, and the amount of change can be obtained as an average of the amount of change of each element, or can be obtained as an average of the difference in amount of change between the elements. The extraction electrode means can include a first electrode and a second electrode. The ion lens means can include a third electrode and a fourth electrode, or subsequent electrodes. The ion guide means can include a multipole electrode and electrodes disposed around it around it. The ion separation means may include a multipole electrode and electrodes disposed before and after the multipole electrode. The voltage can be a voltage applied to each of the ion optical systems including the first electrode, the second electrode, the third electrode, the fourth electrode, and the subsequent electrode.

  According to another aspect of the present invention, plasma means for generating plasma for ionizing a sample to be introduced, interface means for drawing the plasma into a vacuum and generating a supersonic molecular beam, and drawn into the vacuum Extraction electrode means for extracting ions from the plasma as an ion beam, ion lens means for separating the ion beam and photons and transmitting them backward, and ion guide means for removing interfering ions installed as necessary Used to operate an inductively coupled plasma mass spectrometer including ion separation means for separating ions according to mass-to-charge ratio and detection means for detecting ions separated by the ion separation means and outputting a detection signal 1) Introduced into an inductively coupled plasma mass spectrometer The at least one of the voltages applied to the ion optical system including the extraction electrode unit, the ion lens unit, the ion guide unit, and the ion separation unit is changed over time for a pseudo sample containing at least one kind of element. However, a procedure for detecting ions of the element, 2) a procedure for obtaining a change amount in which the detection signal changes during the detection at each voltage, and 3) based on the obtained change amount, The present invention is realized as a computer program for selecting a stable voltage and causing the computer to execute a procedure for setting the voltage in the inductively coupled plasma mass spectrometer for analyzing the sample.

  According to the present invention, signal stability is improved by optimizing the voltage applied to each electrode of the extraction electrode unit, the ion lens unit, the ion guide unit, and the ion separation unit.

It is a figure which shows the example which represented the relationship between the sensitivity (y) as a measurement result of an exemplary pseudo sample, and time (x) as a linear function. 4 is a flowchart illustrating control of a system controller in accordance with the present invention. It is a graph showing the relationship of the sensitivity-vs.-time of the measurement result regarding several elements by a prior art. It is a graph showing the sensitivity-vs.-time relationship of the measurement result regarding a plurality of elements when the present invention is applied. It is a schematic diagram showing the basic concept of an inductively coupled plasma mass spectrometer. It is an enlarged view of the interface part and ion lens part of the apparatus of FIG.

  As described in the background art, when an inductively coupled plasma mass spectrometer 10 shown in FIG. 5 analyzes a high matrix sample (for example, a metal solution) as an analysis sample, signal drift occurs. There was a problem.

  In an inductively coupled plasma mass spectrometer, the electrode voltage of an ion optical system including the electrode of the extraction electrode unit, ion lens unit, ion guide unit and ion separation unit generally maximizes the sensitivity of the device and minimizes background noise. It has been adjusted for the purpose of making it. On the other hand, the electrode voltage of this ion optical system affects the ion beam extraction process, ion transmission efficiency, and the like. The present applicant suppresses signal drift by dealing with fluctuations or fluctuations in the ion beam extraction process and fluctuations in ion transmission efficiency in the ion optical system in the subsequent stage, that is, stabilizes the detection signal output from the ion detector. I found it to improve the sex. In particular, the Applicant has found that the problem of signal drift can be addressed by optimizing the voltage of the electrodes of the ion optics system.

  In the inductively coupled plasma mass spectrometer shown in FIG. 5, the extraction electrode portion is constituted by the first electrode 53 and the second electrode 54, and the ion lens portion is the third electrode 55 and the fourth electrode 56 located at the subsequent stage. It is comprised by. However, it should be noted that the configuration of the extraction electrode portion and the electrode of the ion lens is not limited to such a configuration. For example, the extraction electrode unit may be composed of one electrode or three or more electrodes. In addition, regarding the ion lens, there may be one electrode or three or more electrodes. In addition, the electrodes of other ion optical systems may have a similar role. In the present specification, for the sake of illustration, an example in which the extraction electrode unit is configured by the first electrode 53 and the second electrode 54 and the ion lens unit is configured by the third electrode 55 and the fourth electrode 56 will be described. I do.

  Various voltages can be applied to the ion optical system including the first electrode 53 and the second electrode 54 of the extraction electrode unit and the third electrode 55 and the fourth electrode 56 of the ion lens unit. Applicants measure high matrix samples using various voltage combinations for the voltage applied to the ion optics including first electrode 53, second electrode 54, third electrode 55 and fourth electrode 56. Thus, we have experimentally discovered that there are voltage combinations that can keep signal drift low without significantly reducing the sensitivity of the device. For example, as an example of such a combination of voltages, the first electrode 53 is 0 V, the second electrode 54 is −250 V, the third electrode 55 is 7.5 V, and the fourth electrode 56 is −100 V. However, the signal drift changes depending on the analysis object, analysis conditions, and the element to be analyzed, and even if the same device is used, the signal drift also changes depending on the environment in which the device is used. Therefore, it is not easy to select an optimal voltage combination.

  In the present invention, the electrode of the extraction electrode unit, the ion lens unit, the ion guide unit, and the ion separation unit is measured by measuring a change in signal using a pseudo sample in a preparation stage before analyzing a high matrix sample. Optimizing the voltage of the ion optics system. The pseudo sample can be a sample containing a high concentration component causing a change in signal intensity and at least one element for observing the signal intensity, for example, three kinds of elements. The pseudo sample can be a high matrix sample having a composition similar to that of the sample to be analyzed or a high matrix sample causing a large signal change. It can also be used as a rinse solution. A plurality of types of pseudo samples can be sequentially introduced into the inductively coupled plasma mass spectrometer. Such a pseudo sample is introduced into an inductively coupled plasma mass spectrometer for a certain period of time for measurement. Here, with the passage of time (for example, 5 seconds), it is applied to the ion optical system including the first electrode 53 and the second electrode 54 of the extraction electrode portion and the third electrode 55 and the fourth electrode 56 of the ion lens portion. The pseudo sample is measured while changing each voltage. The voltage used here is a combination of voltages experimentally obtained above (hereinafter referred to as a voltage combination), and two or more kinds of voltage combinations. Using one voltage combination, the pseudo sample is measured for a predetermined time, and measurement results are obtained for at least one element, preferably three elements. An amount of change of the measurement result that changes during a predetermined time is obtained by calculation. A method for calculating the amount of change will be described later. And such a measurement is performed about all the voltage combinations, and the variation | change_quantity with respect to each voltage combination is calculated | required. Among the obtained change amounts, a voltage combination corresponding to the smallest change amount is selected. By using this selected voltage combination as a voltage to be applied to each electrode of the ion optical system including the extraction electrode portion and the ion lens portion, the sample is analyzed. Therefore, by using such a voltage combination, the amount of signal drift is reduced and signal stability is improved. Such a method of the present invention can be implemented as a program executed on a computer. For example, the system controller (not shown) of the apparatus 10 of FIG. 4 can store the above voltage combinations as a table in a memory in the computer.

  In the present invention, as described above, the amount of change is determined for at least one element, preferably three elements. It has been found that the amount of change varies depending on the element even when the same voltage combination is used. For example, although the element A has a small amount of change, the element B has a large amount of change compared to the A element. In the present invention, for example, it is possible to select a voltage combination with a small difference in change amount between three types of elements. By measuring the sample to be analyzed using such a voltage combination, the accuracy and accuracy of the measurement result can be improved even when the correction of the signal drift is calculated.

  As described in the background art, the cause of the signal drift is mainly that deposits are deposited on the sampling cone 31 and the skimmer cone 33. In order to shorten the measurement time of the pseudo sample as described above, that is, to promote the rate of change of the change amount, it is to make deposits easily deposit on the sampling cone 31 and the skimmer cone 33. Therefore, in the present invention, the operating conditions of the inductively coupled plasma means (for example, the temperature of the plasma), the operating conditions of the interface means (for example, the temperature of the sampling cone and the skimmer cone), the concentration of the pseudo sample, and the amount of introduction are also controlled. And shorten the measurement time of the pseudo sample.

  In the mass spectrometer to which the present invention is applied, the system controller of the apparatus performs, for example, the following control in accordance with the flowchart 200 shown in FIG. The system controller sequentially reads the voltage combination from the voltage table stored in the memory as time passes with respect to the pseudo sample (single or plural) introduced into the apparatus, and applies it to each electrode of the extraction electrode unit and the ion optical system. While changing each voltage to the voltage of the read voltage combination, the ions of the element (s) in the pseudo sample are measured. In this measurement, the system controller, as necessary, includes the operating conditions of the plasma means (eg, plasma temperature), the operating conditions of the interface means (eg, the temperature of the sampling cone and skimmer cone), the concentration of the pseudo sample, and the introduction. The amount is changed (step 210). For the element, the system controller obtains the amount of change in the measurement signal during the measurement of the element in each voltage combination, and stores it in the memory as necessary (step 220). The system controller determines the voltage at which the measurement signal is most stable from among the obtained change amounts, for example, the voltage with the smallest change amount, the voltage with the smallest average change amount of multiple elements, or the change amount between multiple elements. The voltage combination with the smallest average difference is selected (step 230). The selected voltage combination is used as a voltage to be applied to the extraction electrode unit and each electrode of the ion optical system (step 240).

Next, a calculation method for obtaining the amount of change will be described. Note that there are two change amounts to be calculated here, each of which is selected according to the application. Emphasizing changes in absolute sensitivity, if you want to suppress signal fluctuations of one or more specific elements, evaluate the amount of change itself, and if you expect similar behavior for a wide range of elements, Evaluate the magnitude of the difference in change. In either case, the calculation is performed after the signal change is expressed as an angle for each element. The three types of elements are, for example, element 1, element 2, and element 3. A relationship between sensitivity (y) and time (x) as a measurement result when measurement is performed during a predetermined time using such a pseudo sample is expressed as a linear function using linear fitting. FIG. In this specification, an example using linear fitting as a statistical process will be described. In particular, the magnitude of the difference in the amount of change in each element can be evaluated. Here, element 1 corresponds to y ₁ , element 2 corresponds to y ₂ , and element 3 corresponds to y ₃ . When each of y ₁ to y ₃ is expressed by an equation,
y ₁ = a ₁ x + b ₁
y ₂ = a ₂ x + b ₂
y ₃ = a ₃ x + b ₃
Where a ₁ to a ₃ and b ₁ to b ₃ are constants. In the present invention, the amount of change is obtained as an angle such as the angles α ₁ , α ₂ , and α ₃ shown in FIG. That is, the inclination of the linear function is converted into an angle formed with the x axis. Such an angle can be calculated, for example, by the following equation: That is,
α ₁ = tan ⁻¹ a ₁
α ₂ = tan ⁻¹ a ₂
α ₃ = tan ⁻¹ a ₃

The first deals with the magnitude of the signal change during the introduction of the pseudo sample (s). Element 1, in order to select the voltage combination of the change is small between elements 2 and the element 3, we obtain the parameter beta ₁ indicating the average value of the variation in size by the following calculation. (In case of 3 elements)
β ₁ = 1/3 (| α ₁ + α ₂ + α ₃ |)
The beta ₁ adopts a voltage combination that minimizes or more.

Elemental 1, in order to select the difference is small voltage combination of variation between elements 2 and the element 3, we obtain the parameter beta ₂ showing the mean value of the magnitude of the difference of the amount of change by the following calculation. (In case of 3 elements)
β ₂ = 1/3 (| α ₁ −α ₂ | + | α ₂ −α ₃ | + | α ₃ −α ₁ |)
A voltage combination that minimizes the above β ₂ is employed.

  The effect of the present invention was verified by measuring a sample containing an element added as an internal standard using an ICP mass spectrometer 7700x manufactured by Agilent Technologies. FIG. 3 shows the measurement results before applying the present invention, and FIG. 4 shows the measurement results when the present invention is applied. 3 and 4, the vertical axis represents the ratio of sensitivity, and the horizontal axis represents time. In FIG. 3, it can be seen that, for example, the sensitivity value of Li element is greatly shifted over time as compared with other elements. On the other hand, in FIG. 4 to which the present invention is applied, the sensitivity of the Li element is slightly different from that of the other elements in the initial stage. It was proved that the signal fluctuation between elements was suppressed.

10 Inductively coupled plasma mass spectrometer
30 Interface section
50 Ion lens section
53, 54, 55, 56 electrodes

Claims (16)

Plasma means for generating plasma for ionizing a sample to be introduced, interface means for drawing the plasma into a vacuum to generate a supersonic molecular beam, and for extracting ions from the plasma drawn into the vacuum as an ion beam Extraction electrode means, ion lens means responsible for separation and transmission of ion beam and photon, ion guide means for removing interfering ions installed as necessary, and ions separated according to mass to charge ratio In the inductively coupled plasma mass spectrometer, the method for improving the stability of the detection signal, comprising: an ion separation means that detects the ions separated by the ion separation means, and outputs a detection signal. ,
1) Prepare a pseudo sample containing at least one element,
2) A voltage applied to an ion optical system composed of the extraction electrode means, the ion lens means, the ion guide means, and the ion separation means as the pseudo sample is introduced into the inductively coupled plasma mass spectrometer and time passes. Detecting ions of the element while changing at least one of
3) Find the amount of change that the detection signal changes during the detection at each voltage;
4) selecting a voltage at which the detection signal is most stable based on the determined amount of change, and using the voltage for analysis of the sample.   The method of claim 1, wherein the sample is a high matrix sample.   The method according to claim 1, wherein the pseudo sample is a high matrix sample.   The method according to claim 1, wherein the pseudo sample comprises a plurality of different types of pseudo samples.   5. The method according to claim 1, wherein when measuring the pseudo sample, the operating condition of the plasma means and the interface means is changed in order to promote the change of the detection signal.   The method according to claim 1, wherein determining the amount of change includes using a statistical process.   The method of claim 6, wherein the statistical process is linear fitting.   The method according to claim 1, wherein the number of elements is plural, and the amount of change is obtained as an average of the amount of change of each element.   The method according to claim 1, wherein the number of elements is plural, and the amount of change is obtained as an average of a difference in amount of change between the elements.   The method according to claim 1, wherein the extraction electrode means includes a first electrode and a second electrode.   The method of claim 10, wherein the ion lens means comprises a third electrode and a fourth electrode.   The method of claim 11, wherein the voltage is a voltage applied to each of the first to fourth electrodes.   The method of claim 12, wherein a voltage applied to each of the electrodes is configured as a plurality of voltage combinations, and changing at least one of the voltages is changing a voltage combination. Plasma means for generating plasma for ionizing a sample to be introduced, interface means for drawing the plasma into a vacuum to generate a supersonic molecular beam, and for extracting ions from the plasma drawn into the vacuum as an ion beam Extraction electrode means, ion lens means responsible for separation and transmission of ion beam and photon, ion guide means for removing interfering ions installed as necessary, and ions separated according to mass to charge ratio A computer program used to operate an inductively coupled plasma mass spectrometer, comprising: an ion separation means that detects the ions separated by the ion separation means and outputs a detection signal;
1) Ion optics comprising the extraction electrode means, the ion lens means, the ion guide means and the ion separation means over time for a pseudo sample containing at least one element introduced into the inductively coupled plasma mass spectrometer Detecting the ions of the element while changing at least one of the voltages applied to the system;
2) A procedure for determining the amount of change in the detection signal during the detection at each voltage,
3) Based on the obtained change amount, select a voltage at which the detection signal is most stable, and cause the computer to execute a procedure for setting the voltage in the inductively coupled plasma mass spectrometer for analysis of the sample. Computer program.   15. The computer program according to claim 14, comprising a procedure of changing operating conditions of the plasma means and the interface means in order to promote a change in the detection signal when detecting ions of the element.   The computer program according to claim 14 or 15, wherein the pseudo sample includes a plurality of different types of pseudo samples.

Images