JP2004234893A - High-frequency inductively-coupled plasma ion trap mass spectrometry device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive high-frequency inductively-coupled plasma ion trap mass spectrometry device capable of restraining generation of low-mass region noise, and of a high-sensitivity quantitative analysis. <P>SOLUTION: The base line of a low-mass region having a mass of 18 to 40 is formed into a table-like shape by noise in an ion trap mass spectrometry device, so that a high-sensitivity quantitative analysis of an element appearing in this region becomes difficult. The cause of the noise drives from water ions due to an ion-molecule reaction between Ar ions and water molecules trapped in an ion trap space, the water ions produced during mass sweep are released from the ion trap and detected regardless of mass of sweep and generate noise on a mass spectrum. Noise is not generated if the water ions produced by the ion-molecule reaction are prevented from being released regardless of mass. A main high-frequency voltage V applied to a ring electrode is reversely swept from a high voltage toward a low voltage, the produced water ions are continuously stably trapped in the ion trap, and never cause noise. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

表１に示した中性分子の中で、上記（６）式と同様のイオン分子反応を、Ａｒイオンと起こす可能性のある中性分子は、次式（９）、（１０）に示す条件を満足するものである。
【０１５４】
ＩＰ（ＮＭ）＜ＩＰ（Ａｒ） ―――（９）
ＭＷ（ＮＭ）＜ＭＷ（Ａｒ） ―――（１０）
すなわち、中性分子（ＮＭ）のイオン化ポテンシャル（ＩＰ）がアルゴン（Ａｒ）のＩＰより低く、また、中性分子の分子量（ＭＷ）がアルゴン（Ａｒ）の原子量より低い場合にマススペクトル上にノイズを与える。
【０１５５】
上記２条件に合致するものは、上記表１中、水（Ｈ_２Ｏ）と酸素（Ｏ_２）のみである。水（Ｈ_２Ｏ）と同様に、酸素（Ｏ_２）は、次式（１１）のように、イオン分子反応を起こす。
【０１５６】
Ｏ_２＋Ａｒ^＋ → Ｏ_２ ^＋＋Ａｒ ―――（１１）
従来の方式によると、つまり、順掃引による方式であれば、質量３２から４０にかけて、検出されたマススペクトルにノイズを発生させる。
【０１５７】
しかし、本発明によれば、水（Ｈ_２Ｏ）の場合と同様に、酸素（Ｏ_２）も、イオントラップ空間２７内に安定してトラップすることができ、酸素（Ｏ_２）による連続ノイズの発生を阻止することができる。
【０１５８】
また、上記式（９）、（１０）の条件を満足する、表１に記載したもの以外の新たな分子がイオントラップ空間２７に導入されても、本発明により連続ノイズを抑制することができる。
【０１５９】
以上のように、本発明の一実施形態によれば、主高周波電圧を高電圧から低電圧へと逆掃引することにより、ノイズの原因である水イオン等をイオントラップ空間内に安定してトラップしつつ、検出対象となるイオンをイオントラップ空間から排出することができる。
【０１６０】
したがって、構造の大幅な変更や、高価なクライオポンプを必要とすることなく、低質量領域ノイズの発生を抑制でき、高感度定量分析が可能な高周波誘導結合プラズマイオントラップ質量分析装置を実現することができる。
【０１６１】
また、低質量領域ノイズの発生を抑制でき、高感度定量分析が可能な高周波誘導結合プラズマイオントラップ質量分析方法も実現することができる。
【０１６２】
なお、制御データ処理装置２３は、表示手段を備え、図７に示したマススペクトルと掃引開始電圧に対応する上限質量値と掃引終了電圧に対応する下限質量値を表示する。
【０１６３】
また、本発明の他の実施形態としては、制御データ処理装置であるコンピュータの動作制御プログラムがある。
【０１６４】
つまり、このコンピュータプログラムは、分析対象物の水溶液をプラズマ中に導入して、イオンを生成し、生成したイオンをイオントラップ空間に捕捉した後、イオントラップ空間からイオンを放出して、イオンの質量を検出して分析する高周波誘導結合プラズマイオントラップ質量分析装置の動作を制御するコンピュータプログラムである。
【０１６５】
そして、このコンピュータプログラムは、イオントラップ空間を形成し、主高周波電圧が供給される主電極に、分析対象質量領域の設定上限質量値に対応する第１の電圧値を供給して、上記分析対象領域のイオンをイオントラップ空間に導入し、主電極と共にイオントラップ空間を形成する補助交流電極に、上限質量より大の質量のイオン共鳴周波数を有する補助交流電圧を供給し、主高周波電圧の電圧値を、第１の電圧値から分析対象質量領域の設定下限質量値に対応する第２の電圧値に向かって傾斜状に減少させ、上限質量のイオンから下限質量のイオンをイオントラップ空間から放出させる。
【０１６６】
その後、イオントラップ空間から放出されるイオンの質量を検出し、検出されたイオンの質量スペクトルを作成する。
【０１６７】
【発明の効果】
本発明によれば、安価でありながら、低質量領域ノイズの発生を抑制でき、高感度定量分析が可能な高周波誘導結合プラズマイオントラップ質量分析装置及び方法を実現することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態が適用される高周波誘導結合プラズマイオントラップ質量分析装置の概略構成図である。
【図２】本発明の原理説明図である。
【図３】本発明の原理説明図である。
【図４】本発明の原理説明図である。
【図５】本発明の原理説明図である。
【図６】本発明の原理説明図である。
【図７】本発明の一実施形態により得られたマススペクトルの表示画面例である。
【図８】本発明の一実施形態における動作タイムシーケンス図である。
【図９】イオントラップ質量分析計の説明図である。
【図１０】イオントラップの動作原理を示すＭａｔｈｉｅｕ安定曲線を示すグラフである。
【図１１】順掃引を行った場合に得られるマススペクトルを示すグラフである。
【図１２】高周波誘導結合プラズマイオントラップ質量分析装置におけるノイズ発生原因の説明図である。
【図１３】ノイズ発生原因の説明図である。
【図１４】ノイズ発生原因の説明図である。
【図１５】ノイズ発生原因の説明図である。
【図１６】ノイズ発生原因の説明図である。
【図１７】ノイズ発生原因の説明図である。
【符号の説明】
１ 試料溶液槽
２ ポンプ
３ 霧化器
４ ガス供給部
５ プラズマイオン源
６ 誘導コイル
７ 高周波電源
８ プラズマ
９ 細孔
１０、２４ スキマー
１１、２５、２６ 真空室
１２ 静電レンズ
１３ 高周波電源
１４ 多重極イオンガイド
１５ イオンゲート電極
１６ イオントラップ質量分析計
１７、１９ エンドキャップ電極
１８ リング電極
２０ 主高周波電圧電源
２１ 補助交流電圧電源
２２ 検出器
２３ 制御データ処理装置
３０ 油回転ポンプ
３１、３２ ターボ分子ポンプ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high frequency inductively coupled plasma ion trap mass spectrometer.
[0002]
[Prior art]
2. Description of the Related Art An inductively coupled plasma-mass spectrometer (ICP-MS) is a device in which a high-temperature plasma ion source of high-frequency inductively coupled plasma (ICP) and a mass spectrometer (MS) are combined. It is used for highly sensitive qualitative and quantitative analysis of trace metal elements.
[0003]
The ICP-MS generates plasma of a gas such as argon (Ar) using a high-frequency voltage of about 20 MHz, atomizes a sample solution into the generated plasma, and introduces the sample solution to generate ions in a high-temperature plasma. . Then, the generated ions are taken into a vacuum vessel through the pores and subjected to mass analysis by a mass spectrometer.
[0004]
ICP-MS targets most of the elements present in the periodic table, and the detection sensitivity is ppt (10^-12) To ppq (10^-15) And extremely high.
[0005]
Here, in order to accurately examine the abundance and behavior of trace elements in living organisms and the environment, higher sensitivity is required for measurement methods and measurement apparatuses. For this reason, all parts constituting the ICP-MS, such as a sample introduction device, an ICP ion source, an ion transfer unit, and a mass spectrometer (MS), have been devised and improved.
[0006]
The mass spectrometer used for ICP-MS is a magnetic field mass spectrometer, a quadrupole mass spectrometer (QMS), or the like. Attempts have been made to improve sensitivity and reduce molecular ions by using an ion trap mass spectrometer for accumulating ions and performing mass spectrometry as a mass spectrometer for ICP-MS. This attempt is described in, for example, Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, and Non-Patent Literature 1.
[0007]
A mass spectrometer is a device that directly measures the mass of a substance with high sensitivity and high accuracy. Therefore, it is used in many fields from space science to bioscience. For this reason, there are many types of mass spectrometers that differ in principle.
[0008]
Among them, ion trap mass spectrometers have recently become widespread in many fields because of their small size and many functions. This ion trap mass spectrometer was introduced in the 1950's by Dr. The basic concept was invented by Paul and is described in, for example, Patent Document 5. Since then, many researchers have improved ion trap mass spectrometers and techniques.
[0009]
FIG. 9 is a schematic configuration diagram of an ion trap mass spectrometer. As shown in FIG. 9, in the ion trap mass spectrometer, a donut-shaped ring electrode 18 having an inner peripheral surface having a hyperbolic shape, and two end cap electrodes having a hyperbolic inner surface and a rotationally symmetric body. 17 and 19 are arranged so as to sandwich the ring electrode 18.
[0010]
When a high-frequency voltage having a frequency f supplied from the main high-frequency power supply 20 is applied between the ring electrode 18 and the two end cap electrodes 17 and 19, the ion trap space 27 surrounded by the three electrodes 18, 17 and 19 is formed. A high-frequency ion trap electric field is formed.
[0011]
This high-frequency ion trap electric field enables the ion trap mass spectrometer to simultaneously trap many ions having different masses in the ion trap space 27.
[0012]
Here, the behavior of the ions in the high-frequency ion trap electric field formed in the ion trap space 27 is mathematically and graphically represented as a Mathieu stability curve, as shown in FIG. The Mathieu stability curve is described in, for example, Patent Documents 5 and 6.
[0013]
Equations (1) and (2) described later are established between the ions of mass m trapped in the ion trap space 27 and the parameters of the high-frequency electric field.
[0014]
When the az and qz values of a certain ion are within the rectangle of the Mathieu stability diagram shown in FIG. 10, this ion is stably trapped in the ion trap space 27. On the other hand, if both or both of the az and qz values of an ion are located in a region outside the Mathieu stability diagram, the ion is no longer stably trapped in the ion trap space 27 and is ejected out of the ion trap. Colliding with the ion trap electrode and losing charge.
[0015]
Assuming that the radius of rotation of the ion trap is r, the frequency of the main high frequency is f, the high frequency voltage is V, and the voltage of the DC component of the main high frequency is U, the following equations (1) and (2) are obtained.
[0016]
az = -8eU / (m * r²Ω²) ――― (1)
qz = 4 eV / (m * r²Ω²) ――― (2)
Here, Ω = 2πf, e is the electron charge (1.6 * 10^-19).
[0017]
If the DC component of the main high-frequency voltage is zero, that is, U = 0, az = 0, and only equation (2) is an equation relating to ion stability.
[0018]
A basic method of acquiring a mass spectrum using an ion trap mass spectrometer is described in Patent Document 7. In this basic method, the high-frequency voltage V of the main high-frequency voltage is linearly swept to push ions from a stable region (0 <qz <0.908) to an unstable region (qz> 0.908) in order of mass. The mass spectrum can be obtained by detecting the ions emitted in the order of mass by the detector.
[0019]
This method is called a mass-selective instability scanning method (Mass-Selective Instability Scanning Method).
[0020]
The ions trapped in the ion trap space 27 oscillate stably at a specific frequency based on trapping parameters (V, r, Ω) such as the mass m and the main high-frequency voltage V. This movement of the ions is called natural motion.
[0021]
Further, the frequency of the natural frequency is called a natural frequency (Secular Frequency), and the natural frequency ω is expressed by the following equation (3).
[0022]
ω = √2 eV / (mr²Ω) ――― (3)
From the above equation (3), it can be seen that the natural frequency ω of the ion is proportional to the main high-frequency voltage V and inversely proportional to the mass m of the ion. Further, the natural frequency ω exists within the range shown by the following equation (4).
[0023]
0 <ω <βΩ / 2 ――― (4)
Here, β has a value from 0 to 1 and is approximated as in the following equation (5).
[0024]
β = (az + qz²/ 2)^1/2      ――― (5)
As in the ion trap mass spectrometer shown in FIG. 9, the auxiliary AC voltage ω ′ supplied from the auxiliary AC voltage power supply 21 is applied between the two end cap electrodes 17 and 19.
[0025]
If the natural frequency ω of the ion matches the frequency ω ′ of the auxiliary AC voltage, they resonate. As a result, the ions absorb energy from the auxiliary AC voltage, and the trajectories of the ions expand rapidly. When the auxiliary AC voltage exceeds several volts, the trajectory of the ions exceeds the ion trap space. In this case, the ions are emitted out of the ion trap space.
[0026]
What utilizes this resonance phenomenon is resonance emission (Resonance Ejection).
[0027]
In addition, a mass spectrum is obtained by linearly sweeping the main high-frequency voltage V while applying an auxiliary AC voltage between the two end cap electrodes 17 and 19, causing ions to resonate in order of mass, and ejecting the ions out of the ion trap for detection. be able to. This is called a resonance emission scanning method, and is described in, for example, Patent Document 8.
[0028]
This resonance emission sweep method can expand the measured mass range by setting the frequency ω 'of the auxiliary AC voltage, and is now widely used because the mass spectrum resolution is superior to the mass selective unstable sweep method. It's being used.
[0029]
Patent Document 9 discloses a method for freely releasing and isolating ions in an ion trap by utilizing the fact that the auxiliary AC voltage has a plurality of frequency components (broadband noise) irrespective of a single frequency. Has been described.
[0030]
This method utilizes the resonance of the natural frequency of the ions and the auxiliary AC voltage, and shows a method of resonating many ions at once. The broadband noise signal disclosed in Patent Document 9 aims to simultaneously emit a wide range of ions.
[0031]
However, a frequency component corresponding to the frequency of the ions left in the ion trap is a notch (cut). That is, the frequency corresponding to the notch is not applied.
[0032]
Therefore, ions corresponding to the frequency of the notch are stably trapped in the ion trap without resonance, and other ions are excluded from the ion trap space.
[0033]
Here, a method for removing background (noise) in an inductively coupled plasma mass spectrometer instead of an ion trap mass spectrometer is described in Patent Document 10.
[0034]
In Patent Document 10, if the analysis sample is iron, carrier gas Ar and H, which is a solvent of the analysis sample, are used.₂It is described that a bond ion ArO is formed by bonding of O to O, and the bond ion ArO is detected as a background (noise) of Fe, so that the detection sensitivity is reduced.
[0035]
Patent Document 10 describes that if an analysis sample is heated and ArO is vaporized in an ashing stage, ArO 2 does not become a background of Fe in a vaporization stage.
[0036]
[Patent Document 1]
U.S. Pat. No. 5,767,512
[Patent Document 2]
U.S. Pat. No. 6,259,091
[Patent Document 3]
JP-A-10-228881
[Patent Document 4]
JP 2000-164169 A
[Patent Document 5]
U.S. Pat. No. 2,939,952
[Patent Document 6]
JP-A-59-134546
[Patent Document 7]
U.S. Pat. No. 4,540,884
[Patent Document 8]
U.S. Pat. No. 4,736,101
[Patent Document 9]
U.S. Pat. No. 5,466,931
[Patent Document 10]
Japanese Patent No. 2767511
[Non-patent document 1]
C. Rapid Communication in Mass Spectrometry, 71 (1994), 71-76; J. Barinaga and D.M. W. Koppenaal
[0037]
[Problems to be solved by the invention]
By the way, when the sample aqueous solution is introduced into the introduction system of the high frequency coupling induction plasma-ion trap mass spectrometer (ICP-ITMS) and the ICP-ITMS is operated for a long time, the low mass region from m / z18 to m / z40 is obtained. Noise gradually increases.
[0038]
Finally, as shown in FIG. 11, the baseline from m / z 18 to m / z 40 rises in a trapezoidal shape and is superimposed on the signal appearing from m / z 16 to m / z 40. That is, some ions are constantly emitted from the ion trap mass spectrometer to the detector during the region from m / z 16 to m / z 40 regardless of the mass sweep of the ion trap mass spectrometer. The ions are detected by the detector and recorded as noise on the mass spectrum.
[0039]
Due to the lifting of the baseline due to the continuous noise, fluorine F, sodium Na, magnesium Mg, aluminum Al, silicon Si, phosphorus P, sulfur S, chlorine Cl, potassium K, which appear in the mass region from m / z 18 to m / z 40, Quantitative analysis and high-sensitivity measurement of elements such as calcium Ca become impossible at all.
[0040]
Therefore, the present inventor conducted the following experiment and consideration in order to investigate the cause of the noise in the low mass region shown in FIG.
[0041]
First, an ICP-ITMS which is evacuated and has no noise in a low mass region is prepared. Mass spectrum measurement is performed while introducing pure water into the ICP-ITMS repeatedly. After 24 hours of measurement, the baseline in the low mass region gradually rises.
[0042]
As the introduction of pure water is continued and the measurement extends to a few days, the noise height increases corresponding to the increase of the measurement duration. As a result, a mass spectrum having a trapezoidal baseline as shown in FIG. 11 is obtained.
[0043]
Next, the vacuum pump in which the ion trap mass spectrometer was placed was replaced with a cryopump having a high water pumping speed from a turbo molecular pump to a change in noise height in a low mass region.
[0044]
When the vacuum pump was changed from a turbo pump to a cryopump, the noise in the low mass region gradually became smaller, and after 24 hours, the noise was reduced to 1/10.
[0045]
From these experiments, it can be inferred that water is involved in the generation of noise in the low mass region in the ion trap mass spectrometer.
[0046]
The high-frequency inductively coupled plasma (ICP) ion source ionizes a metal element sprayed in argon Ar gas by the high temperature of Ar plasma. The sample is often a dilute aqueous solution and is constantly fed into the plasma by a nebulizer.
[0047]
That is, a large amount of water molecules are continuously supplied to the plasma, and the sample and water exist in the form of ions, molecules, and atoms. The ions and gas existing in the high-temperature plasma are simultaneously taken into the vacuum chamber from the pores provided at the tip of the skimmer. The ions are introduced into the ion trap mass spectrometer through the ion transfer area and the multi-stage differential evacuation system, and at the same time, a large amount of water molecules are also sent into the ion trap mass spectrometer.
[0048]
The main ion in high frequency inductively coupled plasma (ICP) is Ar⁺It is an ion. Ar trapped in the ion trap space 27⁺The ions collide with neutral water molecules in the ion trap space 27 and cause an ion molecule reaction represented by the following equation (6).
[0049]
Ar⁺+ H₂O → Ar + H₂O⁺      ――― (6)
The reaction shown in equation (6) is called a charge transfer reaction. The reaction of the equation (6) moves in the right-hand direction because the ionization potential (IP) of water is 15.8 eV and the ionization potential (IP) of water is lower by 12.6 eV. Is due.
[0050]
The ionization potential (IP) of each of the rare gases is higher than that of water. That is, when the rare gas ion and the water molecule are confined in the same space, the two collide and the charge is transferred from the rare gas ion to water. Water molecules and Ar ions are constantly supplied to the ion trap space 27 from the plasma. Therefore, while Ar ions and water molecules are present in the ion trap space 27, the reaction of the formula (6) continues to occur in the ion trap space 27.
[0051]
It is presumed that Ar ions and water molecules are involved in generating noise in the ion trap space 27 according to the following steps.
[0052]
Hereinafter, the cause of noise generation will be described with reference to FIGS.
12A to 17A show the q-axis (horizontal axis) of the Mathieu stability curve. A circle on the q-axis indicates the position of the qz value of the ion.
[0053]
Now, it is assumed that the masses m2 and m1 and Ar ions are simultaneously trapped in the ion trap space 27. If the mass of the ions is m2> 40 (Ar)> m1> 18, the four ions are located in the Mathieu stability curve in the order from the left, m2, Ar, m1, and water ions.
[0054]
The auxiliary AC voltage ω1 is set and applied so as to be extremely near 0.908. Then, the main high-frequency voltage V is swept in the increasing direction. The qz values of the three ions m2, Ar, and m1 increase according to equation (2).
[0055]
That is, on the Mathieu stability curve, the three ions m2, Ar, and m1 apparently shift rightward, respectively. On the other hand, the resonance point ω1 and the boundary 0.908 of the Mathieu stability curve remain fixed.
[0056]
As a result, the natural frequency ω coincides with the auxiliary AC frequency ω1 (ω → ω1) in order from the smaller mass. The ions resonate with the auxiliary AC voltage ω1 and are emitted from the ion trap space 27 to the outside. The emitted ion current value is detected by the detector. When no water molecules are present in the ion trap space 27, a mass spectrum without noise is obtained as shown in FIG.
[0057]
When water molecules are present in the ion trap space 27, the ion molecule reaction shown in the equation (6) occurs, and the generated water ions cause noise.
[0058]
FIG. 13 is a diagram illustrating a state immediately after the start of the mass sweep. In FIG. 13, the mass sweep is a period from m / z1 to m / z18. During this period, H₂O⁺The qz of the ion is 0 <qz <0.908, and exists in the stable region of the Mathieu stability curve. During the mass sweep during this period, the ion-molecule reaction of the formula (6) proceeds between Ar ions and water molecules, and H₂O⁺Ions are generated continuously.
[0059]
H₂O⁺Since the ion exists in the stable region, H generated by the ion molecule reaction₂O⁺The ions continue to be trapped in the ion trap space 27 as they are.
[0060]
As a result, during this period, H₂O⁺The ions do not cause noise, and as shown in FIG. 13B, no noise appears in a region of m / z 18 or less.
[0061]
FIG. 14 shows a situation in which the mass sweep has progressed and a region from m / z 18 to m1 has been reached. H trapped in the ion trap space 27₂O⁺The ions are ejected resonantly and the ion current is detected by a detector. Thereafter, as the mass sweep progresses past m / z 18, H₂O⁺Unlike the case of FIG. 13, the qz value of the ion is qz> 0.908, and the ion is located in the unstable region.
[0062]
H generated by the ion-molecule reaction in the ion trap space 27₂O⁺The ions become unstable immediately after generation, and cannot stay in the ion trap space 27. As a result, H₂O⁺Ions are continuously emitted to the outside of the ion trap space 27 irrespective of the mass sweep, and are detected and become noise.
[0063]
FIG. 15 is an explanatory diagram of a state in which a region from m1 to m / z 40 (Ar) is being swept. The state shown in FIG. 15 is similar to the state shown in FIG.₂O⁺Since the orbit of the ion is unstable, H₂O⁺The ions are continuously emitted to the outside of the ion trap space 27 and cause noise. The ion m1 reaches the resonance point ω1, is ejected resonantly, and is detected. However, at the same time, H₂O⁺It will be buried in the noise of ions.
[0064]
FIG. 16 is an explanatory diagram of a state where a region from m / z 40 to m2 is being swept. In FIG. 16, Ar ions resonate at the resonance point ω 1 and are emitted from the ion trap space 27. As a result, Ar ions no longer exist in the ion trap space 27. Therefore, the ion-molecule reaction of the formula (6) does not occur, and H₂O⁺No ions are generated and H₂O⁺The noise from the ions disappears and the baseline returns to its original zero level.
[0065]
FIG. 17 is a diagram illustrating a state after the maximum mass m2 in the ion trap space 27 has been detected. Since there are no more ions in the ion trap space 27, the ion-molecule reaction of the formula (6) does not occur. No ion peaks or noise appear in this region.
[0066]
Finally, a mass spectrum as shown in FIG. 17B is obtained.
[0067]
The above-described event is considered to be the cause of the generation of the table-shaped continuous noise ranging from masses 18 to 40 on the mass spectrum.
[0068]
If the above hypothesis is correct, the following countermeasures can be considered to reduce noise in the low mass region.
[0069]
First, as a first measure, in order to eliminate the above-described continuous noise, it is only necessary to prevent water molecules, which are noise sources, from being introduced into the ion trap space. Since the sample solution is an aqueous solution, it is conceivable to employ a cryopump having an extremely high water exhaust speed as a vacuum pump for exhausting the space in which the ion trap mass spectrometer is arranged.
[0070]
In experiments conducted by the present inventors, noise in the low mass region can be reduced to 1/10 or less by continuous evacuation using a cryopump for 24 hours.
[0071]
However, since the price of a cryopump is as high as several million yen per unit, it cannot be used for inexpensive ICP-ITMS.
[0072]
A second measure is to eliminate Ar ions, one of the ion-molecule reactions, from the ion trap space. While ions are being introduced into the ion trap space, Ar ions can be selectively eliminated by the above-described resonance emission method.
[0073]
Specifically, if an auxiliary AC voltage having the same natural frequency as that of the Ar ions is applied between the end caps, the Ar ions resonate with the auxiliary AC voltage and are excluded from the ion trap space.
[0074]
However, in this method, Ar ions that cannot be completely resonated may remain in the ion trap space and cause an ion molecule reaction. In addition, ions near m / z 40 (for example, K, Ca, etc.) are excluded from the ion trap space together with Ar ions and cannot be measured.
[0075]
Therefore, the second measure is not desirable.
[0076]
Here, in the plasma ion mass spectrometer, as described above, the aqueous solution in which the sample is diluted is atomized by Ar gas, sprayed into the plasma, converted into ions, and introduced into the ion trap mass spectrometer. Is done. For this reason, in the plasma ion mass spectrometer, H₂O is an essential component.
[0077]
Therefore, it is not possible to discharge water molecules by heating by applying a technique described in Patent Document 10 which is not a technique relating to the ion trap mass spectrometer.
[0078]
An object of the present invention is to realize a high-frequency inductively coupled plasma ion trap mass spectrometer that is inexpensive, can suppress generation of noise in a low mass region, and can perform high-sensitivity quantitative analysis.
[0079]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
(1) An aqueous solution of an analyte is introduced into a plasma to generate ions, the generated ions are captured in an ion trap space, and then the ions are released from the ion trap space to detect the mass of the released ions. In a high-frequency inductively coupled plasma ion trap mass spectrometer for analyzing and analyzing, an auxiliary AC electrode forming an ion trap space, a main electrode forming an ion trap space together with the auxiliary AC electrode, and a mass of ions emitted from the ion trap space And a control data processing means for controlling the frequency of the auxiliary AC voltage and the amplitude value of the main high-frequency voltage to create a mass spectrum of the detected ions.
Then, the control data processing means supplies a first voltage value corresponding to the set upper limit mass value of the analysis target mass region to the main electrode, introduces ions of the analysis target region into the ion trap space, and then sets the auxiliary AC voltage frequency. The ion resonance frequency has a mass larger than the upper limit mass.
Thereafter, the voltage value of the main high-frequency voltage is reduced and swept from the first voltage value toward the second voltage value corresponding to the set lower limit mass value of the analysis target mass region, and the voltage is increased from the ion of the upper limit mass. Ions of the lower limit mass are emitted from the ion trap space. Then, the released ions are detected by the mass detector.
[0080]
(2) Preferably, in the above (1), the ions generated by the ion-molecule reaction in the ion trap space are reduced from the first voltage value to the second voltage value in the ion trap space. Is captured by
[0081]
(3) Preferably, in the above (1) or (2), the lower limit mass value of the mass region to be analyzed is 15.
[0082]
(4) Preferably, in the above (1) or (2), the lower limit mass value of the mass region to be analyzed is 16.
[0083]
(5) Preferably, in the above (1) or (2), the upper limit mass value of the mass region to be analyzed is 280.
[0084]
(6) Preferably, in the above (1) or (2), the upper limit mass of the analysis target mass region is 300.
[0085]
(7) Preferably, in the above (1), a display means is provided for displaying a first voltage value as a sweep start voltage and a second voltage value as a sweep end voltage value together with the ion mass spectrum.
[0086]
(8) The aqueous solution of the analyte is introduced into the plasma to generate ions, the generated ions are captured in the ion trap space, and then the ions are released from the ion trap space to detect the mass of the ions. In the high-frequency inductively coupled plasma ion trap mass spectrometry to be analyzed, an ion trap space is formed, and a first voltage value corresponding to a set upper limit mass value of an analysis target mass region is supplied to a main electrode to which a main high-frequency voltage is supplied. Then, the ions in the analysis target area are introduced into the ion trap space, and an auxiliary AC voltage having an ion resonance frequency having a mass larger than the upper limit mass is supplied to the auxiliary AC electrode forming the ion trap space together with the main electrode.
Then, the voltage value of the main high-frequency voltage is decreased from the first voltage value to the second voltage value corresponding to the set lower limit mass value of the analysis target mass region in an inclined manner, and from the ion having the upper limit mass to the ion having the lower limit mass. Ions are emitted from the ion trap space.
Thereafter, the mass of the ions emitted from the ion trap space is detected, and a mass spectrum of the detected ions is created.
[0087]
(9) The aqueous solution of the analyte is introduced into the plasma to generate ions, the generated ions are captured in the ion trap space, and then the ions are released from the ion trap space to detect the mass of the ions. In a computer program for controlling the operation of a high frequency inductively coupled plasma ion trap mass spectrometer to be analyzed, an ion trap space is formed, and a main electrode to which a main high frequency voltage is supplied corresponds to a set upper limit mass value of a mass region to be analyzed. A first voltage value is supplied to introduce ions in the analysis target region into the ion trap space, and the auxiliary AC electrode forming the ion trap space together with the main electrode has an ion resonance frequency of a mass larger than the upper limit mass. An auxiliary AC voltage is supplied, and the voltage value of the main high-frequency voltage corresponds to the set lower limit mass value of the mass region to be analyzed from the first voltage value. After the ions having the lower mass are discharged from the ion trap space from the ions having the upper mass from the ion trap space, the mass of the ions discharged from the ion trap space is detected, and the detected ions are detected. A computer program that creates a mass spectrum.
[0088]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the basic principle of the present invention will be described.
The inventor of the present application has considered that in the high-frequency inductively coupled plasma ion trap mass spectrometer, noise in the low mass region is derived from an ion molecule reaction generated in the ion trap space while sweeping between masses 18 to 40.
[0089]
That is, the noise in the low mass region is generated H₂O⁺This is due to the fact that the ions become unstable immediately, are ejected out of the ion trap space, and are detected.
[0090]
H generated by ion-molecule reaction₂O⁺If the ions are not ejected out of the ion trap space, that is, if the ions can be stably kept in the ion trap space, the generated H₂O⁺Ions do not contribute to continuous noise.
[0091]
The principle of the present invention will be schematically described with reference to FIGS.
(A) of each figure shows an ion position on the Mathieu stabilization curve q-axis, and (b) of each figure shows a state during mass spectrum acquisition by mass sweep. The mass of the ion is m2> 40 (Ar)> m1> 18 (H₂O⁺).
[0092]
The frequency ω of the auxiliary AC voltage applied between the two end cap electrodes of the ion trap mass spectrometer is set lower than the natural frequency of ions at the upper limit of the measured mass range. For example, Uranium UO₂If the range from to is within the measurement range, an auxiliary AC voltage frequency ω2 having a frequency corresponding to m / z 300 is set and applied.
Thereafter, the main high-frequency voltage V starts to be swept in the decreasing direction.
[0093]
Uranium UO₂The ions are emitted from the ion trap space in resonance with the auxiliary AC voltage frequency ω2 from the higher mass to the lower mass in this order. The emitted ions are detected by a detector to form a mass spectrum. This is the acquisition of a mass spectrum by reverse sweeping in which the mass is swept from the higher direction to the lower direction.
[0094]
In the Mathieu stability curve, stably trapped ions are arranged side by side from left to right in order of increasing mass from lower to higher. The auxiliary AC voltage frequency ω2 for resonance is set on the leftmost side. The main high-frequency voltage V is set so that the water ions of mass 18 are within the rightmost boundary (q = 0.908) of the stability diagram.
[0095]
As shown in FIG. 2, when the main RF voltage scanning is started in reverse sweep (Main RF Voltage Scanning), ions (UO) in the Mathieu stability curve are started.₂To H₂O⁺(Up to the ion) apparently moves slightly to the left.
[0096]
Until ions of mass m2 are resonance-emitted, the ion-molecule reaction of the above formula (6) occurs between Ar ions and water molecules in the ion trap space, and H₂O⁺Ions are generated continuously. H₂O⁺Since the qz value of the ion is less than 0.908,₂O⁺The ions remain stably trapped in the ion trap space.
[0097]
Therefore, the region from m / z 300 to m2 is H₂O⁺No ions are detected and H₂O⁺No noise due to ions appears.
[0098]
FIG. 3 is a diagram showing a situation in which a region of 40 (Ar) is reversely swept from the mass m2. First, m2 ions having a high mass resonate with the frequency ω2, are emitted out of the ion trap space, and are detected. During the reverse sweep of the main high-frequency voltage V, Ar + ions in the ion trap space cause an ion molecule reaction of the formula (6) with water molecules in the ion trap space, and H₂O⁺Generate ions continuously.
[0099]
H generated₂O⁺Since the ions exist in the Mathieu stability curve as in the case shown in FIG. 2, they are not emitted out of the ion trap space. Therefore, no detection is performed, and no noise is generated.
[0100]
FIG. 4 is a diagram illustrating a state in which the region m1 is reversely swept from the mass 40 (Ar). The Ar ions resonate with the auxiliary AC voltage frequency ω2 and are emitted out of the ion trap space, and the ion current value is detected by the detector. After that, since Ar ions no longer exist in the ion trap space, the ion-molecule reaction of the formula (6) does not occur.
[0101]
That is, H₂O⁺No new ions are generated. Also, H₂O⁺The ions remain trapped in the ion trap space, as in the case shown in FIGS. Therefore, no noise is generated.
[0102]
FIG. 5 is a diagram illustrating a state in which the region from mass m1 to 18 is reversely swept, and FIG. 6 is a diagram illustrating a state in which the region having a mass of 18 or less is reversely swept.
[0103]
In the case shown in FIG. 5 and FIG. 6, as in the case shown in FIG. 4, Ar ions do not exist in the ion trap space.₂O⁺No ions are generated. But H₂O⁺If ions remain, H₂O⁺The ions are stably trapped in the ion trap space.
[0104]
H₂O⁺The ions finally resonate with the auxiliary AC voltage frequency ω2 and are ejected out of the ion trap space,₂O⁺Detected as ions. That is, H₂O⁺The ions are detected as ions of mass 18 and do not become noise from mass 18 to mass 40.
[0105]
As described above, finally, m2, Ar, m1, H₂O⁺Ions are emitted and detected by resonance. Then, a mass spectrum without noise as shown in FIG. 6B is obtained.
[0106]
This is caused by the progress of the reverse sweep operation of the main high-frequency voltage V,₂O⁺The qz value of the ions gradually decreases, shifts to the left of the Mathieu stability curve, and₂O⁺The ions do not lie outside the Mathieu stability curve.
[0107]
As a result, the generated H₂O⁺The ions will stably remain in the ion trap space during the reverse sweep operation of the main high-frequency voltage V.
[0108]
FIG. 7 is a graph showing a mass spectrum obtained by the method (reverse sweep) according to the present invention. On the other hand, the graph shown in FIG. 11 is a graph showing a mass spectrum obtained by a normal method (forward sweep) not according to the present invention.
[0109]
The mass spectrum acquisition interval shown in FIGS. 7 and 11 is several minutes, and parameters other than the main high-frequency voltage V and the auxiliary AC voltage are the same under both conditions.
[0110]
By comparing the example of FIG. 7 with the example of FIG. 11, as can be easily understood, the mass spectrum obtained by the normal method (forward sweep) shown in FIG. -Like noise is generated.
[0111]
On the other hand, in the mass spectrum obtained by the method (reverse sweep) of the present invention shown in FIG. 7, no table noise is generated even between the masses 18 to 40, and this noise is It can be understood that it is suppressed.
[0112]
The ratio of the noise in the reverse sweep to the noise in the normal sweep was 1/1000.
[0113]
From this, the noise in the low mass region is caused by the H generated in the ion trap space during the sweep.₂O⁺The correctness of the hypothesis assumed to be derived from ions is proved, and by performing a reverse sweep, H₂O⁺The ions can be stably trapped in the ion trap space, and the occurrence of noise in the detected mass spectrum can be reduced.
[0114]
In the mass spectrum obtained by the reverse sweep of the main high-frequency voltage V according to the method of the present invention, ions appear from high mass to low mass. Therefore, it is conceivable to display the mass spectrum so that the mass changes from high to low as the ions appear from left to right on the display screen.
[0115]
However, it is common to display the mass spectrum from low mass to high mass from left to right. In addition, for the sake of comparison with a mass spectrum obtained by a normal method of performing a forward sweep, the mass axis of the mass spectrum obtained by the reverse sweep is inverted so as to change from low mass to high quality.
[0116]
Further, the example shown in FIG. 7 is an example displayed on the display means, and the frequency, the sweep start voltage, the sweep end voltage, the sweep start mass, and the sweep end mass are displayed together with the mass spectrum. Thereby, it is possible to confirm that the result is the result of performing the reverse sweep and the condition thereof.
[0117]
The above is the basic principle of the present invention.
Next, an embodiment of the present invention will be specifically described.
FIG. 1 is a schematic configuration diagram of a high frequency inductively coupled plasma ion trap mass spectrometer to which one embodiment of the present invention is applied.
[0118]
In FIG. 1, a sample solution containing an analyte is sent from a sample solution tank 1 to an atomizer 3 by a pump 2. In the atomizer 3, the sample solution is atomized by the atomizing gas supplied from the gas supply unit 4.
[0119]
The atomized sample solution becomes fine droplets and is introduced into the plasma ion source 5 via the sample introduction tube. The ion source 5 is formed of a triple quartz tube, and a plasma gas such as an Ar gas or a sheath gas is supplied from the gas supply unit 4.
[0120]
A high frequency voltage from a high frequency power supply 7 is applied to the induction coil 6 of the plasma ion source 5 to heat the Ar gas and generate a plasma 8. Fine droplets generated from the sample solution ride on the flow of the spray gas (Ar) and are supplied into the plasma 8.
[0121]
Droplets generated from the sample solution are vaporized, atomized, and further ionized by the high temperature of the plasma 8. In the plasma 8, there are a large amount of neutral molecules and atoms such as Ar and water in addition to Ar ions and sample ions. Ions, neutral molecules, and atoms in the plasma 8 are introduced into a vacuum chamber 11 evacuated by a vacuum pump (oil rotary pump) 30 from a pore 9 provided at the tip of a skimmer 10.
[0122]
The ions and neutral molecules introduced into the vacuum chamber 11 are introduced into a vacuum chamber 25 evacuated by a vacuum pump (turbo molecular pump) 31 via a skimmer 24. The ions introduced into the vacuum chamber 25 are converged by the electrostatic lens 12 placed in the vacuum chamber 25 and sent to a high vacuum chamber 26 in which the ion trap mass spectrometer 16 is arranged.
[0123]
The ions sent into the high vacuum chamber 26 are efficiently sent to the ion trap mass spectrometer 16 by the multipole ion guide 14 to which the high frequency voltage supplied from the high frequency power supply 13 is applied.
[0124]
On the other hand, most of neutral molecules such as Ar and water having no charge are exhausted to the outside of the vacuum chamber 25 by the differential exhaust system. However, some neutral molecules such as water reach the high vacuum chamber 26 evacuated by the vacuum pump (turbo molecular pump) 32 together with the ions.
[0125]
The ions sent from the ion guide 14 to the mass spectrometer 16 reach the ion gate electrode 15. A DC voltage having a polarity opposite to that of the ions to be sent is applied to the ion gate electrode 15, and the ion gate is turned ON.
[0126]
During the ion gate ON state, ions are introduced into the ion trap mass spectrometer 16 and accumulated in the ion trap space 27. While these ions are accumulated in the trap space 27, a main high frequency voltage V for trapping ions is applied between the ring electrode (main electrode) 18 and the end cap electrodes (auxiliary electrodes) 17 and 19 by the main high frequency power supply. Supplied from 20.
[0127]
As a result, a high-frequency ion trap electric field is formed in the ion trap space 27 surrounded by the three electrodes 17, 18, 19. The ions introduced into the ion trap space 27 are stably trapped in the space 27 by the high-frequency ion trap electric field.
[0128]
In order to trap ions in the mass region to be analyzed in the space 27, it is necessary to set the main high-frequency voltage V to a predetermined value. The main high-frequency voltage to be set and the frequency of the auxiliary AC voltage supplied from the auxiliary AC voltage source 21 can be easily obtained by calculation.
[0129]
Here, the frequency f of the main high-frequency voltage is 4 MHz, and the rotation radius r of the ion trap is 10 MHz.^-2If m, the following equation (7) is derived from the above equation (2).
[0130]
V = qz * mr²Ω²/ 4e ――― (7)
Assuming that the lower limit mass value of the mass region to be measured is 15, the ion of mass 15 is located at the rightmost end in the Mathieu stability curve, that is, the main high-frequency voltage V at which qz = 0.9 can be obtained by the above ( From equation (7), V = 2210 (V) can be calculated.
[0131]
At this time, the qz value of the ion with m / z = 300 is calculated as qz = 0.045 from the above equation (2). That is, if the main high-frequency voltage V (first voltage value) is set to 2210 V, the qz values of all the ions from mass 15 to mass 300 exist in the Mathieu stability curve (0 <qz <0.908). , Can be stably trapped in the ion trap space 27.
[0132]
The following equation (8) is derived from the above equations (2) and (3), and the frequency ω of the auxiliary AC voltage is derived.
[0133]
ω = (Ω / 2√2) * ｛4 eV / (mr²Ω²)｝
ω = (Ω / 2√2) * qz --- (8)
Since the ion of m / z 300 has qz = 0.045, its natural frequency ω can be calculated from the above equation (8) as ω = 0.0636 MHz = 63.6 kHz.
[0134]
Further, the main high-frequency voltage V at which the natural frequency ω ′ of the ion at m / z 15 reaches the auxiliary AC voltage frequency ω can be calculated as V = 110 V from the above equation (7).
[0135]
From this, if the main high-frequency voltage having a frequency of 4 MHz is swept from 2210 V to 110 V (second voltage value), ions from mass 300, which is the set upper limit mass, to mass 15, which is the set mass lower limit, are transferred from the ion trap space 27. It can be released by resonance. Even when the mass range to be measured is other than mass 300 to 15, the main high-frequency voltage value and the frequency of the auxiliary AC voltage are calculated in the same manner, and the main high-frequency voltage and the auxiliary AC voltage can be set from the control data processing device (computer) 23. is there.
[0136]
Accordingly, assuming that the mass region to be analyzed is from m / z 15 to m / z 300, first, in order to trap ions in the mass region to be analyzed in the ion trap space 27, the frequency of the main high-frequency voltage to be applied is 4 MHz and the voltage is 2210 V. Just set it.
[0137]
An auxiliary AC voltage of 3 V is applied between the two end cap electrodes 17 and 19 at a frequency of 63.6 kHz corresponding to a natural frequency of m / z 300, which is the upper limit of the mass region to be analyzed.
[0138]
In an actual measurement operation, if the mass region to be measured is input to the control data processing device 23, the frequencies of the main high-frequency voltage V and the auxiliary AC voltage are automatically calculated, and the corresponding high-frequency waves are set to the calculated values. A control signal is sent from the control data processing device 23 to the power supplies 20 and 21.
[0139]
When the introduction of the ions into the ion trap space 27 is completed, a DC voltage having the same polarity as the ions is applied to the ion gate electrode 15, and the ion gate is turned off. In the ion gate OFF state, ions are not introduced from the ion guide 14 into the ion trap space 27.
[0140]
Then, the control data processing device 23 instructs the main high-frequency power supply 20 to start reverse sweep, and starts sweeping from 2210 V in a direction in which the main high-frequency voltage V decreases (toward zero).
[0141]
As a result, ions are successively emitted from the ion trap space 27 in a resonant manner from the higher mass to the lower mass, and are detected by the detector 22. The ion current detected by the detector 22 is sent to the control data processing device 23.
[0142]
The control data processor 23 collects a mass spectrum by controlling the main high frequency power supply 20, the auxiliary AC power supply 21, the ion gate power supply (not shown), and the like of the ion trap mass spectrometer 16. The Ar ions trapped in the ion trap space 27 cause an ion molecule reaction with neutral water molecules during the mass sweep, and⁺The charge of the ions is transferred to water molecules.
[0143]
However, the generated H₂O⁺The ion qz shifts from 0.9 during mass sweep in the decreasing direction (to the left of the Mathieu stability curve) and is located within the Mathieu stability curve, and is not outside the Mathieu stability curve.
[0144]
That is, H₂O⁺The ions are stably trapped in the ion trap space 27 during the sweep. And even if the sweep is progressing, H₂O⁺Since the ions remain stably trapped, H₂O⁺Even if ions continue to be generated in the ion trap space 27, they do not cause detection noise in the detector 22.
[0145]
When the main high-frequency voltage reaches 110 V and reaches the mass 15, the sweep is stopped. Then, the main high-frequency voltage is once reset to 0, and eliminates unnecessary ions remaining in the ion trap space 27 outside the ion trap space 27. Next, the main high-period voltage is set to 2210 V again, a DC voltage having the opposite polarity to the ions to be introduced is applied to the ion gate electrode 15, and the ion gate is turned on. Thereby, introduction of ions into the ion trap space 27 is enabled.
Thereafter, the same steps as described above are repeated to collect mass spectra.
[0146]
FIG. 8 is an operation sequence diagram of the above-described ion trap.
(A) Period from time t10 to t11 (ion introduction period): The ions are introduced and accumulated in the ion trap space. That is, as shown in FIG. 8A, a potential having a polarity opposite to that of the ions is applied to the ion gate electrode 15 and the ion gate is turned on.
[0147]
As shown in FIG. 8B, the main high-frequency voltage V is maintained at a high voltage which is the sweep start voltage from time t10 to t11, so that ions can be trapped from m / z 300.
[0148]
As shown in FIG. 8C, a notched broadband noise signal is applied to the auxiliary AC voltage by FNF or the like. Thereby, only useful ions can be selectively accumulated from the ions sent to the ion trap space 27, and conversely, unnecessary ions can be eliminated. Ar ions and water ions can be eliminated as much as possible by the notched broadband noise.
[0149]
(B) Period from time t11 to t20 (sweep period): A mass spectrum is obtained by mass sweep. As shown in FIG. 8A, a potential having the same polarity as the ions is applied to the ion gate electrode 15 to turn off the ion gate.
[0150]
After turning off the broadband noise signal of the auxiliary AC voltage as shown in FIG. 8C, the resonance auxiliary AC signal ω is set and applied as shown in FIG. 8D.
[0151]
In addition, as shown in FIG. 8B, the main high-frequency voltage V starts to be swept in a direction in which the voltage is reduced from, for example, 2210 V to 110 V corresponding to m / z 15 (slope is performed by decreasing the voltage in an inclined manner). . Then, the ion intensity and m / z are obtained from the detected ion current value and the main high-frequency voltage V to obtain a mass spectrum. The main high-frequency voltage is reset to 0 at time t20. The time from time t11 to t20 is about 0.1 second to several seconds.
[0152]
Thereafter, the operations shown in the above (a) and (b) are repeated to continuously collect mass spectra.
[0153]
Here, neutral molecules that may exist in the ion trap space 27 include helium (He) and nitrogen (N₂), Oxygen (O₂), Carbon dioxide (CO₂), Hydrocarbons and the like. These ionization potentials (IP) are as shown in Table 1.
[Table 1]

Among the neutral molecules shown in Table 1, the neutral molecules which may cause an ion molecule reaction similar to the above-mentioned formula (6) with Ar ions are the conditions shown in the following formulas (9) and (10). Is satisfied.
[0154]
IP (NM) <IP (Ar) --- (9)
MW (NM) <MW (Ar) --- (10)
That is, when the ionization potential (IP) of the neutral molecule (NM) is lower than the IP of argon (Ar) and the molecular weight (MW) of the neutral molecule is lower than the atomic weight of argon (Ar), noise appears on the mass spectrum. give.
[0155]
Those that meet the above two conditions are shown in Table 1 above with water (H₂O) and oxygen (O₂) Only. Water (H₂As with O), oxygen (O₂) Causes an ionic molecule reaction as in the following equation (11).
[0156]
O₂+ Ar⁺  → O₂ ⁺+ Ar ---- (11)
According to the conventional method, that is, in the case of the method using the forward sweep, noise is generated in the detected mass spectrum from the masses 32 to 40.
[0157]
However, according to the present invention, water (H₂O) as in the case of O).₂) Can also be stably trapped in the ion trap space 27, and oxygen (O₂) Can be prevented.
[0158]
Further, even if new molecules other than those described in Table 1 satisfying the conditions of the above equations (9) and (10) are introduced into the ion trap space 27, continuous noise can be suppressed by the present invention. .
[0159]
As described above, according to one embodiment of the present invention, by reversely sweeping the main high-frequency voltage from a high voltage to a low voltage, water ions and the like that cause noise are stably trapped in the ion trap space. In addition, ions to be detected can be discharged from the ion trap space.
[0160]
Therefore, it is possible to realize a high-frequency inductively coupled plasma ion trap mass spectrometer capable of suppressing the generation of low-mass region noise and performing high-sensitivity quantitative analysis without requiring a significant change in structure or an expensive cryopump. Can be.
[0161]
In addition, it is possible to realize a high-frequency inductively coupled plasma ion trap mass spectrometry method capable of suppressing generation of noise in a low mass region and performing high-sensitivity quantitative analysis.
[0162]
The control data processing device 23 includes a display unit, and displays the mass spectrum and the upper limit mass value corresponding to the sweep start voltage and the lower limit mass value corresponding to the sweep end voltage shown in FIG.
[0163]
Further, as another embodiment of the present invention, there is an operation control program for a computer which is a control data processing device.
[0164]
In other words, this computer program introduces an aqueous solution of the analyte into the plasma, generates ions, captures the generated ions in the ion trap space, releases the ions from the ion trap space, and masses the ions. 9 is a computer program for controlling the operation of a high-frequency inductively coupled plasma ion trap mass spectrometer for detecting and analyzing the mass spectrometry.
[0165]
Then, the computer program forms an ion trap space, and supplies a first voltage value corresponding to the set upper limit mass value of the mass region to be analyzed to a main electrode to which a main high frequency voltage is supplied, and The ions in the region are introduced into the ion trap space, and an auxiliary AC voltage having an ion resonance frequency of a mass greater than the upper limit mass is supplied to an auxiliary AC electrode that forms the ion trap space together with the main electrode, and the voltage value of the main high-frequency voltage From the first voltage value to the second voltage value corresponding to the set lower limit mass value of the analysis target mass region, and the lower limit mass ions are released from the upper limit mass ions to the lower limit mass ions from the ion trap space. .
[0166]
Thereafter, the mass of the ions emitted from the ion trap space is detected, and a mass spectrum of the detected ions is created.
[0167]
【The invention's effect】
According to the present invention, it is possible to realize a high-frequency inductively coupled plasma ion trap mass spectrometer and a method that are inexpensive, can suppress generation of noise in a low mass region, and can perform high-sensitivity quantitative analysis.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a high-frequency inductively coupled plasma ion trap mass spectrometer to which an embodiment of the present invention is applied.
FIG. 2 is a diagram illustrating the principle of the present invention.
FIG. 3 is a diagram illustrating the principle of the present invention.
FIG. 4 is a diagram illustrating the principle of the present invention.
FIG. 5 is a diagram illustrating the principle of the present invention.
FIG. 6 is a diagram illustrating the principle of the present invention.
FIG. 7 is a display screen example of a mass spectrum obtained according to an embodiment of the present invention.
FIG. 8 is an operation time sequence diagram in one embodiment of the present invention.
FIG. 9 is an explanatory diagram of an ion trap mass spectrometer.
FIG. 10 is a graph showing a Mathieu stability curve showing the operation principle of the ion trap.
FIG. 11 is a graph showing a mass spectrum obtained when a forward sweep is performed.
FIG. 12 is an explanatory diagram of a cause of noise generation in the high frequency inductively coupled plasma ion trap mass spectrometer.
FIG. 13 is an explanatory diagram of a cause of noise generation.
FIG. 14 is an explanatory diagram of a cause of noise generation.
FIG. 15 is an explanatory diagram of a cause of noise generation.
FIG. 16 is an explanatory diagram of a cause of noise generation.
FIG. 17 is an explanatory diagram of a cause of noise generation.
[Explanation of symbols]
1 Sample solution tank
2 pump
3 atomizer
4 Gas supply unit
5 Plasma ion source
6 Induction coil
7 High frequency power supply
8 Plasma
9 pores
10, 24 Skimmer
11, 25, 26 vacuum chamber
12 Electrostatic lens
13 High frequency power supply
14 Multipole ion guide
15 Ion gate electrode
16 Ion trap mass spectrometer
17, 19 End cap electrode
18 Ring electrode
20 Main high frequency voltage power supply
21 Auxiliary AC voltage power supply
22 Detector
23 Control data processing device
30 oil rotary pump
31, 32 Turbo molecular pump

Claims (8)

An aqueous solution of the analyte is introduced into the plasma to generate ions, and the generated ions are captured in the ion trap space. The ions are released from the ion trap space, and the mass of the released ions is detected and analyzed. High frequency inductively coupled plasma ion trap mass spectrometer,
An auxiliary AC electrode that forms the ion trap space and is supplied with an auxiliary AC voltage;
A main electrode that forms an ion trap space with the auxiliary AC electrode and is supplied with a main high-frequency voltage;
A mass detector for detecting the mass of ions emitted from the ion trap space,
Control data processing means for controlling the frequency of the auxiliary AC voltage and the amplitude value of the main high-frequency voltage, and creating a mass spectrum of ions detected by the mass detector,
Wherein the control data processing means sets the main high-frequency voltage to a first voltage value corresponding to the set upper limit mass value of the analysis target mass region, supplies the main high frequency voltage to a main electrode, and supplies ions to the analysis target region. Is introduced into the ion trap space, the frequency of the auxiliary AC voltage is set to the ion resonance frequency of a mass larger than the upper limit mass, and the voltage value of the main high-frequency voltage is calculated from the first voltage value in the mass region to be analyzed. The voltage is swept toward the second voltage value corresponding to the set lower limit mass value in a slanting manner, and ions of the lower limit mass are released from the ions of the upper limit mass in the analysis target region from the ion trap space and released. A high-frequency inductively coupled plasma ion trap mass spectrometer characterized in that ions are detected by a mass detector. 2. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1, wherein ions generated by an ion-molecule reaction in the ion trap space are inclined from the first voltage value to a second voltage value. A high-frequency inductively coupled plasma ion trap mass spectrometer, wherein the mass spectrometer is trapped in the ion trap space during a period in which it is reduced. 3. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1, wherein a lower limit mass value of the mass region to be analyzed is 15. 3. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1, wherein a lower limit mass value of the mass region to be analyzed is 16. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1 or 2, wherein an upper limit mass value of the mass region to be analyzed is 280. 3. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1, wherein an upper limit mass of the mass to be analyzed is 300. 2. The high-frequency inductively coupled plasma ion trap mass spectrometer according to claim 1, wherein the upper limit mass value corresponding to the sweep start voltage and the lower limit mass value corresponding to the sweep end voltage value together with the mass spectrum of the created ions. A high frequency inductively coupled plasma ion trap mass spectrometer comprising a display means for displaying. An aqueous solution of the analyte is introduced into the plasma to generate ions, and the generated ions are captured in the ion trap space. The ions are released from the ion trap space, and the mass of the released ions is detected and analyzed. High frequency inductively coupled plasma ion trap mass spectrometry method,
A first voltage value corresponding to the set upper limit mass value of the mass area to be analyzed is supplied to the main electrode to which the ion trap space is formed and to which the main high frequency voltage is supplied, so that ions in the analysis area are trapped by the ion trap. Introduced into the space,
An auxiliary AC voltage having an ion resonance frequency of a mass larger than the upper limit mass is supplied to an auxiliary AC electrode forming an ion trap space together with the main electrode,
The voltage value of the main high-frequency voltage is decreased from the first voltage value to a second voltage value corresponding to the set lower limit mass value of the analysis target mass region in an inclined manner, and the ion of the upper limit mass of the analysis target region is reduced. From the ion trap space to emit ions of the lower limit mass,
A high-frequency inductively-coupled plasma ion trap mass spectrometric method comprising detecting a mass of ions emitted from an ion trap space and creating a mass spectrum of the detected ions.

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