JP2901628B2 - Mass spectrometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mass spectrometer.

[Conventional technology]

The conventional apparatus is the patent 1136 for atmospheric pressure ionization.
As described in Japanese Patent No. 983, a method utilizing corona discharge using a needle electrode is used for analyzing gas molecules, and no consideration is given to ionization of a liquid. Also, Analytical Chemistry No. 54, No. 1, (1982), p. 143 to 1
46 pages (Analitycal Chemistry, vol, 54, No. 11982 pp143-
146) discusses the ionization method of liquid vaporization.

Further, for example, as described in JP-A-63-187548, by changing the drift voltage,
It is known to control the dissociation of cluster ions.

[Problems to be Solved by the Invention] However, in the above-described conventional technology, it has not been possible to appropriately set the drift voltage in accordance with the analysis parameter that slightly changes for each analysis.

An object of the present invention is to provide a mass spectrometer capable of appropriately setting a drift voltage and performing highly accurate analysis.

[Means for solving the problem]

In order to achieve the above object, in the present invention, the drift voltage is continuously changed, the detected value of the ion having the mass corresponding to the specific component is obtained for each drift voltage, and the obtained detected values are mutually compared. The drift voltage is automatically selected for comparison and set to the selected drift voltage.

[Action]

According to the above configuration, since the comparison is made based on the mass corresponding to the specific component, for example, a determination including the declustering state is made, and an appropriate drift voltage can be set according to each analysis condition.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. Liquid chromatograph (I) for separating a mixed solution for each component
Is used as a solvent 1 with methanol (CH ₃ OH) or water (H ₂ O) and pumped into a column 4 by a pump 2. When the mixed sample separated from the injector 3 is injected, the mixed sample is separated by the interaction with the column 4 and elutes with time.

The amount of solution is too large to directly introduce the eluate containing the solvent 1 and the sample into the mass spectrometer, and it is impossible to ionize by the electron impact method using a general filament. It becomes possible if used.

When the eluate is introduced into the atomizer 6 heated by the heater 7 through the microtube 5, the eluate becomes a vaporized jet and is atomized (II). Since the atomized droplets float as droplets adhered to the solvent, they are separated into the solvent and the sample molecules in the desolvation chamber 8 heated by the heater 9.

The solvent molecules are ionized together with the remaining gas (N ₂ ) by corona discharge with the high potential (5 to 10 kV) needle electrode 10 (primary ionization). Since the generated primary ions are under atmospheric pressure, they collide with the sample and the like one after another, and the sample molecules mainly having a low ionization potential are ionized by charge transfer or the like (atmospheric pressure ionization section III). The generated ions are ejected from the first pores 11 to the intermediate pressure section IV exhausted by the oil rotary pump 24 or the like. At this time, many cluster ions including sample ions are generated. Excess neutral molecules escape to the outside through the opening 12. By using such an atmospheric pressure ionization method, it is possible to directly ionize a large amount of eluent and sample molecules from a liquid chromatograph.

The total ion beam mainly composed of the cluster ions including the sample molecules generated in this way is physically dissociated by colliding with the neutral molecules existing in the intermediate pressure section IV to form a simple pseudo molecular ion ( Hydrogen addition ion).
The degree of this dissociation can be controlled by changing the energy of the ions. The voltage between the first and second fine holes 11 and 14 insulated by insulators A15 and B23 is controlled by a drift power supply 29. The target molecular ion amount is set to be maximum. The intermediate pressure section IV is surrounded by an insulated drift chamber 13, evacuated to about 10 Pa by an oil rotary pump R, P 24 or the like, and is measured by a pressure gauge 25. Since the dissociation of the cluster ions depends on the number of collisions and the energy of the neutral molecule, the pressure and drift voltage of this portion are parameters for the target molecular ion. The ions exiting the second pores 14 are efficiently extracted, accelerated, decelerated, and converged by the lens system 16. The convergent beam C at the converging section V is incident on the next quadrupole mass analyzer VI at the incident energy (10
eV). An ion energy of about 10 eV incident on the quadrupole mass spectrometer is a good condition in terms of ion transmittance and resolution, but this corresponds to a field voltage difference between the drift chamber 13 and the Q pole 17. API ion source II
In the experiment of the voltage difference between I, IV and the converging portion V, the drift chamber 13 has good beam characteristics at about 120 V with respect to the ground, and the maximum ion beam amount can be obtained. For this reason, the field voltage of the Q-pole 17 is set to be lower than the normal ground potential in the atmospheric pressure ionization system by grounding and about 10 eV lower than the drift chamber 13. As the focused ion beam C vibrates inside the Q pole 17, only ions having a mass number satisfying the conditions pass therethrough, and pass through the Q pole 17 as a mass separation beam D. The mass separation beam D deflected by the deflection electrode 18 for removing neutral particles is amplified by the secondary electron multiplier 19, and detected and recorded as a mass spectrum by the detector 20.

The mass separator VI is surrounded by a shield 21, and the housing 22 is evacuated to a high vacuum by an oil diffusion pump DP26 or the like. Flange
From 27, introduction to the internal electrodes such as the Q pole 17 is performed. The control system includes a drift power supply 29, a lens power supply 30, a drift chamber power supply 28, a field power supply 34, and a Q pole power supply 3.
1. A deflection power supply 32, a secondary electron multiplier power supply 33, and the like are controlled by an overall control system 35 using a CPU.

In a liquid chromatograph / quadrupole analyzer system, it is important to detect the ions of the sample components with high sensitivity (increase the amount of ions) as in a general analyzer. For that,
Alignment of the ion beam is important. In the present invention, the first pore 11, the second pore 14, the lens system 16, and the Q pole 17 are arranged in a straight line, and neutral particles are removed to reduce S / N. The beam is deflected and detected for improvement. In experiments, the energy voltage (drift voltage) characteristics of the ions in the intermediate pressure section IV are the most effective as parameters. For the detection of unknown samples, the pressure and the drift voltage are determined, for example, by using the solvent ethanol (CH ₃ OH). It has been found that the conditions for maximum detection of molecular ions (CH ₃ OH · H +) are good. Since there are beam intensity characteristics as shown in FIGS. 2A, 2B, and 2C, these conditions can be stored in advance in the CPU overall control system 35 and automatically set to the best point. .

According to the present invention, efficient coupling and setting of conditions with an atmospheric pressure ionization method and a quadrupole mass spectrometer can be easily performed,
Complex conditions are automatically set for the liquid chromatograph / quadrupole mass spectrometer, improving operability.

There are a wide variety of compounds to be analyzed by a liquid chromatograph / quadrupole mass spectrometer direct connection system, but the mass spectrum is composed of molecular ions reflecting molecular structure and cleavage ions. There are also cluster ions in which molecules are gathered. Depending on the pressure of the system and the energy of the ions, they depend on the energy of collisional dissociation and often give complex spectra, but the setting conditions of the equipment can be set, for example, by the mass spectrum of methanol, which is most often used as a solvent. Confirmed by experiment. That is, the pseudo molecular ion of methanol (CH ₃ OH · H + mass 3
3) and cleavage ion (CH ₃ + mass number 15) 9 ratio is 1
The range of 0: 1 to 10:10 is good.

Moreover, fragment ions (C +, CH +, CH 2 + mass number 12 and 13,
A large number of ions, such as 14), indicates that cleavage is in progress.

While displaying these peaks in real time on the CRT screen, the ion energy control voltage and lens voltage are automatically set to the point where the peak intensity of CH ₃ OH · H + is large according to the pressure of the intermediate pressure chamber, so that the reproducibility is high. Good atmospheric pressure ionization mass spectra are obtained. FIG. 3 shows an example of a mass spectrum with respect to the energy control voltage (drift voltage) of methanol ions. The setting value is preferably a condition as shown in FIG.

In the case of detecting a small amount of sample ions, depending on the conditions of the drift voltage, the flow rate of the liquid chromatograph, the temperature of the desolvation chamber, the pressure of the intermediate pressure chamber, etc., the ions are generated by collisions with the neutral particles. There are many neutral particles that travel straight, which may enter the quadrupole mass spectrometer and lower the detection limit. In this case, providing an ion deflection electrode in front of the quadrupole analyzer to prevent neutral particles from being taken is effective in improving the detection limit of ions, and FIG. 4 shows an example of the arrangement.

According to this embodiment, it is effective in improving the operability in which conditions can be easily set as a small liquid chromatograph / quadrupole mass spectrometer.

〔The invention's effect〕

As described above, according to the present invention, an analysis can be performed by setting an appropriate drift voltage according to analysis conditions. Therefore, high-precision mass spectrometry becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment of the present invention, and FIG.
(B) is a beam amount characteristic diagram with respect to a drift voltage and a liquid chromatographic flow rate, respectively, (C) is an ion transmittance and resolution characteristic diagram with respect to a Q pole field voltage, and FIG.
The figure shows a mass spectrum of methanol, and FIG. 4 is an ion beam deflection arrangement diagram. DESCRIPTION OF SYMBOLS 1 ... Solvent, 2 ... Pump, 3 ... Injector, 4 ... Column, 5 ... Microtube, 6 ... Atomizer, 7 ... Heater, 8 ... Solvent removal chamber, 9 ... Heater, 10 ... Needle electrode, 11 ... 1st Pores, 12 ... Opening, 13 ... Drift chamber, 14 ... Second
Pores, 15: Insulator A, 16: Lens system, 17: Q pole, 18
... deflection electrode, 19 ... secondary electron multiplier, 20 ... detector, 21 ... shield, 22 ... housing, 23 ... insulator B, 24 ... oil rotary pump, 25 ... pressure gauge, 26 ... oil diffusion pump, 27 … Flange,
28: Drift chamber power supply, 29: Drift power supply, 30: Lens power supply, 31: Q pole power supply, 32: Deflection electrode power supply, 33 ...
Secondary electron multiplier power supply, 34 field power supply, 35 CPU overall control system, 36 CRT, A ... atomized droplet beam, B ...
Total ion beam, C: convergent beam, D: mass separation beam, I: liquid chromatograph part, II: atomization part, III: atmospheric pressure ionization part, IV: intermediate pressure part, V: convergent part, VI: quadruple Extreme mass separator.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-127453 (JP, A) JP-A-61-292847 (JP, A) JP-A-63-187548 (JP, A) JP-A-62-187548 264546 (JP, A) Japanese Utility Model 62-109345 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/62 G01N 30/72 H01J 49/00-49/48

Claims (6)

(57) [Claims] 1. An ionization section for ionizing a sample, an intermediate pressure section having a lower pressure than the ionization section, a mass analysis section having a lower pressure than the intermediate pressure section, and a mass separation section provided in the mass analysis section. A mass spectrometer that has a detecting means, and guides the sample ions to the mass spectrometric section through the intermediate pressure section, and separates and detects the mass by the mass separation detecting means. A first electrode and a second electrode, a drift voltage control means for continuously changing a drift voltage applied between the first electrode and the second electrode, Means for determining a detected value of an ion having a mass corresponding to a specific component with respect to each drift voltage; and comparing and selecting means for automatically selecting the drift voltage by comparing the respective detected values with each other. And, the mass spectrometer, characterized in that it is composed of the selected drift voltage as applied to the mass separation and detection between the first electrode and the second electrode. 2. The mass spectrometer according to claim 1, wherein a peak of a pseudo molecular ion of a proton-loaded ion of methanol is detected, and a drift voltage is selected based on the detected peak. 3. The method according to claim 1, wherein a peak of a pseudo molecular ion of a proton-loaded ion of methanol and a peak of a decomposition ion are detected, and the drift voltage is adjusted so that the ratio of these ions becomes 10: 1 to 10:10. A mass spectrometer characterized by selecting. 4. The mass spectrometer according to claim 1, wherein said ionization section is maintained at substantially atmospheric pressure. 5. The mass spectrometer according to claim 4, wherein the effluent from the liquid chromatograph is guided to the ionization section to be ionized. 6. The mass spectrometer according to claim 5, wherein a corona discharge electrode is disposed in the ionization section, and ionization is performed by discharge from the corona discharge electrode.