Ion detector and mass spectrometer

Abstract

To provide an ion detector capable of determining a component to be ionized with high sensitivity without depending on the polarity of ions.SOLUTION: An ion detector (24) includes a conversion dynode (241), a secondary electron multiplier (242), and a DC voltage application unit (243) that applies a DC voltage between the conversion dynode (241) and the secondary electron multiplier (242), in which a part or all of a surface of the conversion dynode (241) including an ion collision surface (2410) with which ions collide is made of a material containing one or more elements of titanium, vanadium, and chromium at a higher density than iron and aluminum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ion detector and a mass spectrometer including the ion detector. [Background technology]

[0002] One type of mass spectrometer known to the public uses a quadrupole mass filter. A quadrupole mass filter has four rod-shaped electrodes, and by controlling the voltage applied to these electrodes, it allows only ions with a specific m / z (mass-to-charge ratio) to pass through, among the ions generated from the sample to be analyzed. By varying the frequency or amplitude over time, the m / z of the ions passing through the quadrupole mass filter is varied over time. The ions passing through the quadrupole mass filter are sequentially detected by an ion detector, yielding a mass spectrum that shows the relationship between m / z and the detected intensity of the ions.

[0003] One type of ion detector used in such mass spectrometers includes a conversion dynode and a secondary electron multiplier (see, for example, Patent Document 1). When a conversion dynode is struck by a primary ion, which is the ion to be detected, it emits secondary particles having a charge of the opposite polarity to that of the primary ion. If the primary ion is positive, the secondary particles are electrons or negative ions, and if the primary ion is negative, the secondary particles are positive ions. A secondary electron multiplier has multiple dynodes connected together. When an ion or electron strikes the first dynode, multiple electrons are emitted. When each of these multiple electrons strikes a second dynode, multiple electrons are further emitted. This operation is repeated, generating a large number of electrons. The large number of electrons thus generated are detected as a current.

[0004] In this ion detector, a secondary electron multiplier is located off the optical axis of the incident ions, and a conversion dynode is positioned opposite the secondary electron multiplier across the optical axis. A predetermined negative potential is always applied to the secondary electron multiplier, and a voltage of an appropriate magnitude corresponding to the polarity of the primary ions to be detected is applied between the conversion dynode and the secondary electron multiplier. That is, to detect positive ions, a DC voltage is applied to the conversion dynode, which has a negative potential that is lower (larger in absolute value) than the secondary electron multiplier. To detect negative ions, a DC voltage is applied to the conversion dynode, which has a positive potential. As a result, a force is applied to the primary ions toward the conversion dynode. The primary ions are then accelerated by the DC voltage and collide with the conversion dynode. The secondary particles released are then accelerated by the DC voltage in the opposite direction to the primary ions and enter the secondary electron multiplier. This allows primary ions that pass through the quadrupole mass filter to collide with the conversion dynode without escaping, and secondary particles emitted from the conversion dynode can be collected in the secondary electron multiplier without waste, thereby improving detection sensitivity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-254668 [Non-patent literature]

[0006] [Non-Patent Document 1] Ishikawa, Makishi, "Secondary Ion Mass Spectrometry (SIMS) - Overview and Recent Applications," Kyushu University Central Analysis Center News, Kyushu University Central Analysis Center, No. 103, pp. 1-6, January 31, 2009 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, quantitative analysis of PFAS and haloacetic acids in the environment and food has been conducted to investigate the effects of these suspected carcinogens on the human body. PFAS is a collective term for perfluoroalkyl and polyfluoroalkyl compounds (PFASs) and is used in a wide range of applications, including water and oil repellents, surfactants, firefighting foams, and cooking utensil coatings. Haloacetic acids are byproducts generated during tap water disinfection. Mass spectrometers are used to quantify these PFASs and haloacetic acids with high sensitivity. In mass spectrometers, PFASs and haloacetic acids are ionized into negative ions in the ionization section. However, with ion detectors equipped with a conversion dynode and a secondary electron multiplier, the number of secondary particles emitted from the conversion dynode is generally lower when the primary ion to be detected is negative than when it is positive. Therefore, mass spectrometers using conventional ion detectors are unable to quantify components that ionize into negative ions, such as PFASs and haloacetic acids, with high sensitivity.

[0008] The problem to be solved by the present invention is to provide an ion detector that can quantify ionized components with high sensitivity regardless of the polarity of the ions, and a mass spectrometer equipped with the ion detector. [Means for solving the problem]

[0009] The ion detector according to the present invention, which has been made to solve the above problems, comprises: an ion detector having a conversion dynode, a secondary electron multiplier, and a DC voltage application unit that applies a DC voltage between the conversion dynode and the secondary electron multiplier; Equipped with A part or the whole of the surface of the conversion dynode, including the ion collision surface with which ions collide, is made of a material containing one or more elements of titanium, vanadium, and chromium at a higher density than iron and aluminum.

[0010] The mass spectrometer according to the present invention comprises: an ionization unit that ionizes a substance to be analyzed; an ion selector that selects and releases ions having a specific m / z value from among the ions ionized by the ionization unit; the ion detector, which is disposed downstream of the ion selector; It has. [Effects of the Invention]

[0011] Titanium, vanadium, and chromium have the advantage of producing a greater number of positive secondary ions when negative primary ions collide with them than stainless steel (mainly composed of iron (Fe)) or aluminum, which have traditionally been used as materials for conversion dynodes in ion detectors. In the ion detector and mass spectrometer according to the present invention, a portion or the entire surface of the conversion dynode, including the ion collision surface where the (primary) ions collide, is made of a material containing one or more elements selected from titanium, vanadium, and chromium, which have the above-described characteristics, at a higher density than iron and aluminum. This allows for high-sensitivity quantification of not only positive ions but also negative ions, i.e., regardless of ion polarity. In particular, this allows for high-sensitivity quantification of components that ionize to negative ions, such as PFAS and haloacetic acids, which have traditionally been difficult to quantify with high sensitivity. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a mass spectrometer according to the present invention; [Figure 2] FIG. 2 is a longitudinal sectional view of a conversion dynode included in the mass spectrometer of the present embodiment. [Figure 3] 10 is a graph showing the results of an experiment conducted to determine the detection sensitivity of negative ions cleaved from perfluorooctanesulfonic acid (PFOS) for the mass spectrometers of this embodiment and two conventional examples. [Figure 4] 10 is a graph showing experimental results of the detection sensitivity of positive ions obtained by cleaving reserpine using the mass spectrometers of this embodiment and the conventional example. [Figure 5] FIG. 10 is a longitudinal sectional view of a conversion dynode included in a mass spectrometer according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a mass spectrometer according to the present invention will be described with reference to FIGS.

[0014] (1) Configuration of the mass spectrometer of this embodiment 1, the mass spectrometer 1 of this embodiment is an LC-MS having a liquid chromatograph (LC) section 10 in front of a mass spectrometer (MS) section 20. The LC section 10 separates components contained in a liquid sample over time using a column (not shown) and sends each component to the MS 20.

[0015] The MS section 20 has a chamber 28 provided with an ionization chamber 280, a first intermediate vacuum chamber 281, a second intermediate vacuum chamber 282, and a high vacuum chamber 283. The inside of the ionization chamber 280 is maintained at approximately atmospheric pressure, and is differentially evacuated by a vacuum pump (not shown) so that the degree of vacuum increases stepwise from the ionization chamber 280 to the high vacuum chamber 283.

[0016] The ionization chamber 280 is equipped with an electrospray ionization (ESI) nozzle 211 that sprays the liquid sample delivered from the LC unit 10 while generating a high electric field within the chamber. This spraying generates charged droplets, and the compounds in the droplets are ionized as the droplets split and the solvent evaporates. The ionization chamber 280 and ESI nozzle 211 constitute the ionization unit 21.

[0017] A heated capillary 291 is provided between the ionization chamber 280 and the first intermediate vacuum chamber 281, which heats ions in the ionization chamber while passing them toward the first intermediate vacuum chamber 281. A first ion guide 221 is provided in the first intermediate vacuum chamber 281, and a second ion guide 222 is provided in the second intermediate vacuum chamber 282, and a skimmer 292 is provided between the first intermediate vacuum chamber 281 and the second intermediate vacuum chamber 282. Ions are converged onto the ion optical axis C by the first ion guide 221 and the second ion guide 222, and are introduced into the high vacuum chamber 283 through an aperture 293 provided between the second intermediate vacuum chamber 282 and the high vacuum chamber 283.

[0018] A front-stage quadrupole mass filter 231, a collision cell 232, a rear-stage quadrupole mass filter 233, and an ion detector 24 are provided in this order from the side of the aperture 293 inside the high vacuum chamber 283. The front-stage quadrupole mass filter 231 and the rear-stage quadrupole mass filter 233 correspond to the ion selector.

[0019] Both the front-stage quadrupole mass filter 231 and the rear-stage quadrupole mass filter 233 have four rod-shaped electrodes, and voltages are applied between the rod-shaped electrodes from a front-stage QMF voltage power supply unit 237 and a rear-stage QMF voltage power supply unit 238, respectively. A quadrupole ion guide 2321 is disposed within the collision cell 232. A collision-induced dissociation (CID) gas is introduced into the collision cell 232.

[0020] The ion detector 24 includes a conversion dynode (CD) 241, a secondary electron multiplier tube (SEM) 242, a CD voltage power supply unit 243, and an SEM operating power supply unit 244. The CD 241 and the SEM 242 are arranged with the ion optical axis C sandwiched therebetween.

[0021] As shown in FIG. 2, the CD 241 has a base material 2411 and a surface layer 2412 formed on the surface of the base material 2411 .

[0022] In this embodiment, the base material 2411 is made of a material containing 90% or more aluminum (Al) because it is easy to machine. Instead of Al, a base material made of other materials such as stainless steel (mainly composed of iron (Fe)) may be used.

[0023] In this embodiment, the surface layer 2412 is formed by plating the surface of the base material 2411 with chromium (Cr), and its main component is Cr oxide (Cr2O3). The surface layer 2412, which is mainly composed of Cr2O3, has the advantage that it can be easily formed on the surface of the base material 2411 made of Al or stainless steel by wet plating.

[0024] Although stainless steel generally contains a small amount of chromium, the chromium content density in stainless steel is much smaller than the iron content density. In contrast, the surface layer 2412 of the CD 241 in the mass spectrometer 1 of this embodiment contains almost no iron (although a small amount may be contained as an impurity), and the chromium content density is much larger than the iron content density. Similarly, the surface layer 2412 contains almost no aluminum, and the chromium content density is much larger than the aluminum content density.

[0025] The material of the surface layer 2412 is not limited to this example and may be, for example, elemental Cr, Cr compounds other than oxides, elemental titanium (Ti) and compounds, elemental vanadium (V) and compounds, an alloy of two or three of Ti, V, and Cr, or a compound of these two or three elements with another element. That is, the material of the surface layer 2412 may contain one or more of Ti, V, and Cr. Note that a surface layer 2412 containing Ti and / or V as its main components cannot be produced by wet plating, and is therefore produced by a method such as CVD or sputtering. A surface layer 2412 containing only Cr, without Ti or V, is preferred because it can be easily produced by wet plating.

[0026] Since the surface layer 2412 is gradually sputtered during use of the mass spectrometer 1 (during detection of negative ions), it is desirable that the initial surface layer 2412 has a certain thickness, specifically a thickness of 0.1 μm or more. In this embodiment, the thickness of the surface layer 2412 is set to 0.5 μm. Note that, since the wet plating method is used for fabrication in this embodiment, the surface layer 2412 is provided on the entire surface of the base material 2411. However, as long as the surface layer 2412 is provided on the ion collision surface 2410 on which primary ions collide, it is not necessary to provide the surface layer 2412 on other parts of the surface.

[0027] The CD voltage power supply unit 243 is a power supply that applies a DC voltage (hereinafter referred to as "CD voltage") between the CD 241 and the SEM 242. When the ions emitted from the rear quadrupole mass filter 233 are negative ions, a DC voltage is applied so that the CD 241 side is positive and the SEM 242 side is negative. By setting the polarity of the CD voltage so that the CD 241 side is positive in this way, an electric field is formed from the CD 241 toward the SEM 242. As a result, the negative ions emitted from the rear quadrupole mass filter 233 move toward the CD 241 side as primary ions, and the positive ions emitted from the surface layer 2412 move toward the SEM 242 side as secondary particles. On the other hand, when the ions emitted from the rear quadrupole mass filter 233 are positive ions, the CD voltage power supply unit 243 applies a CD voltage between the CD241 and the SEM242 so that both are at negative potential and the CD241 side is at a lower potential than the SEM242, thereby forming an electric field from the SEM242 to the CD241. As a result, the positive ions emitted from the rear quadrupole mass filter 233 move toward the CD241 side as primary ions, and the negative ions emitted from the surface layer 2412 move toward the SEM242 side as secondary particles.

[0028] A recess 2413 is provided in a part of the ion collision surface 2410 of the CD 241. By forming such a recess 2413, an equipotential surface is formed between the CD 241 and the SEM 242, with the CD 241 side being convex and the SEM 242 side being concave. When primary ions are incident on this surface, secondary particles are emitted and fly in a direction perpendicular to the equipotential surface. This allows the secondary particles to be focused and incident on the SEM 242.

[0029] The SEM 242 is similar to that used in conventional ion detectors, and therefore a detailed description thereof will be omitted. The SEM operating power supply unit 244 is a power supply for supplying power for operating the SEM 242.

[0030] The front stage QMF voltage power supply unit 237, rear stage QMF voltage power supply unit 238, CD voltage power supply unit 243, and SEM operation power supply unit 244 are controlled by the control unit 25. The control unit 25 is realized by hardware such as a CPU and memory, and software.

[0031] (2) Operation of the mass spectrometer of this embodiment Next, the analytical operation of the mass spectrometer 1 of this embodiment will be described. The components contained in the liquid sample to be analyzed are separated over time in the LC section 10, and each component is introduced into the ESI nozzle 211 of the ionization section 21, where each component is ionized into positive ions or negative ions. These ions pass through the first ion guide 221 and the second ion guide 222 and are introduced into the pre-quadrupole mass filter 231.

[0032] The front-stage quadrupole mass filter 231 allows only those ions introduced thereinto to pass that have an m / z value corresponding to the voltage applied between the rod-shaped electrodes by the front-stage QMF voltage power supply 237. In the collision cell 232, the ions that have passed through the front-stage quadrupole mass filter 231 are fragmented by colliding with CID gas molecules. The rear-stage quadrupole mass filter 233 allows only those ions fragmented in the collision cell 232 to pass that have an m / z value corresponding to the voltage applied between the rod-shaped electrodes by the rear-stage QMF voltage power supply 238. By changing the applied voltage, the m / z values ​​of the ions passing through the rear-stage quadrupole mass filter 233 are sequentially changed, and these ions are sequentially detected by the ion detector 24 as follows to obtain a mass spectrum.

[0033] In the ion detector 24, a CD voltage is applied between the CD241 and the SEM242 as described above. If the ions emitted from the rear-stage quadrupole mass filter 233 are negative ions, the negative ions are directed toward the CD241 side by a force from the electric field directed from the CD241 to the SEM242, which is formed by the CD voltage such that the CD241 side is positive and the SEM242 side is negative. The ions then move toward the CD241 side and collide with the surface of the CD241. This causes positive ions to be emitted as secondary particles from the surface of the CD241. The emitted positive ions are directed toward the SEM242 by a force from the electric field, enter the SEM242, and are detected. If the ions emitted from the rear-stage quadrupole mass filter 233 are positive ions, the negative ions are directed toward the CD241 side by a force from the electric field directed from the CD241 to the SEM242, which is formed by the CD voltage such that both the CD241 and the SEM242 are at negative potentials and the CD241 side is at a lower potential than the SEM242. The negative ions then move toward the CD241 side and collide with the surface of the CD241. As a result, negative ions or electrons are emitted as secondary particles from the surface of the CD 241 and enter the SEM 242. Whether the ions emitted from the rear-stage quadrupole mass filter 233 are negative ions or positive ions, the recesses 2413 formed on the surface of the CD 241 facing the ion optical axis C allow the secondary particles emitted from the surface of the CD 241 to be focused and enter the SEM 242.

[0034] (3) Effects of the mass spectrometer of this embodiment To explain the effects of the mass spectrometer 1 of this embodiment, we will first describe an example (Non-Patent Document 1) in which the intensity (number) of positive ions emitted as secondary ions was measured when negative ions as primary ions were collided with various targets composed of different constituent elements. In this example, monovalent oxygen ions, O - The target is irradiated with an ion beam having an energy of 13.5 keV. The emission intensities of positive ions from the main constituent elements of the target can be read from the diagram in Non-Patent Document 1, as shown in the table below. [Table 1]

[0035] Thus, when the target's constituent element is any of Ti, V, and Cr, positive secondary ions are obtained with a greater intensity (approximately 3 to 5 times greater) than when the target is made of Al or Fe (the main constituent elements of stainless steel), which are materials used in conventional CDs. Note that for each constituent element listed as a comparative example in the table above, the intensity of the secondary ions is either similar to that of Al (in the case of manganese (Mn)) or weaker than that of Al (in the case of magnesium (Mg), silicon (Si), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn)).

[0036] According to the mass spectrometer 1 of this embodiment, at least the portion of the surface of the CD 241 facing the ion optical axis C is the surface layer 2412 containing Cr, which has a higher emission intensity of positive ions (secondary ions) than conventional Al or stainless steel (Fe), as described above. This makes it possible to generate a larger number of positive ions when negative ions collide with the CD than with conventional CDs made entirely of Al, stainless steel, etc. This increases the detection sensitivity of negative ions in the ion detector 24, thereby enabling highly sensitive quantification of components such as PFASs and haloacetic acids that are ionized into negative ions in the ionization unit 21.

[0037] This effect is not only exhibited when the surface layer 2412 is mainly composed of Cr oxide as in the present embodiment, but also when it is composed of Cr simple substance or a Cr compound other than an oxide. Furthermore, the above effect is also exhibited when the surface layer 2412 is mainly composed of Ti or V simple substance or a compound, which have the same emission intensity of positive ions (secondary ions) as Cr, or an alloy or compound of two or three of Ti, V, and Cr.

[0038] Next, we present the results of an experiment to measure the detection intensity of negative ions using the mass spectrometer 1 of this embodiment and two conventional mass spectrometers with the same configuration as this embodiment, except that they used conventional CDs made only of Al or stainless steel. In this experiment, the same concentration and amount of a sample containing perfluorooctane sulfonic acid (PFOS, molecular weight 500.13), a type of PFAS, was introduced into each of the mass spectrometers of this embodiment and the two conventional examples. The negative ions (m / z = 80) generated by cleavage of PFOS were detected using an ion detector. The experimental results are shown in Figure 3. If the detection sensitivity of the conventional example using CDs made only of stainless steel is set to 1, the detection sensitivity of the conventional example using CDs made only of Al is approximately 1, which is similar to that of stainless steel, while the detection sensitivity of this embodiment is approximately 1.8. Thus, the mass spectrometer 1 of this embodiment can detect PFOS negative ions with a detection sensitivity approximately 1.8 times higher than the two conventional examples. Here, the experiment was conducted using PFOS as an example, but it is believed that this embodiment will also improve detection sensitivity compared to the two conventional examples when measuring PFASs other than PFOS or substances other than PFASs that generate negative ions, such as haloacetic acids.

[0039] Next, we present the results of an experiment to measure the detection intensity of positive ions using the mass spectrometer 1 of this embodiment and a conventional mass spectrometer using a conventional CD made entirely of stainless steel. In this experiment, the ion detector of each of the mass spectrometers of this embodiment and two conventional examples detected positive ions (m / z = 197) generated by the cleavage of reserpine (molecular weight 608.68), a drug used as a tranquilizer and antihypertensive. The experimental results are shown in Figure 4. If the detection sensitivity of the conventional example using a CD made entirely of stainless steel is set to 1, the detection sensitivity of this embodiment was approximately 1.8. As such, the mass spectrometer 1 of this embodiment can achieve higher detection sensitivity for both negative ions and positive ions than the conventional mass spectrometers.

[0040] The above experimental results show that when the surface layer 2412 is mainly composed of chromium oxide, the detection sensitivity for negative ions and positive ions is improved compared to conventional examples. However, it is believed that the detection sensitivity for negative ions and positive ions will also be improved when the surface layer 2412 is made of a material other than an oxide, such as Cr, or a compound thereof, or when titanium or vanadium, or a compound thereof, is used.

[0041] (4) Modifications The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0042] For example, in the above embodiment, a CD241 was used in which a surface layer 2412 containing one or more elements selected from Ti, V, and Cr was provided near the surface of a substrate 2411 made of Al, stainless steel, or the like. However, instead, a CD2415 entirely made of a material containing one or more elements selected from Ti, V, and Cr may be used, as shown in FIG. 5.

[0043] In the above embodiment, the recess 2413 is provided on the surface of the CD 241 facing the ion optical axis C, but the recess 2413 may be omitted.

[0044] In the above embodiment, quadrupole mass filters (pre-quadrupole mass filter 231, post-quadrupole mass filter 233) are used as the ion selector, but mass filters with other configurations may also be used. Furthermore, instead of mass filters, ion traps such as a three-dimensional quadrupole ion trap consisting of a ring electrode and two endcap electrodes, or a linear ion trap consisting of four (or more) electrodes may also be used.

[0045] The mass spectrometer 1 according to the above embodiment is an LC-MS that combines an MS unit 20 and an LC unit 10. However, the present invention can also be applied to a GC-MS that combines an MS unit with a gas chromatograph (GC), or to a standalone mass spectrometer that is not combined with a chromatograph (LC, GC). Furthermore, the configuration of the MS unit 20 is not limited to that described above, and any MS unit having an ionization unit, an ion selection unit (mass filter, ion trap), and an ion detector using a conversion dynode and a secondary electron multiplier can be used. For example, the ionization unit is not limited to that using the ESI method in this embodiment, and any ionization method can be used.

[0046] [Aspect] It will be apparent to those skilled in the art that the above-described exemplary embodiments are examples of the following aspects.

[0047] (Item 1) An ion detector according to one aspect of the present invention comprises: a conversion dynode, a secondary electron multiplier, and a DC voltage application unit that applies a DC voltage between the conversion dynode and the secondary electron multiplier; Equipped with A part or the whole of the surface of the conversion dynode, including the ion collision surface with which ions collide, is made of a material containing one or more elements of titanium (Ti), vanadium (V), and chromium (Cr) at a higher density than iron and aluminum.

[0048] (Item 6) A mass spectrometer according to one aspect of the present invention comprises: an ionization unit that ionizes a substance to be analyzed; an ion selector that selects and releases ions having a specific m / z value from among the ions ionized by the ionization unit; The ion detector according to any one of items 1 to 5 (items 2 to 5 will be described later) is disposed downstream of the ion selector.

[0049] In Non-Patent Document 1, O ions are used as primary ions for various targets made of different elements. - The results of an experiment were presented to determine the relative intensity (the value obtained by dividing the number of detected secondary ions by the number of atoms sputtered by the ion beam irradiation) of secondary ions generated when an ion beam consisting of monovalent negative oxygen ions (single-valent negative oxygen ions) was irradiated at a specific intensity (13.5 keV). According to this experiment, the relative intensity of secondary ions in a target consisting of titanium, vanadium, and chromium components was higher than that in a target consisting of iron and aluminum components.

[0050] These experimental results indicate that titanium, vanadium, and chromium have the advantage of producing a greater number of positive secondary ions when collided with negative primary ions than stainless steel (mainly composed of Fe) or aluminum, which are conventionally used materials for the conversion dynode of ion detectors. In the ion detector according to paragraph 1 and the mass spectrometer according to paragraph 6, the portion of the conversion dynode surface facing the optical axis or secondary electron multiplier, where the primary ions collide, is made of a material containing one or more of the above-described elements, titanium, vanadium, and chromium, at a higher density than iron and aluminum. This allows for high-sensitivity quantification of both positive and negative ions, i.e., regardless of ion polarity. In particular, this allows for high-sensitivity quantification of components that ionize to negative ions, such as PFAS and haloacetic acids, which have traditionally been difficult to quantify with high sensitivity.

[0051] Titanium, vanadium and / or chromium may be present in the form of a simple substance in the portion where the primary ions collide, or may be present as a compound such as an oxide.

[0052] The ion selector may be a mass filter such as a quadrupole mass filter or an ion trap such as a quadrupole ion trap. The ion selector used in the present invention may be any that can select and release at least negative ions having a specific m / z, and may also be capable of releasing positive ions having a specific m / z in addition to negative ions. The ionization unit and ion selector (mass filter, ion trap, etc.) may be the same as those used in conventional mass spectrometers.

[0053] (Item 2) The ion detector according to item 2 is the ion detector according to item 1, wherein the conversion dynode comprises a substrate made of a material different from the substance, and a surface layer made of the substance provided on part or the entire surface of the substrate, and part or the entire surface of the surface layer is the ion collision surface.

[0054] According to the ion detector of paragraph 2, the detection sensitivity of the negative ions in the ion detector can be increased by selecting a material for the substrate depending on the overall shape and cost of the conversion dynode, and providing a surface layer made of the material. The substrate can be made of stainless steel, aluminum, or the like, for example.

[0055] Since the surface layer is gradually sputtered by incident primary ions during use, it is desirable that the surface layer have a certain thickness (for example, 0.1 μm or more).

[0056] (Item 3) The ion detector according to item 3 is the ion detector according to item 2, wherein the substance is chromium oxide.

[0057] (Item 4) The ion detector according to item 4 is the ion detector according to item 3, wherein the surface layer is made of a plated film.

[0058] Of the titanium, vanadium, and chromium components of the surface layer listed in paragraph 1, chromium can easily form a film on the metal surface by wet plating. In such a film, chromium exists in the form of an oxide (usually Cr2O3, where Cr is +3). In other words, with the ion detectors according to paragraphs 3 and 4, a surface layer can be easily formed on the surface of the base material by plating, allowing the use of a conversion dynode that is easy to fabricate.

[0059] (Item 5) The ion detector according to item 5 is the ion detector according to any one of items 2 to 4, wherein the base material is made of a material containing 90% or more of aluminum.

[0060] According to the ion detector of item 5, by using a base material made of a material containing 90% or more of aluminum, mechanical processing can be performed more easily during fabrication than with a base material made of stainless steel or the like. [Explanation of symbols]

[0061] 1...Mass spectrometer 10...Liquid chromatograph (LC) section 20…Mass spectrometry (MS) department 21...Ionization section 211...Electrospray ionization (ESI) nozzle 221...First ion guide 222...Second ion guide 231...Pre-quadrupole mass filter (part of the ion selection section) 232...Collision cell 2321...Quadrupole ion guide 233...Post-quadrupole mass filter (part of the ion selection section) 237…Pre-stage QMF voltage power supply section 238…Post-stage QMF voltage power supply section 24...Ion detector 241, 2415...Conversion dynode (CD) 2410...Ion impact surface 2411…Base material 2412…Surface layer 2413...recess 242…Secondary electron multiplier (SEM) 243...CD voltage power supply section 244...SEM operation power supply section 25...Control unit 28...Chamber 280...Ionization chamber 281...First intermediate vacuum chamber 282...Second intermediate vacuum chamber 283…High vacuum chamber 291...Heated capillary 292...Skimmer 293...pore C...Ion optical axis

Claims

1. a conversion dynode, a secondary electron multiplier, and a DC voltage application unit that applies a DC voltage between the conversion dynode and the secondary electron multiplier; An ion detector in which a part or the entire surface of the conversion dynode, including the ion collision surface with which ions collide, is made of a material containing one or more elements of titanium, vanadium, and chromium at a higher density than iron and aluminum.

2. 2. The ion detector according to claim 1, wherein the conversion dynode comprises a substrate made of a material different from the substance, and a surface layer made of the substance provided on a part or all of the surface of the substrate, the surface of the surface layer being the ion collision surface.

3. 3. The ion detector of claim 2, wherein the material is chromium oxide.

4. 4. The ion detector according to claim 3, wherein the surface layer is made of a plating film.

5. 3. The ion detector according to claim 2, wherein the substrate is made of a material containing at least 90% aluminum.

6. an ionization unit that ionizes a substance to be analyzed; an ion selector that selects and releases ions having a specific m / z value from among the ions ionized by the ionization unit; the ion detector according to any one of claims 1 to 5, which is arranged downstream of the ion selector; A mass spectrometer having:

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