JPS6215747A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To accurately fix the kind of observed ions, by providing a vacuum heating gas evacuation means in an ionizing section to clean up a sample gas feed system and the ionizing section to exactly determine the spectral intensity of an analyzed sample. CONSTITUTION:An ionizing section 2 is provided with a gas evacuation pipe 14 and a gas evacuation means 15. A heater 16 is provided for a gas introduction pipe 8, the ionizing section 2 and the gas evacuation pipe 14. A contaminative substance such as a solid or gaseous impurity which is clinging to or adsorbed in the walls of the pipe 8 and the ionizing section 2 is removed by vacuum heating gas evacuation for cleaning. As a result, cluster ions of the contaminative substance other than a measured sample are not generated in cluster ions produced in the ionizing section 2. An exact spectrum of the analyzed sample is thus obtained to accurately fix the kind of observed ions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement in a mass spectrometer, particularly a mass spectrometer having a mechanism for dissociating cluster ions generated by atmospheric pressure ionization and ion-molecule reactions.

[Background of the invention]

As a means of analyzing trace impurities in gases, a method has been developed and put into practical use that efficiently ionizes a sample under a pressure of several Torr to one atmosphere, introduces the sample in the form of ions into a mass spectrometer through a pore, and analyzes it. has been done.

[Analytical Chemistry
lChemistry), Volume 45, No. 6, No. 93
See pages 6-943 (May 1973), Vol. 46 of the same magazine, No. 6, pages 706-710 (May 1974), and Japanese Patent Application No. 78293/1974]. This method generates ions in two steps: primary ionization by corona discharge or Nip ray irradiation under 1 atm, and secondary ionization by subsequent ion-molecule reactions, which makes it more effective than conventional electron impact ionization methods. It has a high sensitivity of 3 to 6 orders of magnitude, and
There is little decomposition of sample molecules, and a simple and easy-to-interpret spectrum can be obtained.

FIG. 1 shows an atmospheric pressure ionization mass spectrometer equipped with a corona discharge needle electrode 1 as an ionization means, and an ionization section 2. Intermediate pressure section 3. It consists of a mass spectrometer section 4 connected by pores 5 and 6, respectively.

In the same figure, a sample 7 contained in a carrier gas passes through a gas introduction pipe 8 and is delivered to an ionization section 2 by a corona discharge needle electrode 1.
The ions of the molecules to be measured are primary ionized, and then secondary ionization is performed by an ion-molecule reaction, and the generated ions of the molecules to be measured pass through the pores 5 to the intermediate pressure section 3 . This intermediate pressure section 3 is maintained at approximately I Torr by the primary exhaust 9.

Next, it passes through the second pore 6, enters the mass spectrometer 4 which is subjected to secondary exhaust 10, is subjected to mass analysis by a mass spectrometer, and is then detected by a detector 11. Note that the intermediate pressure section 3 is provided with an ion focusing electrode 12 that applies a centripetal electric field so that the ions are focused onto the second pores 6 . Further, an ionization means 13 for calibration is provided upstream of the mass spectrometer 4. In the figure, it is an electron impact ion source.

Various gases such as nitrogen, air, oxygen, argon, or helium can be used as carriers for introducing the sample 7, but nitrogen gas is most commonly used. Therefore, the case where nitrogen gas is used as the carrier gas will be described in detail below.

In the sample 7, primary ions are generated by the corona discharge needle electrode 1 in the ionization section 2 at atmospheric pressure.

-order ions are N+ or N2° generated by ionization of nitrogen, which is the majority component. These immediately react with nitrogen to give N4+ and N,+.

Corona discharge N2 → N”, N2”N”+
2 N2 → Nff”+H.

Nage+2N2 → N4+ten N2N4++
02 → o2++2N2N4”+H,
O→ N20++2N2 H20”+2N, → N20+・N2+
N20□"+H, O+N2-+ O,"-H, O+N
2H20”・N2+H20+ H-401+OH1N2
O2+・N20+H, ○ → H, O+・OH+
02H30"・OR+H20-*H" (N20)
2+0HH309+ Hzo+N2 → H”
(N20> z+N2H”(H,O), 1+H20+
N, → H” (N20), +NzH” (H, O),, 1
+M+H-) MH", (H,o),-t)I+・
MAs shown in these reactions, oxygen, water, etc. that exist as trace impurities in nitrogen are directly ionized from N4''. Molecules with low ionization potential and molecules with large proton affinity (M) are water cluster ions. H
'''(N20), -□H+.H are generated.The generated ions containing M and H''(N20)- are stable and do not change even if they collide with nitrogen. In this way, MH” and (+(,
Q), 11("・Ions such as H increase in number with each collision, selectively ionizing sample molecules and producing many types of cluster ions. In this way, clusters generated at atmospheric pressure is introduced into the intermediate pressure section (approximately I Torr) 3 through the first pore 5.
When a voltage (hereinafter referred to as a drift voltage) is applied to the pores 5 and 6 at both ends of the cluster, an electric field is formed, and the cluster starts to drift in the direction of the electric field. This electric field allows the ions to be efficiently focused on one point, resulting in electric field concentration of the ions, but at the same time, the internal energy of the ions is excited. In other words, the cluster is accelerated by the drift electric field,
It has kinetic energy and collides with neutral molecules that are carrier gas. At this time, part of the kinetic energy of the cluster is vibration of the cluster.

Some of it is given to internal energy such as rotation, and some of it is given to neutral molecules. Excitation of such internal degrees of freedom is performed every time there is a collision. If there are enough collisions, the cluster will eventually dissociate from the weaker bonds. The kinetic energy of ions can be controlled by changing the drift voltage, so by increasing the drift voltage, dissociation starts from the weaker cluster bonds.

In this way, cluster ions generated by ionized molecular reactions under atmospheric pressure are dissociated by collisional excitation with neutral molecules in the aforementioned electrolytic region near I Torr, and the ions are identified from the state of the dissociation change. The generation and dissociation processes of various cluster ions can be inferred, and since there is a correlation between the dissociation energy of cluster ions and the electric field strength in the electrolytic region, it is possible to estimate the dissociation of cluster ions. These facts provide useful information for fixing the observed ion species.

As explained above, atmospheric pressure ionization mass spectrometers utilize ion-molecule reactions under 1 atm to efficiently ionize components in gases for mass spectrometry. Great care must be taken with the gas introduction system.

In particular, spectra of trace impurities and impure gases emitted from the tube wall of the sample gas introduction pipe 8 and the inner wall of the ionization section 2 appear in the sample spectrum. Figure 2 shows a background spectrum when nitrogen gas is used as a carrier using an atmospheric pressure ionization mass spectrometer in which the inner walls of the sample introduction pipe 8 and the ionization section 2 have not been sufficiently purified.
(,”,NH,”H,O.

Alternatively, ・t-ons such as C, H5'', C, H,'' due to hydrocarbons are observed.

As described above, with conventional atmospheric pressure mass spectrometers, it is difficult to estimate the dissociation of generated cluster ions, and
This method has the disadvantage that it becomes difficult to fix the observed ion species, which significantly reduces the accuracy of mass spectrometry.

[Purpose of the invention]

Therefore, the purpose of the present invention is to solve the above-mentioned difficulties of conventional atmospheric pressure mass spectrometers, to obtain the correct analytical spectrum intensity of the sample, and to obtain analytical accuracy that can accurately fix the observed ion species. The objective is to provide an improved mass spectrometer.

[Summary of the invention]

In order to achieve the above object, the present invention provides a vacuum evacuation means in the ionization section, further provides a heating heater in the sample gas introduction pipe and the ionization section, and performs vacuum heating and degassing. It is characterized in that it is configured to remove and clean impurity substances and impure gases that have adhered to or adsorbed on the introduction pipe or the inner wall of the ionization section.

[Embodiments of the invention] The present invention will be explained below using examples.

FIG. 3 shows an atmospheric pressure ionization mass spectrometer according to the present invention, which is provided with a heater in the sample gas introduction conduit and the ionization section, and equipped with vacuum degassing means. Hereinafter, in FIG. 3, parts having the same reference numerals as those in FIG. 1 represent the same things, and therefore their description will be omitted here.

As shown in FIG. 3, the ionization section 2 is provided with an evacuation pipe 14 and evacuation means 15, and the gas introduction pipe 8, the ionization section 2, and the evacuation pipe 14 are further provided with a heating heater 16. The structure is such that contaminants such as impurities and impure gases adhering to and adsorbed on the channel 8 and the inner wall of the ionization section 2 are cleaned by vacuum heating and exhaust gas removal. In an atmospheric pressure ionization mass spectrometer, the ionization section 2 is a region where cluster ions are generated due to ionized molecular reactions, so the sample 7 introduced into the ionization section may adhere to the gas introduction pipe 8 or the inner wall of the ionization section 2. Since the adsorbed contaminants are simultaneously generated as cluster ions, a contaminant spectrum is generated in the sample spectrum, making it difficult to fix the ionic species and significantly reducing analysis accuracy. Therefore,
In the atmospheric pressure ionization mass spectrometer, the gas introduction pipe 8 of the sample 7
It is important to clean the inside wall of the ionization section 2.

In this embodiment, the gas introduction pipe 8. The ionization 2 and vacuum exhaust pipes are heated (200 to 300°C) to perform vacuum heating and degassing to remove impurity substances and impurity gases that have adhered to or adsorbed to the gas introduction pipe 8 and the ionization section 2, and to clean them. Figure 4 shows a case where the primary exhaust 9 of the intermediate pressure section 2 is used as a vacuum heating degassing means to achieve the same effect as explained in Figure 3; The secondary exhaust 10 of the mass spectrometer can also be used. In the figure, 17 is a separate valve provided in the vacuum exhaust pipe 14.

In this way, according to the above embodiment, among the cluster ions generated in the ionization section 2, cluster ions of impurity substances and impure gases other than the sample to be measured due to the dirty window are no longer generated, and the correct analysis spectrum of the sample is obtained. It is possible to estimate the dissociation of cluster ions and identify the observed ion species accurately and accurately.

FIG. 5 shows a background spectrum when nitrogen gas is used as a carrier after thorough cleaning according to this example.

〔Effect of the invention〕

As explained above, according to the present invention, cluster ions of impurity substances and impure gases due to contamination other than the sample to be measured are generated in the cluster ions generated in the ionization section.
><7> Since the dissociation of cluster ions can be easily estimated and a correct spectrum of the sample can be obtained, the ion species can be accurately identified. This can significantly improve mass spectrometry accuracy.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a conventional atmospheric pressure ionization mass spectrometer, Fig. 2 is a background spectrum when nitrogen gas is used as a carrier in the conventional device, and Figs. 3 and 4 are diagrams showing an example of the present invention. FIG. 5 is a cross-sectional view of an atmospheric pressure ionization mass spectrometer, and FIG. 5 shows a background spectrum when nitrogen gas is used as a carrier in an apparatus according to an embodiment of the present invention. 2... Ionization section, 3... Intermediate pressure section, 4... Mass spectrometry section, 5, 6... Pore, 7... Sample, 8...
Sample introduction pipe, 9... Primary exhaust, 10... Secondary exhaust, 14... Vacuum exhaust pipe, 15... Vacuum exhaust, 16.
・Heating heater. 7ρ＼ Agent Patent Attorney Ogawa Layer, Male... ゝ、 Figure 1 'fJ2 Figure Tomi 5 Figure %, ? ? L/z 33 Figure 4

Claims (1)

[Claims] 1. An ionization section into which a sample is introduced, an intermediate pressure section where differential pumping is performed and has an ion focusing means, and a mass spectrometry section, the ionization section and the intermediate pressure section An atmospheric pressure ionization mass spectrometer in which a mass spectrometer and a mass spectrometer are connected by a slit, characterized in that the ionization section is provided with a vacuum heating degassing means to purify the sample gas supply system and the ionization section. mass spectrometer. 2. The mass spectrometer according to claim 1, characterized in that the mass spectrometer is constituted by an exhaust device independently provided with a vacuum heating degassing exhaust means. 3. The vacuum heating degassing exhaust means is configured to purify the sample gas supply system and the ionization section using an exhaust device of an intermediate pressure section or a mass spectrometry section. Mass spectrometer as described in section.