JP3039933B2 - Mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an apparatus for combining a liquid chromatograph and a mass spectrometer, which is particularly important for the separation and analysis of biological substances, that is, an improvement of an ion source in a liquid chromatograph / mass spectrometer.

[Prior art]

At present, in the field of analysis, development of a liquid chromatograph / mass spectrometer is emphasized. For reference, FIG. 7 shows the entire configuration of a liquid chromatograph / mass spectrometer using a double focusing mass spectrometer comprising an electric field and a magnetic field as the mass spectrometer. The sample in the solution eluted from the liquid chromatograph 1 is introduced into the ion source 19 through the pipe 9. The ion source 19 is controlled by a power source 14 for the ion source. The ions related to the sample molecules generated by the ion source 19 are introduced into the vacuum through the pores. Further, it is introduced into the mass analyzer 12 composed of the electric field analyzer 12a and the magnetic field analyzer 12b and subjected to mass analysis. The mass-analyzed ions are detected by the ion detector 20, and the detection signal is transmitted to the data processing device via the signal line 10.
Sent to 15. At this time, the electric field analyzer 12a and the magnetic field analyzer 1
The mass analysis unit 12 composed of 2b is exhausted by an appropriate exhaust system 13. By the way, the principle of the liquid chromatograph / mass spectrometer is simple as described above, but the liquid chromatograph deals with a sample in a solution, whereas the mass spectrometer deals with a sample in a gas. The development of this device has been very difficult. Several methods have been proposed to solve this challenge, but the typical ones are analytical
Chemistry 1983, vol. 55, p. 750. There is a thermospray method. As shown in FIG.
In this method, a sample solution containing an electrolyte such as ammonium acetate from a liquid chromatograph is sprayed by a heated capillary 2 into a vacuum of several Torr or less, and when the droplets generated by the spray are vaporized, In this method, ions to be generated are introduced into the mass spectrometer through the pores 7'a of the electrode 7 'with pores located in a direction perpendicular to the traveling direction of the spray flow to perform mass analysis. In FIG. 8, reference numeral 16 denotes a heater,
4 'is a temperature sensor such as a thermocouple. In the above-mentioned conventional method, as shown in FIG. 3 (a), when the mobile phase in the liquid chromatograph is water, an ionic current cannot be obtained, and therefore, as shown in FIG. Add ammonium. At this time, a high ion current (peak at 250 ° C) is obtained when the capillary tip temperature is less than 300 ° C. However, in this region, protonated molecules in which protons are added to the molecule, such as ammonium ions, are observed. is there. However, in this conventional method, a high ion current is obtained when the proton affinity of the molecule to be observed is high, but there is a problem that a substance having a low proton affinity such as sugar or lipid has a low ion current.

[Problems to be solved by the invention]

As described above, the conventional technique has a problem that a high ion current cannot be obtained when measuring a sugar or lipid having a weak proton affinity. Accordingly, an object of the present invention is to provide a mass spectrometer capable of extracting a sufficient amount of ions from the gas phase and performing mass spectrometry even in the case of sugars or lipids having a weak proton affinity.

[Means for Solving the Problems]

The object of the present invention is to provide a mass spectrometer using a spray ion source that ionizes the sample molecules by spraying a solution containing the sample molecules from the tip of the heatable metal capillary. At 300 ° C. or higher to operate the ion source. At this time, the pores for introducing the generated ions into the mass spectrometry section are formed in the capillary in order to efficiently introduce the ions generated at the center of the spray flow from the capillary tip into the mass spectrometry section. It is desirable to arrange the pores such that the central axis of the pore is located on the extension of the central axis.

[Operation]

As a result of the study of the present inventors, by setting the temperature at the tip of the capillary in the spray ion source to 300 ° C. or higher, by positioning a pore for introducing ions to the mass spectrometer on the central axis of the capillary, It was confirmed that cations dissolved in the solution were added to molecules such as sugars and lipids, and were taken out as gaseous molecules into the gas phase, and that they could be efficiently introduced into the mass spectrometer.

【Example】

Hereinafter, an embodiment of the present invention will be described with reference to FIG. Here, a case where a double focusing mass spectrometer including an electric field analyzing unit and a magnetic field analyzing unit is used will be described as an example, but another type of mass spectrometer such as a quadrupole mass spectrometer may be used. Needless to say. FIGS. 1A and 1B show the configuration of an ion source portion according to an embodiment of the present invention. The difference between FIGS. 1 (a) and 1 (b) is that the capillary 2 to be heated is placed under atmospheric pressure as shown in FIG. 1 (a), or a rotary pump as shown in FIG. 1 (b). Exhaust with a number
The only difference is that they are arranged under a reduced pressure of about Torr. The merit of positioning the capillary 2 under atmospheric pressure is that the exhaust system is simplified, while the capillary 2
Is positioned under reduced pressure, the vacuum of the mass spectrometer does not deteriorate even if the tip of the capillary 2 is positioned very close to the first electrode 6 with pores, which is effective in increasing the sensitivity. However, the result obtained with either mode is the same. The sample in the solution that is separated by the liquid chromatograph 1 and eluted from the column is introduced into the metallic capillary 2. The capillary 2 is capable of heating and controlling the temperature. The capillary 2 may be heated indirectly by welding a metallic block having a cartridge heater built therein, thereby heating the capillary.
It may be heated directly by energizing itself. FIG. 1 shows the latter case of direct electric heating. The heating of the capillary 2 is controlled by a heating power supply 5 with a temperature control function and a thermocouple 4. Reference numeral 3 denotes an energizing terminal. The sample solution that passes through the heated capillary 2 and is sprayed from the tip is heated and vaporized, but a part of the solution is released as ions. What is important at this time is the temperature of the tip portion of the capillary 2. FIG. 2 clearly shows this difference. With the conventional thermospray method, ions are not generated unless a solution such as an aqueous solution of ammonium acetate is used, and when the solution is used at a flow rate of 1 ml / min, an ion current is obtained only at the tip of the capillary. In contrast to the case where the temperature is lower than 300 ° C., in the present invention, ions are generated even when simple water is used, and the ion current is measured when the temperature at the tip of the capillary 2 is 300 ° C. or higher (the peak is 450 ° C.). ). As can be seen from this figure, the temperature at the tip of the capillary 2 is 300 ° C.
It is good to use above, and it is good to use in the range of 400-500 ° C desirably. The optimum temperature is 450 ° C. The generated ions are introduced into the high-vacuum mass spectrometer through the pores 6a of the first electrode 6 and the pores 7a of the second electrode 7 which are present on the central axis of the capillary 2. As shown in FIG. 4, in the conventional thermospray method, the traveling direction 11 of the spray flow emitted from the tip of the capillary 2 is perpendicular to the axis of the pore 7'a for introducing ions into a high vacuum. Although the direction 17 of ion extraction and the direction 11 of the spray flow are perpendicular to each other, in the present invention, the direction 11 of the spray flow emitted from the tip of the capillary 2 is different from the pore 6a of the first electrode 6 and the second The electrode 7 is arranged so as to coincide with the axis of the pore 7a. That is, the pore
6a is provided on the extension of the central axis of the capillary 2, and the ion extraction direction 18 coincides with the spray flow direction 11. With this arrangement, even if the temperature of the tip portion of the capillary 2 is increased, as shown in FIGS.
Whether the mobile phase is water or ammonium acetate, a sufficient ion current can be obtained. On the other hand, the first electrode 6 and the second electrode 7 are electrically insulated by an insulator 8 such as a ceramic plate, and a voltage is applied between the two electrodes. Further, the space between the electrodes 6 and 7 can be exhausted.
The voltage applied between the electrodes 6 and 7 is such that when ions are introduced from the pores 6 a of the first electrode 6, the cluster ions generated by adiabatic expansion are accelerated and collide with neutral molecules, resulting in the analysis. This is for cleaving unfavorable cluster ions. As described above, the ions passing through the first electrode pore 6a and the second electrode pore 7a are further subjected to mass analysis by a double focusing mass spectrometer comprising an electric field analysis unit and a magnetic field analysis unit. Will be detected. By the way, looking at the mass spectra obtained by the conventional method and the present invention, the difference becomes clearer (see FIG. 5). In the conventional thermospray method, the background ions observed at 250 ° C. are mainly ammonium ions and their cluster ions, but in the present invention, the ions observed at 450 ° C. are hydronium ions (H ₃ O ⁺ ) and cations (Na ⁺ , K ⁺ ). In this way, if the temperature of the heating part of the capillary is increased and sufficient heat is applied to the liquid in the capillary to promote vaporization, even ions with large solvation energies such as cations (Na ⁺ , K ⁺ ) It turns out that it can observe enough. As shown in FIG. 6, sucrose (a kind of sugar) having a low proton affinity but a strong cation affinity is measured. Although (M + H) ⁺ is observed but the intensity is not so strong, the method of adding a cation according to the present invention employs a cation-added molecule (M + N).
a) ⁺ is strongly obtained, which also indicates the superiority of the present invention.

【The invention's effect】

According to the present invention, sugars that have been difficult to ionize by the ionization method in a conventional liquid chromatograph / mass spectrometer,
Even for substances such as lipids, Na ⁺ ,
It becomes possible to add K ⁺ cations, take them out as a cation addition molecule in the gas phase, and perform mass spectrometry, and detect substances such as sugars and lipids with high sensitivity.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are diagrams each showing a configuration of an ion source portion of a liquid chromatograph / mass spectrometer according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) show conventional methods. 3 (a) to 3 (d) show a comparison between the operating temperature ranges of the ion source according to the present invention and the ion source according to the present invention, and FIGS. FIG. 4 is a curve diagram showing the comparison of currents, FIG. 4 is a schematic diagram illustrating the difference in configuration between the ion source according to the conventional method and the ion source according to the present invention, and FIGS. 6 (a) and 6 (b) are diagrams showing a comparison of mass spectra obtained by the ion source according to the present invention and the ion source according to the present invention.
Is a diagram showing a comparison of mass spectra of sucrose (a kind of sugar) obtained by an ion source according to a conventional method and an ion source according to the present invention, and FIG. 7 is a schematic configuration of a liquid chromatograph / mass spectrometer. FIG. 8 is a block diagram of an ion source according to a conventional method. 1 ... liquid chromatograph, 2 ... capillary, 3 ...
... Terminal for electric heating, 4... Thermocouple, 5... Heating power supply with temperature control function, 6... 1st electrode with pores, 6a... 1st electrode pore, 7. , 7a: second electrode pore, 8: insulator, 9: piping, 10: signal line, 12
…… Mass spectrometer, 13… Vacuum pump, 14… Power supply for ion source, 15… Data processor, 19… Ion source, 20…
Ion detector.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-127453 (JP, A) JP-A-63-193454 (JP, A) JP-A-1-270660 (JP, A) JP-A-2- 260364 (JP, A) JP-A-1-276560 (JP, A) JP-A-59-190655 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 49/00-49 / 48

Claims (9)

(57) [Claims] 1. A passage for guiding a solution containing a sample into an ionization space, a heating means provided at an end of the passage, a pore, and a high vacuum space from which ions to be analyzed are taken out. The ion source is configured, wherein the solution guided through the passage is ionized in an ionization space, and the ions are guided to the high vacuum space through the pores and extracted from the high vacuum space, The ion source, wherein the heating means is heated at a temperature of 300 ° C. or more at which the solution is sprayed from the passage into the ionization space, whereby the solution is sprayed into the ionization space and ionized. 2. The ion source according to claim 1, wherein said passage comprises a capillary. 3. The ion source according to claim 1, wherein said capillary comprises a metal capillary. 4. The ion source according to claim 1, wherein said heating means is a heating means provided around said passage and having a built-in heater. 5. The ion source according to claim 1, wherein the pressure in said ionization space is in the range of several Torr to atmospheric pressure. 6. A passage for introducing a solution containing a sample into an ionization space, a pore, and a high vacuum space from which ions to be analyzed are taken out, wherein said solution introduced through said passage is provided. The ion source is ionized in an ionization space, wherein the ions are guided to the high vacuum space through the pores, and are extracted from the high vacuum space, wherein the passage is a passage having a heating function, An ion source characterized in that the solution is sprayed into the ionization space and is ionized by being heated at a temperature of 300 ° C. or higher at which the solution is sprayed into the ionization space by a passage. 7. The ion source according to claim 6, wherein said passage has a structure heated by energization. 8. A passage for introducing a solution containing a sample into an ionization space, a heating means provided at an end of the passage, a pore, a high vacuum space for extracting ions to be analyzed, A mass spectrometer for analyzing ions extracted from the pores into the high vacuum space, wherein the heating means heats the solution at a temperature of 300 ° C. or more at which the solution is sprayed from the passage into the ionization space, A mass spectrometer characterized in that the solution is sprayed into an ionization space and ionized. 9. A system comprising a passage for introducing a solution containing a sample into an ionization space, a pore, and a high vacuum space from which ions to be analyzed are taken out. A mass spectrometer comprising: means for heating to a temperature of 300 ° C. or higher to be sprayed and ionizing only by the heated spray; and a mass spectrometer for capturing and analyzing generated ions.