JP3618262B2 - Mass spectrometer and its ion source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a device that combines a liquid chromatograph and a mass spectrometer, that is, a liquid chromatograph / mass spectrometer, which is used for separating and analyzing biologically related mixed samples such as sugars, peptides, and proteins.
[0002]
[Prior art]
Currently, in the field of analysis, development of mass spectrometry for biological materials is regarded as important. Since biological substances are usually dissolved in a solution as a mixture, development of a device that couples a means for separating the mixture and a mass spectrometer is underway. A typical apparatus for this method is a liquid chromatograph / mass spectrometer (hereinafter abbreviated as LC / MS). A liquid chromatograph (hereinafter abbreviated as LC) is excellent in separating a mixture but cannot identify a substance. On the other hand, a mass spectrometer (hereinafter abbreviated as MS) has high sensitivity and excellent substance identification ability. Analysis is difficult. Therefore, LC / MS using MS as an LC detector is very effective for analysis of a mixture.
[0003]
FIG. 8 illustrates LC / MS using the conventional atmospheric pressure chemical ionization method described in Analytical Chemistry, 1988, Vol. 60, p. 774 [Analytical Chemistry, 60 , 774 (1988)]. .
[0004]
The sample solution eluted from the LC is introduced into the metal tube 3 through the pipe 1 and the connector 2. The metal tube 3 is embedded in the metal block 4a. The sample solution introduced into the metal tube 3 is sprayed by heating the metal block 4a by a heating means such as a heater. Fine droplets generated by spraying are introduced into the vaporizing section 5 constituted by the heated metal block 4b. The sample molecules vaporized in the vaporization unit 5 are introduced into the ionization unit 6. The ionization unit 6 is provided with a needle-like electrode 7. By applying a high voltage of several kV to the needle electrode 7 by a high voltage power supply 8a, a corona discharge is generated in the ionization section 6.
[0005]
In the atmospheric pressure chemical ionization method, when A is a sample molecule to be analyzed and B is a molecule of a reaction gas, ions related to the sample molecule A are generated mainly by the following proton addition reaction or proton desorption reaction.
[0006]
A + BH + → AH ++ B (proton addition reaction)
A + B ⁻ → (A−H) ⁻ + BH (proton elimination reaction)
Therefore, in the prior art shown in FIG. 8, hydronium ions (H ₃ O +) are generated by causing corona discharge in the atmosphere, and ions AH + relating to sample A are utilized by utilizing the following reaction with sample molecules A. Is generated.
[0007]
A + H ₃ O + → AH ++ H ₂ O
In the ionization unit 6, ions related to the sample generated by the chemical reaction represented by the reaction shown above pass through the differential introduction part 11 and the ion introduction hole 9b exhausted by the ion introduction pore 9a and the exhaust system 10a. Then, it is introduced into the high vacuum portion 12 that has been exhausted to a high vacuum by the exhaust system 10b. The ions introduced into the vacuum are subjected to mass analysis by the mass analyzer 13.
[0008]
[Problems to be solved by the invention]
In a detector other than MS, for example, an LC having an ultraviolet absorption detector that detects a sample by a change in absorbance of ultraviolet rays, a mobile phase containing a hardly volatile salt is used to improve the reproducibility of the separation ability and elution time of the sample. A solvent may be used. However, when a mobile phase solvent containing a hardly volatile salt is used for LC / MS, this salt precipitates around the ion introduction pore for introducing ions from the atmosphere to the vacuum, and the ion introduction pore is formed. It will be blocked. For this reason, in LC / MS, the mobile phase solvent containing a hardly volatile salt is difficult to use, and analysis using the high separation ability of LC could not be performed.
[0009]
For these reasons, there is a need for LC / MS that is less susceptible to non-volatile salts in mobile phase solvents and that can fully utilize the high separation performance of LC.
[0010]
An object of the present invention is to make it possible to use a mobile phase solvent containing a hardly volatile salt, which is difficult to use with conventional LC / MS.
[0011]
[Means for Solving the Problems]
In the present invention, the sample solution sent from the LC is atomized by an electrostatic spray method, and gaseous sample molecules obtained by vaporizing the obtained droplets are ionized by a chemical reaction, and ions related to the sample molecules are ionized. Is achieved by MS analysis.
[0012]
FIG. 1 is a schematic diagram showing the configuration of the LC / MS of the present invention. The sample separated by the LC 14 is sprayed by the electrostatic spray unit 15 together with the mobile phase solvent. The vaporization of the droplets obtained by spraying is promoted in the vaporization unit 5. Gaseous sample molecules generated in the vaporization unit 5 are ionized by a chemical reaction in the ionization unit 6. Ions related to the sample generated in the ionization section 6 are introduced into the ion introduction pore 9a, the differential exhaust section 11 exhausted by the exhaust system, 9b through the ion introduction pore, and the high vacuum section 12 exhausted by the exhaust system. The The ions introduced into the vacuum are subjected to mass analysis by the mass analyzer 13.
[0013]
The ionization unit 6 may be provided in the differential exhaust unit 11. The differential evacuation unit 11 has a pressure of several to hundreds of pascals, and collision between the sample molecules and the reaction gas occurs, so that ions can be generated by a chemical reaction. Moreover, in the vaporization part 5, vaporization means, such as a heated metal block and infrared irradiation, can be used.
[0014]
Since the mobile phase solvent sent from the LC is electrostatically sprayed, the salt that is dissociated and becomes ions in the solvent is converted into gaseous ions just by spraying. For this reason, the ions derived from the salt are trapped in the metal block that constitutes the vaporization part, or the trajectory is bent by the potential applied to the needle electrode provided in the ionization part, so that the ions reach the ion introduction pore. Can not. Therefore, even when a mobile phase solvent containing a hardly volatile salt is used, the salt does not precipitate around the ion-introduced pores, and the ion-introduced pores are not clogged. For the above reasons, the LC / MS of the present invention can use a mobile phase solvent containing a hardly volatile salt that has been difficult to use in the past.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a diagram showing a more detailed structure of the configuration shown in FIG. The sample solution eluted from the LC is introduced into the metal tube 3 through the pipe 1 and the connector 2. The sample solution is electrostatically sprayed by applying a voltage of several kV between the metal tube 3 and the metal block 4b by the high voltage power source 8b. Fine droplets generated by spraying are introduced into the vaporizing section 5 constituted by the heated metal block 4b. The metal block 4b is heated to about 300 ° C. by a heater (not shown). The droplet generated by spraying is vaporized by heat while passing through the opening of the metal block 4b.
[0016]
The sample molecules vaporized in the vaporization unit 5 are introduced into the ionization unit 6. The ionization unit 6 is provided with a needle-like electrode 7. By applying a high voltage of several kV to the needle electrode 7 by a high voltage power supply 8a, a corona discharge is generated in the ionization section 6.
[0017]
When the gaseous sample molecules obtained by vaporization of the droplets reach the corona discharge portion, they undergo a chemical reaction with primary ions such as hydronium ions generated by the corona discharge, thereby achieving ionization of the sample molecules. At this time, since the hardly volatile salt in the solvent is dissociated into ions, it is converted into gaseous ions only by electrostatic spraying.
[0018]
Since the ions derived from the salt are captured by the metal block 4b constituting the vaporization section 5, or the trajectory is bent by the potential applied to the needle-like electrode 7 provided in the ionization section 6, the ion introduction pore 9a. Cannot reach. Therefore, even when a mobile phase solvent containing a hardly volatile salt is used, the salt does not precipitate around the ion-introducing pores 9a, and the ion-introducing pores 9a are not clogged. Therefore, the LC / MS of the present invention can use a mobile phase solvent containing a hardly volatile salt, which has been difficult to use in the past, and can perform LC / MS analysis making full use of the separation ability of LC. .
[0019]
When the flow rate of the solution sent from the LC is large and it is difficult to stably maintain electrostatic spraying, as shown in FIG. 2, a splitter 16 is provided, and only a part of the solution is placed in a metal tube. 3 may be introduced. Similarly, as shown in FIG. 2, the spraying gas 17 may be flowed from the outside of the metal tube 3 to assist the electrostatic spraying.
[0020]
If the flow rate of the solution sent from the LC is small and it is difficult to maintain a stable electrostatic spray, or the viscosity and electrical conductivity of the solution are too high to maintain a stable electrostatic spray. In some cases, as shown in FIG. 2, the spray auxiliary solution 18 is allowed to flow from the outside of the metal tube 3 and mixed with the solution sent from the LC, so that conditions such as flow rate, viscosity, electrical conductivity, etc. May be adjusted to conditions under which electrostatic spraying can be stably maintained.
[0021]
The tip of the metal tube 3 may be provided in the vaporizing section 6 as shown in FIG. Similarly, as shown in FIG. 3, the solution may be sprayed directly toward the metal block 4b. The sample solution is electrostatically sprayed between the metal tube 3 and the metal block 4b by a high voltage applied from the high voltage power source 8b. Insulation between the metal tube 3 and the metal block 4 b is performed by an insulating tube 19. The droplets sprayed on the metal block 4b heated to a temperature higher than the boiling point of the solution are instantaneously vaporized to obtain gaseous sample molecules. When the sample molecules reach the corona discharge portion, they undergo a chemical reaction with primary ions such as hydronium ions generated by the corona discharge, and ionization of the sample molecules is achieved. Ions relating to the sample molecules are exhausted to about 10 ⁻³ Pa by the exhaust system 10 b through the differential exhaust section 11 exhausted by the ion introduction pore 9 a and the exhaust system 10 a to about several tens of Pa to several hundred Pa. The mass analysis unit 13 performs mass analysis.
[0022]
In order to increase the arrival efficiency of the sample molecules to the ionization part, as shown in FIG. 3, an inclined wall is provided inside the metal block 4b, and electrostatic spraying is performed obliquely toward the inclined wall and directed toward the ionization part. Alternatively, a gas 20 such as nitrogen may be flowed. The gas 20 is preferably heated to room temperature or higher in advance.
[0023]
Further, in the configuration shown in FIG. 2, if large droplets are generated by electrostatic spraying, the vaporization part 5 by the heating metal block 4 b cannot be completely vaporized, and a corona discharge is generated by the needle-like electrode 7. In some cases, the ionization unit 6 that has been in the form of droplets may be reached. When the droplet reaches the portion where the corona is generated, there is a possibility that the needle-like electrode 7 and the ion introduction pore 9a are short-circuited and the high-voltage power supply 8a or the like is broken.
[0024]
In order to prevent this, as shown in FIG. 4, an electrode 21a is arranged so as to shield the end of the metal tube 3 and the ionized portion 6 where the corona discharge is generated by the needle-like electrode 7, and the electrode 21a is arranged on the electrode 21a. You may make it spray electrostatically. In this case, the electrode 21a is preferably heated by the heater 22a in order to increase the vaporization efficiency of the droplets. With the configuration shown in FIG. 4, only gaseous molecules are transported to the ionization unit 6 and ionized, so that a short circuit due to the droplets adhering to the needle-like electrode 7 is avoided. In FIG. 4, the shape of the electrode 21a is not limited to a plate shape, and may be a mesh. In order to increase the efficiency with which the sample molecules reach the ionization unit 6, the gas 20 may flow toward the ionization unit 6 as in FIG. 3.
[0025]
In the embodiment shown in FIGS. 2 to 4, a configuration in which a heated metal block is used as a means for vaporizing droplets is shown. However, a method of irradiating infrared rays may be used for vaporizing droplets.
[0026]
FIG. 5 shows an embodiment in which infrared irradiation is used as the vaporizing means. The sample solution is electrostatically sprayed by a voltage applied between the metal tube 3 and the mesh 23a. The mesh 23a is preferably heated. The droplets obtained by spraying are sent to the vaporization unit 5. In the vaporization unit 5, the droplets are irradiated with infrared rays emitted from the heater 22b connected to the power source 24 to vaporize the droplets. In the case where the heater 22b is deteriorated by the direct contact of the droplets with the heater 22b, a glass tube 25 for protecting the heater 22b may be provided inside the heater 22b. In order to improve the efficiency of vaporization of the droplets, it is desirable that the water vapor in the atomizing gas 17 is removed. The atomizing gas 17 is preferably heated to room temperature or higher. The gaseous sample molecules obtained in the vaporization section 5 are ionized in the ionization section 6 where hydronium ions and the like are generated by corona discharge by the needle electrode 7.
[0027]
The structure shown in FIGS. 2 to 5 makes it possible to use a mobile phase solvent containing a hardly volatile salt in LC / MS. However, when a very high concentration salt is used or analysis takes a long time. If necessary, as shown in FIG. 6, it may be sprayed in a direction perpendicular to the central axis of the ion introduction pore 9a. The sample solution introduced into the metal tube 3 is sprayed toward the opposing electrode 21b. The electrode 21b is preferably heated to the boiling point of the solution or higher.
[0028]
The hardly volatile salt is deposited on the electrode 21b. Volatile sample molecules are vaporized and introduced into the ionization section 6 through the heated metal block 4b. In order to improve the efficiency with which the sample molecules reach the ionization unit 6, a gas supply port 26 may be provided and a gas 20 such as dry nitrogen may flow toward the ionization unit 6. The gas 20 is preferably heated. Further, by providing an exhaust port 27 and exhausting gas from the exhaust port to the outside, an air flow in the direction of the ionization unit 6 is generated from a portion where the solution is sprayed, and sample molecules are efficiently introduced to the ionization unit 6. Also good.
[0029]
In FIG. 6, the electrostatic spraying method is described as a method of spraying the solution. However, when spraying in the direction perpendicular to the central axis of the ion introduction pore 9a, a spraying method other than electrostatic spraying, for example, heating spraying or super Sonic spraying or the like may be used.
[0030]
Further, in the structure shown in FIG. 6, since the hardly volatile salt is deposited on the electrode 21b, the maintenance can be easily performed by removing and cleaning only the electrode 21b.
[0031]
FIG. 7 is a diagram illustrating a configuration in which spraying is performed toward the mesh 23b instead of the counter electrode 21b illustrated in FIG. The mesh 23b is preferably heated. A saucer 28 can be provided on the back of the mesh 23b, and maintenance can be easily performed by exchanging the saucer 28. In addition, the solution accumulated in the saucer 28 is separated, and an analysis method other than mass spectrometry, for example, fluorescence Analytical methods using luminescence and immunological analysis can be performed.
[0032]
【The invention's effect】
According to the present invention, it is possible to use a mobile phase solvent containing a hardly volatile salt that has been difficult to use in conventional LC / MS. For this reason, the high separation ability of LC can be fully utilized, the applicable range of LC / MS is expanded, and more substances can be analyzed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a mass spectrometer according to the present invention.
FIG. 2 is an explanatory diagram of an embodiment of the present invention.
FIG. 3 is a view showing an embodiment in which a tip of a metal tube is provided in a vaporizing section and a sample solution is directly sprayed toward a metal block.
FIG. 4 is a view showing an embodiment in which a shielding plate is provided for preventing large droplets from flying and reaching an ionization unit.
FIG. 5 is a diagram showing an embodiment in which infrared irradiation is used for a vaporization method of a vaporization unit.
FIG. 6 is a view showing an embodiment in which spraying is performed in a direction perpendicular to the central axis of the ion introduction pore.
FIG. 7 is a view showing an embodiment using a saucer for collecting droplets.
FIG. 8 is a diagram showing a configuration of a liquid chromatograph / mass spectrometer using a conventional atmospheric pressure chemical ionization method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piping, 2 ... Connector, 3 ... Metal pipe, 4a, 4b ... Metal block, 5 ... Evaporation part, 6 ... Ionization part, 7 ... Needle electrode, 8a, 8b ... High voltage power supply, 9a, 9b ... Ion introduction fine Holes, 10a, 10b ... exhaust system, 11 ... differential exhaust part, 12 ... high vacuum part, 13 ... mass analysis part, 14 ... liquid chromatograph, 15 ... electrostatic spray part, 16 ... splitter, 17 ... gas for spraying 18 ... Spray auxiliary solution, 19 ... Insulating tube, 20 ... Gas, 21a, 21b ... Electrode, 22a, 22b ... Heater, 23a, 23b ... Mesh, 24 ... Power source, 25 ... Glass tube, 26 ... Air inlet, 27 ... exhaust vent, 28 ... sallet.

Claims (12)

A liquid chromatograph for separating a mixed sample in the solution; a sample solution supply means for supplying a sample solution eluted from the liquid chromatograph; an atomizing means for atomizing and spraying the sample solution; An ionization means for ionizing a gaseous sample obtained by vaporizing the droplets obtained by the vaporization means, and a mass analysis means for performing mass spectrometry by taking in ions related to the sample through the ion introduction pores, The atomization means and the mass analysis means are arranged so that the spray direction of the sample solution and the central axis of the ion introduction pore are perpendicular to each other. Total. A liquid chromatograph for separating a mixed sample in a solution, an atomizing means for atomizing a sample solution containing the sample obtained by separation by the liquid chromatograph by electrostatic spraying, and the atomizing means An ionization means for ionizing the gaseous sample obtained by vaporizing the droplet, and a mass analysis means for taking in the ions related to the sample through the ion introduction pores and performing mass spectrometry, and A mass spectrometer characterized in that the atomizing means and the mass analyzing means are arranged so that the direction of spraying and the central axis of the introduction pore are perpendicular to each other. The mass spectrometer according to claim 1 or 2, wherein the ionization means is made to ionize by a chemical reaction. 3. The mass spectrometer according to claim 1, further comprising vaporization means for vaporizing the droplets generated by the atomization means by heating. The mass spectrometer according to claim 1, further comprising a shielding unit that is in front of the ionizing unit and shields a part of the droplet generated by the atomizing unit. The mass spectrometer according to claim 1 or 2, wherein the ionization means includes a needle-like electrode that generates electric discharge. The mass spectrometer according to claim 1, wherein the atomizing means is configured by using any one of an electrostatic spraying method, a heating spraying method, and an ultrasonic spraying method. 6. The mass spectrometer according to claim 5, wherein the blocking means includes means for performing the shielding by applying an electric field. A liquid chromatograph for separating a mixed sample in a solution, an atomization means for atomizing and spraying a sample solution eluted from the liquid chromatograph, and a liquid droplet obtained by the atomization means is obtained by vaporization Ionizing means for ionizing and ejecting a gaseous sample, and the atomizing means and the ionization so that the direction of spraying the sample solution and the direction of ejecting ions related to the sample are perpendicular to each other. And an ion source. A liquid chromatograph for separating a mixed sample in the solution; an atomizing means for atomizing and spraying the sample solution eluted from the liquid chromatograph by electrostatic spray; and a droplet obtained by the atomizing means. An ionization means for ionizing and ejecting a gaseous sample obtained by crystallization, and the atomization so that the direction of spraying the sample solution and the direction of ejecting ions with respect to the sample are perpendicular to each other An ion source comprising: means and the ionization means. The ion source according to claim 9 or 10, wherein the ionization means includes a needle-like electrode for generating discharge. The ion source according to claim 9, wherein the atomizing means is configured by using any one of an electrostatic spraying method, a heating spraying method, and an ultrasonic spraying method.

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