JP2004294453A - Ion source, mass spectrometric method, and mass spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve separative power of a mixed sample in a liquid chromatograph/mass spectrometer by enabling the use of a movable-phase solvent containing hardly volatile salts. <P>SOLUTION: After the sample separated by a liquid chromatograph 14 is sprayed by an electrostatic spray part 15, heated and vaporized by a vaporization part 5, obtained gaseous sample molecules are ionized by protonation reaction etc. by chemical reaction at an ionization part 6 provided with a corona discharge part, introduced to a high-vacuum part 12 from ion inlet apertures 9a and 9b, and analyzed at a mass analyzing part 13. The salts contained in a solution are converted into gaseous ions and their tracks are bent by electric field in the vicinity of the ion inlet apertures, and the ion inlet apertures are prevented from being blocked by the deposition of the hardly volatile salts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an apparatus in which a liquid chromatograph and a mass spectrometer are combined, that is, a liquid chromatograph / mass spectrometer, which is used for separating and analyzing a biologically related mixed sample such as a sugar, a peptide, and a protein.

  At present, in the field of analysis, development of mass spectrometry for biologically relevant substances has been emphasized. Since bio-related substances are usually dissolved in a solution as a mixture, development of an apparatus for connecting a means for separating a mixture to a mass spectrometer has been advanced. As a typical apparatus of this method, there 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, whereas a mass spectrometer (hereinafter abbreviated as MS) is highly sensitive and has an excellent ability to identify a substance, Analysis is difficult. Therefore, LC / MS using MS as an LC detector is very effective for analyzing a mixture.

Referring to FIG. 8, LC / MS using the conventional atmospheric pressure chemical ionization method described in Analytical Chemistry, 1988, vol. 60, p. 774 [Analytical Chemistry, 60 , 774 (1988)] will be described. .

  The sample solution eluted from the LC is introduced into the metal tube 3 via the pipe 1 and the connector 2. The metal tube 3 is embedded in a 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 the spraying are introduced into the vaporizing section 5 constituted by the heated metal block 4b. The sample molecules vaporized in the vaporization section 5 are introduced into the ionization section 6. The ionization section 6 is provided with a needle electrode 7. A high voltage of several kV is applied to the needle-shaped electrode 7 by a high-voltage power supply 8a to generate a corona discharge in the ionization unit 6.

  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 relating to the sample molecule A are generated mainly by the following proton addition reaction or proton desorption reaction.

A + BH + → AH ++ B (proton addition reaction)
A + B ⁻ → (A−H) ⁻ + BH (proton elimination reaction)
Therefore, in the prior art shown in FIG. 8, a hydronium ion (H ₃ O +) is generated by causing a corona discharge in the atmosphere, and an ion relating to the sample A is generated by utilizing the following reaction between the hydronium ion and the sample molecule A. Generates AH +.

_{A + H 3 O + → AH} ++ H 2 O
In the ionization section 6, ions related to the sample generated by the chemical reaction represented by the above-described reaction pass through the ion introduction pore 9a, the differential exhaust section 11 exhausted by the exhaust system 10a, and the ion introduction pore 9b. Is introduced into the high vacuum section 12 evacuated to a high vacuum by the exhaust system 10b. The ions introduced into the vacuum are subjected to mass analysis in the mass analyzer 13.

Analytical Chemistry, 1988, 60, 774 [Analytical Chemistry, 60, 774 (1988)]

For LCs with detectors other than MS, for example, an LC with an ultraviolet absorption detector that detects a sample by a change in the absorbance of ultraviolet light, a mobile phase containing a non-volatile salt is used to improve the separation performance and the reproducibility of the elution time of the sample. A solvent may be used. However, when a mobile phase solvent containing a non-volatile salt is used for LC / MS, this salt precipitates around the ion introduction pore for introducing ions from the atmosphere into the vacuum, and the ion introduction pore is formed. It will be blocked. For this reason, in LC / MS, it is difficult to use a mobile phase solvent containing a non-volatile salt, and it was not possible to perform an analysis sufficiently utilizing the high separation ability of LC.
For these reasons, there is a need for an LC / MS that is less susceptible to the effects of non-volatile salts in the mobile phase solvent and that can fully utilize the high separation capability of LC.

  An object of the present invention is to make it possible to use a mobile phase solvent containing a hardly volatile salt, which has been difficult to use in conventional LC / MS.

  In the present invention, the sample solution sent from the LC is atomized by an electrostatic spraying method, and gaseous sample molecules obtained by vaporizing the obtained droplets are ionized by a chemical reaction. The above object is achieved by analyzing with a MS.

  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 spraying unit 15 together with the mobile phase solvent. The vaporization of the droplets obtained by the spraying is promoted in the vaporization section 5. The gaseous sample molecules generated in the vaporization section 5 are ionized by a chemical reaction in the ionization section 6. Ions related to the sample generated in the ionization section 6 are introduced into the ion introduction holes 9a, the differential exhaust section 11 exhausted by the exhaust system, 9b through the ion introduction pores, and the high vacuum section 12 exhausted by the exhaust system. You. The ions introduced into the vacuum are subjected to mass analysis in the mass analyzer 13.

  The ionization section 6 may be provided in the differential exhaust section 11. The differential evacuation unit 11 has a pressure of several Pascals to several hundreds Pascals, and collisions between sample molecules and a reaction gas occur, so that ions can be generated by chemical reaction. In the vaporizing section 5, a vaporizing means such as a heated metal block or infrared irradiation can be used.

  Since the mobile phase solvent sent from the LC is electrostatically sprayed, the salts that are dissociated and ionized in the solvent are converted into gaseous ions only by spraying. For this reason, the ions derived from the salt are trapped by the metal block constituting the vaporizing portion, or the trajectory is bent by the potential applied to the needle electrode provided in the ionizing portion, 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 introduction pores, and there is no possibility of blocking the ion introduction pores. For the above reasons, the LC / MS of the present invention can use a mobile phase solvent containing a hardly volatile salt, which has been conventionally difficult to use.

  According to the present invention, it is possible to use a mobile phase solvent containing a hardly volatile salt, which 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.

  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 via the pipe 1 and the connector 2. A 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 supply 8b. Fine droplets generated by the 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 droplets generated by the spraying are vaporized by heat while passing through the opening of the metal block 4b.

The sample molecules vaporized in the vaporization section 5 are introduced into the ionization section 6. The ionization section 6 is provided with a needle electrode 7. By applying a high voltage of several kV to the needle electrode 7 by the high voltage power supply 8a, a corona discharge is generated in the ionization section 6.
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 non-volatile salts in the solvent are dissociated into ions, they are converted into gaseous ions only by electrostatic spraying.

  The ions derived from the salt are captured by the metal block 4b constituting the vaporizing section 5, or the trajectory is bent by the potential applied to the needle electrode 7 provided in the ionizing section 6, so that the ion introduction pore 9a Can not be reached. Therefore, even when a mobile phase solvent containing a hardly volatile salt is used, the salt does not precipitate around the ion introduction pore 9a, and there is no possibility that the ion introduction pore 9a is closed. Therefore, the LC / MS of the present invention can use a mobile phase solvent containing a hardly volatile salt, which has been conventionally difficult to use, and enables LC / MS analysis to make full use of the LC separation ability. .

  When the flow rate of the solution sent from the LC is large and it is difficult to maintain stable electrostatic spraying, a splitter 16 is provided as shown in FIG. 3 may be introduced. Also, as shown in FIG. 2, the spraying gas 17 may be supplied from outside the metal tube 3 to assist electrostatic spraying.

  When the flow rate of the solution sent from the LC is small and it is difficult to maintain the electrostatic spray stably, or when the viscosity or the electric conductivity of the solution is too high, it is difficult to maintain the electrostatic spray stably. In some cases, as shown in FIG. 2, the spray auxiliary solution 18 is supplied from the outside of the metal tube 3 and mixed with the solution sent from the LC to obtain conditions such as flow rate, viscosity, electric conductivity, and the like. May be adjusted to a condition that enables stable electrostatic spraying.

The distal end of the metal tube 3 may be provided in the vaporizing section 6 as shown in FIG. Alternatively, as shown in FIG. 3, the solution may be directly sprayed 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 a high voltage power supply 8b. Insulation between the metal tube 3 and the metal block 4b 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, and gaseous sample molecules are obtained. When the sample molecules reach the corona discharge portion, they undergo a chemical reaction with primary ions such as hydronium ions generated by corona discharge, and ionization of the sample molecules is achieved. The ions related to the sample molecules are pumped to about 10 ⁻³ Pa by the evacuation system 10b through the differential evacuation unit 11 evacuated to about several tens Pa to several hundreds Pa by the ion introduction pore 9a and the evacuation system 10a. It is taken into the unit 12 and subjected to mass analysis by the mass analysis unit 13.

  As shown in FIG. 3, an inclined wall is provided inside the metal block 4b, electrostatic spraying is performed obliquely toward the inclined wall, and the sample is directed toward the ionizing section. Gas 20 such as nitrogen. It is desirable that the gas 20 be heated to room temperature or higher in advance.

  Further, in the configuration shown in FIG. 2, if large droplets are generated by electrostatic spraying, the vaporized portion 5 by the heated metal block 4b cannot be completely vaporized, and corona discharge is generated by the needle-shaped electrode 7. In some cases, the droplets may reach the ionized part 6 as they are. When the droplet reaches the portion where the corona is generated, there is a possibility that the needle-shaped electrode 7 and the ion introduction pore 9a are short-circuited and the high-voltage power supply 8a or the like breaks down.

  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 corona discharge is generated by the needle-shaped electrode 7, and the electrode 21a is provided on the electrode 21a. Electrostatic spraying may be performed. In this case, it is desirable that the electrode 21a is heated by the heater 22a in order to increase the vaporization efficiency of the droplet. According to the configuration shown in FIG. 4, only gaseous molecules are carried to the ionization unit 6 and ionized, so that a short circuit caused by a droplet adhering to the needle electrode 7 is avoided. In FIG. 4, the shape of the electrode 21a is not limited to a plate, and may be a mesh. In order to increase the efficiency at which the sample molecules reach the ionization unit 6, the gas 20 may be flowed toward the ionization unit 6 as in FIG.

  In the embodiment shown in FIG. 2 to FIG. 4, a configuration in which a heated metal block is used as a means for vaporizing droplets has been described, but a method of irradiating infrared rays or the like may be used for vaporizing droplets.

  FIG. 5 shows an embodiment in which infrared irradiation is used for the vaporizing means. The sample solution is electrostatically sprayed by a voltage applied between the metal tube 3 and the mesh 23a. This mesh 23a is desirably heated. The droplets obtained by spraying are sent to the vaporizing section 5. In the vaporization unit 5, the droplets are irradiated with infrared rays radiated from the heater 22b connected to the power supply 24 to vaporize the droplets. When the heater 22b is deteriorated due to 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 vaporizing the droplets, it is desirable that the water vapor in the atomizing gas 17 be removed. Further, the spray gas 17 is desirably heated to a 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-shaped electrode 7.

  The structure shown in FIGS. 2 to 5 allows the use of a mobile phase solvent containing a hardly volatile salt in LC / MS. If necessary, as shown in FIG. 6, the ion 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. This electrode 21b is desirably heated to a temperature higher than the boiling point of the solution.

  The non-volatile salt is deposited on the electrode 21b. Volatile sample molecules are vaporized and introduced into the ionization unit 6 via the heated metal block 4b. In order to improve the efficiency with which the sample molecules reach the ionization unit 6, an air supply port 26 may be provided to allow the gas 20 such as dry nitrogen to flow toward the ionization unit 6. This gas 20 is preferably heated. Further, an exhaust port 27 is provided, and by exhausting gas from the exhaust port to the outside, an airflow is generated in a direction of the ionization unit 6 from a portion where the solution is sprayed, and sample molecules are efficiently introduced to the ionization unit 6. Is also good.

  In FIG. 6, the electrostatic spraying method is described as a method for spraying the solution. However, when the solution is sprayed in a direction perpendicular to the central axis of the ion introduction pore 9a, a spraying method other than the electrostatic spraying, for example, heating spraying or super spraying is used. Ultrasonic spraying or the like may be used.

  Further, in the structure shown in FIG. 6, since the non-volatile salt precipitates on the electrode 21b, maintenance can be easily performed by removing and cleaning only the electrode 21b.

  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. This mesh 23b is desirably heated. A saucer 28 can be provided on the back of the mesh 23b, maintenance can be easily performed by replacing the saucer 28, and the solution collected in the saucer 28 can be separated and analyzed by methods other than mass spectrometry, such as fluorescence. Or luminescence analysis or immunological analysis.

FIG. 1 is a schematic diagram illustrating a configuration of a mass spectrometer according to the present invention. FIG. 3 is an explanatory diagram of one embodiment of the present invention. The figure which shows the Example which provides the front-end | tip of a metal tube in a vaporization part, and sprays a sample solution directly to a metal block. The figure which shows the Example which provided the shielding plate for preventing a large droplet from flying and reaching the ionization part. The figure which shows the Example which uses infrared irradiation for the vaporization method of a vaporization part. The figure which shows the Example which sprays in the direction perpendicular | vertical to the central axis of an ion introduction pore. The figure which shows the Example using the saucer which stores a droplet. The figure which shows the structure of the conventional liquid chromatograph / mass spectrometer using the atmospheric pressure chemical ionization method.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 1 ... Piping, 2 ... Connector, 3 ... Metal tube, 4a, 4b ... Metal block, 5 ... Vaporization 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 unit, 12: High vacuum unit, 13: Mass spectrometer, 14: Liquid chromatograph, 15: Electrostatic spray unit, 16: Splitter, 17: Spray gas , 18: spray auxiliary solution, 19: insulating tube, 20: gas, 21a, 21b: electrode, 22a, 22b: heater, 23a, 23b: mesh, 24: power supply, 25: glass tube, 26: air supply port, 27 ... exhaust vent, 28 ... pan.

Claims (14)

  A spraying section for spraying a sample separated by liquid chromatography using a mobile phase solvent containing a hardly volatile salt together with the mobile phase solvent, a vaporizing section for vaporizing droplets generated by the spraying section by heating, An ion source comprising: an ionization unit that ionizes gaseous sample molecules generated in a vaporization unit by a chemical reaction.   2. The ion source according to claim 1, wherein the spraying unit sprays the sample together with the mobile phase solvent by any one of an electrostatic spraying method, an ultrasonic spraying method, and a heating spraying method. Ion source.   2. The ion source according to claim 1, wherein the ionization unit has a needle-like electrode for generating a corona discharge.   A metal tube into which the sample solution eluted from the liquid chromatograph is introduced, a metal block for electrostatically spraying the sample solution by applying a voltage between the metal tube, and a corona discharge by applying the voltage And a needle-like electrode for generating the ions and ionizing the sample molecules in the sample solution.   A metal tube into which a sample solution eluted from the liquid chromatograph is introduced, a mesh electrode for electrostatically spraying the sample solution by applying a voltage between the metal tube, and a corona discharge by applying a voltage And an ionization unit including a needle-like electrode for ionizing sample molecules in the sample solution. The sample solution is electrostatically sprayed toward the mesh electrode, and the mesh electrode is an end of the metal tube. An ion source that shields the ionization part from the liquid and prevents droplets generated by electrostatic spray from adhering to the needle electrode.   A spraying step in which a sample separated by liquid chromatography is sprayed together with a mobile phase solvent, a vaporizing step for promoting the vaporization of droplets obtained in the spraying step, and a gaseous sample molecule obtained in the vaporizing step A mass spectrometry method comprising: an ionization step of ionizing by a chemical reaction; and a mass spectrometry step of mass spectrometry of ions relating to the sample obtained in the ionization step.   7. The mass spectrometric method according to claim 6, wherein, in the spraying step, the sample solution is sprayed by any one of an electrostatic spraying method, an ultrasonic spraying method, and a heating spraying method. Analysis method.   An atomization step of atomizing and spraying a sample solution eluted from a liquid chromatograph for separating a mixed sample in a solution, and ionizing a gaseous sample obtained by vaporizing droplets obtained in the atomization step. A mass spectrometry method comprising: an ionization step of jetting out; and a mass spectrometry step of performing mass spectrometry on ions of the sample obtained in the ionization step.   9. The mass spectrometry method according to claim 8, wherein a direction of spraying of the sample solution in the atomization step and a direction of ejection of ions related to the sample generated in the ionization step are perpendicular directions. Mass spectrometry method.   9. The mass spectrometry method according to claim 8, wherein a direction of spraying the sample solution in the atomizing step and a direction of ejecting ions of the sample generated in the ionizing step are perpendicular to each other, The mass spectrometry method, wherein, in the atomizing step, the sample solution is atomized and sprayed by any one of electrostatic spraying, heating spraying, and ultrasonic spraying.   An atomization step of atomizing a sample solution eluted from a liquid chromatograph for separating a mixed sample in a solution by an electrostatic spraying method, and a gaseous state obtained by vaporizing droplets obtained in the atomization step. A mass spectrometry method comprising: an ionization step of ionizing a sample molecule by a chemical reaction; and a mass spectrometry step of mass spectrometry of ions related to the sample molecule.   An atomization step of atomizing a solution containing a sample eluted from a liquid chromatograph that separates a mixed sample in a solution by an electrostatic spray method, and a vaporization step of vaporizing droplets obtained in the atomization step, An ionization step of generating a discharge at a needle-shaped electrode provided in a passage through which a vaporized gas passes to generate ions of the sample passing through the passage; and mass analysis of ions of the sample generated in the ionization step Mass spectrometry step of performing mass spectrometry.   Atomization means for atomizing and spraying a sample solution eluted from a liquid chromatograph for separating a mixed sample in a solution, and ionizing a gaseous sample obtained by vaporizing droplets obtained by the atomization means Ionization means for causing ejection, and mass spectrometry means for taking in ions relating to the sample through the ion introduction hole and performing mass spectrometry, wherein the direction of spraying of the sample solution and the central axis of the introduction hole intersect. A mass spectrometer, wherein the atomization means and the mass analysis means are disposed on the mass spectrometer.   14. The mass spectrometer according to claim 13, wherein the atomizing means uses any one of electrostatic spraying, heating spraying, and ultrasonic spraying.

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