JP4400284B2 - Liquid chromatograph mass spectrometer - Google Patents

Description

  The present invention relates to a liquid chromatograph mass spectrometer using a mass spectrometer as a detector of a liquid chromatograph.

  Various detectors are used in liquid chromatographs depending on the purpose of analysis and the type of sample. In recent years, liquid chromatograph mass spectrometry using a mass spectrometer with high component selectivity and qualitative analysis capability as a detector. An apparatus (hereinafter referred to as “LC / MS”) has been actively used. In LC / MS, an atmospheric pressure ionization interface is used to convert sample components contained in a liquid sample eluted from the column of the LC section into gas ions. As typical atmospheric pressure ionization methods, an electrospray ionization method (ESI), an atmospheric pressure chemical ionization method (APCI), and the like are known.

  In ESI, a high voltage of about several kV is applied to the tip of a nozzle into which a liquid sample is introduced to generate a strong unequal electric field. When the liquid sample flows through the nozzle, the electric field is separated by this electric field and atomized so as to be torn off by the Coulomb attractive force. Gas ions are generated in the process of evaporating the solvent in the droplets by touching the surrounding dry air. Based on these principles, ESI is suitable for ionization of highly polar compounds and thermally unstable compounds, but is not suitable for low polarity or nonpolar compounds. On the other hand, in APCI, a needle electrode is disposed in front of the tip of a nozzle, and carrier gas ions generated by corona discharge from the needle electrode are chemically reacted with droplets of a liquid sample atomized by heating at the nozzle. Perform ionization. From such a principle, APCI is suitable for ionization of a compound having a relatively low polarity to a polar compound, but is not suitable for a highly polar compound or a thermally unstable compound.

  In conventional LC / MS, analysis can be performed by switching the atmospheric pressure ionization interface between ESI and APCI (for example, by exchanging probes). However, as described above, the compounds suitable for ionization are different. When analyzing a sample whose kind of substance is completely unknown, if analysis is performed only with one of the atmospheric pressure ionization interfaces, there is a possibility that an analysis leakage may occur. However, it is very troublesome to perform the measurement twice by switching the atmospheric pressure ionization interface, and an extra amount of sample is required. In addition, nonpolar compounds and low polarity compounds, particularly those with lower polarity, cannot be ionized even by APCI, or even if ionized, the sensitivity is very low and impractical.

  In order to make up for the analysis omission in such a mass spectrometer, a method of using another detector of a conventionally known liquid chromatograph in combination is also conceivable. That is, a liquid sample eluted from a column of a liquid chromatograph is branched and one is introduced into a mass spectrometer, and the other is introduced into an ultraviolet-visible spectrophotometer or an evaporative light scattering detector so that detection can be performed simultaneously. . An LC / MS described in Patent Document 1 is known as such an apparatus. In this LC / MS, a part of the fine droplet sprayed from the nozzle of the atmospheric pressure ionization interface is sucked into the evaporation tube, and the vaporization of the solvent in the droplet is promoted when passing through the evaporation tube, The scattered light is detected by irradiating a laser beam to the target compound. Thereby, the analysis of the sample by the mass analyzer and the analysis by the evaporative light scattering detector can be performed in parallel.

  However, in such a configuration, it is inevitable that the apparatus becomes large, and it is difficult to reduce the size of the apparatus, and the price is high. In addition, forcibly sucking a part of the droplet sprayed from the nozzle in order to ionize the sample molecules reduces the amount of ions introduced into the mass analyzer and lowers the analysis sensitivity. There are also concerns.

JP 2002-372516 A

  The present invention has been made to solve the above-mentioned problems, and its main object is to make it difficult for the mass spectrometer to detect by changing / adding a simple configuration based on LC / MS. An object of the present invention is to provide a liquid chromatograph mass spectrometer capable of easily acquiring information about components in parallel with mass spectrometry.

In order to solve the above problems, the present invention provides a liquid chromatograph in which sample components contained in a sample solution eluted from a column of a liquid chromatograph are ionized by an atmospheric pressure ionization interface and detected by an ion detector for mass analysis. In the graph mass spectrometer,
a) a spraying means for spraying the sample liquid into the ionization chamber in a substantially atmospheric pressure atmosphere;
b) ion transporting means for collecting and transporting ions generated from the sample droplet sprayed by the spraying means to the subsequent stage;
c) light irradiating means for directly irradiating measurement light toward the spray flow of the sample liquid sprayed by the spraying means;
d) a light detecting means for detecting light scattered by the measurement light directly irradiated from the light irradiating means upon being sprayed and / or light after being absorbed;
e) a calculation processing unit that performs a calculation process of the detection result by the light detection unit and the detection result by the ion detector, and outputs a mass analysis result;
It is characterized by having.

  In the atmospheric pressure ionization interface, a sample liquid is sprayed with the help of, for example, a nebulization gas in an ionization chamber in an atmosphere of substantially atmospheric pressure. In the case of the atmospheric pressure chemical ionization method, the mobile phase (solvent) in the droplets is vaporized by heating, and carrier gas ions generated by corona discharge are reacted with sample molecules to perform ionization. On the other hand, in the case of the electrospray ionization method, an electric charge is applied when the droplet is sprayed, and ions are generated in the process of evaporating the mobile phase from the droplet. The ions generated in this way are collected by the ion transport means in a state where micro droplets are mixed and transported to the subsequent stage, but in the portion near the tip of the spray flow, the mobile phase in the droplet is in a vaporized state. There are many fine particles of a sample (compound). When the measurement light emitted from the light irradiating means hits such fine particles, scattering and absorption occur. Therefore, the sample can be detected by detecting the light after receiving the scattered light and absorption by the light detecting means. That is, a simple evaporative light scattering detector can be configured by the light irradiation means and the light detection means.

  In such detection by evaporation light scattering, sufficient sensitivity cannot be obtained when the mobile phase in the droplet is insufficiently evaporated in the spray flow from the spray means. In general, the density of droplets is high in the portion near the central axis in the spray flow, so that the droplets are likely to come into contact with each other to form large droplets. Not suitable. Therefore, it is preferable that the light irradiating unit emits light so that the measurement light is applied to the peripheral portion of the spray flow sprayed from the spraying unit and spreads in a substantially conical shape. According to this configuration, the measurement light is irradiated to a portion where the sample has a relatively large amount of fine particles, which is advantageous in increasing the sensitivity of the evaporative light scattering detection.

  According to the liquid chromatograph mass spectrometer according to the present invention, it is possible to obtain complementary information by evaporative light scattering detection for sample components that are difficult to be ionized by the atmospheric pressure ionization interface. Can improve the accuracy of analysis. Further, in the liquid chromatograph mass spectrometer according to the present invention, it is only necessary to provide light irradiation means and light detection means for detecting evaporated light scattering in the ionization chamber, and it is not necessary to separately provide an evaporation tube or an aspirator. The apparatus configuration is simple, and the size of the apparatus is not increased, which is advantageous in terms of cost. Furthermore, since the evaporative light scattering detection does not interfere with the collection and transport of ions used for mass analysis, the analysis sensitivity of the mass analyzer is not affected.

  Hereinafter, an LC / MS according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a main part of the LC / MS according to the present embodiment, and FIG. 2 is a configuration diagram of an atmospheric pressure ionization interface which is a feature of the present embodiment.

  In the LC unit 1, the liquid feeding unit 12 sucks the mobile phase (eluent) from the mobile phase container 11 and feeds it to the sample injection unit 13 while maintaining a constant liquid feeding amount. The sample injection unit 13 injects the sample liquid into the mobile phase at a predetermined timing. The mobile phase mixed with the sample solution is sent to the column 14 and separated for each component while passing through the column 14. Each mobile phase is eluted with a time lag and reaches the atmospheric pressure ionization interface 2.

  The atmospheric pressure ionization interface 2 includes an ionization chamber 21, and a tip portion of an ionization probe 22 connected to the end of the column 14 protrudes from the ionization chamber 21. The configuration inside the ionization chamber 21 will be described in detail later.

  In the MS unit 3, a first intermediate vacuum chamber 31 and a second intermediate vacuum chamber 34 are provided between the mass spectrometry chamber 37 and the ionization chamber 21, respectively, separated by a partition wall. In the mass analysis chamber 37, a quadrupole filter 38 and an ion detector 39 as a mass separation unit are provided. An ion lens 32 and a second ion lens 35 are provided. Between the ionization chamber 21 and the first intermediate vacuum chamber 31, a small-diameter solvent removal tube 23 is provided, and between the first intermediate vacuum chamber 31 and the second intermediate vacuum chamber 34, a very small diameter passage hole is formed at the top. It communicates through a conical skimmer 33.

The inside of the ionization chamber 21 is almost at atmospheric pressure by vaporized molecules of the liquid sample supplied from the ionization probe 22 almost continuously. The first intermediate vacuum chamber 31 is evacuated to about 10 ² [Pa] by the rotary pump 40 and the second intermediate vacuum chamber 34 is evacuated to about 10 ⁻¹ to 10 ⁻² [Pa] by the turbo molecular pump 41. Further, the inside of the mass analysis chamber 37 is evacuated to a high vacuum state of about 10 ⁻³ to 10 ⁻⁴ [Pa] by the turbo molecular pump 42. In this way, the ionization chamber 21, the first intermediate vacuum chamber 31, the second intermediate vacuum chamber 34, the mass analysis chamber 37, and the multistage differential exhaust system that increases the degree of vacuum stepwise can be used for mass analysis. A high degree of vacuum in the chamber 37 is maintained.

  The analysis operation in the atmospheric pressure ionization interface 2 and the MS unit 3 will be described. The sample liquid is sprayed into the ionization chamber 21 from the tip of the ionization probe 22, and the sample molecules in the spray flow are ionized as described later. The generated ions are drawn into the desolvation tube 23 by the differential pressure between the ionization chamber 21 and the first intermediate vacuum chamber 31 together with fine droplets that have not yet been ionized. The first ion lens 32 helps the ions to be drawn through the desolvation tube 23 by the electric field and converges the ions in the vicinity of the passage hole of the skimmer 33. The ions introduced into the second intermediate vacuum chamber 34 through the passage hole of the skimmer 33 are converged and accelerated by the second ion lens 35, and then sent to the mass analysis chamber 37 through the small hole 36. In the mass analysis chamber 37, only ions having a specific mass number pass through the quadrupole filter 38, reach the ion detector 39, and are detected as an ion current.

In the LC / MS of this embodiment, ESI or APCI can be selectively performed by exchanging the ionization probe 22.
In the case of ESI, as shown in FIG. 2A, an ionization probe 22 for spraying a sample solution is coaxial with the sample solution tube 221 to which the sample solution is supplied and surrounds the sample solution tube 221 as an outer cylinder. A high voltage is applied from the DC power source 223 to the nebulization gas pipe 222 or a metal cylinder provided around the nebulization gas pipe 222. Under the influence of the electric field due to this voltage, the sample liquid flowing through the sample liquid pipe 221 is biased to be charged, and in this state, with the help of the nebulization gas (usually N ₂ gas) ejected from the nebulization gas pipe 222, a fine droplet And erupts. The ejected microdroplets come into contact with the surrounding dry nitrogen gas, and the mobile phase and solvent in the droplets rapidly evaporate, reducing the size of the droplets. Then, the droplets are finely divided by the repulsive force of the charged charges, and gas ions derived from the sample molecules are generated in the process.

  The ionization probe 22 sprays the sample liquid in a direction substantially perpendicular to the central axis of the inlet opening of the desolvation tube 23, and the spray flow 27 proceeds while spreading in a substantially conical shape. In the process of progress, sample ions are generated as described above, and the ions are sucked into the desolvation tube 23 in a state where droplets are mixed. However, in the spray flow 27, not all samples are ionized and sucked into the desolvation tube 23. Therefore, the spray flow 27 includes a large number of sample fine particles in which the mobile phase is simply evaporated from the droplets. It is. Further, since there are compounds that are difficult to ionize in the sample, many of these compounds are present in a portion near the tip of the spray flow 27 in the form of fine particles.

  In this LC / MS, in order to detect such a sample, a light emitting source 25 that irradiates the measurement light so as to cross the spray flow 27 on the side close to the tip of the spray flow 27, and in the spray flow 27 with respect to the measurement light. And a photomultiplier tube 26 for detecting light scattered or absorbed light are arranged at appropriate positions. FIG. 3 is a schematic view of the configuration shown in FIG. 2A when viewed in a plane perpendicular to the central axis C of the spray flow 27. The optical path of the measurement light emitted from the light emission source 25 is set so as to cross the peripheral edge of the spray flow 27. In the vicinity of the central axis C of the spray flow 27, since the density of the droplets is high, there is a high probability that the droplets are in contact with each other, and the droplets are large and the mobile phase is difficult to evaporate. Conversely, at the peripheral edge of the spray flow 27, the droplet size is small and the evaporation of the mobile phase is promoted, so that there is a relatively high probability that sample fine particles are present. Thus, by applying the measurement light to the peripheral edge of the spray flow 27 in this way, the measurement light can be efficiently irradiated to the fine particles of the sample that is the measurement target here, thereby increasing the detection sensitivity.

  Note that sample liquids and gases other than those sucked into the desolvation tube 23 are finally discharged out of the ionization chamber 21 from the drain 24 provided in front of the spray flow 27.

  As shown in FIG. 1, the detection output of the photomultiplier tube 26 is sent to the data processing unit 43 together with the detection output of the ion detector 39 of the MS unit 3, and the data processing unit 43 performs arithmetic processing, for example, a mass spectrum. In addition to the mass chromatogram and the total ion chromatogram, a chromatogram showing the intensity change of the scattered light is generated. Since the combination of the light emission source 25 and the photomultiplier tube 26 can detect a compound that cannot be detected by the MS unit 3 or that can be detected, but has a very low sensitivity, the result of the MS unit 3 is complemented. , Analysis accuracy can be improved.

  In the case of APCI, as shown in FIG. 2B, a sample liquid pipe 221, a nebulization gas pipe 222, a heater 224 surrounding the front space of the sample liquid pipe 221 opening, and a needle-like shape provided further in front of the heater 224 are provided. The ionization probe 22 in which the discharge electrode 225 is integrated is used. The sample liquid that has reached the tip of the sample liquid tube 221 (uncharged unlike ESI) is ejected as fine droplets with the help of the nebulizing gas ejected from the nebulizing gas tube 222. Since the front space is surrounded by the heater 224, the solvent in the droplets is vaporized by the heating of the heater 224 to become solvent gas. When a high voltage is applied to the discharge electrode 225 from a high voltage source (not shown), corona discharge occurs, and the solvent gas molecules become solvent ions. The solvent ions and the sample molecules in the droplets chemically react, and the sample molecules are ionized to become sample ions. Even in this case, the emission source 25 and the photomultiplier tube 26 are arranged in the same manner as in the above ESI so that the measurement light crosses a position near the tip of the spray flow 27 spreading in a substantially conical shape. In the case of this APCI, the vaporization of the mobile phase from the droplets by heating by the heater 224 is performed more efficiently than in the case of ESI. Therefore, the detection sensitivity can be expected to be higher than in the case of ESI.

  Note that the above embodiment is merely an example of the present invention, and it is obvious that changes and modifications can be made as appropriate within the scope of the gist of the present invention. For example, in the above embodiment, only ESI and APCI which are typical as atmospheric pressure ionization interfaces have been described, but the present invention is also applied to ionization by other ionization methods, for example, a method of irradiating a laser in a spray flow. can do.

The block diagram of the principal part of the liquid chromatograph mass spectrometer which is one Example of this invention. The schematic of the atmospheric pressure ionization interface in LC / MS of a present Example. The schematic when the atmospheric pressure ionization interface in LC / MS of a present Example is seen in the surface orthogonal to the axis | shaft C. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... LC part 14 ... Column 2 ... Atmospheric pressure ionization interface 21 ... Ionization chamber 22 ... Ionization probe 221 ... Sample liquid tube 222 ... Nebulize gas tube 223 ... DC power supply 224 ... Heater 225 ... Discharge electrode 23 ... Desolvation tube 25 ... Light emission Source 26 ... Photomultiplier tube 27 ... Spray flow 3 ... MS section

Claims (2)

In a liquid chromatograph mass spectrometer that ionizes a sample component contained in a sample solution eluted from a column of a liquid chromatograph by an atmospheric pressure ionization interface , detects it with an ion detector, and performs mass analysis,
a) a spraying means for spraying the sample liquid into the ionization chamber in a substantially atmospheric pressure atmosphere;
b) ion transporting means for collecting and transporting ions generated from the sample droplet sprayed by the spraying means to the subsequent stage;
c) light irradiating means for directly irradiating measurement light toward the spray flow of the sample liquid sprayed by the spraying means;
d) a light detecting means for detecting light scattered by the measurement light directly irradiated from the light irradiating means upon being sprayed and / or light after being absorbed;
e) a calculation processing unit that performs a calculation process of the detection result by the light detection unit and the detection result by the ion detector, and outputs a mass analysis result;
A liquid chromatograph mass spectrometer comprising:   2. The liquid chromatograph mass spectrometer according to claim 1, wherein the light irradiating means irradiates light so that the measurement light strikes a peripheral portion of a spray flow sprayed from the spraying means and spreading in a substantially conical shape.

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