JP2010014539A - Liquid sample ionization method, mass spectrometry, and devices thereof - Google Patents

Abstract

An object of the present invention is to improve sensitivity with a simple apparatus in a method for ionizing a sample by irradiating the sample with a laser, guiding the ionized sample to a mass analyzer, and identifying the sample. That is.
According to the present invention, a liquid sample mixed with an ionizing agent is made into fine droplets (mist form) by a spraying device, and the fine droplet sample is irradiated with laser light. This improved the sensitivity several hundred times compared to simply irradiating the droplets with laser light.
[Selection] Figure 1

Description

  The present invention relates to mass spectrometry of substances, and more particularly to ionization of a sample prior to mass analysis.

  It is still new in memory that Koichi Tanaka invented the matrix-assisted laser desorption ionization method (MALDI) effective for soft ionization mass spectrometry of macromolecules and won the Nobel Prize. However, this MALDI cannot avoid the generation of fragments for environmental samples with many impurities, and is not a sufficient analysis method.

  In addition, the electrospray ionization method (ESI) and the atmospheric pressure ionization method (APCI) can be applied to a relatively large number of target samples. In 1984, Fujii of the National Institute for Environmental Studies developed mass spectrometry for the purpose of gas phase radical detection, with lithium ions attached in the gas phase, and in 2000, commercialized as an ion attachment mass spectrometer (IAMS). ing.

  Research that elucidates the risks and dynamics of chemical substances, such as “I want to prove that there are no harmful substances going back in the past”, “I want to measure all chemical substances in the environment as they are”, etc. It has become an important research subject in advanced environmental science with a view to formatting analysis.

  Environmental administrative research institutes also pointed out the importance of comprehensive testing for searching for harmful substances in the environment, and improved the method for separating and extracting harmful substances in order to assess the abundance by chemical substance unit. Recently, the idea of comprehensive evaluation and database creation by screening and bioassay has been started.

  Airborne particulate matter (SPM), which is attracting international attention for its influence on the human body, has a particle size widely distributed from several tens of μm to several nm. Among them, nanoparticles having a particle size of less than 0.1 μm may be taken directly into the body from the lungs by respiration, and are regarded as dangerous.

  In the current SPM composition analysis, it is difficult to detect all the constituent molecules of fine particles as they are, and multi-component / simultaneous measurement is desired. As for suspended particles, it has been possible to measure one particle in Europe and the United States, but it left a problem in the pretreatment, and only a main component and only a simple inorganic component could be identified. Organic arsenic compounds are a recent representative example of environmental substances that are difficult to perform mass spectrometry.

  Soft ionization technologies such as MALDI and ESI are highly evaluated for their practicality in the advanced biotechnology field. In 2003, AP-MALDI method was developed by Professor Johns Hopkins University, USA, under atmospheric pressure. MALDI was performed and sugar chain compounds in breast milk were detected as lithium adducts, indicating that they can be applied to biochemistry, medicine and pharmacy.

  US JEOL was awarded the Gold Prize at the 2005 Pittsburgh Conference for developing a DART (Direct Analysis in Real Time) ion source and demonstrating its power for on-site detection of low molecular weight volatile sample materials. Thus, soft ionization research related to mass spectrometers has made significant progress worldwide.

  By the way, environmental substances exist in the environment in various forms such as gas, suspended particles, droplets, and solids. Ionization has been performed by dripping and irradiating it with laser light.

  However, when laser light is applied to the droplet on the substrate, the incident laser light is applied not only to the sample but also to the substrate, so we will discuss quantitatively how the laser energy is absorbed by the sample. I couldn't.

  At this time, a technique has been developed in which a mass analysis is performed by evaporating and ionizing the droplet by irradiating the droplet with laser light while the droplet is falling (see Patent Document 1).

However, this method does not necessarily increase the sensitivity, and is insufficient for practical use.
Japanese Patent Laid-Open No. 3-105841

  An object of the present invention is to add an ionizing agent to a liquid sample to ionize it, refine the ionized sample (mist), introduce the ionized fine droplet sample to a mass analyzer, and identify the sample The method is to improve sensitivity by a simple method.

  When the laser beam is irradiated to the center of the falling droplet, it is confirmed that the droplet evaporates instantaneously and ionizes, but when the laser beam deviates from the center of the droplet, It has been confirmed that evaporation is inadequate and ionization is inadequate because energy is not sufficiently absorbed by the droplets.

  In the present invention, the liquid sample to which the ionizing agent is added is made into fine droplets (mist form), and the fine droplet sample is irradiated with laser light, thereby further miniaturizing and improving ion extraction efficiency, To analyze.

In the present invention, a droplet sample mixed with an ionizing agent is ejected by a spraying device (nebulizer), the sample is refined (misted), and laser light is irradiated to the refined sample. It is not necessary to care much about the irradiation accuracy, and the collision probability between the sample and the laser is improved, and the sensitivity can be improved several hundred times as compared with the case where the laser is irradiated to the droplet.

  The best mode for carrying out the present invention will be described below.

An outline of the apparatus will be described.
As shown in FIG. 1, an outline of the mass spectrometer of the present invention includes an ionizing agent mixing unit 1 that mixes an ionizing agent with a liquid sample, and a spray that makes the liquid sample mixed with the ionizing agent into fine droplets with an atomizing gas. The apparatus 2 includes a laser beam irradiation device 3 that irradiates laser light onto the droplet sample that has been made into fine droplets, and a mass analyzer (MS) 4 that performs mass analysis on the fine droplets.

  In the ionizing agent mixing unit 1, a liquid sample and an ionizing agent (such as Li addition or proton addition) are mixed to generate ions in the liquid. The spraying device 2 introduces a liquid sample into the inner tube of the double tube and introduces a propellant into the outer tube. The sample blown out from the spray device 2 is in the form of fine droplets (mist), and the laser beam is irradiated to the fine droplets in the laser beam irradiation unit 3. The laser-irradiated droplet is guided to the mass analyzer 4 for mass analysis. At this time, the mass spectrometer is provided with a repeller electrode, and a voltage is applied to the electrode in order to guide fine droplet ions to the mass analyzer.

  As a sample to be analyzed, various substances can be targeted, but a sample that dissolves in a nonpolar solvent (terpenes and other substances that have poor compatibility with water) is preferable as an analysis target of the present invention.

  In addition, a substance that can be decomposed by a high electric field and difficult to analyze by other methods can be analyzed by the method of the present invention.

  The results when 1 mM dicyclohexyl phthalate and a molecular weight of 329 are employed as samples and trifluoroacetic acid (TFA) 0.1% (w / w) is added as an ionizing agent are shown.

  The nebulizer device produced was used as the spraying device, and nitrogen was used as the spraying gas.

  The laser used was a pulsed YAG laser (1024 nm, 60-100 Hz, 10 ns).

  FIG. 2 shows a mass spectrum in the case where dicyclohexyl phthalate is used as a sample, TFA is used as an ionizing agent, and laser irradiation is performed.

  For comparison, FIG. 3 shows a mass spectrum in the case where dicyclohexyl phthalate is used as a sample, TFA is used as an ionizing agent, and laser irradiation is not performed.

As apparent from the comparison between FIG. 2 and FIG. 3, when the laser was not irradiated, it was about 80 × 10 ³ counts / minute, but when the laser was irradiated, about 550 × 10 ³ counts / minute. Thus, the sensitivity is improved about 7 times by irradiating the laser.

FIG. 4 shows the time change of the mass chromatogram with respect to the peak intensity of dicyclohexyl phthalate when dicyclohexyl phthalate is used as a sample, TFA is used as an ionizing agent, and laser irradiation is performed. As is apparent from this figure, the method of the present invention was also advantageous for continuous mass monitor operation.

  Next, the result when Dibenzyl-14-crown-4 0.005 mM was adopted as a sample and tetrakis [3,5-bis (trifluoromethyl) phenyl] boron lithium (LiTFPB) 0.025 mM was added as an ionizing agent. Indicates. The spraying device and the laser are the same as in Example 1.

FIG. 5 shows a mass spectrum when the laser is irradiated.
For comparison, FIG. 6 shows a mass spectrum when no laser is irradiated.

As is clear from the comparison between FIG. 5 and FIG. 6, it was about 50 × 10 ³ counts / minute when the laser was not irradiated, but about 140 × 10 ³ counts / minute when the laser was irradiated. Thus, the sensitivity is improved about 3 times by irradiating the laser.

As a comparison, FIG. 7 shows a mass spectrum in the case of directly irradiating a laser without diminishing Dibenzyl-14-crown-4 0.5 mM and LiTFPB 5 mM droplets. In this case, since it was about 20 × 10 ³ counts / minute, when the concentration of the sample is taken into consideration, the sensitivity is improved about 700 times when the fine droplet (mist) according to the present invention is irradiated with laser. Yes. In other words, in the present invention, a sample can be identified even for a very small amount of sample that cannot be identified by the method of irradiating a droplet with laser light. Further, it is considered that further improvement in ion extraction efficiency can be obtained when a laser with a high repetition frequency is used.

Schematic diagram of the device according to the present invention Mass spectrum when dicyclohexyl phthalate is used as a sample, trifluoroacetic acid (TFA) is used as an ionizing agent, and laser is applied to a fine droplet Using dicyclohexyl phthalate as sample and TFA as ionizing agent, mass spectrum of fine droplets (without laser irradiation) Changes in time of mass chromatogram regarding peak intensity of dicyclohexyl phthalate when dicyclohexyl phthalate is used as sample, TFA is used as ionizing agent, and laser is irradiated to fine droplets Mass spectrum when dibenzyl-14-crown-4 is used as sample, tetrakis [3,5-bis (trifluoromethyl) phenyl] boron lithium (LiTFPB) is used as ionizing agent, and laser is irradiated to fine droplets Dibenzyl-14-crown-4 as sample and LiTFPB as ionizing agent, mass spectrum of fine droplet (no laser irradiation) Dibenzyl-14-crown-4 as a sample, LiTFPB as an ionizing agent, and mass spectrum when a droplet is irradiated with a laser (not refined)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ionizing agent mixing part 2 Droplet spray apparatus 3 Laser beam irradiation part 4 Mass analyzer 5 Liquid sample 6 Ionizing agent 7 Spraying agent

Claims (8)

In a liquid sample ionization method, a liquid sample to which an ionizing agent is added is made into fine droplets, and the fine droplets are irradiated with laser light. 2. The liquid sample ionization method according to claim 1, wherein the micronization of the sample is performed by a spraying device. 3. The liquid sample ionization method according to claim 1, wherein the ionizing agent is a lithium compound. 2. The liquid sample ionization method according to claim 1, wherein the laser is a YAG laser or a long pulse laser. A mass spectrometric method comprising the steps of: guiding a microdroplet sample ionized by the liquid sample ionization method according to claim 1 to a mass analyzer and identifying the sample. An ionization device for a liquid sample, the ionization device comprising a mixing device for injecting and mixing an ionizing agent into the liquid sample, a spray device for supplying the sample as fine droplets, and the fine liquid supplied from the spray device An ionization apparatus for a liquid sample, comprising: a laser beam irradiation device that irradiates a droplet with laser beam. A mass spectrometer comprising: a microdroplet sample ionized by the liquid sample ionizer according to claim 6, wherein the microdroplet sample is guided to a mass analyzer, and the sample is identified. The mass spectrometer according to claim 7, wherein the mass spectrometer includes a repeller electrode, and a voltage is applied to the electrode to guide droplet ions to the mass analyzer. .

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