JP2008051504A - Method and apparatus for ionizing sample gas under atmospheric pressure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To analyze even a trace amount of sample with high sensitivity. <P>SOLUTION: Carrier gas is introduced into the first ionization chamber 11 and excited/ionized, and a high-speed current of the excited/ionized carrier gas is formed and jetted into the second ionization chamber 21, and sample gas is introduced into the second ionization chamber 21 by a negative pressure generated by jetting of the high-speed current, and an excitation species or ions included in the carrier gas are applied to the sample gas in the second ionization chamber 21, to thereby generate sample gas ions. The generated sample gas ions are jetted from a nozzle 20A into a mass spectrometer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for ionizing a sample gas under atmospheric pressure.

An ionization method and apparatus for direct analysis in real time (DART) has already been proposed.
Robert B. Cody, James A. Laramee, and H. Dupont Durst “Versatile New lon Source for the Analysis of Materials in Open Air under Ambient Conditions” Analytical Chemistry, Vol. 77, No. 8, April 15, 2005 2297

  In this method, ions generated in the tube and excited species are ejected from a nozzle to ionize the vapor of the outside air. In this method, ions generated by discharge and excited species diverge widely under atmospheric pressure, and sample molecules cannot be effectively ionized. For this reason, there is a great sacrifice of sensitivity.

  The present invention provides an ionization method and apparatus capable of analyzing even a very small amount of sample with high sensitivity.

  In the ionization method according to the present invention, a carrier gas is introduced into a first ionization chamber and excited and ionized (excitation and / or ionization), and a high-speed flow of the excited and ionized carrier gas is formed and injected into the second ionization chamber. The sample gas is introduced into the second ionization chamber by the negative pressure (aspirator effect) generated by the jet of the high-speed flow, and the excited species or ions contained in the carrier gas are allowed to act on the sample gas in the second ionization chamber. Sample gas ions are generated.

  The ionization apparatus according to the present invention includes a first housing having an ionization apparatus connected to a carrier gas introduction pipe and excited and ionized (excitation and / or ionization) of the carrier gas introduced through the carrier gas introduction pipe. A high-speed flow forming channel that is provided continuously in the housing and forms a high-speed flow of excited and ionized carrier gas, and an outlet of the high-speed flow forming channel is open, and the high-speed jet ejected from the outlet A sample gas introduction pipe introduced by the negative pressure generated by the flow is connected, and a nozzle for injecting ion gas sample ions to the analyzer by causing the excited and ionized carrier gas to act on the introduced sample gas. A second housing provided with the second housing;

  The nozzle of the second housing is arranged near the ion introduction orifice of the mass spectrometer, and sample gas ions ejected from the nozzle are introduced into the analyzer and subjected to mass analysis.

  According to the present invention, since the excited and ionized carrier gas is injected into the second ionization chamber, the sample gas is introduced into the second ionization chamber by the negative pressure. Since the excited species and ions in the carrier gas act on the sample gas in the second ionization chamber, the sample gas is efficiently ionized. As a result, even a very small amount of sample can be analyzed with high sensitivity.

  FIG. 1 shows an ionization apparatus.

  Insulating tube (for example, glass tube) (insulating first housing) 10 is held in a state in which discharge electrode needle (for example, stainless steel or tungsten) (metal linear body) 14 is not in contact with the inner wall of tube 10 and is insulative It extends to the vicinity of the tip of the tube 10. For example, an insulating holding member (rubber or synthetic resin) 13 is tightly fitted in the insulating tube 10 near its end, and the discharge electrode needle 14 is inserted into the insulating holding member 13 to hold the discharge needle 14 Is done. The inside of the insulating tube 10 where the discharge electrode needle 14 exists is a first ionization chamber 11.

  A carrier gas introduction pipe 12 is connected to the insulating tube 10, and a carrier gas is introduced from the carrier gas source through the introduction pipe 12 into the first ionization chamber 11. As the carrier gas, helium, oxygen, nitrogen gas or rare gas is used.

  A positive or negative high voltage is applied to the discharge electrode needle 14 to cause corona discharge (discharge plasma). As a result, the carrier gas introduced into the first ionization chamber 11 is excited and ionized (excited and / or ionized). Specifically, in positive voltage discharge, positive ions and atoms and molecular excited species are generated, and in negative voltage discharge, electrons, atoms and molecular excited species are generated. In the following description, it is assumed that a negative high voltage is applied to the discharge electrode needle 14. Other carrier gas excitation / ionization methods include high-frequency discharge.

  A metal tube (for example, stainless steel or brass) 10A is fixed to the tip of the insulating tube 10, and a metal (for example, stainless steel or brass) throttle tube (high-speed flow forming flow) having a conical portion is attached to the metal tube 10A. A path (member) 30 is inserted and fixed. The throttle tube 30 has a short cylindrical portion 30B inserted into the metal tube 10A of the insulating tube 10, a narrow outlet portion 30A, and a conical (conical) portion connecting these portions 30B and 30A. I have.

  Further, a metal cap (for example, stainless steel or brass) (second housing) 20 is provided so as to cover the throttle tube 30. That is, the cap 20 has a cylindrical shape, and its base portion is fitted into the cylindrical portion 30B of the throttle tube 30, almost the entire tip portion is closed, and only the central portion of the tip portion opens as a nozzle 20A protruding outward. Yes.

  There is a space between the cap 20 and the throttle tube 30 (inside the cap 20), and this is the second ionization chamber 21. A tip end of a sample gas introduction tube (sample capillary) 23 is connected to the peripheral surface of the cap 20 and opens to the second ionization chamber 21.

  The throttle tube 30 has two functions. One of them is that it works as a counter electrode of the discharge electrode needle 14 together with the metal tube 10A at the tip of the insulating tube 10. For this purpose, the throttle tube 30 is grounded (the cap 20 fitted therein is also at the same potential). Further, electrons generated by excitation and ionization of the carrier gas in the first ionization chamber are captured by the throttle tube 30 to prevent recombination of carrier gas ions.

  Another action of the throttle tube 30 is to act as a flow path that forms a high-speed flow of the excited and ionized carrier gas by gradually reducing the inner diameter of the throttle tube 30 in the traveling direction of the carrier gas. Accordingly, the excited and ionized carrier gas ions are ejected from the outlet portion 30A toward the second ionization chamber 21.

  The outer end of the sample gas introduction pipe 23 opens near the sample or to the sample gas source. For example, the outer end of the sample gas introduction pipe 23 can be connected to the outlet of the gas chromatograph, can be placed in a sample gas container, or simply be close to the object. The sample gas may be positively injected into the sample gas introduction pipe 23.

  In any case, as described above, the carrier gas excited and ionized from the outlet 30A of the throttle tube 30 is jetted into the second ionization chamber 21 as a high-speed flow, thereby generating a negative pressure (aspirator effect). The sample gas is sucked into the second ionization chamber 21 through the sample gas introduction pipe 23. In the second ionization chamber 21, ions and excited species in the carrier gas act on the introduced sample gas, and the sample gas is ionized. For example, the sample gas is ionized by an ion-molecule reaction. The sample gas is also ionized by excited species (Penning ionization) or electrons (electron attachment reaction) of the generated carrier gas. When negative high voltage is applied to the discharge electrode needle 14, molecules with various ionization energies are selectively ionized by causing Penning ionization using excited species of carrier gas (especially rare gas). it can. It is particularly suitable for ionization of nonpolar molecules such as gasoline and petroleum components.

  The nozzle 20A of the cap 20 is disposed close to the ion sampling orifice 42 of the schema 41 of the mass spectrometer 40. The ionized sample gas is ejected (injected or sprayed) from the nozzle 20A, introduced into the vacuum portion of the analyzer from the orifice 42, and subjected to mass analysis.

  If necessary, the cap 20 can be provided with a heater, or the temperature in the second ionization chamber can be adjusted (heated) by laser light irradiation to increase the sensitivity.

FIG. 2 shows a mass analysis result (mass spectrum) obtained for anisole (CH ₃ OCH ₆ H ₅ ) ionized using the ionizer under atmospheric pressure shown in FIG. Atmospheric-pressure penning ionization (APPeI) using helium (He) gas, a sniffing method was used (that is, anisole gas was sucked by the aspirator effect). Since anisole is ionized in the second ionization chamber and does not diverge widely, it can be seen that high sensitivity is obtained.

It is sectional drawing which shows the structure of an ionization apparatus. It is a mass spectrum which shows an example of the mass spectrometry result about the sample ionized by the ionizer.

Explanation of symbols

10 Insulating tube (first housing)
11 First ionization chamber
12 Carrier gas introduction pipe
14 Discharge electrode needle
20 Cap (second housing)
20A nozzle
21 Second ionization chamber
23 Sample gas introduction pipe
30 Restrictor (High-speed flow forming flow path)

Claims (5)

A carrier gas is introduced into the first ionization chamber to be excited and ionized,
A high-speed flow of excited and ionized carrier gas is formed and injected into the second ionization chamber,
The sample gas is introduced into the second ionization chamber by the negative pressure generated by the jet of the high-speed flow, and the sample gas ions are generated by causing the excited species or ions contained in the carrier gas to act on the sample gas in the second ionization chamber. Do,
A method for ionizing a sample gas under atmospheric pressure.   The ionization method according to claim 1, wherein the generated sample gas ions are jetted to an analyzer.   The ionization method according to claim 1 or 2, wherein the carrier gas is excited and ionized by corona discharge in the first ionization chamber. A first housing having an ionizer connected to a carrier gas introduction pipe and exciting and ionizing the carrier gas introduced through the carrier gas introduction pipe;
A high-speed flow forming channel that is continuously provided in the first housing and forms a high-speed flow of excited and ionized carrier gas, and an outlet of the high-speed flow forming channel are opened, and are injected from the outlet. A sample gas introduction tube introduced by the negative pressure generated by the high-speed flow is connected, and the excited and ionized carrier gas is allowed to act on the introduced sample gas to inject ionized sample gas ions to the analyzer. A second housing with a nozzle to perform,
A sample gas ionization apparatus under atmospheric pressure.   The ionization apparatus according to claim 4, wherein the ionization apparatus of the first housing includes a discharge electrode and excites and ionizes the carrier gas by corona discharge.

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