Discharge ionization current detector

Patent metadata

Field	Value
Publication number	US-9791410-B2
Application number	US-201214123582-A
Country	US
Kind code	B2
Filing date	May 31, 2012
Priority date	Jun 7, 2011
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

A low-OH-content quartz glass with an OH content equal to or lower than 5 ppm is used as a cylindrical tube ( 2 ) covering the surface of metallic plasma generation electrodes ( 4, 5 and 6 ) for generating a low-frequency barrier discharge. It has been found that, in the low-frequency barrier discharge, hydrogen and oxygen originating from the OH contained in a dielectric material are released into plasma gas for a long period of time, constituting a primary cause of an increase in the baseline current. The use of a low-OH-content quartz glass dramatically lowers the baseline current and thereby improves the S/N ratio and the detection limit.

First claim

The invention claimed is:

1. A discharge ionization current detector, comprising: a discharge electrode having a surface covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein quartz glass with a hydroxyl-group content equal to or lower than 5 ppm is used as the dielectric member.

2. A discharge ionization current detector, comprising: a discharge electrode having a surface covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein a material prepared by performing a heat treatment on quartz glass with an upper limit of a hydroxyl-group content higher than 5 ppm at a temperature of 500° C. or higher in a predetermined kind of inert-gas atmosphere is used as the dielectric member.

3. A discharge ionization current detector, comprising: a discharge electrode having a surface covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein sapphire is used as the dielectric member, thereby reducing a concentration of impurities mainly composed of hydrogen and oxygen released from the discharge electrode into the plasma gas.

4. A discharge ionization current detector, comprising: a discharge electrode having a surface covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein high-purity alumina is used as the dielectric member, thereby reducing a concentration of impurities mainly composed of hydrogen and oxygen released from the discharge electrode into the plasma gas.

5. A discharge ionization current detector, comprising: a discharge electrode having a surface covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein the dielectric member has a thin-film layer made of a dielectric material with a hydroxyl-group content equal to or lower than 5 ppm and forming a 2-μm depth range from the surface coming in contact with plasma.

6. A discharge ionization current detector, comprising: a discharge electrode on a cylindrical tube covered with a dielectric member and provided so as to be exposed to an inside of a gas passage through which plasma gas is passed; an alternating voltage supplier for applying a low-frequency alternating voltage to the discharge electrode so as to generate a dielectric barrier discharge in the gas passage and thereby produce plasma from the plasma gas; and a current detector for detecting an ion current due to a sample component in a sample gas ionized by an action of the plasma in the gas passage,
wherein a coating layer with a thickness of 2 μm or greater is formed on the surface of the cylindrical tube by deposition techniques using silica glass, silicon nitride, alumina, or diamond-like carbon as the low-OH-content dielectric material.

Assignees

• Shinada Kei
• Horiike Shigeyoshi
• Nishimoto Takahiro
• Shimadzu Corp

Inventors

• Shinada Kei
• Horiike Shigeyoshi
• Nishimoto Takahiro

Classifications

• G01N30/64 Primary

  Electrical detectors · CPC title

• G01R19/0061

  Measuring currents of particle-beams, currents from electron multipliers, photocurrents, ion currents; Measuring in plasmas · CPC title

• G01N27/70

  and measuring current or voltage · CPC title

• G01N27/62 Primary

  by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode · CPC title