Discharge Ionization Current Detector

A discharge ionization current detector comprising:

• a) a first gas passage through which a plasma generation gas is passed, and in which a plasma is generated from the plasma generation gas with an electric discharge;
• b) a second gas passage extending from the downstream end of the first gas passage, in which a sample component in a sample gas supplied to the second gas passage is ionized by the action of the plasma;
• c) a current detector for detecting an electric current due to the ionized sample component;
• d) a dielectric tube forming at least a portion of the first gas passage;
• e) a plasma generating excitation electrode attached to an outer circumference of the dielectric tube;
• f) a metal electrode provided in the second gas passage so as to come in contact with the sample gas;
• and
• g) an electrode structure provided in the first gas passage, wherein:
• the electrode structure includes a metal tube covered with a dielectric material and a metal wire covered with an insulating material and inserted in the metal tube;
• the metal tube has one end electrically connected to a ground on an upstream side of the first gas passage and another end reaching at least a point facing the plasma generating excitation electrode;
• one end of the metal wire is extracted from the upstream side of the first gas passage to an outside, and another end thereof is provided with an area that is not covered with the insulating material, the area being located within the second gas passage so as to come in contact with the sample gas;
• and
• either the aforementioned one end of the metal wire or the metal electrode is connected to a bias power source, and the remaining one is connected to an ionization current detecting circuit.