Dielectric barrier discharge ionization detector

A dielectric barrier discharge ionization detector for ionizing and detecting a sample component in a sample gas by using plasma induced by an electric discharge within a gas passage through which a plasma generation gas containing argon is passed, the detector comprising:

• a) a dielectric tube made of a dielectric material and containing an upstream section of the gas passage;
• b) an electrically grounded tube-line tip member made of metal, for introducing the plasma generation gas into the dielectric tube;
• c) a high-voltage electrode circumferentially arranged on an outside of the dielectric tube;
• d) an electrically grounded upstream-side ground electrode circumferentially arranged on the outside of the dielectric tube and located upstream of the high-voltage electrode as well as downstream of the tube-line tip member in a flow direction of the plasma generation gas;
• e) an electrically grounded downstream-side ground electrode circumferentially arranged on the outside of the dielectric tube and located downstream of the high-voltage electrode in the flow direction of the plasma generation gas;
• f) an AC power source connected to the high-voltage electrode, for applying an AC voltage between the high-voltage electrode and the upstream-side ground electrode as well as between the high-voltage electrode and the downstream-side ground electrode so as to induce a dielectric barrier discharge within the gas passage and thereby generate plasma;
• and
• g) a charge-collecting section forming a downstream section of the gas passage and located downstream of the dielectric tube, including a sample-gas introducer for introducing a sample gas into the downstream section and a collecting electrode for collecting ions generated from a sample component in the sample gas by light emitted from the plasma,
• where one or both of following conditions is satisfied:
• a length of the upstream-side ground electrode in the flow direction is longer than a first predetermined initiation distance for a creeping discharge between the tube-line tip member and the high-voltage electrode;
• or a length of the area of the dielectric tube provided with the downstream-side ground electrode in the flow direction is longer than a second predetermined initiation distance for a creeping discharge between the high-voltage electrode and the charge-collecting section, and
• wherein the first and second predetermined initiation distances are determined based on at least one parameter of a frequency of the AC voltage and an amplitude of the AC voltage, a waveform of the AC voltage, a property of the plasma generation gas and a material of the dielectric body.