The present invention relates to detectors for gas chromatography; and more particularly, it relates to discharge ionization detectors which provide an output indication functionally related to the quantity of ionizable material present in the column effluent from a gas chromatograph.
Helium ionization detectors using a nonradioactive source of ionizing radiation have been found to be stable and reliable. Further, such detectors have very good sensitivity. The principle of operation of the detector is based upon the use of photons to produce ionic species. A high voltage imposed across discharge electrodes in a chamber produces a glow discharge. In the presence of helium, a characteristic discharge emission of photons occurs. The photons irradiate a port connecting the discharge chamber to an ionization chamber receiving the gas chromatograph column effluent. Electrons are produced in the ionization chamber as a result of photon interaction with ionizable molecules in the column effluent. Electrons produced by the glow discharge are repelled by a negatively charged polarizing electrode. Electrons produced in the ionization chamber are attracted to a collector electrode and result in a current to an electrometer.